Milestones in Geosciences: Selected Benchmark Papers Published in the Journal Geologische Rundschau

Wolf-Christian Dullo Geologische Vereinigung e.V. (Eds.)

Milestones in Geosciences Selected Benchmark Papers Published in the Journal ,Geologische Rundschau" With 59 Figures, 4 Tables, and 50 Facsimiles

'

Springer

EDITED BY: Professor Dr. Wol f-Christian Dullo GEOMAR Research Center of Marine Geosciences WischhofstrttBe 1-3 24148 Kiel Gcnnany E-mail: [email protected]

Geologische Vereinigung e.V. Secretrary VulkanstraBe 23 56743 Mendig Germany E-mail: geol .ver@t -ouliue.de

hup://www.g-v.de

T he contents of thi s book were ttlso published as a supplement to the lmemational l oumal of Earrh Sciences, formerly the Geologische Rtmdschau

ISBN 3-540-4422 1-9 Springer-Verlag Berlin Heidelberg New York Library of Congress Cataloging-in-Pubhcntinn Dntaupplied for Die Deutsche Bibliothek - CIP E-inhcitsaufnJhme

Milestones in geosciences : selc<:,ted benchmark papers publi"hed in the journal ..OeoiQgis.chc Ruodsch:m·· t Gcologis.chc Vcrcini,gung c. V. Wolf·Chtistian Oullo (ed.).- Bel'! in ~ Heidelberg: New Yol'k : ~long Kong : Lonc.lon : .\tlilan : Pari.s: Tokyu : Springer 2003 tSSN 3·540·4422t-9 TI1is work is subjex.~t to copyright. All rights art rest.rn:d, whether the whole v r part of the material ts cmM:crned, spccificltlly the right~ of trnnslmion. reprinting. reuse of illu.str:uions.. rocilation. btOttdcasling. reproduction Otl rniC"rofilrn or in any other way. and Momge in tb l~• banks. Duplication of 1hls publication (If ptu1s thereof is pcnmued only under the provi~i ons ot' the German Copyright L:.w of Se1nembcr 9. 1965. in its cutrelll vei'Sion. and permission for use must always be obcainl."d from Springer·Vcrhtg. Viohttions are liable for prosccmton under the German Copyright Law. Springer· Verlag Berlin Heidelberg New York <1 member o f BertclsmannSpringer Sc:ientc+Bustness Meditt GmbH hup://www.sptinger.de @Springer·Verlttg Berlin Heidelberg 2003 Printl."d in Germany The use of general ly. even in chc absence of :.t specific stmemelll. that such munes are exempt from the relevatU Product liubilit)': T he publishers ctmnot guamntcc the nceurucy o f uny information abou1 dlC :•pplication of operative 1echniques and medic.-lions contained in this book. In every indi\•idual case the user must ch<.ock surh information hy consulting 1hc relevant litcralurc. Cover design: dcblik Bertin TypeM:.ning. printing and binding: Sllirtt. AG. Wi.irt.burg Prillled on acid· ftee pape.•· SPIN 10892653 3213 130/as 5 4 3 2 I 0

Contents

Pn.:l';u.:c ( II . DliLI .O . D. BEKNOI.:LLI. W. FRANKE

Phmog,raphs o f aulhors

2

C'11 . Dt ll o

Thc origin> of continents A . WI W ' i· K

Arc 1herc ancient deep-sea deposits of geologic 'ignificance?

18

G. STIII\\Ii\1'" Amcrika and Eurafrika: the origin of the Atl:mtic-Arctic: Ocean A.L. l>t. Torr

43

Stratigraphy of recent deep-sea sediments based upon foramin i feral fauna

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w. SC'IIOT1' No geology wi thout marine geology P.l-l. Kllt· 'J~.r.. The phy,ical-chcmical conditions relating to lhe formation of sail deposits and their application to geologic problem<; S. ARRIII 'Jil S. R. LACfl~tA;-;N The chemical and Mructural metamorphosi' of coab M . TIICII\tLLLtR. R. TEICHMiiLLtR Geochro no logy o f I he last 12,000 years

54

62 75 100

G. Dl' GH, I( On ex peri menial tectonics

Ill

FlUid inclu;ions with ga~ bubbles as geo1hermometer..

123

1-l. c100!.

W . CoRRL's

lnvc"igating the Earth's crust with the help of explosions E. WII .CIIlRT

134

The ,u·ucture of the Earth 's crust in Europe

140

B. G~'l i.NiltRG

W.Ch. Dullo · D. Bernoulli · W. Franke

Preface

This “Golden Volume” of the International Journal of Earth Sciences presents papers published in the Geologische Rundschau, which we consider to be milestones in the evolution of Earth Sciences. The idea arose during a board meeting several years ago and was put forward by our former Vice President, Celal S¸engör, who argued that many important papers were to be found in our Society’s journal and that they should be reprinted and translated into English. Many of these contributions paved the way to modern Earth Systems Science. The plan was enthusiastically accepted by all members of the executive board, however, how to proceed? Which papers should be selected? While browsing through the older volumes of the journal, we discovered a wealth of scientific and intellectual heritage. In view of the large number of potential papers, we decided to include only papers from scientists who are unfortunately no longer among us. Even then, the number of outstanding papers remained far too high. Therefore, we decided to concentrate on a few of the most important scientific contributions, which are still valid today. We are grateful to all who helped to make this selection. In particular, we would like to acknowledge the advice of Eugen Seibold. Furthermore, we thank all the translators of the German texts. Sometimes it was a difficult task to shape the old-fashioned language into proper English. Therefore, some of our colleagues chose a freer translation. For those, who would like to compare the translation with the original version, the latter is included as a facsimile which is reduced in size, but still readable. This makes the Golden Volume a still more important source for the history of our science. We also discussed whether we should redraw the graphs and figures. We finally decided to include them as facsimiles within the translated text, because the original illustrations reveal a lot about the personal style and the power of imagination of the authors and, at same time, document their thoughts in a historical context. The bouquet of papers starts with Alfred Wegener’s paper on the origin of continents, the first formulation of his hypothesis of continental drift. Our Society is very proud to have this pioneer of modern geology among its early authors. During the 1920s and the 1930s of the past century, when the Anglo-Saxon mainstream of geology

was firmly rooted in fixism, Geologische Rundschau accepted papers with a mobilistic, global perspective of which Gustav Steinmann’s and Alexander Du Toit’s articles are brilliant examples. Combined with the early interest in marine geology, documented in the papers by Schott and many others, they laid some of the foundations for a modern global geology which included not only the continents, but also the oceans; indeed, “No Geology without Marine Geology” (Ph. H. Kuenen)! Already in its first year, the Geologische Rundschau was defined as a “Zeitschrift für Allgemeine Geologie” which, in modern terminology, means process-oriented. The papers dealing with fundamental geological processes span a time interval of 40 years, from Arrhenius and Lachmann’s (1912) classic work on evaporites to the seminal study on the metamorphism of coal by M. and R. Teichmüller (1954). Historical geology is represented in the article by de Geer, which is probably the first serious attempt to establish a numerical chronology for the latest Quaternary. Experimental studies include the publications by Hans Cloos and by C.W. Correns. Together with the classical geophysical papers of E. Wiechert and Benno Gutenberg, they document the wide scope and the interdisciplinary approach of the journal. Articles published in Geologische Rundschau were originally called “Aufsätze”, which is best translated by the word “essay”. Many of the most stimulating essays included new ideas which were often in conflict with conventional wisdom. As a consequence, the journal was always a place of scientific debate on a high intellectual level. Outstanding examples include the discussion meeting on the Atlantic Ocean and Continental Drift (1939), or the controversy between Stille and Gilluly on episodicity or continuity of orogenic movements (1950). It was a common feature of these contributions that they were directed towards what we now call Earth Systems Science and is still in the limelight of our journal. With this selection of benchmark papers, the Geologische Vereinigung wants to pay tribute to those outstanding scientists and teachers, who had close ties with our Society. Their classical publications promoted our understanding of Planet Earth and its evolution, and are the Society’s grateful contribution to the GEO-year 2002.

Some of the authors whose articles have been published in this issue. Unfortunately, it was not possible to obtain photographs from all the authors.

Alfred Wegener

Gustav Steinmann

Phillip H. Kuenen

Richard Lachmann

Gerard de Geer

Wolfgang Schott

Marlies und Rolf Teichmüller

Hans Cloos

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Carl W. Correns

Emil Wiechert

Benno Gutenberg

A. Wegener

The origins of continents Geol Rundsch 3:276–292

Translation received: 28 February 2002 © Springer-Verlag 2002

Translated by Roland von Huene Translation note: This translation was made onboard the research vessel Sonne during a scientific cruise. After leaving the harbour I discovered that the file of my initial work was lost and begin again. My German shipboard colleagues became my technical dictionary. As a scientist rather than linguist or translator I attempted to compose an easily read English account conveying ideas rather than a literal conversion from the original German. The reader searching for an exact literal translation should consult the original German text. Foremost in this effort was to show Wegener’s thinking and his construction of the continental drift argument. I tried to avoid terms employed in plate tectonics but soon found it difficult not to occasionally use the term plate for “Scholle”. Wegener picked up on many arguments voiced by others of the time and assembled them into his own comprehensive argument. Indeed, from today’s perspective, and by his own admission, strong arguments were mixed with weak and fallacious arguments, so it was easy for opponents to refute the latter and thereby claim that the whole scientific argument was wrong. I remember seminars of my student days at UCLA where the whole idea was lambasted because there was no discontinuity at the proper depth to slide continents half way around the Earth. I was amazed during translation how much of the present “new geoscience” is contained in this initial paper and in the works of Hein, Suess, Wallace, and others of the time.

rupted at the sea, we will assume continental separation and drift. The resulting picture of our Earth is new and paradoxical, but it does not reveal the physical causes. On the other hand, even with only an initial argument, many surprising simplifications and interdependent connections are evident so that it seems correct to substitute the new more usable working hypothesis in place of the old hypothesis of submerged continents. The long life of the latter comes from its usefulness as a counter-argument to ocean permanence. Despite its broad basis, I would prefer that the new principle be used as a working hypothesis until exact astronomical measurements establish a more lasting basis for the horizontal movements. In judging single aspects of the hypothesis one should remain aware that in the first version of such a comprehensive idea single mistakes cannot be avoided. On the basis of general geology and geophysics, we will first discuss how, if at all, large horizontal drift of continents in an apparently stiff Earth crust can occur.1 Thereafter, we will make an initial attempt to follow the existing rifts and movement of the continents in Earth history. The connection of continental drift with the construction of major mountain ranges will be revealed, and finally we will discuss the closely connected polar wander and the measurement of continual continental movements. It has been said that the idea of rigid areas rifting apart has already been often brought up. W.H. Pickering uses it in connection with the obviously false hypothesis of extraction of the moon from Earth, during which America parted and drifted from Europe and Africa. More important is a work by Taylor in which he proposed the Tertiary separation of Greenland from North America and connects it with the building of the Tertiary mountains. For the Atlantic he assumes that only a small part was accomplished by the pulling away of the American continent and that the Mid-Atlantic Rise is the remains of

R. von Huene (✉) 2910 North Canyon Road, Camino, CA 95709, USA e-mail: [email protected]

1 This part is extremely condensed. Please note the more detailed discourse in Petermann’s Mitteilungen.

Introduction The following is a first attempt to explain the origins of large Earth features, or the continents and ocean basins with a comprehensive principal, namely continental drift. Wherever once continuous old land features are interLecture held on the general meeting of the Geologische Vereinigung in Frankfurt a. M. on 6 January 1912. The following is an extract from a larger work with the same title that appears on Petermann’s communication. The essential contents of this study were presented during the annual meeting of the Geologische Vereinigung in Frankfurt a. M. under a title “Die Herausbildung der Grossformen der Erdrinde (Kontinente und Ozeane), auf geophysikalischer Grundlage “and again on 10 January at the “Gesellschaft zur Förderung der gesamten Naturwissenschaften zu Marburg” with the title “Horizontalverschiebungen der Kontinente”.

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the connecting segment. In the following we interpret the rise as a former rift feature. One finds that Taylor’s work contains some points that are in the following presentation, but he failed to realize the immense and extensive consequences of such horizontal movements.

Geophysical arguments Heim, in 1878, described the continents as broad massive elevated platforms. And, in fact, the hypsographic curve of the Earth’s surface shows clearly that there are two main elevations, namely the surface of the continents (700 m above) and the deep sea floor (4,300 m below sea level). The lowest parts of the continents lie up to 500 m below sea level (the shelves). European geologists for the most part accept the contraction theory, which is so dramatically illustrated by the dried apple. Suess summarizes it in the expression, “it is the collapse of the Earth with which we live”. In the time since this useful analogy was proposed by Heim serious considerations have been raised and E. Boese, for instance, characterizes the current rationale. The contraction theory is no longer widely accepted and in the interim no theory has been found that completely explains all circumstances observed. In particular, the contraction theory must be abandon because of geophysical considerations. The seminal apparent principal that the Earth is cooling has not remained untouched because, from research on radium, the question has been raised as to whether the temperature of the Earth’s interior is increasing. Because one can say that in all likelihood the Earth’s core is formed of compressed nickel steel, it is apparent that simple cooling is not sufficient to account for the large folds in the Earth’s shell, especially since the recognition of large folded overthrust sheets. The inferred stress in the outer skin and concentrated contraction of only a single side of a great circle has been found impossible. Molecular strength is insufficient to support the thrusting of a 100-mthick sheet over another. The sheet of rock would not move, but beak into pieces (Rudzki) or as Loukaschewitsch says it “les forces molaires l’importent sur les forces moléculaires”. The Earth’s outer shell could in this way experience a weak and above all very uniform roughening as Ampferer, Reyer and others have correctly put forth. Furthermore, it is difficult to envision how the processes of Earth contraction in one instance causes roughening and, in another, the subsidence of enormous areas and development of horsts. Above all, these ideas are contradicted by gravity observations, showing that the floor of the ocean is composed of more dense and different material than the continental areas. These unsubstantiated conclusions have been justified on the ever clearer evidence that essentially all sediment on the continents originated through gradual transgressions. The dubious teachings regarding permanence of the oceans can be attributed to such names as Dana and Wallace, which Bailey Willis declared “outside the category of debatable questions”. With justification, European geolo-

Fig. 1 Schematic section through a continental margin

gists hesitate to accept this teaching because we cannot see how the wide earlier land-bridge could span the ocean. We remain skeptics regarding the unsubstantiated collapse of the Earth. Both sides derive key premises, which are further elaborated. We will attempt to show that the basic premises of both views can be answered through rifting and horizontal drift of the continents. The gravity measurements at sea, namely those of Hecker, show that the ocean crust is not only composed of material of greater density than the continents, but that the density is equivalent to the mass deficit of the ocean water and thereby compensates for the oceans. The many investigations of isostasy are well known, both those regarding methodology, but also its validity. I will not go into these, but point out that for larger regions such as continents and oceans, or for large mountain masses, one can assume isostasy whereas for single mountains and particularly plateaus, the total mass is supported, but not isostatically compensated. Other features of unknown tectonic structures are similarly uncompensated. One can visualize the boundaries between the light material of the continents and the heavy material of the ocean floor in various ways. The presentation of Airy (1855) which was then used by Stokes and more recently by Loukaschewitsch that a dense magma supports a thick light continent and a thin heavy ocean, is currently accepted. In the following, we take another tack that is equally justifiable and, as will be shown, has other advantages. It is pictured in Fig. 1. Continents are pieces of lithosphere embedded in a heavy material. One can assume that the thickness of continental plates is around 100 km. Hayford found from deflection of the vertical in the United States a value of 114 km, although not without some questionable assumptions. Helmert, using another approach, namely pendulum measurements at continental margins, came to a similar value of 120 km. Recently, Kohlschuetter came to the same result using the same approach. If we take the view that an approximate middle value is 100 km, then 50 km may be in order for some places in the world and one can expect 200 km in others. The variable heights of the sea must correspond with a strong variability in thickness of the lighter plate. Similar conclusions with larger uncertainty in the numbers are encountered in earthquake research. It was not just determined through waveforms in the Eigenperiods of the Earth’s crust (Wiechert), but also with the help of reflected rays from earthquake data and from the source depths of earthquakes.

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Fig. 2 Section along a great circle through South America and Africa which are shown as separated large features

Fig. 3 Hypsographic curve of the Earth’s upper layer: a in the future, b the present, c in the past

To illustrate the large-scale relationships, Fig. 2 contains a section through the Earth along a great circle between South America and Africa. The unevenness of the Earth’s surface and the great deeps of the Atlantic Ocean are small enough to be contained within a circular line describing the Earth’s surface. For comparison, the figure also contains the iron core of Wiechert and the main atmospheres: the nitrogen sphere, water sphere and an upwardly unconstrained sphere, the theoretical Geokoronium. The zone of clouds (troposphere) is not thick enough to be shown. It is now necessary to clarify that the sediments are an unremarkable part of continental structure. Commonly, the total thickness of sediment is cited in multiple kilometres and these are maximum values because in adjacent areas the source of these sediments is exposed. But only when we consider isostasy does it become obvious how little sediment is visible in the larger features. If the sediment were striped from the continents, the Earth would rise to the same level again and the Earth’s relief would change little. From this it is obvious that continental plates are forms of a higher order compared with the secondary and more superficial role that erosion and sedimentation play. They can develop into a basement rock whose fundamental nature is not arguable. If we constrain ourselves to the major representative rock type, one could say the continents are gneiss. In his great three-volume work “Antlitz der Erde”, Suess (pp. 626) introduced the name ‘sal’ for these rocks whereas eruptive volcanic rock was called ‘sima’. The latter differ not only chemically, but also physically from the former. They vary greatly and are on average denser than salic rock with a 200–300° higher melting temperature. The assumption is not too remote that dense materials of the oceans are identical to sima, an assumption that is confirmed numerically with specific gravities. The continents are 2.8, and from the ocean deeps a specific gravity of 2.9 can be calculated. This is a good average value for sima. In considering further the physical properties of these rocks, as well as the assumed temperatures for the

Earth’s interior, one concludes that both materials, sal and sima, must be plastic. It also concerns the paradoxical, as exemplified by black tar. If you let a piece sit for longer time it flows by itself: small lead pellets sink into it after a time; but when dealt a hammer blow it shatters like glass. The duration over which such materials react is a factor. From this overview one must conclude that there are no objections to possible, unusually slow, but large horizontal movements of the continents under a steady force during geologic time. Because mountain building indicates continental contraction where the surface contracts and the thickness increases, and because such mountain building occurred during all geologic periods, one can explain the gradual elevation of the continents above the oceans. This process must be one-way because there cannot be a pull to undo contractile deformation, only a rifting of the continent. We have a progressive process through which the probable conservative salic Earth’s crust looses area and gains thickness. Figure 3 illustrates this with hypsographic curves for the past and future. During early ancient time, a roughly 3-km-deep Panthalassa covered the whole of the Earth’s surface, and the sea was not divided into shallow and deep areas until the continents emerged. The process has not ended yet and will only be finished after a further uplift of 0.5 km. In this way, past transgressions of a larger extent than the current ones can be explained. During the rifting of plates, the underlying hot sima must be released, which produces submarine lava flows. This appears to be the case along the mid-Atlantic swell. Because submarine eruptions are silent and the feeder pipes allow lava to rise only to isostatic equilibrium, and if there are no unusual pressures to drive lava higher, the opening of a rift will produce no catastrophic displays. The trailing flank of rifted blocks will be less volcanic than the frontal flanks where pressure is greater. Perhaps this is an explanation for the non-interdependence of volcanoes and rifts as noted by Geikie and Branca. From the above, one must expect that because of large horizontal movements there are periods in the

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Earth’s history of accelerated and diminished volcanism. Note that, in fact, the time of greatest drift assumed by us, the Tertiary, is recognized for vigorous volcanism whereas, during the prior Jurassic and Cretaceous, drift and volcanism was less. We are not yet able to explain the cause of drift. It is likely to be attributed to extraction of the moon from Earth, which is consistent with a preference for rifting along meridians. This is shown by the shapes of the continents, namely the convergence of oceans toward the poles. Currently it is easiest to recognize toward the old South Pole where the rift configuration has not been disturbed by contraction. Also in the Bering Strait, where the North Pole was probably located in earlier times, land pinches out, only here, through later contraction, the configuration was altered. Perhaps at some time continental drift may be considered coincident with currents in the Earth. I believe the time has not yet come for an analysis of cause.

Geological arguments Faults bordering graben Before we follow processes of continental division and contraction through the Earth’s history, be advised that a first attempt will be incomplete regarding some points and possibly wrong in others. The attempt must be evaluated. Once the main points are established, it will be no problem for further research to extract the mistakes. In studying the tectonics of graben faulting, the gravity measurements are ignored and most persons are satisfied after establishing that the upper layers of the Earth are depressed along linear trends. But gravity measurements show that, in most cases, the specific gravity of material under the graben is greater than that of the adjacent area. So we must assume that we are dealing with a rift in the continental crust in which heavier sima has risen to establish an isostatic balance. As one can compute, when the sima is still 3.5 km deep, such a deep rift will naturally be filled with slides from the graben sides so that it is no wonder when a fill of surface materials occurs similar to what Lepsius showed from drilling in the upper Rhine valley. In my opinion, we can consider all graben as the beginnings of rifts. It may be that we are dealing with some truly recent structures, whereas others may be older attempted rifts in which the forces have relaxed. A very interesting example is the east African graben and its continuation through the Red Sea to the valley of Jordan. Suess considered this from purely geologic evidence as a large cleft. Kohlschuetter made a series of gravity measurements in this area of which most are out of isostatic balance and, except for the obvious defects in structure, they indicated a low density layer. With this overall picture of rifts, which penetrate into, but not through the continent, the heavy sima has not completely risen in them. The graben forming the continental margin show an isostatic compensation. That

means that here the heavy sima rose fully up into the wide rift. This holds true for the width of the Red Sea as was found by Triulzi and Hecker. Atlantic and Andes The general parallelism of the Atlantic coasts should not be underestimated as an argument that these boundaries represent a huge broadened rift. With only a cursory look at the map one recognizes similar mountain ranges on either side (Greenland and Scandinavia), fault zones (Middle America–Mediterranean) and planar regions (South America–Africa) with congruent morphology. In addition, in the parts that are best known, namely Europe and North America, the rocks have continuity on either side. Suess discussed this relationship in various places in his great work. The northern zone is composed of gneiss on both sides; in western European terrains it is the gneiss zone of the Lofoten and Hebrides, to the west is the gneiss massif of Greenland. Also the west coast of Davis straits and Baffin Bay is composed of a gneissic mountain range that can be followed southward through Cumberland and Labrador to the Belle-Isle Strait. Most convincing are the comparisons between the Carboniferous southern foothills structures of the mountains called the Amorican by Suess and their apparent continuation as the Carboniferous coal deposits of North America, as first pointed out by Marcel Bertrand (1887). These locally well-eroded mountains emerge from the interior of the European continent in an arc that begins WNW and then trends west along the west coast of Ireland and Brittany to build a wildly deformed coast (the so called Rias coast). It would be contrary to all previous learning to consider the Rias coast between Dingle Bay and La Rochell as the natural termination of this massive structure. Its continuation is to be found under the Atlantic Ocean (Suess). The continuation on the American side are the Appalachians in Nova Scotia and Newfoundland that trend seaward. Here the Carboniferous fold belt is deformed with a northward vergence, like the European deformed belt, with the typical geomorphology of a Rias coast. Its trend changes from north-east to east. Carboniferous fauna and flora are not only identical, but the ever increasing collection of older strata are identical as well. The many investigations of Dawson, Bertrand, Walcott, Ami, Salter and others are beyond the scope of this discussion. This ripping apart of these transatlantic “altaiden”, as Suess called them, exactly across from each other, is the strongest case for the juxtaposition of these coasts. Older assumptions, that the connecting mountains sunk into the Atlantic as proposed by Penck, run into difficulty because the missing part must be longer than the known part. Further south, the regions are not sufficiently well investigated to draw comparisons. Yet B. Le Gentil believes that the High Atlas continues to the Canary and Cap Verde islands and then the Antilles. Based on a

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comparison of flora and fauna, Engler came to the conclusion that a continental connection existed between coastal points, namely northern Brazil south-east of the Amazon river mouth, and the Bai of Baifra (Kameroon). Suess, in comparing both sides of the Atlantic, commented on a striking similarity with the results of Engler. However, a detailed comparison remains for future investigation. In addition to this so-to-say anatomical description, two interesting questions, which in perspective may appear particularly important, will be touched on only briefly. First the question if on the basis of palaeontological descriptions we can possibly make the connection between America on one side and Europe and Africa on the other up to a specific point in time. Secondly, if this is the case, when did separation occur? Both of these familiar questions have long been worked on and every new theory that comes along is immediately used to correct previous assumptions. These questions are independent of whether one assumes continental drift or submergence of a land bridge. On these grounds it is sufficient to give a short sketch as to what has previously been concluded. First, let’s bring up the points that have made palaeontological results difficult for us: the transgressions. Even for gradual transgressions that can be divided by their fauna and flora, the decision of whether the division is from rifting or transitional seas is difficult. Concerning South America and Africa, biologists and geologists are in close agreement that a Brazilian–African continent existed in the Mesozoic2. V. Ihering called it “Archhelenis”. The newer work of this author and others like Ortmann, Stromer, Keilhack and Eigenmann date the separation with increasing certainty in Tertiary time and specifically at the end of the Eocene or beginning of the Oligocene3. The exact determination of the time is naturally the object of further palaeontologic research. In our hypothesis the great and nearly meridianal rift was formed during this time and the opening of the Atlantic began. A broad connecting land is also assumed between Europe and North America in older Tertiary time, making similarity of coastal configuration possible. Already in the Oligocene it slowed and in the Miocene it stopped altogether. We can assume that the opening of the rift migrated slowly from south to north. Later rifting took place in Europe and North America, at least in the far high northern latitudes of Scandinavia and Greenland. In our view, North America, Greenland and Europe were still connected during glaciation and the sheet of ice had a much smaller extent than has been assumed till now. This does not simplify our understanding of the glacial phenomenon. The picture also agrees with the fact that a steppe climate dominated Europe during interglacial 2 For comparison, among others: ARLDT, “Die Entwicklung der Kontinente und ihrer Lebewelt. Leipzig 1907. 3 According to Haug and Kayser the separation took place before the beginning of Miocene, V. Ihering, Ortmann and Stromer date it Eocene, Stromer and Eigenmann suppose that there was still a connection in late Eocene.

time, as shown by the many remains of steppe animals and is not explainable considering the current proximity of the deep ocean in the west4. So, in these times, the North Atlantic was a small arm of the sea that could not yet influence the climate of Europe. A further interesting relation occurs between North and South America. As Osborn first thought, and was developed further by Schaff, an unconstrained connection between these two continents existed until the beginning of the Tertiary time, broken only towards the end of the Tertiary (Pliocene according to Kayser), to be then re-established in its present form. Until now this pre-Tertiary land-bridge was sought in the area of the Galapagos. We assume it was simply constructed of the northwestern African area and was broken during rifting of the Atlantic. It was re-established simultaneously with folding of the Andes in its narrow form. Because folding of the Andes is of the same age as opening of the Atlantic Ocean, a concept of its origin is a given. During rifting, the American continents migrated westward against the probably old and rigid Pacific Ocean floor, which caused the broad shelf with its thick sediment to contract into folded mountains. This example shows that the salic crust can also be plastic and the sima can behave relatively stiffly. We can assume it likely that sima also deformed so that folding of the Andes does not require a shortening equivalent to the full width of the Atlantic. If we consider the earlier discussed nappe construction, which like in the Alps involved a four to eight times wider area before folding than after folding, then I see nothing contrary to this combination of drift and mountain building.5 Gondwanaland If we apply our previous insights regarding the association between folding and horizontal drift onto the Tertiary folding of the Himalayas, we find a series of surprising relations. If every plate that produced the highest mountain on Earth during collision were of the same size as nappe theory predicts the plates of the Alps were, then a long peninsula must have extended from India whose southern extremity reached the extremity of South Africa. This contractional collapse of a long peninsula explains the unique conditions that surround India “ringsum ein Bruchstueck” Suess. Indeed, based on palaeontology, this kind of an extensive Indo-Madagascar peninsula called “Lemuria” has been assumed for some time. Before its inferred 4 They are sometimes explained by the eastern wind associated with the zone of high pressure above the sheet of ice. Yet, that should not be present in interglacial periods when there are no sheets of ice. 5 The author would like to point out especially that it was necessary to use a schematic presentation. Particularly in North America only the westernmost ranges of the Cordillera are of Tertiary origin, and are getting progressively older towards the east. Of course, only Tertiary folds can be related to the separation of America from Europe.

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submergence it was for a long time attached to the African block and was then separated from it by the widening Mozambique Channel. In our opinion, it migrated north because of the wide meridianal rift. According to Dacque and others, this rift had already formed in the first period of the Mesozoic, namely the Triassic, because in the early Jurassic (Lias) the separation had taken place. Douville also concludes that Madagascar had no connection to Africa in the Triassic. If this is true, this rift between the Indian Peninsula and Africa formed earlier than the one in the South Atlantic Ocean. Contraction of the Indian peninsula was probably not active until the Tertiary and apparently it continues today.6 Furthermore, palaeontological discoveries leave no doubt that Australia once had a direct connection with India, as South Africa and South America once had. This extensive continent, recognized by its current remnants of unchanged size, is called “Gondwana-Land”. We must assume that the Australian continent was also part of the ancient continent that separated during the course of geological time. Australia’s separation from Africa and India appears to have occurred at the same time (Triassic) as the latter two separated from one another. In the Permian these were connected as will be shown in more detail below, and in the Jurassic they were not. On the other hand, Hedley, Osborn, and others state that a connection with South America remained until the Quaternary. This connection probably went through the South Polar continent, but because of little knowledge about this continent the connection is uncertain. Meanwhile it appears that the west coast of Australia was earlier connected with the east coast of India until the Triassic as previously mentioned, whereas the south coast was still bound to the Antarctic. Thereafter, the Antarctic continent migrated from South Africa to the Pacific side in a similar manner as South America. The large mountain chain, of which we only know the ends in Graham-land and Victoria-land, is considered by many to be a direct continuation of the Andes. Australia only parted in the Quaternary and along its east coast it still maintained connection to the Antarctic Andes, which later became New Zealand. These ideas should be viewed as an initial conjecture as mentioned before. The map of the Australian area seems of importance in that this continent and its projection New Guinea travels north, and collides with the southern projection of India. Wallace first noted the great difference between the Australian and New Guinean faunas compared with the sub-Indian ones of Sunda, which are currently con6 In geology, mountain building is commonly regarded in the context of a one-sided force. In particular, the Himalayan mountain building is regarded as coming from the north and not the south. On the contrary, the well-known principle in physics of equal and opposite forces must be noted. Observed asymmetrical structures do not result from one-sided forces, but from other factors such as the differences in size and thickness of the plates, or frictional behaviour that neutralizes the above arguments.

sidered fortuitous.7 Whether the high mountains of northern New Guinea are a product of this northward drift is not yet definitive. Permian glaciation One of the strongest proofs of these ideas are to be found in Permian glaciation (some say Carboniferous), the traces of which have been observed at some places in the southern hemisphere, but are missing in the northern hemisphere. This Permian glaciation was the concern of palaeogeographers. These undoubted moraines on abraded basal surfaces are found in Australia8, South Africa9, South America10 and above all in east India. Koken showed in a special treatment of this subject and on a map with the current distribution of land, that such a large extent of a polar ice cap is impossible. Even if one considers the South American discoveries uncertain, which is hardly possible anymore, and we place the pole in the best position namely in the middle of the Indian Ocean, the most distant inland ice is still 30–33° across. With a glaciation of this magnitude no part of the Earth’s surface would have been ice free. With such a south polar location, the north pole would fall in Mexico where no trace of Permian glaciation is found. The South American glacial outcrops would lie on the equator. Therefore, without continental drift, the Permian glaciation poses an insoluble problem. As Penck has stated, even without all the other arguments, these conditions have brought forth “die bewegung der Erdkruste im horizontalem Sinne als eine ernsthaft in Erwaegung zu ziehende Arbeitshypothese das Auge zu fassen” (horizontal movement of the Earth’s crust is to be viewed as a development of a thoughtful working hypothesis). If we apply the ideas previously developed and reconstruct the Permian glaciation, all the glaciated areas are concentrated at the pointed south end of Africa, and it is only necessary to place the south pole in a greatly reduced area. This appears to remove the unexplained points. The north pole was located approximately in the Bering Strait. We will return to the old pole location and the migration of the pole below. Atlantic and Pacific side of the Earth The gross morphological differences between the Atlantic and Pacific sides of the Earth have been noted for 7 “Wallace’s border”, which mainly applies for mammals, runs through the Lombok Strait between the Sunda Islands of Bali and Lombok and through the Massakar Strait, thus it does not completely correspond to the tectonic continental margins any more. 8 Victoria, New South Wales and Queensland, as well as Tasmania and New Zealand. 9 Lately, similar block clays have been found in the state of Congo and in Togo. 10 In Brazil, the Province of Rio Grande do Sul, and north-western Argentina the layers are still poorly investigated. According to the Swedish expedition to the South Pole, there appear to be similar traces on the Falkland Islands. See E. Kayser, Lehrb. der. geol. Formationslehre, 4. Aufl. 1911, S. 266.

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some time. Suess described them in the following way: the structural trend of folded mountains, rugged Rias coasts, which indicate the submergence of mountain chains, normal fault scarps and plains compose the variable borders of the Atlantic Ocean. A similar structure occurs in the Indian Ocean eastward to the Ganges river mouth, where the end of the Eurasian mountain chain reaches the sea. The west coast of Australia also has an Atlantic structure. With the exception of a part of the middle American coast in Guatemala, where the sweeping cordillera of the Antilles has terminated, all well-known borders of the Pacific Ocean consists of folded mountains with a seaward vergence. The outer structural trends are either borders of the land or fringe them as peninsulas or chains of islands. Around the Pacific, no landward facing mountain flanks meet the sea and no plains extend to the coast. This morphological difference between Atlantic and Pacific has been noted by many others. Becke (1903) recognized a difference between Atlantic and Pacific volcanic lavas. The Atlantic lavas were more alkaline, containing Na, whereas the Pacific lavas are poorer in alkaline components and richer in Ca and Mg. Therefore, Suess poses the question “ob das Zureucktreten von Ca und Mg in der atlantischen Erdhaelfte nicht mit dem Fortschreiten der Erstarrung in verbindung stehen Koennte” (whether the depletion of Ca and Mg in the Atlantic half of the Earth could be connected with solidification processes). Furthermore, a systematic difference occurs in ocean depths. Kruemmel gives an average depth of the Pacific Ocean as 4,097 m and that of the Atlantic as only 3,858 m, whereas the Indian Ocean, with its half Atlantic and half Pacific character, has a 3,929-m average depth. Also the west Atlantic is shallower than the east Pacific. The relation is seen in the deep sea sediment. The red, deep sea clay and radiolarian mud, the two real abyssal sediments, are confined to the west Pacific and the eastern Indian Oceans whereas the Atlantic and west Indian Oceans are covered with “epilophischem” sediment, whose larger calcium content is a result of shallower water depths. As obvious as these differences may be, little was known as to how they could be explained. “the fundamental reason for the difference between the Atlantic and Pacific hemispheres is not known” (Suess). Our hypothesis makes the reasons for this basic difference selfexplanatory. Opening of the Atlantic requires extensive shoving of the continent against the Pacific Ocean. An extensive pressure and contraction occurs along the Pacific coast with each Atlantic tug and rift. The first rifting began off South Africa in Triassic time according to our postulate. This is consistent with the absence of folding after the Permian in Cape Town mountain. In Saharan Africa folding stopped after the upper Silurian along the Armorican Line. One can assume that every broadening rift that brought contraction and compression to the Gondwanan Pacific margins began in earliest geologic time and ended some time ago when Atlantic-form-

ing forces stopped. It is not unimportant that the picture we have drawn of a great age for the Pacific is contradicted by other observations. We certainly have no possibility of establishing this age without question. The sharks teeth of Tertiary age, which are found enclosed in red clays of large Manganese nodules, and also the many meteoritic spheres, mean only that the nodules are formed slowly, as according to many investigators. Because they are also found in the deepest parts of the Atlantic, below 4,000 m, their origin is obviously more a function of depth rather than time. The views of Koken, Frech (Lethaea palaeoyoica) and others, that the Pacific has existed for a geologically long time, is generally accepted by geologists and oceanographers. Perhaps we have now won the opportunity to explain the differences in ocean depths. Because we must assume regional isostasy for the seafloor, the difference, according to our postulate, indicates that the older seafloor is denser than the younger. The idea is not out of hand that fresh vesicular expanses of sima, as in the Atlantic or the western Indian Ocean, are not only less rigid, but also retain a higher temperature (perhaps around 100° in the middle of the upper 100 km) than the cool, older strong seafloor. And such a temperature difference is probably sufficient to explain the relatively small comparative differences in depths of the large ocean basins. Polar wander Despite the broad and justified view brought from a geological perspective against assumptions of polar wandering, it is exactly from this same perspective that so much material has been recently discussed regarding extensive polar movement. This information can be regarded as substantiated. During Tertiary time, the North Pole wandered from the side of the Bering Strait towards the Atlantic and in the same way the South Pole wandered from South Africa towards the Pacific. In the two oldest divisions of Tertiary time, namely the Palaeocene and Eocene, the western European climate was definitely tropical. Also, in the Oligocene, palms and other evergreens were distributed along the current coasts of the Baltic Sea. Upper Oligocene rock of the Wetterau contains much wood and the remains of fossil palm leaves. But in the beginning of the Miocene, there were many subtropical plants in Germany such as rare palms, Magnolia, laurel, myrtle, etc. These later disappeared as it became progressively colder so that in the last part of the Tertiary, the temperatures in middle Europe were not much different from current ones. Then followed glaciation. These changes clearly showed the approach of the Pole. The same polar wander is observed outside Europe. At the beginning of the Tertiary, when the Pole was in its old position, classical investigations like those of Heers, show beach, poplar, elms, oak and even “taxodien”, banana, and Magnolia on Greenland, Grinnell land, Barren Island, Spitzbergen, – locations that are currently 10–22° north of the tree line.

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That we are in fact dealing with a change in Pole position and not a climate change over the whole Earth is shown by the investigations of Nathorst regarding the Tertiary flora of east Asia. He concludes that the climate of this area underwent a warming during European glaciation. He positioned the North Pole at 70°N and 120°E. The strongly polar Tertiary flora of the new Siberian islands was at 80°N during that time. The flora of Kamchatka, the Amur lands, and Sakalin had a somewhat warmer character and latitude of 67–68°, whereas flora with an even warmer character such as those of Spitzbergen, Grinell land, Greenland, etc., had evergreen trees and were outside the polar circle at that time, with latitudes of 64, 62 and 53–51°N, respectively. Other authors, like Semper, came to similar conclusions and the reality of these large wandering paths can no longer be seriously doubted. It seems impossible that during its Tertiary wandering, the North Pole came directly to its present position and has remained here unchanged since glacial times because its location would have been 10° from the border of every large continental ice cap. In those times the glaciers had a distribution similar to the current Antarctic ice cap and covered north America and Europe. Naturally it can be assumed that the Pole was first at least 10° farther toward Greenland and wandered back to its present position since glacial time. It is of great interest to reconstruct the coeval location of the South Pole. If the North Pole was translated 30° toward the Bering Strait, so the South Pole must have lain 25° south of the Cape of Good Hope or on the South Polar continent that apparently reached this latitude in those times. In the better known parts of the southern hemisphere very few, or perhaps no signs of glaciation would be expected. Contrary to this is the previously discussed Permian glaciation during which drift was greater (perhaps 50°). At that time, the North Pole was far from the Bering Strait in the Pacific, but here, after considering the evidence, we are persuaded to remain more cautious because our picture of the shapes of the ancient continents becomes increasingly unclear. Therefore, it seems to me that investigation of conditions in even older geologic times, such as the traces of pre-Cambrian glaciation of China (in the Zangtse area), in south Australia near Adelaide (Willis), and apparently also in Norway (Hans Reusch) is not worthwhile. Only a unique situation is considered. Green and Emerson have concerned themselves with the great Mediterranean zone of deformation that circles the Earth, and concluded that it is an old equator. In fact this could be the equator for all assumed Mesozoic pole positions during which time the North Pole was in the Bering Strait and the South Pole was south of Africa. Even if there are some doubts about the concepts of these authors, it is worth considering that this deformed zone might be the result of extraction of the moon from the Pacific, which affected the equator most. Of greatest importance for an understanding of all observations is that major polar drift is apparently coeval

with the greatest continental drift. Particularly evident is the temporal correspondence between opening of the Atlantic and the most believably established Tertiary polar wander. Also, the relatively small return wander of the North Pole since glacial times can be correlated with the separation and drift of Greenland and Australia. Thus, it appears that large continental drift is the cause of polar wander. In any event, the pole of the Earth’s rotation must follow the “traegheitspol”. If the “traegheitspol” changes, so too must the pole of rotation. (If the Earth’s mass shifts through continental drift it will perturb the pole of the Earth’s rotation.) These relations were investigated by Schiaparelli. He found that if the Earth is considered rigid, the large geologic changes (assumed up to now) will cause the “traegheitsachse” and the pole of the Earth’s rotation to change even with a small change in drift. If a particular plasticity is assumed for the Earth, which allows a latent adjustment of the Earth’s shape to the new rotation, fairly significant polar wandering is observed. In the case of even greater masses and more plasticity, there is no delay in adjustment of the Earth’s shape to the conditions of rotation. Here we must make use of results from geophysics in a context of geologic time as seen in the preceding text. Multiple attempts have been made to calculate polar wandering, which might be substantiated by an observed shift of mass, as for instance by that measured during earthquakes. This led to the conclusion that polar wandering must be small. Hayford and Baldwin found that, during the 1906 San Francisco earthquake, a 40,000-km2 section of the Earth’s surface, 118 km thick with an average density of 4, moved 3 m northward and that this resulted in a shift of the “traegheitsachse” of only 0.0007”, or 2 mm. In our concept we deal with movements of plates 100 times larger and thus could reach the required amount. In any event, one can see that in this way small progressive migrations of the “traegheitspole” could occur amounting to some one-hundredth of a second (of arc) per year (or 1° in 360,000 years). With this amount we come to an order of magnitude with which we can explain the geologic polar wander. The correspondence between these values and our inferred continental drift appears theoretically plausible even though a rigorous investigation has not yet been made.

Current horizontal movement Greenland Lets assume that the separation of Scandinavia from Greenland occurred 50,000–100,000 years ago (about at the time of major glaciation, because the recent investigations of HEIM and American geologists indicate only about 10,000 years appear to have passed since the last glaciation). If we assume the movement was at a uniform rate during the whole time and continues today, it would be 14–28m/year, a rate that should be confirmed without difficulty by astronomical observations. At only one

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point, namely on Sabine Island on the east coast, are measurements of latitude from various times available. It is shown that between 1823 (Sabine) and 1870 (Börgen and Copeland) an increase in distance of around 260 m occurred, and between 1870 and 1907 (Koch) a further increase of 690 m occurred, which together make an increase in distance of around ca. 950 m in 84 years or about 11 m/year. Unfortunately, these measurements, using the moon, are not very accurate and, in addition, there is a certain uncertainty about the position of Sabine’s observatorium. Therefore, one can hope that a repeat and precise determination of longitude and a revision of Sabine’s observatorium will soon remove the last doubts about the reality of this movement. North America For North America, we expect a much smaller rate because the separation from Europe occurred in the Tertiary. On the other hand, we have here the trans-Atlantic cable making possible a much more exact determination. According to Schott, the three great measurements of length from 1866, 1870 and 1892, show the following values of distance (time) differences between Cambridge and Greenwich: 1866: 4 h, 44 m, 30.89 s; 1870: 4 h, 44 m 31.065 s; 1892: 4 h, 44 m 31.12 s. These observations appear to indicate an increase in distance of about 1/100 second in time or 4 m/year. Because the current distance is about 3,500 km, this movement would account for the separation distance after 1 Ma of drift. Naturally these values are hardly considered adequate to prove continental drift because the observed difference of 0.23 s is in the worst case uncertain due to the

precision of older observations. Because 20 years have passed since the last determination of length, it might be possible, by a repeat measurement today, to produce one that is definitive. A similar investigation of the expected distance change to Australia has not been possible. If the numbers are, as it appears to me, not better than the accuracy of current measurements, then it is clear that more accurate determinations will be needed before the proof of continental drift, in the sense of our hypothesis, can be considered accomplished.

References Ampferer, Über das Bewegungsbild von Faltengebirgen. Jahrb D Kais, Kgl Geol. Reichsanst, 56, Wien 196, S 539–622 Böse E Die Erdbeben, Sammlung: Die Natur. Ohne Jahreszahl, S 16, Anmerkung Kohlschütter E, Über den Bau der Erdkruste in Deutsch-Ostafrika. Vorläufige Mitteilung. Mitt K Ges Wiss. zu Göttingen 1911 Koken (1907) Indisches Perm und die permische Eiszeit. Festband d neuen Jahrb Min Geol Paläont Krümmel (1907) Handbuch der Ozeanographie I, Stuttgart, 87 Loukaschewitsch (1911) Sur le mécanisme de l’écorce terrestre et l’origine des continents. St. Petersburg, S 7 Penck (1906) Süd-Afrika und die Sambesifälle. Geogr Z 12.22: 601–611 Reyer (1907) Geologische Prinzipienfragen. Leipzig Rudzki (1911) Physik der Erde. Leipzig, S 122 Scharff (1909) Über die Beweisgründe für eine frühere Landbrücke zwischen Nordeuropa und Nordamerika. Prod R Iris Ac, 28, Bd 1, 1–28 Suess (1885) Das Antlitz der Erde, Bd I, 778 Suess, Antlitz der Erde II, 164; 256; III, 60 u 77 Suess (1881) E. Beiträge zur geologischen Kenntnis des östlichen Afrika. Die Brüche des östlichen Afrika. Wien Taylor FB (1910) Bearing of the tertiary mountain belt on the origin of the earths plan. Bull Geol Soc Am 21:179–226 Willis B (1910) Principles of paleogeography. Science, N. S. 31(790):241–260

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G. Steinmann

Are there ancient deep-sea deposits of geologic significance? Geol Rundsch 16:435–468

Translation received: 28 February 2002 © Springer-Verlag 2002

Today, when the permanency of continents and of the Pacific is a favorite topic of scientific discussion, with the breakup of an ancient landmass into today’s continents (as proposed by Wegener) high on the agenda and even accepted by some as firmly established, the need for an accurate answer to the above question seems especially urgent – for the answers given are entirely irreconcilable, as is well known. There are researchers who categorically deny the occurrence of deep-sea deposits on today’s landmasses, as do Dacqué, Deecke, Scrivenor, Soergel, Walther and others, and on the other hand, there are those who admit a not insignificant dispersion on today’s landmasses of such deposits, and thus a considerable importance for the problems of geogeny, as does this author and, with him, many others such as Andrée, Cornelius, the two Heims, Hinde, Kober, Molengraaff, Neumayr, Nicholson, Parona, Suess, Staub, Uhlig, and Wähner. An intermediate position is taken, for example, by Diener (1925) who finds it necessary to call on the yet poorly known Danau formation of the Sunda region to find examples for ancient deep-sea deposits, as he denies that the much closer occurrences in the Alps and Apennines in fact possess the character of deep-sea deposits, basing his case on the chert breccia of the Sonnenwend mountains, which is in every way disputable and unascertained in its significance. Such large differences in opinions naturally can proceed only from an incomplete knowledge of the occurrences in question. In fact, intensive and comparative investigations of the matter are almost entirely missing and, in particular, there is yet lacking a clarification of certain disputable or uncertain occurrences which have been identified as of decisive significance by some authors. Translated by Wolfgang H. Berger W.H. Berger (✉) Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA e-mail: [email protected]

Apparently, there is, in many instances, a fundamental aversion to admit the existence of ancient deep-sea deposits within today’s landmasses. And yet there is in essence no basis for this attitude. We know full well of marine and terrestrial deposits which were created in sufficient abundance within a relatively short period, with thicknesses of, say, 5–6 km. In such cases, no one doubts that the Earth’s crust subsided by an appropriate amount. If the subsidence involves a region close to a mountainous landmass with high rainfall, and perhaps rising concurrently, the basin can be entirely filled with clastic sediments. In another region, with similar subsidence but little or no clastic sediment input, a calcareous or calcareous-clayey sediment perhaps half as thick or even less will deposit over the same time interval, so that at the end of subsidence a deep-sea environment of 2,000– 3,000 m will exist, in which the seafloor is composed of eupelagic calcareous ooze. If, at the same time, conditions are favorable for dissolving carbonate within the subsiding basin, a thin layer of deep-sea Red Clay must form within a deep-sea environment of 4–5 km, the seafloor being then covered by typical deep-sea sediment. The difference between these three geotectonically equivalent regions is rather one of chance and is independent of the process of subsidence by itself. Of these similar regions, therefore, it is not evident why only those which are wholly or partially filled with thick sequences of sediment qualify for later incorporation into a continental mass but not the others which, for reasons unrelated to orogenic or epeirogenic processes, received but little deposition. This fictitious example is meant as a reminder for the obvious fact that, with respect to tectonics, the significance of deep-sea deposits does not differ from that of shallow-water deposits of corresponding thickness. It is by no means easy to arrive at a correct judgement of the issue of ancient deep-sea deposits from one’s own observations. Among the widespread epicontinental sequences which are generally but little deformed and easily accessed, such deposits are missing – one must look for them in the intensely folded orogenic belts of the

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past. There too, however, they are sufficiently inconspicuous compared to other sediments, because of their modest thickness and the lack of macroscopic fossils, to be easily overlooked or, at least, not given the attention they deserve. Within highly deformed and largely covered, ancient folded mountains, such as the Caledonian and Variscan chains, they can be followed for only short distances whereas in the younger alpine belts, where conditions are less severe, acquisition of clear insights is often impeded by the commonly extreme complication of the geologic structure. As a result of the nappe structure, sequences of entirely different ages and from greatly separated regions of origin are quite regularly brought into direct contact, and are melded so closely and also so greatly altered that the visible relationships are readily interpreted incorrectly, as I shall show in the following. When interpreting the sequences in question, therefore, it is necessary to choose areas where they occur in minimally altered condition and within tectonic settings which are not inordinately complex. Within the alpine mountains, examples are found in the Lombardian belt of the Dinarides and in certain parts of the Apennines, especially the Ligurian and Toscanian [mountains]. Having occupied myself with these matters for several decades but having published my observations in a brief manner only, and having been enabled by the arrival of normal travel conditions to review and extend my earlier observations in the Alps and Apennines, I believe I can contribute something new to the solution of the problem being debated. For those desiring to study the present state of the problem, the publications of Andrée (1920, 1924) offer the best summaries.

Classification of marine sediments The known deposits of recent seas provide the basis for the interpretation and classification of ancient sediments. However, it is obvious that this basis is incomplete. Not only is our knowledge of the character of the seafloor quite limited but especially there is a lack of extensive profiles across the seafloor. In addition, the particular historic moment in which we happen to live takes too much center stage regarding our knowledge and the scheme of classification. An independent classification, equally applicable to ancient and recent formations, would be highly desirable instead. For example, when we find a dense limestone of the lower Cretaceous which consists almost entirely of coccoliths and some radiolarians and calpionellids but with few globigerines, and when this sediment, in terms of both lithologic character and geologic setting, must be interpreted as a deposit from considerable ocean depth, corresponding to Globigerina ooze, the label Globigerina ooze is still misleading for this sediment – neither does it contain globigerines in high abundance nor is it an ooze. It seems that not until the younger Cretaceous do the globigerines attain a dominant role among planktonic foraminifers; one knows them as but sparsely represented in older layers

(and apparently, the same holds for pteropods). Such deposits of similar origin from different periods and in different diagenetic stages would merit uniform classification. The same is true for an ancient Red Clay which we find as sericite shale of yellowish or greenish color. In this case, too, the name leads astray. Our meager knowledge of modern marine deposits and the fact that they represent but one of the many historically available conditions make it indispensable to complete the present classification on the basis of ancient sediments. It seems appropriate to use the Haugian labels neritic, bathyal and abyssal besides the groups introduced by Murray – littoral, hemipelagic and eupelagic. Hereafter, I shall employ the following classification of eupelagic sediments.

Subdivision of eupelagic deposits In correspondence to the categories of depth zones proposed by Haug, I label all deposits outside of the neritic and bathyal regions (that is, generally those formed in depths of more than 900–1,000 m) as abyssites and subdivide these further into: 1. Hemiabyssites (or hemipelagic deposits) [These are] formed in depths of 1,000–2,000 m on average. We will not further consider these very variable sediments here, since they do not represent deep-sea deposits in the geologic sense, and since hardly anyone can doubt that they are significantly represented in the fossil state. 2. Hypabyssites Under this name I include the calcareous or clayeycalcareous deposits which today are formed in depths of about 2,000–4,000 or 5,000 m. To this group belong above all the white deep-sea ooze (Globigerina and coccolith ooze) as well as the pteropod ooze which is close to hemiabyssal deposits, and also clayey-calcareous to purely clayey deposits such as form today as Blue Mud at considerable depth. The silica-rich diatom oozes likewise would be part of this group. Within the hypabyssites I recognize a) Abyssokonite (from konia = Kalk) I define [this] to include all pure or almost pure calcareous deposits with dominantly whitish or also light gray or light reddish and greenish color, which are known among the present marine deposits as Globigerina ooze and coccolith ooze (or pteropod ooze). When lithified, they appear mostly as dense, lightcolored limestones or marly limestones, on occasion with some chert, or as irregular lenticular [flaser] limestones with thin, mostly wavy clay layers, such as the aptychus limestones, or as nodular, gray, yellow and red cephalopod limestones with etch sutures [stylolites]. By addition of large amounts of radiolari-

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ans, such deposits grade into radiolarian limestone which in turn passes into euabyssal radiolarites. Outstanding features are a paucity of iron sulfide and an abundance of stylolites, both a result of significant participation of oxygen and carbon dioxide in the origin of this facies.

mented extensively on the characteristics of these true deep-sea deposits on earlier occasion (1905), I feel it necessary to make additional remarks since erroneous interpretations did not fail to materialize. For the rest, I can refer to the accurate remarks of Andrée (1925, pp. 519–525).

b) Koniapelite As the name is supposed to indicate, these are clayey to clayey-calcareous deposits with a marly character or clays with dark limestone nodules or layers. The Blue Muds occurring at considerable depth are presumably the equivalent sediment in today’s ocean, as yet unaltered by diagenesis. A more or less important admixture of dark clay, and a commonly finely distributed component of iron sulfide (and the consequent rusty weathering) must be interpreted as typical markers and a result of poor aeration during genesis of the rock. For the ancient deposits, as for the hypabyssal sediments, the general lack or the extreme rarity of true benthic organisms can be taken as typical, as well as perhaps the fact that bituminous matter becomes unimportant. An accurate separation of such dark hypabyssal nodular clays from similar hemiabyssal deposits will not always be easy.

a) Radiolarite [Radiolarite] – a label which I herewith extend to all pure radiolarian accumulations with a deep-sea origin, independent of the condition of preservation – is distinct from similar radiolaria-rich deposits with which it is commonly compared or even lumped, in that these sediments are practically wholly carbonatefree and clay-poor but commonly manganese-rich. Also, they often occur in intimate connection with rocks of the colored, deep-sea clay type, and furthermore are found under- and overlain by true hypabyssal sediments but never in primary association with true shallow-water deposits. Some observations apparently in conflict with these characteristics will be shown below to rest on erroneous interpretations. The known radiolarites of Paleozoic and Mesozoic age moreover turn out to be free of remains of benthic organisms, like most of the other euabyssal and hypabyssal deposits of those periods. It is obvious that a real radiolarite cannot occur in sequences alternating with shallow-water sediments, or form transgression conglomerates, as claimed in a number of cases. In the Alps as in the Apennines, one commonly observes how the radiolarite of the upper Jurassic changes into colored deep-sea clays – upwards, downwards, or laterally – within alternating sequences. For such clays I propose the inclusive term [abyssopelite].

c) Skleropelite We may be certain that the ancient equivalents of today’s diatom ooze are practically unknown as marine deposits; yet, we must assume with high probability that they are not absent. They should be represented by silica-rich rocks with varying content of carbonate, such as siliceous shales or clay-rich limestones without the remains of benthic organisms. There is little chance, however, that the siliceous fossils themselves will still be found therein. As one observes in the skeletons of siliceous sponges and radiolarians, the organically produced amorphous opal is almost invariably transformed by diagenesis, that is, it is dissolved and replaced by calcite, pyrite, glauconite, etc. Given sizeable organisms (which includes also the radiolarians), the characteristic morphology of the fossil or some of its parts still permits recognition in most cases. This is not so for the diatoms, however, because successful observation in thin section is limited to low magnification (owing to pervasive alteration by diagenesis or regional metamorphism) and it is therefore impossible to recognize such small objects if one cannot prepare them by etching with hydrochloric acid. True, one has found some diatoms here and there within Mesozoic deposits, but one knows almost nothing of the plethora of species and individuals which, seeing their abundance in the Tertiary, are to be expected in older times, too. There is a wide field for research remaining here. 3. Euabyssites Here belong the colorful, otherwise red, deep-sea clays and the pure radiolarites. Although I have com-

b) Abyssopelite This type of rock shows varied coloration, is extremely fine-grained, almost free of organic remains with the exception of occasional radiolarians, and not uncommonly rich in manganese, like the radiolarite. In its lithologic character as in its distribution and association, the abyssopelite displays all the characteristics of the so-called “red” deep-sea clay.

The Mesozoic abyssites in the Alps and Apennines The fact that even today many an author disputes that radiolarites, abyssopelites and abyssokonites of these mountains have the character of deep-sea deposits reflects mainly the lack of sufficient, detailed investigation. It is known for some time now that such rocks, with surprising uniformity in their character and association, extend not only throughout these two mountain chains but also through the Dinaric chains right to the Peloponnesus and beyond, but there are essentially no specialized investigations supported by microscopic investigations on these rocks. Furthermore, a few occurrences

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where apparently coarse clastic sediments are in primary association with these rocks are brought up again and again to dispute their nature as deep-sea deposits. The following observations may redress this deficiency, at least in part. A. Abyssal rock formations of the Southern Alps No second region within the Mediterranean mountain chains is probably better suited for the investigation of the nature of the rocks in question than the western portion of the Southern Alps. Here, especially in the region of the Lombardy, they not only become much more accessible than in most other parts of the Alps but they also occur in a nappe-free zone, below little disturbed and only locally somewhat complex tectonics, where metamorphism is practically lacking. Sections such as the one often described from the Breggia canyon near Como (Heim 1906, Renz 1920) reveal a distinct sequence from the Liassic to the Cretaceous. The radiolarite stands out as the most prominent member with a thickness of about 40 m (gradually thinning to the east). Its age is here more easily determined than elsewhere because it contains, besides the well-preserved radiolarians, only fossils of the Malm and it is in many places overlain by upper Tithonian aptychus limestones with characteristic fossils. What remains uncertain is how deep down it reaches into the Jurassic. Presumably it embraces in essence Oxfordian, Kimmeridgian and lower Tithonian. All observers of this region – myself included – agree that we have here a continuous sequence of layers from the Liassic to the Barremian, as well as a grand cycle whose core is the radiolarite and the colored shales, that is, euabyssal deposits. From the lower Liassic to the Sowerbyi horizon of the middle Dogger, the various intervals are readily recognized based on rich ammonite occurrences, but then there begins a roughly 50–60 m thick sequence of calcareous to marly character which has no fossils up to the radiolarite. Purplish red or grayish green clays occur within the limestones, chert nodules and chert strings are dispersed rough it, and large lime nodules are found within the colored marls. A detailed microscopic investigation which this sequence merits is yet to be done, but one can nevertheless agree with the interpretation, repeatedly expressed since Neumayr, that the sequence must contain the unfossiliferous intervals of the middle and upper Dogger and likely also of the lowermost Malm, and that the paucity of fossils is sufficiently explained by its deep-sea nature. Within the overlying radiolarite, which gradually emerges from the older layers by an increase of siliceous layers, there are indeed fossils but remarkably no benthic ones, only plankton and nekton – aptychus, belemnites, cephalopod beaks and radiolarians. In this context, I would like to mention an extraordinary and rare find which we made in the year 1924 during a student field trip above the Breggia canyon in the

radiolarite. On the surface of an outcropping bed one noticed many, quasi-circular thin shells of calcite, lying closely next to each other, which appeared to be the first remains of benthic organisms. Upon closer inspection these shells could be recognized as having a spiral arrangement in their aggregate, and also there emerged the shadowy imprint of an ammonite spiral with a wide omphalus, fitting the shape of Perisphinctes. I made a second, similar find within the Breggia canyon proper. These finds prove that in reality ammonite shells, overgrown with the thin-shelled Ostrea roemeri, were embedded within the deep-sea sediment but subsequently dissolved, an occurrence which is likewise known from the Solenhofen limestone. The calcitic composition protected the shells from dissolution here and there, as well as the aptychi, belemnites and cephalopod beaks, whereas the aragonitic ammonite shells disappeared already during sedimentation. Overlying the radiolarite there is either Tithonian aptychus limestone or else, as here, directly the white, compact limestone of the Biancone (or Majolica) which still belongs to the Tithonian in its lower parts but to the Neocomian to Barremian in its upper ones; it can be followed throughout the Southern Alps in a thickness of about 100 m. What is this limestone which represents the declining limb of the deep-sea cycle? Blumer, who studied Heim’s (1906) collections microscopically, describes it as “extraordinarily pure limestone, a typical foraminiferal rock with extraordinarily uniform foraminifer fauna”. The foraminifer is Calpionella alpina which is characteristic for the transitional layers between Jurassic and Cretaceous (Steinmann 1913), and whose value as a guide fossil is being thrown in doubt by Parona (1917), without apparent reason. Nevertheless, the rock is yet incompletely characterized, and as such not entirely correctly. It is not, to be sure, a foraminiferal rock in the true sense of the word. Although calpionellids are indeed widely dispersed throughout the rock, their share in the composition of the formation remains nevertheless negligible. Arn. Heim (1924) has rightly emphasized the fact (known to all microscopists) that the proportion of foraminifers or radiolarians in the composition of the rock which is named after them is quite minor, even when the shells are densely packed and fill the entire rock. The interior of the shells and the interstitial spaces between them contain by far the dominant mass of the rock. In the case at hand, however, the calpionellids are dispersed, albeit sparsely, throughout the basic matrix, even in the richest of the thin sections, so that one readily arrives at the thought that this fine-grained matrix is an inorganic precipitation of calcitic carbonate, and the shells of the planktonic organisms therein are but “accessory components”. This interpretation was advocated for the dense limestones by Arn. Heim (1924) with strong conviction, and he has ascribed the presumed error in deriving such limestones from an organogenic origin to “the old-fashioned single-track paleontologic-stratigraphic methodology as still practiced today at important universities”. And yet Arn. Heim had but to apply this outmoded

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Fig. 1 Polished piece of the fault breccia next to Sass Ronzöl near St. Moritz, somewhat greater than twice natural size. White Verrucano, black radiolarite and abyssopelite; the finest veinlets of the latter are not visible. The various clasts of the Verrucano cannot be distinguished where they are in direct contact; only near a can a crushed granitic clast be recognized

methodology to the pure limestones of his country, such as the Biancone under discussion, to come to wholly different and positively certain results. To wit, especially if one studies thin sections of the Biancone at magnifications of about 20–40, the matrix appears finely dotted, as if pricked with the finest needles, and makes it seem as though we are dealing with a finely crystalline aggregate of inorganic structure. When taking the magnifications to about 80 and beyond (up to 200), the dots emerge as well-bounded, quasi-circular disklets with a diameter of 5–14 µm and with a dark core, [i.e.,] as excellently preserved and reliably identifiable coccoliths! They are packed so densely that the matrix is almost entirely composed of them. Since it is not possible to gain a clear picture using microphotography, I have asked the masterful R. Schilling, formerly illustrator for the university, now artist and painter, to produce a drawing (Fig. 1) which reflects what one can observe on such difficult objects. The picture is admittedly [and] necessarily incorrect, inasmuch as only those coccoliths appear in it which lie in the plane of the section, but not those which were cut at an angle or vertically. These are commonly not distinguishable from the very fine, grainy pattern between the distinct coccolith disks and were therefore depicted as grainy background. Owing to the nature of the object, the application of even higher magnification is not possible. Still, the important fact remains – the seemingly purely inorganic rock is a genuine coccolith limestone, dominantly composed solely from these remains, and the calpionellids appear in it only as guiding inclusions. The disks of the coccoliths lie densely crowded next to each other but even so there remains a certain amount of space between them, which is filled with the very finest grainlets, just barely distinguishable at 200 times magnification, with a diameter of about 1 µm. They do not at all appear as crystals, but as roundish globulets for which one may perhaps presume a fine, fibrocrystalline

structure. Yet, nothing certain can be observed about this. What are the globules of this matrix? We do not know organisms making such globules of calcitic carbonate. I can accept this precipitation of calcite only for the “lime precipitate of decay”, as it is called somewhat ponderously, that is, calcite which originated as a chemical precipitation through the intermediate stage of marine decay-derived ammonium carbonate produced within decaying protein itself. The precipitation which one obtains experimentally from protein decay likewise consists originally of such minute “calcosphaerites”, from which develop subsequently during continuing growth somewhat larger globules with clearly recognizable sphaerolithic structure or aggregates. Yet, they all remain very small in this case, although we need to remark that size determination, here at the limit of microscopic resolution, presents great difficulties in itself. Unindurated carbonate sediments such as writing chalk would probably be more suitable for a more detailed investigation. Finally, within the rock there must be yet a last kind of calcite, to wit that component which binds the others into a compact rock. Since originally only a soft ooze was deposited, this cement can be formed only through diagenesis. We may perhaps be allowed to imagine that, in the course of decay of the remains of organic material within the ooze, there was the production of carbonic acid which dissolved a portion of the calcareous components which was then reprecipitated upon expulsion of water and carbonic acid, and thus cemented the ooze. Where carbonic acid was available in insufficient amounts, the cementation would have been incomplete or lacking, as for the writing chalk. With respect to this cement, we cannot say more regarding the formations we are describing; its presence can only be deduced from theory. To summarize, then, the dense Biancone limestone is composed of 1. Planktonic foraminifers and radiolarians in low abundance. Rocks which essentially consist of accumulations of such tests could best be referred to as ostracokonite. Many a Globigerina ooze, present and past, would merit this label. 2. Coccoliths, which provide the dominant mass of the rock. Therefore, such a rock can be labeled coccokonite. 3. Calcosphaerites, which fill the narrow interstitial space between the coccoliths. According to the origin postulated herein, a rock which is formed essentially from these elements would be a saprokonite. We do not yet know whether such formations exist as ancient deposits. Moreover, their recognition would present great difficulties, but the present-day calcareous muds and oozes probably partly belong here. 4. Diagenetic calcite, which would best be referred to as metakonite, since it was evidently formed from the secondary transformation of existing carbonate. Naturally, this type of calcitic carbonate can only occur as a subordinate component in other limestones.

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The Biancone exhibits the composition here described not only in the Breggia canyon but also in other places in the Southern Alps, e.g., at the exit of the Olona canyon. I found the coccoliths most readily recognizable in a piece of dense Tithonian limestone from Col Torond in Venetia, collected by the late Georg Boehm (Fig. 1). As is well known, Biancone is not only present with a thickness of on average 100 m throughout the entire realm of the Southern Alps but it also forms a ubiquitous member of the calcareous Apennines, showing the same macroscopic appearance and the same rarity of fossils, essentially but rare ammonites. It is the “Felsenkalk” of Zittel, the “calcare rupestre” of the Italian geologists. Similarly, it forms, as a rule, the formation overlying the radiolarite within the ophiolite nappe of the schistose Apennines (Lepontine facies), just as it does in the Southern Alps. These are dense and bright, at times somewhat reddish or grayish green limestones with siliceous nodules, “litografici” as they are nicely called, in distinction to the Tertiary marly limestones. I have reported earlier (1913) about their nature and their association with radiolarites, and about the occurrence of Calpionella therein, and have emphasized their congruency with Biancone. When studying their matrix by microscope, one notes at low magnification the same fine dot pattern as with the Biancone. However, because of the greater transformation experienced by these rocks, the picture is not resolved into recognizable coccolith disks at higher magnification. Still, once one has seen the clear images of the Biancone, one has no more doubts about the coccokonitic nature of these rocks as well. According to the rare ammonite finds in the Biancone, it represents, besides the upper Tithonian, the lower Cretaceous up to and including the Barremian, which is present in the uppermost, rather more marly and dark shales (Rasmuss 1912), without there being even a hint of a break in deposition. Compared to the kilometerthick sequences of the same time period in other alpine regions, for example, in the Helvetids, the diminutive thickness is readily explained by the nature of the Biancone as deep-sea sediment. The sections studied prove the rock to be a pure coccokonite with hardly more than 10% of other components. This argues for a true, deepsea deposit in depths of 3–4,000 m, according to presentday experience (Andrée 1920, p. 453), and the immense extent of the uniform sediment, which I estimate as about 1,200 km long with a width of 100–400 km for the Southern Alps and Apennines, marks it as a normal deposit of a true ocean, in no way formed under special circumstances. If we take the Biancone in its entire thickness as consisting of the same material represented by the samples so far investigated, the time necessary for its deposition would span at least 50, but more probably 100 million years, according to the calculations made by Lohmann (Andrée 1920, p. 453). However, I consider that these estimates are much too high and believe that as yet they lack a reliable basis. Besides, it would have to be established through additional studies whether the Biancone is indeed a coccokonite in its entire thickness.

According to the consensus of researchers who have studied these sediments, the sea shallowed towards the end of the early Cretaceous, so that the deep-sea cycle was completed with the beginning of the upper Cretaceous. Rudist limestones in the eastern parts of the Southern Alps, a Scaglia which becomes more sandy, and the Hippurite conglomerate of Sirone are typically neritic formations. Wähner (1886, 1892) has shown for the Northern Alps, and after him Rasmuss (1912) for the Southern Alps, how the Jurassic sea deepened gradually, beginning with the Liassic. In the middle Liassic it becomes bathyal in the Dogger abyssal, whereupon the remains of benthic organisms, if preservable at all, disappear. The upper parts of the Dogger are already truly hypabyssal in the Southern Alps, the radiolarite and the associated abyssopelites are obviously euabyssal, and the aptychus limestones and the lower parts of the Biancone again hypabyssal. Also, many of the red nodular cephalopod limestones of the upper Malm must be counted as hypabyssal, as they represent the aptychus limestone facies, for example, in the lake region, in narrow, locally restricted occurrences (Rasmuss 1922). The increase in the content of clay, together with the darker coloration in the uppermost layers of the Biancone, may probably be ascribed to the beginning of a hemiabyssal regime. The subsidence of the floor of the Jurassic sea towards hemi- and hypabyssal depths resulted generally in a disappearance of the remains of benthic organisms which are still present in the deposits of the preceding, shallower seas. Evidently these organisms were unable to adapt rapidly enough to the unfavorable conditions at great depths in the ocean. Cephalopods and shark teeth remain almost on their own. Stem sections of crinoids, which were found very occasionally, were probably transported on nektonic organisms on which they resided, like the above-mentioned, thin-shelled oysters. Only one group of brachiopods, the Diphyae (Pygope), seems to have emigrated early on to great depths. Thus, Zittel as well as Italian researchers and Rassmuss found representatives at a number of places in the Tithonian hypabyssites of the Southern Alps and the Apennines, and I myself encountered the species in a silica-rich clast of the same horizon in the Val Trupchun (Bünden). Otherwise, also in the lower Cretaceous we often find only Pygope, besides the cephalopods, as in the Stockhorn limestone of the Buochser Klippen and elsewhere. In the aptychus limestones of the Oberengadin, Zöppritz (1906) documented, besides cephalopods and shark teeth, also the small solitary coral Trochocyathus truncatus Zittel, as well as Phyllocrinus cf. oosteri which is also known from the Neocomian of the Freiburg Alps. Likewise, Schiller (1906) reports, from the neighboring Lischanna region, Trochocyathus truncatus, crinoids, sea-urchin spines and a gastropod, but from horizons which presumably are already quite close to the boundary towards the hemiabyssal. From these fossil finds we may deduce with some certainty that only few shelled organisms had settled the hypabyssal regions between 3,000 and 4,000 m, near the boundary of the Jurassic and Cretaceous periods.

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B. Abyssal formations of the Apennines Because of their accessibility, the formations in question are especially suited for more detailed study in the Apennines. As in the Alps, they too are not limited to a single orogenic unit but extend both across the region of the Ligurids (Lepontine) which correspond to the Pennines of the Alps, and across the Toscanids (austro-alpine) which are equivalent to the eastern alpine region (Grisonids, etc.)1. In the Toscanids they were indeed early on correctly recognized as terminal member of the fossil-bearing Jurassic series and as the first layers in the Cretaceous sequence, both in terms of age and mode of origin, whereas in the Ligurids the nappe-like overthrust (Steinmann 1907) across the Eocene of the Toscanids and their close association with the ophiolites prevented the recognition of their true character for a long time, whereby the lack of macrofossils provided for additional difficulty. Within the Jurassic sedimentary sequence of the Toscanids, there clearly emerges the same grand cycle in the general character of the deposits which we have recorded in the Southern Alps and partly also in the Eastern Alps – the earlier intervals of the Liassic with neritic fossils are followed by the cephalopod-rich rock formations of the higher intervals of more or less bathyal character, and these yield upwards to rather thin, fossil-poor, only occasionally ammonite-bearing layers with hypabyssal characteristics. In turn, these are followed by radiolarites and abyssopelites with the same characteristics as in the Alps, to end with the “calcare rupestre”, a complete equivalent of the hypabyssal Biancone. Detailed investigations for the Jurassic-Cretaceous sedimentary sequence in the Ligurids are almost entirely lacking since, at one time, before the nappe structure was recognized, one generally took the entire sequence including its granitic base for a normal intercalation within the upper Eocene of the Toscanids. Nevertheless, Italian geologists often correctly interpreted the deep-sea nature of the formation, but ascribed the paucity of fossils to highly unfavorable conditions presumed to be associated with the intrusion of the ophiolites, an event which in reality occurred much later and was in any case not effusive. I have described earlier in some detail the upper portion of the abyssal rock sequence based on the exemplary profile near Figline in the Monteferrato near Prato (1913): the radiolarite in the normal thickness of about 60 m, alternating upwards with abyssopelite and including an exceptional carbonate layer of 0.5 m thickness. Where the radiolarite reaches a thickness of 250 m and by itself forms craggy mountains, as in the eastern Elba, we doubtlessly deal with tectonic complications. Above the radiolarite and abyssopelite there follow, in normal sequence, the light gray limestones (calcari grigiochari) 1 A detailed description and a comparison with the alpine units will be given in the next volume of this journal in the article: On the structure of the Apennines by G. Steinmann and N. Tilmann.

with Calpionella alpina, which here allow the recognition of the remains of the coccolith structure even better than the equivalent rocks in the Toscanids. The name Alberese should not, as I have done myself earlier, be applied to these layers – it should be reserved for the late Eocene marly limestones. It would be better to call them “Felsenkalke” (calcare rupestre), as in the Limestone Apennines, or “Majolica”, as there is complete congruency with those formations. Below the radiolarite there follows, however, a system of clayey-calcareous rock formations which differ considerably from the light “Felsenkalke”. The Italian geologists call them “argille scagliose” and include them in the latter. Since a great many rock types of wholly different ages and discrepant origins have been lumped under this name, which is as undefined and misleading as the label “flysch” in the Alps, we should avoid it altogether. Near Figline it is an approximately 200 m thick system of dark shales which bear, in the lower layers, isolated dark calcareous nodules of various sizes. These become more abundant and larger upwards in the section, and merge into beds, eventually resulting in a clayey-calcareous to almost purely calcareous (and therefore lighter colored) rock type. The limestones received the label “calcari grigio-cupi” (dark gray limestones, in contrast to the overlying light gray “grigiochiari”). For brevity sake, we shall refer to this entire sedimentary sequence as dark, nodular clays or shales, corresponding to the Italian label “argilloscisti nodulosi” (Taramelli). The microscopic study of the calcareous nodules and beds gave the following results. The limestones contain some admixture of clay and, in addition, finely disseminated iron-sulfide which, however, is mostly limonitized. Besides occasional calpionellids and very small globigerines and textulariids, one finds radiolarians in larger or smaller amounts, but the skeletons are rarely intact and only partly transformed into pyrite or iron hydroxide. As a result, the finest details of the test and spine structure are commonly preserved as limonite skeletons and, since one can isolate them from the limestone by etching with hydrochloric acid, their recognition is greatly facilitated, especially in comparison with the radiolarians contained within the chert. These can nevertheless also be separated by means of hydrofluoric acid, as recently shown by Schwarz. I could not find any larger mineral grains within these rocks. On the basis of its character, the fossils [composition] (including the absence of macroscopic fossils), and the close association with euabyssal radiolarite, I am led to the conviction that we are dealing here with a sediment from great depth which acquired, in its lower portions, originally the character of Blue Mud but in the higher parts that of an abyssokonite. In any case, the Blue Mud was deposited already at depths of several thousand meters, analogous to the Blue Muds which are found in such depths along the eastern coast of Asia, especially in the Ryu-Kyu Trench (Andrée 1920, p. 548). A special label commends itself therefore for this hypabyssal sedi-

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ment which, it is true, does not differ essentially in its general character from the Blue Mud of lesser depths, being at most distinguished from it by its higher carbonate content. In this region also, however, the continuing deepening of the Jurassic sea is expressed very clearly by the decrease of clay contents upwards in the section, concomitant with a corresponding increase in carbonate content. The parts of the Jurassic formation to which the dark nodular shales correspond cannot be precisely ascertained, of course, because of the lack of fossils. Since they are directly overlain by the radiolarite or, where it peters out, by the hypabyssal Biancone, and since the radiolarite as far as we know probably belongs to the Oxfordian and the Kimmeridgian, perhaps partly to the Tithonian, we can only assign on the whole a greater age to the nodular shale, that is, Callovian and Dogger, perhaps including Liassic. The sequence would be a chronologic equivalent of the thinner, intermediate sediment layers of clayey-calcareous-siliceous character, ranging from the Liassic to the radiolarite, as known from the Southern and also from the Eastern Alps. In the present case, however, a somewhat greater supply of clay and insufficient ventilation has resulted in a deviant sediment type. If we remove, in thought, the larger part of the clay content and also the pyrite, we are left with a rather thin, clayey-calcareous-siliceous sediment rich in radiolarians and with some foraminifers, a facies which represents these Jurassic intervals in the Southern Alps. Since the rock formations of the “Rhät” nappe show otherwise extensive agreement between Alps and Apennines, it seems sensible to search for the lithologic equivalents of the dark nodular shales in the Rhät (Margna-) nappe of the Alps. Indeed, they do occur there. Shales with dark calcareous nodules and beds occur, for example, in the region of Arosa, intercalated between Liassic layers and the radiolarite, that is, they occupy the same stratigraphic position as the nodular shales of the Apennines, in addition to being extraordinarily similar, except for the degree of preservation. They are sufficiently transformed by pressure and weak regional metamorphism so that more delicate remains become poorly discernible. Nevertheless, it was possible to recognize occasional globigerines, and finely disseminated pyrite or limonite occurs here, too. The rock formation described acquires its character as a Blue Mud originating at great depth not only through the close association with euabyssal or hypabyssal sediments, but also through the paucity of macroscopic fossils, especially benthic ones. Andrée (1925, p. 508) considered a number of fossil-bearing rock sequences from various periods as being equivalent to today’s Blue Mud at lesser depths – the brachiopod, trilobite and graptolite shales of the Silurian, the Hunsrück shale, the speckled marls [Fleckenmergel], the Pholadomya and Varians marls of the Jurassic, the clays of the Jurassic and Cretaceous which bear dominantly ammonites and belemnites, the Nierental sequence, the Pleurotome- and Dentalia clays of the Tertiary, and the London and Septaria clays. The abundant remains of benthic organisms already

identify most of these formations as deposits from rather shallow depths. In addition, there is frequently a close association with explicitly littoral deposits. They may be assigned to bathyal and partly probably hemiabyssal deposits. I am limiting myself to these two examples from the Southern Alps and from the Apennines, which demonstrate the existence of a grand deep-sea cycle with culmination in the upper Jurassic with sufficient clarity. As is the case for the Southern Alps, the cycle ends in the Apennines with the lower Cretaceous, and the Gaultian interval probably signifies complete emergence here, all over. Accordingly, the transgressing sediments of the upper Cretaceous possess a well-expressed neritic character; those from the Southern Alps have already been mentioned. In the Apennines this sequence is represented by the lime-rich sandstones of the “pietraforte”, with ammonites and inoceramids from the upper Cretaceous which are intercalated, nappe-like, between the older and the younger eogenic [Paleogene?] formations, just like the older deep-sea sediments and the ophiolites injected therein. Prospects are poor for frequently encountering the final periods of the deep-sea cycle, its record having been destroyed almost everywhere by the transgression of the upper Cretaceous. In the Alps, too, one has found them but occasionally, as demonstrated by the ammonite-bearing Gaultian of Hindelang. Many researchers find insufficient evidence to recognize the existence of a deep ocean, among the great number of regular sections showing the deep-sea cycle of the Jurassic and the euabyssal nature of the radiolarites and abyssopelites, the reason resting above all with the coarse clastic rock formations which in many instances seem in the closest stratigraphic association with the layers addressed as eu- or hypabyssal. Such cases have been documented from more than a few places in the northern and central regions of the Eastern Alps, and very rarely from the Southern Alps but, to my knowledge, never from the Ligurid region of the Apennines where I neither have ever encountered any myself. Already this distribution of the occurrences in question must seem suspect, because it runs generally parallel to the tectonic complexity of the three regions. Regarding the central and northern parts of the Eastern Alps, not only does nappe structure dominate here but, as is documented in many studies, there is much intensive tectonic deformation which posits formations of wholly distinct ages and entirely different character in direct contact, and reworks them into seemingly uniform masses. The process of squeezing out [portions of a formation] explains the phenomenon, mentioned on several occasions, that radiolarite directly overlies Liassic deposits of maximally bathyal origin. Examples of fault breccias of simple or polygene nature are often given in the literature for these regions. However, they do occur in the Western Alps, too. One needs only to remind oneself of the gneiss wedges of the Berner Oberland, the Lochseiten limestone, the Nummulite lenses in the Senonian of the Fähnern (Richter 1925) or the intimately mixed lime-

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stone-shale tectonite of the Käswald Tobel near Iberg (Steinmann). In the Southern Alps significant tectonic complexity is quite rare, in contrast to other alpine regions, as here there are no overlying nappes to deform the formations. The same is true for the Ligurids where strong deformation is almost excluded by the fact that the nappe is on top and was not in turn subject to overthrusting. In the Toscanids, however, which were rolled over by the Ligurids, we should again expect deformation, and this is indeed the case. The differentiation between normal sedimentary breccias and tectonic breccias is, however, by no means always easy, as shown by the many cases in dispute. It is also not sufficient, therefore, to categorically pronounce that the breccias in question originate from tectonic friction, but the cases must rather be studied one by one. With the description of a number of such cases, I hope to be able to contribute to the solution of this problem.

The tectonites of St. Moritz in the Oberengadin Upon ascending from the Alp Nova northwest of St. Moritz towards the skiing cottage Corviglia (situated at the eastern foot of the Piz Nair Pitschen), using the south side of Sass Ronzöl, one finds, among the coarse wackes and gypsum deposits of the lower Triassic (which here forms the basis of the Trais Fluors schuppe (Cornelius 1914) and belongs to the Julier schuppe [imbricate overthrusts] of the Bernina nappe, according to Staub), several good outcrops of radiolarite which here forms the uppermost member of the Err nappe (Cornelius Prof. XX). The radiolarite is commonly developed here in its typical, pure facies, in part with high contents of manganese ore, as already described by Cornelius, but yet somewhat differing in that there occur, in association with the compact chert beds (separated by but thin clayey layers), red or greenish very fine shales (abyssopelites) of considerable thickness. These shales are either entirely lacking in fossils or they contain occasional radiolarians, that is, they correspond fully to the true Red Clays of the deep sea. Somewhat higher at the eastern foot of the Piz Nair Pitschen, there is another, larger outcrop in these rock formations which is readily seen from the nearby Corviglia cottage (Cornelius Prof. XVIII). Here the colored deep-sea clays are even more in evidence. A more detailed study of these two occurrences of euabyssites of the upper Jurassic reveals a remarkable peculiarity which already attracted the attention of Escher and Studer without, of course, them being able to clearly recognize the significance [at that time]. They report (Geologische Beschreibung von Mittelbünden, 1839, p. 128) that a crystalline gneiss-like rock alternates with these colored shales, similar to an occurrence (as Verrucano) on the Kärpfstock and Sandhubel. This alternation of the two differing rocks, so basically contrasting in their origin, is indeed of singular nature. At the outcrops lower down near the Sass Ronzöl one observes, within the extremely fine-grained abyssop-

elites and in the radiolarites, small and larger pieces of Verrucano as irregular inclusions, some in the form of quite large, multi-edged clasts, others as more flattish shards. One is easily convinced, from this kind of appearance, that this is not a regular alternation of layers but rather a fault breccia such as is quite commonly found at the larger overthrusts, not the least in Bünden itself. In a large block of radiolarite, about to fall apart, I was able to observe an inclusion of Verrucano which was about 1 m long, 0.4 m wide, and 0.25 m thick, being thinner towards the edge, like a true wedge of the pressed-in rock. Since the Verrucano attains greater thickness as base of the Julier schuppe somewhat to the southwest of this location (cf. Cornelius Prof. XVII and XVIII), the occurrence of such a tectonic friction breccia (which Cornelius, too, hints at) is not a matter of surprise at this place: a report on the alternation of the two rock facies, a counterfeit produced by this fault breccia, seems quite explicable for a time when such phenomena were but little known. The occurrence also, however, delivers the key to an error which entrapped later researchers including Rothpletz, and which has tended to obscure the stratigraphy of Bünden: I refer to the inclusion of the radiolarite and its associated rock formations into the Permian (Verrucano, Sernifit). The outcrop higher up at the foot of the Piz Nair Pitschen shows another blending of the two rock types which goes even further: small and large blebs of red shale are contained within the Verrucano, and the shale bears layers and lenses of Verrucano. Indeed, the conspicuous mica flakes of the latter are dispersed upon the surfaces of the parting shale, solitary or in aggregates, so that one thinks one is confronted with a uniform, micarich slate. The more detailed study of this twin formation, which reaches a thickness of several meters, yields the following. In the outcrops at the Sass Ronzöl (Fig. 1), we find that coarse-grained Verrucano and radiolarite commonly form apparently rather distinct contacts, as one can see in Fig. 1 at the lower right. Towards the Verrucano, however, the radiolarite (here with distinct radiolarians) takes up small pieces of Verrucano and subsequently branches, initially into broader ribbons with small Verrucano clasts, then towards the interior like a network between the clasts of the crushed Verrucano. During this process, the radiolarite enters in places in such fine lamellas between the clasts, or into the cracks of the Verrucano, that these delicate branchings could not be redrawn from the photographic positive which forms the basis of this figure, or else they had to be made visible with excessive thickness. It is clear, not only from the general pattern of distribution of the radiolarite in the rock formation but especially convincingly from the granitic clast marked a, that the radiolarite was injected under pressure into the crushed Verrucano and does not perchance constitute the cement for a sedimentary breccia consisting of Verrucano pieces. The clast marked a was originally uniform, was [subsequently] crushed into three pieces, and the abyssopelite [then] forced its way into the two mylonitic

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Fig. 2 Split-off piece from the fault breccia from the foot of the Piz Nair Pitschen. About 4/5 natural size. White Verrucano, black abyssopelite. Left Verrucano with injected flasers and shards of abyssopelite. Right Abyssopelite with injected layers (a), torn layers (b), and dispersed grains and mica flakes (c) of the Verrucano. x = fold veins

separation zones between the three pieces, as very fine layers, and thus formed, together with the ground-up granite, a polygenetic tectonite. In this the displacement between the three pieces was insignificant, so that the original relationship remains unmistakable. Furthermore, one can observe how in places the injected shale material decreases in importance with increasing distance from the contact until it disappears entirely: the polygenetic tectonite then transitions to a monogenetic one. I need hardly add that everywhere the blocks of granite and quartz are thoroughly crushed and turned to mylonite, which is nicely evident from the optical properties under the microscope. In correspondence to the largely clayey character of the euabyssites at the foot of the Piz Nair Pitschen, the interpenetration of the two formations expresses itself in a somewhat different way – it proceeds so much further, presumably also because the green Verrucano is very mica-rich here and relatively poor in large blocks of firm rock. Figure 2 shows a well-defined yet somewhat wavy contact between the two rock types. However, in the middle of the grayish green Verrucano (white), one observes an isolated, larger bleb and extremely numerous smaller ones of the red shale (black). We are faced with a completely mixed rock – the shaly blebs invade the Verrucano everywhere and here, too, it is impossible to reproduce the finest of the branchings in the figure. Nevertheless, it shows the complete interpenetration of the two very well, albeit somewhat schematically. In the red abyssopelite (black) there are, stretched and smoothed or winding, linked layers of Verrucano (a), readily recognized by their clastic nature and especially by the mica flakes. In the plane of the figure, they are partly cut at

right angles, tangentially, or at an angle. They show larger and smaller swellings and pursue a winding course in places. At other locations, as at b, the components of the Verrucano seem dispersed into fine but interrupted layers, and at yet other places one sees but single grainlets or mica flakes distributed along the plane of parting (c). They are commonly so small that they easily escape detection by the observer unless aided by magnifying glass or microscope. Thus, the mylonitic-tectonic structure of the rock formation is quite evident here also. Neither the outcrops at the Sass Ronzöl, nor those at the foot of the Piz Nair Pitschen are sufficiently deep to allow determination of the thickness of these tectonic friction breccias with certainty. It is certain, however, that a formation of a thickness of several meters is at hand. In passing, I do not think it impossible that the tectonites described here, if subjected to further study, will throw new light on the much-discussed but still open question about the nature of the “Saluver Series”. The repeated occurrence of Verrucano-like rocks, in part with dolomitic components, at least invites the thought that we are dealing here with a tectonic friction breccia of larger extent, with parts of the squeezed middle limb worked into it, similar to the chert breccia of the Sonnenwend mountains, of which more later. The restricted distribution of the Saluver rock types additionally suggests the contemplation of a localized phenomenon, rather than a regional one, which is also supported by the purely local character of the coarser components. Such deformation breccias were correctly described already 20 years ago from other parts of the Oberengadin. One need only read the extremely lucid and convincing expositions of Zöppritz (1906, p. 60) about the deformation breccias at the Murtiröl, where they reach a thickness of 10 m. From my own observations I can vouch for the complete agreement with the ones described here.

The tectonites of Maran near Arosa On the occasion of an initial exploration of the region around Arosa (1895), I found near Maran a peculiar breccia made of Triassic dolomite, radiolarite and abyssopelite. The finding that the radiolarite was a component of the breccia, hitherto interpreted as sedimentary, suggested a younger age, that is, Cretaceous and, since at that time one had but the Cenomanian chert breccia of the Bavarian Alps as a comparable rock formation, the Maran breccia was included with it [as contemporaneous]. Based on his extensive studies, Hoek (1903 and 1906) accepted this interpretation but at the same time described a tectonic megabreccia from the neighboring Brüggerhorn, which raised the possibility that the Maran breccia could be interpreted in the same way which, incidentally, was hinted at by Spitz. The renewed investigation of the agglomerate of the “schuppen-zone” [imbricate thrust zone] of Arosa by Arbenz and his collaborators

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Cadisch (1919, 1923) and Brauchli (1921) resulted in many improvements of the earlier surveys and assignments of horizons, but the burning question concerning the original positional relationships of the various nappes within the “schuppen region” could not be resolved once and for all. As concerns the Maran breccia and similar formations of this highly crushed (for squeeze zones, rightly classical) region, a new interpretation has been put forward: it is supposed to be a transgression breccia of the upper Jurassic radiolarite complex itself. On this [basis], the researchers working this area believe that they can explain not just the characteristics of the breccia itself but also the fact that the upper Jurassic overlies the Triassic in direct contact, and even ancient crystalline rocks, with omission of the intermediate Jurassic intervals. Reports about such a transgression in the upper Jurassic also are occasionally being put forward for other parts of the Alps. Thus, Arbenz attempts to explain also the Saluver Series in this context. I consider this interpretation by the Bern School to be quite incorrect, based on my renewed studies on the Maran breccia and on other, similar occurrences in the Arose region. With the exception of occasional crystalline clasts, the Maran breccia consists of a mixture of Triassic dolomite and euabyssite of varying clast sizes. There are sequences where the euabyssite dominates, and others in which both components are about equally important. However, the abyssites are quite subordinate to the dolomite in places and finally one may find, indeed as entire beds, pure dolomite with the same breccia structure as the other types. All these different types have one common property – they do not possess cement and they are highly pressure-damaged, as can be recognized on the one hand from the strong interlocking of neighboring components, and on the other from the abundant, newly formed calcite veins which often crosscut the various dolomite clasts and also the abyssites, rendering them in places into a finely grained, crushed mass. The component elements of the compact radiolarite occur in the form of angular clasts, whereas the ductile abyssopelite occurs preferentially in the form of a coating jammed between the dolomite clasts. In Fig. 2, this difference in appearance is well evident, as well as the highly crushed nature of the dolomite at the site where the light veins contrast with the darker dolomite. In my opinion, these facts allow but one interpretation – the Maran breccia is, like the other breccias in this region which have a coarse structure, a tectonic friction breccia and not a transgression breccia. For one must assume that in a sedimentary breccia the fine, as yet unindurated radiolarian sand with the clayey components should have functioned as matrix, within which the dolomite clasts were embedded. Nothing of the sort is to be seen. Indeed, the radiolarite was already entirely indurated and brittle, since it appears regularly as angular clasts, just like the dolomite. The abyssopelite, however, which should display the characteristics of a matrix in the most perfect manner, does not fulfill the required conditions either. Not only is it, similarly to the radiolarite, entirely

lacking in some parts of the breccia while being of considerable importance in others but also, in terms of its distribution within the formation, it behaves precisely like the pelitic component within the above described tectonites of St. Moritz – here as there, it is injected into the interstices and into the newly formed cracks of the dolomite in a highly irregular fashion. One need only compare the image of the Maran breccia (Fig. 2, with Fig. 1). The fact that beds of pure dolomite several meters thick exhibit the same breccia structure as the mixed formation, to wit, the matrix being entirely missing yet available close-by in rich abundance, hardly conforms to a sedimentary origin but it accords with a tectonite character as naturally and simply as the occurrence of unmixed (but crushed) Verrucano or of pure radiolarite in closest vicinity to the tectonites of St. Moritz. It seems to me that, of special importance for the correct explanation of the breccia, is the distribution and the circumstances within the close-by environment of its occurrence. Although the alps of Maran and the neighboring Brüggerhorn provide for outcrops of this breccia at several places, and the breccias are also seen in the Tschirpen schuppe which belongs to a different nappe, and although genuine fault breccias are indeed developed in excellent manner at the Brüggerhorn, there is no trace of such phenomena in the sections in the neighborhood or in between occurrences. On the other hand, entirely unambiguous and wholly undisputed transgression breccias are indeed represented by the Liassic breccias and by the upper Jurassic Falknis breccia of the same region, and these are so strikingly different from the Maran breccia and the established tectonites, both in structure and in restricted occurrence, that even the less experienced observer immediately makes the distinction. The Maran breccia and similar rock types of the Arose region are, therefore, genuine tectonites in my opinion, and transgression breccias of neither the Cenomanian nor the upper Jurassic – all those deductions which build on these latter interpretations must be rejected. The Maran breccia, then, proves nothing regarding the age of the ophiolites, as I once thought, and neither does it provide (nor the similar tectonites of the region) evidence for a transgression of euabyssal Jurassic deposits across all horizons down to the ancient crystalline masses. One should, it seems, proceed with more circumspection and skepticism before extracting sweeping conclusions from such uncertain information. Of the other disputed breccias in the region of the Eastern and Southern Alps, I shall choose but two and touch on these briefly, as I do not know them from own observation. On the basis of extremely careful investigations and reasoning, the chert breccia of the Sonnenwend mountains was pronounced a deformation breccia by Wähner (1903) but Ampferer (1908), in contrast, branded it a transgression breccia of the Gosau series. I must leave it to the reader to judge the matter on his own from the publications of the two researchers. In order to put the

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situation into clear perspective, nevertheless, I would like to make a few remarks necessitated by the progress of alpine research during the last two decades. In the Sonnenwend mountains there is a breccia of greatly varying thickness, including not only clasts but entire “packages” of layers between the upper Jurassic radiolarite below and the so-called “hornsteinkalk” (flinty limestone) above, linked to both through irregular “alternate bedding”. Wähner interpreted the hornsteinkalk above as upper Jurassic, because its uppermost beds contain rocks and fossils of the upper Jurassic Plassen limestone, and Ampferer accepted this. The problem lies precisely with this age determination. According to the descriptions of Wähner, the hornsteinkalk is a typical Liassic cherty limestone with sponge-spicule flintstone but not an upper Jurassic formation. It merely carries a cap of upper Jurassic reef limestone. Thus, in the upper parts of the Sonnenwend, two partial nappes of the Inntal nappe are moved on top of each other, a lower one with red Liassic and abyssal Malm, and an upper one with sponge-flint-limestone Liassic and reef-like Plassen limestone, the latter commonly known of being typical for the Inntal nappe. Between the two there is the breccia complex, that is, in a situation of a large horizontal thrust, as at St. Moritz and Arosa. Just alone the fact that the chert breccia in question often shows wedge-like interpenetrations with both the underlying euabyssite and the overlying Liassic – as pointed out by both authors – speaks for a tectonic origin. The interpretation of the breccia as the product of friction at the basis of an overthrusted nappe provides a natural and simple explanation also for the fossil-bearing clasts of middle and upper Jurassic age (Parkinsonia, Perisphinctes, corals) which are nowhere in the environs known from outcrops. These are the traces of the intermediate limb, completely crushed and transformed into a fault breccia and now, of course, no longer visible. Wähner, to be sure, realized the nature of the breccia from its structure – I ask to compare his figures with mine – but he could not, at that time (1903), take into account the possibility of an overthrusted partial nappe, and thus went astray regarding the interpretation of the stratigraphic position of the hornsteinkalk. Ampferer accepted the incorrect age determination and, lacking knowledge of the extant nappe tectonics, made the futile attempt to dictate to the alpine movements which type of deformation breccia they were allowed to form. Such deductions are bound to fail in this case as in others, given the invincibility of the facts revealed by the progress in research. When comparing the breccia with the Gosau series, he overlooked that the red conglomerates at the basis of the Gosau series must not be taken as equivalent to the chert breccia. In considering his rejection of the nature of the breccia as fault breccia, we must not forget that tectonic breccias from other parts of the Alps were only beginning to be described in some number and detail at about the same time (Zöppritz 1906, and others). Another solution, but not at all satisfactory in my view, was attempted by Heritsch (1915, p. 69) who

linked the breccia to “submarine sliding but without significant uplift”. The chert breccia as well as the tectonics of the upper parts of the Sonnenwend would seem to very much merit a new investigation taking into account the points of view developed here. Of the sediment breccias of the upper Jurassic which are occasionally mentioned from the Southern Alps, I would like to but briefly bring up those which Rassmuss (1912, p. 85) has described from Val Varea in the Alta Brianza. There the Tithonian aptychus limestones contain a breccia which consists of angular clasts of red limestone, with an admixture of clasts of a white and gray limestone. He did not study them in any detail or pursue the matter and says only “Higher up in the overlying layers there is indeed an overthrust; nevertheless, it seems to me a tectonic origin is excluded; in addition, I have nowhere seen something like it at the various overthrusts and imbricate thrusts within my study area”. One may comment that given a region such as the one under discussion, where numerous good sections uniformly display just the normal deep-sea cycle but naught of a sedimentary breccia formation therein, it seems more reasonable to draw the opposite conclusion, especially when an overthrust is visible above. From the presently known distribution of the eu- and hypabyssal sediments in the Alps and Apennines, it follows that by far the greatest part of the ocean area from which these mountains arose had depths of about 3,000–6,000 m towards the end of the Jurassic and the beginning of the Cretaceous. We take these values to be minima, since it is quite possible that the radiolarites came from even greater depths, corresponding to present circumstances. In the Apennines the deep-sea deposits belong to two orogenic units, the Ligurids and the Toscanids, and within these they generally dominate, as far as we know. Since these two regions are today thrust on top of each other, without there being another member lacking intercalated abyssal formations, we must then assume that the deep sea extended across the entire width of the two zones; they were perhaps not separated from each other by a shallow ridge, the deep-sea basin filling the entire width [of the depositional realm]. If we wish to determine this width we must first move the Ligurids off the underlying Toscanids back towards the west and, in addition, straighten out the folds and imbricate thrusts of both, to be able to calculate the original width of the deep-sea region. The Ligurids extend orthogonally to the run of the mountains from Corsica across Elba to east of the origins of the Tiber, and furthermore in the south to east of Perugia, this being a distance (orthogonal to the trend) of about 250 km. The nappe is foreshortened, as is clearly seen everywhere, but the amount of secondary narrowing from folding cannot be accurately determined. Moreover, it is governed by two different movements, that is, by the compression linked to the nappe motion and by the post-nappe folding which involved the entire complex of basement, nappe, and eogene sediments thereon deposited.

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Even if we imagine the process of nappe formation essentially as a sliding, in the manner of Schardt, it cannot have taken its course without a measure of compression and foreshortening, and we can confidently set the narrowing of the nappe thus achieved to about 20%. In this fashion we obtain a total width of 300 km for the Ligurid euabyssal environment. According to the record now visible, the minimum length of this deep-sea region must be taken as 800 km, that is, from Savona to the Gulf of Policastro, but we may reasonably surmise its probable turning and continuation far towards southern Spain. The Toscanids with euabyssal characteristics reach their eastern limit along a line which runs from Rimini via Aquila to Gaeta, or thereabout. To the east of this line they are replaced by the Abruzzids, comprising the Abruzzi and the southern Apennines in which euabyssal sediments of Jurassic to Cretaceous age are apparently entirely lacking. However, hypabyssal upper Jurassic and Biancone-like sediments still occur in their western parts – a style of formation which corresponds closely to that of the eastern Dinarids (Venetian region). To avoid the criticism of overestimation, we draw the western limit with the Elba, since one does not know for sure whether this region continues to the west and, if so, how far. Thus, we obtain a width of 200 km. We must add to this value the amount of average narrowing by folding. Here also calculations remain as yet uncertain but, judging from the structure of the Apuanic Alps, taught to us by Zaccagna, and from the overthrusts demonstrated by Lotti in the Monti Pisani and also shown elsewhere, we must deduce a foreshortening of at least 25% or possibly considerably more. On the whole, therefore, the width of the Toscanid euabyssal amounted to a minimum of 250 km; the length may be set equal to that of the Ligurids. As far as we can tell, the two regions were not separated by an element of a different nature (see above). Thus, the combined width of the complete Apenninic euabyssal environment is computed at a minimum of 550 km, with a visible length of 800, and a possible or even probable length of 2,000 km. For the Alps, calculations are somewhat more difficult. According to Rovereto (1909) and Staub (1924), whose concepts I share based on my observations between Genoa and Savona, there is no boundary whatever between the Alps and the Apennines, as supposed by Termier and Kober. Instead, the zone of the Ligurids continues uninterruptedly into the Pennines of the Alps, for example, into the Dentblanch nappe (Rhät-, Margna nappe), whereby the important facies association of euabyssites and ophiolites is preserved. Accordingly, one could expect that the situation reigning in the Alps should be similar to that in the Apennines, inasmuch as the euabyssal region of the Ligurid-Pennid realm should be followed immediately by a second euabyssal sequence of Toscanid composition – in this case, a lower eastern alpine one. In the nappe sequence defined by me for Bünden, this is indeed the case. I believed to have demonstrated there that the (lower) Eastern Alpine nappe

with euabyssites forms everywhere the unit tectonically overlying the Rhät nappe with euabyssites and ophiolites. Accordingly, a comprehensive deep ocean would have extended uniformly over the units of both mountain areas, with the northern limit delineated only by the upper Jurassic zone of klippen and breccia nappes characterized by conglomerates and breccias, which are certain to indicate the presence of an island chain or a continental margin, as do the wildflysch regions of the Ultrahelveticum with their exotic clasts. This proposed nappe sequence was pushed aside by the Swiss geologists on the basis of observations and deliberations (which cannot be discussed here in detail), despite the fact that it reappears again and again in great regularity from the Freiburg Alps well into the heart of Bünden. The Rücken breccia region now has been declared as lower Eastern Alpine, and was intercalated between the Rhät nappe with euabyssal Jurassic deposits and the similarly composed lower Eastern Alpine one. With this nappe sequence we would then have, in the upper Penninicum and the lower Eastern Alpine, not an encompassing upper Jurassic deep ocean area but, according to Staub (1917), even several emerging land ridges between the various deep-sea trenches and, in addition, a number of submarine ridges lacking sediment accumulation. The occurrence and general distribution of the euabyssal sediments in these regions would, however, be essentially unaffected. The difficulties and discord linked to this problem is evident even today, for example, from the position of Cornelius (1923, p. 13) who reaches the following results based on his studies in the Piz d’Err group: “Rather, we must reinvest the earlier concepts of Steinmann, whereby all these ophiolite masses at the western border of the Eastern Alps belong to one unit at the basis of the Eastern Alps”. Moreover, he found only radiolarite everywhere in the Err nappe, from which Staub derives the littoral deposits of the Rücken region, with no hint of a transition into the facies of breccia or reef limestone. Whichever way the question may be decided, there is no doubt about the continuation of the Apenninic deep ocean into the Alpine region, even if this does not occur everywhere in the simple, compact configuration which we believe to have recognized. According to Argand and Staub (1917), it was already in the Mesozoic that the doming began which, through the subsequent folding, delivered nappe fronts, and indications for enormous differences in the depth of the sea do indeed emerge in the upper and high Eastern Alpine (Tirolid) region of the Eastern Alps, to which we turn next. Here we must foremost state the important fact that neritic deposits occur in considerable extent, such as the well-known, coral-bearing Plassen limestone in the highup nappes of the Eastern Alps, in addition to the widespread eu- and hypabyssal formations of the Malm. We must add, however, the apparently well-based observation that euabyssal deposits grade into hypabyssal or hemiabyssal beds towards the fronts of nappes, and hypabyssal to neritic or even true, clastic shallow-water for-

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mations with conglomeratic or breccious layers. Such occurrences were observed especially at the frontal margins of the upper Eastern Alpine nappe system. One should refer in this matter to the communications of Boden (1916, p. 211 ff.) and of Richter (1924, pp. 36, 37). But when, based on such facts, one draws the conclusion that the radiolarites, aptychus limestones, etc., are not at all deep-sea formations, then we must unconditionally reject it in view of all other experiences. What it indicates, solely, is that axial rises formed during the Jurassic (or even earlier) – one may suppose that these correspond in part to the later nappe fronts – which were uplifted as narrow strips of the seafloor towards the ocean’s surface and settled by coral reefs (Plassen limestone); or which emerged as narrow strips of land, subject to erosion, their products being reworked into marine deposits as clastic inclusions. After all, today’s coralligenic island chains and island arcs in the Pacific, Sunda or Antilles region are hardly incompatible with the existence of neighboring deep-sea trenches or areas, and likewise are those ridges generally unable to serve in contesting the deep-sea character of the radiolarites and abyssopelites. Indeed, Horn (1915) invoked, already some time ago, the analogy to the present situation in the western Pacific in explaining alpine mountain building. It is well for us to consider these circumstances not only in the pursuit of the earlier phases of alpine mountain building, but also when comparing the Jurassic deep-sea deposits with today’s. Whereas the Apenninic euabyssal environment – and I think also the Rhätic– lower Eastern Alpine – could be likened to a uniform deep-sea region of the present, the Tirolian must be compared to the situation reigning today in the western Pacific where the deep-sea zones are separated by coralligenic island chains and island arcs. For the calculation of the width of the Alpine euabyssicum, we must keep in mind that, in contrast to the Apennines, a gigantic squeezing of the sequences took place here and that, as a result, the width seems now greater than it was originally. On the other hand, there also have been several phases of imbricate overthrustings, whereby the original width seems diminished. These secondary changes are difficult to evaluate but, assuming that the thinning out and thickening are approximately balanced, one may not be off by much if one sets today’s visible width roughly equal to the original one. On this basis I compute as extreme minimal values for the middle of the Alps, after the map of Staub2: ● ● ●

●

for the Rhät (Margna-) nappe a width of 110 km for the lower Eastern Alpine nappes 90 km for the upper Eastern Alpine nappes to about the middle of the Inntal nappe 250 km Total 450 km

2 I neglect hereby entirely the higher-up Eastern Alpine nappes, even though they contain radiolarite, because the upper Jurassic is commonly represented by the thick sequence of upper Malm beds with more hypabyssal-hemiabyssal characteristics, or even littoral ones marked by conglomerates, and by the doubtlessly neritic Plassen limestone.

To this would have to be added an amount of 30–50 km for the deep-sea zone of the northern Dinarids (DrauzugLombardy), resulting in a total width of about 500 km. This is approximately the same value as the one I determined for the Appenines (550 km). Thus, one may well surmise that an Alpine deep-sea region of at least 500 km width with an estimated length of about 600 km was joined to the Appenninic deep-sea region during upper Jurassic times. To be sure, in the southeastern part of the Alpine geosyncline the deep-sea region becomes wider. However, it was divided by ridges or tongues of the coralligenic region with Plassen limestone of the upper Malm series, and by at least one small ridge at the northern border of the Tirolian region. If one prefers the nappe structure at present favored by the Swiss geologists, then the ridge which we here identify as the northern boundary of the Alpine deep ocean in the lower Penninicum must be set into the deep sea itself. It would then separate a northern deep-sea band of about 100 km width from the southern one of about 350 km width. This would, however, not affect the extent of the deep ocean region as a whole. The overall extent of the Apenninic-Alpine deep sea at the time of the late Jurassic, to which I have assigned generally minimal values, may be summarized as follows: A winding sigmoid band of about 500 km width, probably much less than that delineated by the run of the two mountain regions today, possessed an average depth of 4–6 km and bore euabyssal deposits, except for a tongue of some width and several ridges or island chains in the Alpine region. Towards the north and south (or east and west), the sea became shallower, and within these marginal seas originated hypabyssal, hemiabyssal, bathyal, and neritic deposits (Helvetids, southern Pennines, southern Dinarids, Abruzzids) of much greater thickness. The visible length of the deep-sea band may be calculated as 1,500 km but probably it was as high as 2,500 km when including the western Mediterranean region. As far as can be ascertained today, this is nothing but a diminutive part of the colossal deep-sea trench (or trench system) of the Tethys, whose extent reached from the Antilles via Eurasia to the western Pacific and into the same, and which later became – in this I agree with R. Staub (1924) – the guiding axis of the most complicated mountain system. I believe to have shown that many an objection which was raised against the deep-sea nature of the Alpine euand hypabyssites of the late Jurassic rests partly upon erroneous interpretation of tectonic friction breccias, and partly upon unacceptable generalizations from the undisputed “ridges”. On the other hand, a more detailed study of Jurassic sections in the eu- and hypabyssal sequences yielded an unmistakable grand cycle and confirmation of the deep-sea nature of these deposits. Further investigations in both directions are extraordinarily desirable. In particular, a broad-based comparison of as many sections as possible from the Liassic up to the middle Cretaceous

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Fig. 3 Coccokonite [coccolith limestone] of the Biancone. Col Torond, Venetia

would yield a clear picture of the bathymetry of the Tethys of the late Jurassic – a project which could not call on fieldwork alone, of course, but would rather have to employ all the tools of sediment-petrographic research. Well-founded results can be offered already at present. The middle part of the Alpine-Apenninic geosyncline was a deep-sea trench of considerable extent, fully comparable in length and width to one of the larger deep-sea trenches in the Pacific, e.g., to that of Chile and Peru, but on both sides bounded by a broad band of rather shallow sea with hemiabyssal, bathyal and neritic sediments. One can place this sea rather with a “narrow ocean” (Kober compared it to the Atlantic) than with today’s Mediterranean. From this ocean the alpine folded mountains grew. In view of this fact it is somewhat perplexing when even today scientific and popular books announce “Never has genuine (?!) ocean floor turned into folded mountains”, or “The Alpine sea was always a shallow sea, even though with a few deeps which went well beyond the average of 200 m, as can be observed, however, in today’s shelf seas, too” (Dacqué). Or when an expert of the Apennines, like Rovereto, announces as seemingly established fact: “Till now we do not know any rocks which are composed of the same elements as the Red Clay of today’s great depths. Abyssal regions have never formed parts of the Earth’s crust”. Indeed, one should be more cautious with such utterances at this time, for we are not at the end of research in these questions, but in the midst of it. Explanation for Plate I: Thin section of a limestone of Tithonian age from Col Torond, Venetia. Consists dominantly of coccoliths. The figure shows only the ones which lie flat in the plane of the picture and are distinctly visible. The ones cut at an angle or vertically are not drawn, but are represented by the same dotted pattern as the sparse matrix between the coccoliths. This matrix consists of small globules of saprokonite. Drawn at 200 times magnification, and magnified 3 times in the figure. Polished piece of the Maran breccia, in natural size. The dolomitic material appears light to dark gray. In general, the newly formed calcite veins, which crosscut the dolo-

Fig. 4 Maran Breccia. Maran near Arosa, Bünden

mite clasts, are brighter. Radiolarite and abyssopelite are in black, but only the larger clasts and layers are shown; the thinnest blebs of red clay are not recognizable. The larger, angular pieces are radiolarite, containing discernible radiolarians at the three marked (x) places. The veins of newly formed calcite within the radiolarite, although not missing, were lost in reproduction. The streaky parts are dominantly abyssopelite; here and there they include small dolomite clasts. See Figs. 3 and 4 (in the german version Figs. 1 and 2).

Translator’s comments I thank Prof. E.L. Winterer for helpful comments in the choice of technical terms. Square brackets [] indicate additions to the original text used to facilitate language flow and clarity.

References 1908 O. Ampferer, Studien über die Tektonik des Sonnenwendgebirges. Jahrb. d. k. k. Geol. Reichsanst. 58, p. 281–804 1920 K. Andrée, Geologie des Meeresbodens 2. Berlin 1925 – –, Das Meer und seine geologische Tätigkeit. Salomons Grundz. d. Geol. pp. 361–533 1916 K. Boden, Geologische Untersuchungen am Geigerstein und Fockenstein usw. Geogn. Jahresh. 28, p. 211ff 1921 R. Brauchli, Geologie der Lenzerhorngruppe. Beitr. z. geol. Karte der Schweiz 79.

S33 1919 C. Cadisch, W. Leupold, H. Eugster und R. Brauchli, Geologische Untersuchungen in Mittelbünden. Heim-Festschrift. Vierteljahrsschr. d. Naturf. Ges. Zürich 64, p. 359 1923 J. Cadisch, Zur Geologie des zentralen Plessurgebirges. Eclog. geol. Helvetiae 17, p. 495 1914 P. Cornelius, Über die Stratigraphie und Tektonik der sedimentären Zone von Samaden. Beitr. z. geol. Karte d. Schweiz, N. F. 45 1923 – –, Vorläufige Mitteilung über geologische Aufnahmen in der Piz d’Err-Gruppe (Graubünden). Ebenda, 80. Lief 1925 C. Diener, Grundzüge der Biostratigraphie. Leipzig u. Wien, F. Deuticke 1906 Albert Heim, Ein Profil am Südrand der Alpen, der Pliozänfjord der Breggiaschlucht. Geol. Nachlese Nr. 15. Vierteljahrsschr. d. Naturf. Ges. Zürich 51, p. 1–49, t. 1, 2 1924 Arnold Heim, Über submarine Denudation und chemische Sedimente. Geol Rundschau 15, p. 1–47 1915 F. Heritsch, Die österreichischen und deutschen Alpen (Ostalpen). Handb. d. reg. Geol. II, 5 1903 H. Hoek, Geologische Untersuchungen im Plessurgebirge um Arosa. Ber. d. Naturf. Ges. Freiburg i. B. 13, p. 215–271, 5 t 1906 – –, Das zentrale Plessurgebirge. Geologische Untersuchungen. Ebenda, 16, p. 367–449, 2 K 1915 E. Horn, Über die geologische Bedeutung der Tiefseegräben Geol. Rundschau 5, p. 422 1917 C.F. Parona, Del contributo portato alla litogenesi dai piccoli organismi. Natura 8, p. 174–205, 17 Fig 1912 H. Rassmuss, Beiträge zur Stratigraphie und Tektonik der südöstlichen Alta Brianza. Geol. u. pal. Abh. 14

1920 C. Renz, Beiträge zur Kenntnis der Juraformation im Gebiete des Monte Generoso. Eclog. geol. Helvetiae 15, p. 523–584 1924 M. Richter, Geologischer Führer durch die Allgäuer Alpen 1925 – –, Die Fähnermulde am Nordrand des Säntis und das Problem der Kreide-Nummuliten. Geol. Rundschau 16, p. 81 1909 G. Rovereto, La zona di ricoprimento del Savonese etc. Bol. Soc. geol. Italiana 28, p. 389 1906 W. Schiller, Geologische Untersuchungen im östlichen Unterengadin. II. Piz-Lad-Gruppe. Ber. d. Naturf. Ges. Freiburg 16, p. 108 1917 A.R. Staub, Über Faziesverteilung und Orogenese in den südöstlichen Schweizeralpen. Beitr. z. geol. Karte d. Schweiz, N. F. 46 1924 R. Staub, Der Bau der Alpen. Ebenda, N. F. 52 1905 G. Steinmann, Geologische Beobachtungen in den Alpen. II. Die Schardtsche Überfaltungstheorie und die geologische Bedeutung der Tiefseeabsätze und der ophiolithischen Massengesteine. Ber. d. Naturf. Ges. Freiburg 16, p. 18–67 1907 – –, Alpen und Apennin. Monatsber. d. Deutsch. Geol. Ges. 59, p. 177–183 1913 – –, Über Tiefenabsätze des Oberjura im Apennin. Geol. Rundschau 4, p. 572–575 1892 F. Wähner, Korallenriffe und Tiefseeablagerungen in den Alpen. Ver. f. Verbreitung naturwiss. Kentnisse, Wien 1903 – –, Das Sonnenwendgebirge im Unterinntal. I. Teil. Leipzig und Wien, Fr. Deuticke 1906 K. Zöppritz, Geologische Untersuchungen im Oberengadin zwischen Albulapaß und Livigno. Ber. d. Naturf. Ges. Freiburg i. B. 16, p. 164–232, t. 5, 6

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A. L. du Toit

Amerika und Eurafrika: the origin of the Atlantic–Arctic Ocean Geol Rundsch 30:138–147

Received: 8 April 2002 © Springer-Verlag 2002

Abstract The Atlantic–Arctic Basin is antipodal to the Pacific. Powerful evidence is cited to indicate its development through continental drift, as suggested by Pickering in 1907. Initiated from the Mesozoic Tethys and progressively enlarged during the Tertiary, its outlines were essentially determined by tensional-rifting oriented mainly NE and NW within a zone extending more than half round the circumference of the Earth, from the Antarctic to Alaska. During the Alpine diastrophism fold linkages, which functioned as land bridges, were pushed up across the ocean between the West Indies and Eurafrica and subsequently destroyed by the continued westerly drift of the Americas. Crustal stretching was accompanied by widespread volcanicity. The Mid-Atlantic Rise is recent and has an isostatic basis. The Atlantic–Arctic stretch-basin is largely bordered by fault-line coasts and by down-warped shores that show the marginal, entrenched, terrestrially-evolved drainage areas known as submarine canyons.

Introduction The Arctic Ocean forms the physiographical continuation of the Atlantic, and in discussing the evolution of the latter, the Arctic must be included. In the following account, therefore, the general term “Atlantic” will be taken to embrace the Arctic. Together they stretch over more than half the circumference of the Earth and, suggestively, are antipodal to the Pacific. It is usually agreed that the Atlantic is a relatively youthful basin and that its bordering lands on east and west were, as shown by their terrestrial life, united in one section or another at more than one period during the past. Attention cannot, however, be restricted to their framework because the genesis of the Atlantic is intiW.-C. Dullo (✉) Forschungszentrum GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany e-mail: [email protected]

mately bound up with the far wider problem of Earth evolution as a whole, that is to say the development of the lands and oceans. The various hypotheses propounded for its existence fall into two categories involving either (1) sinking of a great north–south sector of the crust, or (2) continental drifting or displacement. Both concepts are simple, but the first, though generally favored, is hard to reconcile with isostatic principles, while the second, advocated by relatively few persons, is not generally acceptable owing to the apparent lack of a physical basis for the postulated horizontal forces. The author’s viewpoint, supporting the second interpretation, has been set forth at length elsewhere1 and he can add little fresh to that account; still, the problem having been narrowed down to one specific region, and on the kind invitation of Prof. H. Cloos, the more relevant evidence bearing on the Atlantic Trough is summarized here. Before doing so one must briefly set down the chief reasons for accepting the doctrine of drift, and thereafter interpret the history of that supposed “disjunctive rift” in the light of that hypothesis. Such a preliminary is imperative because the explanations thereby disclosed are so utterly and fundamentally different from those of current conception.

Merits of the displacement hypothesis Unlike any other theory this hypothesis can be tested on the basis of prediction, for, with the closer fitting that is postulated of particular landmasses, vital relationships necessarily show themselves, which can be verified or rejected in the field. Moreover, it is singular to observe how new discoveries would tend to fall into line with previous evidence or deduction. In eastern Brazil, for example, V. Leinz2 has mapped a horizon of reddish tillite underlying the well-known blue and green Itararé (Carboniferous) glacials, which duplicates in striking fashion the succession in South-West Africa, while the respective directions of ice-flow in the two countries are furthermore brought into accord.

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Fig. 1 The Paleozoic fold zones crossing the North Atlantic Ocean: T Taconian; C Caledonian; A Acadian; H Appalachian– Hercynian. Arrows mark the direction of pressure

There is a wealth of evidence – stratigraphical, lithological, paleontological, etc. – in favor of these views, but, as has been detailed elsewhere, they will, despite their significance, be omitted from this discussion. The most important criteria are those based upon (1) Archean grain, (2) intersection of orogenic zones, (3) formational phasal variation, (4) past climatic zoning, and (5) faunas and floras. South America and South Africa were undoubtedly rigid masses that, after their assumed separation, experienced scarcely any internal distortion, and their re-assembly as a portion of Gondwana is therefore not in doubt. On the contrary, the great distortion produced during the Alpine diastrophism renders the fitting of North America and Greenland against Eurasia less easy, though such uncertainties will be reduced with further investigation.

Archaean grain Noteworthy is the close agreement between the dominant foliation-trends in the platforms bordering the South Atlantic, for example between northeastern Brazil and West Africa and eastern Brazil and southern Angola (Fig. 1).

Intersection of orogenic zones The value of such tectonic zones as reach near to the coasts mounts with the length and regularity in pattern of the visible extensions in the opposed lands. When not only structures, but stratigraphies, lithologies, and dates agree closely, the likelihood increases that the so-called “free ends” that disappear into the ocean were formerly more closely connected. If two such zones of different ages converge or intersect in the opposed lands, the probability becomes enormously raised, whereas, if three or more such fold-zones are represented, such a probability becomes a practical certainty because the former

Fig. 2 The fold-zones crossing the South Atlantic Ocean: 1 Archaean; 2 Pre-Cambrian; 3 Post-Cambrian; 4 Permo-Triassic; 5 Mid-Cretaceous; 6 Andean; 7 Axes of probably Late Mesozoic uplift; 8 Falkland Islands. Arrows mark the directions of pressure

spacing of the coasts can then be fixed approximately or even more closely, with the precision depending largely upon geometrical considerations. The Atlantic possesses two such transverse compound tectonic systems: 1. North America–Europe. As first pointed out by Bailey3, the divergent Paleozoic fold-bundles on both sides of the ocean are striking, even when one concedes a generous amount of space between the reassembled blocks (Fig. 1). If displacement is not invoked, these four zones must be assumed to diverge eastwards at acute angles in eastern North America, to run thereafter more or less parallel right through the ocean, and in western Europe, to start radiating abruptly, though at wider angles. Failing that, one must assume the dying-out of one or more of the compression-zones and its replacement across the waters by a parallel or sub-parallel zone, which, in view of the scale and persistence of the folding, the stratigraphical similarities, and other coincidences, is asking too much of credence. The relatively small angle of intersection in this system unfortunately introduces a rather large error in this attempt to reconstruct Laurasia. 2. South America–South Africa. In contrast here are large angled intersections from four zones of widely differing ages forming two connected linkages (Fig. 2) that affect similar formations, the Permo-Triassic involving overfolding towards the north, and the Mid-Cretaceous accompanied by strong down-faulting to the south traced by Weaver in Argentina to the Chilean border. The southerly linkage was first stressed by Keidel4 in 1916, the northerly by Maack5 in 1934.

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The plotting of these differently oriented trends enables the coastlines to be satisfactorily apposed and this section of Gondwana to be reconstructed with a probable error of about 400 km. Into the gap – formerly land – the Falkland Islands fit both stratigraphically and tectonically6.

Formational phasal variation Of high importance, best seen in the South Atlantic region, is the remarkable way in which the nearest outcrops of corresponding formations on the two opposite sides of the ocean resemble one another more closely than either one – because of the usual lateral change in phase – and resembles its own actual extension within its own continent. Thus, the Siluro-Devonian sandstone formation of eastern Argentina and the western Cape, now 5,000 km. apart, are more alike than their two extensions within a distance of 1,000–1,500 km back from the Atlantic. The Lower Permian “Green Ecca” of the same two areas behaves in an identical fashion transversely to the ocean, however, in addition, changes in a northerly direction in both lands into the “Red Ecca”, which in each case is replaced by a third facies some distance inland. Such systematic variation, affecting strata of different ages and latitudes, can hardly be due to mere coincidence.

Past climatic zoning Of vital significance are the numerous and extensive formations that reveal tropical, arid, or glacial conditions, in various lands and of various ages, and provide convincing evidence of past climatic zoning. As first clearly set out by Kreichgauer, and later by Köppen and Wegener, the deduced courses for the principal climatic zones, when plotted for each epoch prior to the Tertiary, proves to be wholly inconsistent with their present latitudinal positions and in certain cases seems indeed to be meteorologically impossible. By reassembling the lands under the displacement hypothesis, a fairly consistent picture of climatic zoning is not only disclosed, but “Pole-wandering” becomes inevitable. Because a shifting of the Earth’s axis is denied by geophysicists, a horizontal creeping of the crustal covering over the rotating core has to be presumed, which, in turn, implies drift.

Faunas and floras Much of the support for the principle of drift has come from biologists who, in their intensive studies of scattered orders and families, past as well as present, have found themselves unable satisfactorily to account for the distribution of forms, living and extinct, save by postulating some kind of continental displacement. Embracing

extensive evidence from the most diverse kinds of life, such a collective opinion cannot well be disregarded.

Reality of drift Taking into consideration all these lines of evidence, as well as a host of supporting data, is has to be concluded that the lands of the New and the Old Worlds must have drifted apart and thereby produced the stupendous Atlantic–Arctic “rift”, as visualized by W.H. Pickering7 as long ago as 1907, in which he was long afterwards followed by Taylor and Wegener. Once that momentous conclusion is accepted, explanation is forthcoming for many geological and biological puzzles and it becomes possible to reconstitute period for period the approximate limits of the Atlantic Ocean with what is fancied to be a fair probability.

Continental movements Right down to the Mid-Mesozoic, the continents of Laurasia and Gondwana must have remained nearly intact, being parted roughly from east to west, though it fluctuated, by Tethys. As a result of squeezing on several occasions during the Paleozoic through pressures directed between NW–SE and N–S, there was induced at approximately right angles to, that is to say roughly E–W, an intermittent tension that reached its maximum during the later Cretaceous. The Primitive Atlantic can be visualized as evolving out of two opposed furrows of crustal sagging that removed from the Tethys in the early Mesozoic, their margins that were determinable from the Mesozoic fringes along the existing lands. The northern gulf progressed northeastwards and then northwards between Greenland and Norway during the later Cretaceous and spread widely over the Arctic region, but failed to reach the Pacific. The southern gulf penetrated south-eastwards and then southwards between South America and Africa. Before the close of the Cretaceous the fold-link between Argentina and the Cape had been ruptured, and Africa, which had already been severed on the southeast and south by a similar gulf, had become surrounded by sea. However, South America remained attached to Antarctica, India, and Australia until the early Tertiary, when it drifted away westwards. The persistence of east–west crustal tension is shown by subordinate roughly north–south seaways, for instance the Ural trough and that between Tunis and the Cameroon, both of which were later short-circuited by the dominating rift of the Atlantic.

Transatlantic links The Alpine Orogeny is conceived as having involved not only the mutual approach of North America and South

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America and of Europe and Africa – with the throwing up of subparallel E–W marginal folds – but the drawing away of North America from Europe and South America from Africa – with the consequent stretching of the transatlantic chains just produced. Stratigraphical considerations show that the three main tectonic phases of the Upper Cretaceous, Oligocene, and Pliocene did not exactly synchronize throughout this vast region. Therefore, one obtains the picture of the progressive rising of complex fold-chains between the West Indies and Spain and between Venezuela and Morocco, respectively, and of their subsequent distortion and dismemberment through the continuance of drifting. In the Upper Cretaceous, compression was dominant in the Mid-Atlantic region. In the Oligocene, tension had become of importance, whereas in the Pliocene the basin had become too wide and the compressive forces too feeble to maintain the transatlantic ridges and the new V-shaped linkages were accordingly built up between the West Indies and Venezuela and between Spain and Morocco respectively. The former existence of isthmian connections or island chains produced in such a way must indeed be postulated to explain the observed close resemblances between the terrestrial life and shallow-water marine faunas of the West Indian and Mediterranean regions during the first half of the Tertiary, a resemblance that fades out after the Miocene. This is, incidentally, the sole section of the Atlantic across which land-bridges could, on geophysical as well as tectonic grounds, have been built up and destroyed during the Tertiary. Here alone could South America and Africa have once more been linked together since their severance in the south at the close of the Cretaceous. In the extreme north, at a much later date, however, Greenland seems to have become joined to Scandinavia, Iceland, and the British Isles by the gigantic ice-body of the Pleistocene. In the far east, the Alaskan–Siberian connection was maintained throughout most of the Tertiary, and only submerged temporarily in the late Miocene and finally in Recent times.

Crustal fracturing Progressive rifting in the Arctic proceeded no further than the Bering Strait, where it ended against the Alpine compression-zone girdling the Pacific. It only succeeded in bending this deep-rooted barrier, and not in severing it. Several lines of evidence, such as the “plateau basalts” of Siberia, suggest that the section between Greenland and Norway possibly had through flowage to Siberia and Alaska towards the Pacific. Novaya Zemlya was bent, and the westerly drift of Spitzbergen led to the Tertiary folding in that island, while the Davis Strait opened and the Canadian archipelago became defined. Tensional enlargement of the North Atlantic is suggested by the ubiquitous Tertiary fracture pattern in that region, as splendidly developed in Scandinavia (SederHolm) and the British Isles; the shatter-lines subsequently picked out by ice-action in higher latitudes. Notewor-

thy is the lengthy graben system of Europe, traceable from southern Spain through the Rhine area to Sweden (G. Richter) running parallel to the axis of the Atlantic. It may causally be connected with the drifting away of Labrador and Greenland. With the European block weakened in that fashion, the youngest Alpine pulses would have been enable to push northwards and so reach the British Isles. Long ago, Osmond Fisher proved mathematically that tensional forces set up in the crust of a rotating Earth would reach their maxima in low and middle latitudes across planes making angles of 45° with the equator. Assuming that the Alpine fold-girdle was developed more or less equatorially across the Atlantic, an explanation is obtained for the prevalent fracturing within belts to north and south along azimuths approximately NE and NW, and hence for the zig-zag shape of the ocean. The Cameroon volcanic line can be cited. Such a fracture pattern is well brought out in a diagram by Sonder (his Fig. 7)8, which, though not intended to support the idea of drift, is distinctly suggestive in that direction. Remarkable again is a slight bending of Africa, revealed by tension on its eastern side, as evinced by the Great Rift System, and by local post-Eocene compression to the west – Benguela and Southern Nigeria – a feature conceivably due to drag at its northwestern corner by the Tertiary linkage with South America.

Igneous activity The abundance of basic effusives is spectacular, especially the plateau basalts, within the northern part of this immense fracture region, which were erupted partly from volcanoes, though more extensively from fissures, and are now represented by dyke-swarms following the dominant fracture-systems. Included, though not quite central, is the series of volcanic islands ranging from Wrangel to Bouvet. Admitting drift, a much smaller Tertiary lava-field would be demanded, whereas the extruded magma could be regarded as the product of such crustal dispersal. It is significant too that those spots where measurements have indicated a change in longitude are situated in this area. Accepting the generalization that alkalic differentiates tend to characterize regions of tension and calcic differentiates characterize neutral areas or regions of compression, it is impressive to observe the abundance of alkalic or subalkalic types within or along the shores of the Central and Southern Atlantic, where they may cut through older neutral types, or contrast with the calcic types of the transverse Alpine compression zone both to east and west, e.g., Morocco (Middle Atlas) and West Indies.

Ocean floor The relief of the Atlantic bottom shows all the characters of a stretch-basin – particularly in the symmetrically-set,

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though crooked, Mid-Atlantic Rise, with its lateral branches that reach out to either shore following northeasterly and northwesterly trends. The writer has viewed the rise as a youthful and secondary feature initiated in the mid-ocean because the sedimentary loading would have been least there, but was aided perhaps by uplift in such a position through light igneous differentiates, as suggested by Van Bemmelen9. A similar rise traverses the Indian Ocean. It can scarcely be doubted that continental rocks extend out far into the ocean, presumably with fracturing, stretching, and thinning. That the basement must include, above the sima acid to sub-acid materials, either stretched crustal rocks or lighter magma-differentiates, is indicated by the behavior of earthquake waves and by gravity anomalies. The depth of isostatic compensation of the west coast of Africa is unusually deep: 150 – 200 km (Meisner).

Physiographical evidence The border-lands present phenomena that point furthermore towards tension. The Great Rift System of East Africa is impressive and runs N–S for about 5,000 km. from Syria to the Transvaal, and forms the opening of the basin of the Indian Ocean in the same way as that of the Atlantic. Considerable sections of the land fronting both these oceans show, at a distance back from the shore of from tens up to some hundreds of kilometers, a scarp facing seawards surmounted by a peneplained surface tilted gently away from the ocean, for example, South Africa, Brazil, Spain, Labrador, Greenland, etc. Its planing-down was done essentially during the later Mesozoic, though it continued in places during the Tertiary. From analogy with Rift Valley abutments, the writer 1(p 256) has regarded these back-tilted surfaces as due to powerful faulting of the continental margins as the Atlantic Rift was produced. The fractured edge of the continental block would thereupon have been uplifted and the peneplain tilted inland in accordance with isostatic and paramorphic principles, and the fault-scarp exposed to active erosion. Such fault-line coasts are characteristic of the Atlantic and Indian Oceans. The hypothetical boundary fault could be expected to lie close to or else beyond the edge of the continental shelf, and suitable geophysical methods would probably serve to determine its position. In the considerable period that has since elapsed, the primary fault-topography developed at its base. Such lightening of the block coupled with general erosion would have induced isostatic uplift of the block, while deposition of the waste therefrom off-shore would have loaded the adjacent ocean floor, whereby a down-warping along the coastal strip would have resulted, excellently illustrated round the southern end of Africa, which shows a history rather like that of the eastern United States. Such flexing would have been accentuated by further suboceanic stretching, and modified by faulting, uptilting, and erosion.

The author1(p 226) has already suggested that those very remarkable features, the submarine canyons, so typical of the Atlantic, might in part at least mark the original cuts made sub-aerially by the existing rivers through the primary up-tilted boundary scarps. Some display all the characters of normal river gorges, and were cut in late Tertiary or Pleistocene times. The land surface with its deeply entrenched ravine became thereafter downwarped and depressed below sea-level with steepening of the canyon gradient. During the Glacial Period – just as in the case of the coral island platforms – the continental shelf was evolved by marine erosion plus some deposition, and such feature proceeded to the down-tilted (or nearly horizontal) surface and its contained canyon and, in extreme instances, severed the latter from its headwaters. This would explain the many cases where the head of the canyon starts suddenly within the shelf. The outer margin of the shelf could, under these views, be wholly or in part built up of detritus. It is certain that local conditions would have played an important part and that the details would have varied in particular cases. Admittedly several difficulties remain to be met under this new hypothesis. Only through acceptance of the paramorphic principle with all its implications does it seem possible to explain the enormous depths to which these apparently terrestrially-evolved and normal ravines have been sunk, yet almost within sight of land that merely shows erosional surfaces inclined faintly seawards. Despite to-day’s consensus of opinion some tectonic agency that affected the coast along its length and not across it, as suggested by a few, has to be invoked and the only one to hand is suboceanic stretching and coastal downsinking. Submarine mud-flows could have been effective in keeping such canyons clear of sediment, but is not thought to have been responsible for their actual formation. A corollary is the rapid oceanward sinking of the crystalline basement beneath the shelf, which has definitely been proved in two cases in the eastern part of the United States. To conclude this very brief review, it will perhaps come to be better appreciated that the Atlantic region offers a most fascinating field for scientific research and that it provides answers to many of the major problems of Earth evolution.

References 1. Du Toit AL (1937) Our wandering continents. Edinburgh 2. Leinz V (1938) Petrographische und geologische Beobachtungen an den Sedimenten der permo-karbonischen Vereisungen Südbrasiliens. N Jahrb Mineral etc. 79(B):26 3. Bailey EB (1929) Pres Add Sect C, Brit Assoc AS, Glasgow, p 57 4. Keidel H (1916) An Minist Agric Argent XI(3) 5. Maack R (1934) Z Ges Erdk, Berlin, p 194 6. Du Toit AL (1927) Carnegie Institute, Washington, DC, p 381 7. Pickering WH (1907) J Geol 15:23 8. Sonder RA (1938) Die Lineamenttektonik und ihre Probleme. Eclog Geol Helv 31(1) 9. van Bemmelen RW (1936) XVI Int Geol Congr 11:965

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W. Schott

Stratigraphy of recent deep-sea sediments based upon foraminiferal fauna Geol Rundsch 29:330–333

Translation received: 4 March 2002 © Springer-Verlag 2002

Stratigraphy is the fundament for the establishment and clarification of numerous questions in geology. The problem of the stratification of fossil sediments played a decisive role in the past, and continues to do so today. If one wishes to gain insight regarding the nature of the formation of today’s deposits, and avoid serious errors in the comparison of the same, one must, of necessity, first concern oneself with the sequence of recent sediment layers. The German South Polar Expedition’s geologist, E. Philippi, was the first to thoroughly pursue the problem of stratification, something that initially appeared to present no difficulty, as stratification amongst recent deep-sea deposits had long been refuted, following the first meager ocean-floor samples. After, however, larger ocean-floor cross sections from various parts of the oceans had become available, it was recognized that foraminifer-rich, calciferous Globigerina Clay was overlying the carbonate-poor, or even non-calcareous Red Deep Sea Clay in various samples, a definitive petrographic stratification. Moreover, among petrographically uniform ocean-floor samples, a reduction in the carbonate content in deeper regions was ascertained, as well as a vertical change in the foraminiferal fauna of long Globigerina Clay samples by Philippi. These observations, which appeared to have regional importance, applied, however, mainly to fairly scattered sites. A continuous stratigraphical subdivision of deepShort report on the lecture given at the assembly of the Geological Association at Frankfurt a. M. on 8th January 1938 by Wolfgang Schott (Berlin, currently at Hannover). Translated by C.J. Adamson and J. Schönfeld C.J. Adamson Jungfernstieg 3, Kiel, Germany J. Schönfeld (✉) GEOMAR Research Center for Marine Geosciences, Wischhofstr. 1–3, Kiel, Germany e-mail: [email protected] Tel.: +49-431-6002315, Fax: +49-431-6002926

sea sediments, based on their fossil content, was not available, and it had not yet been proven that such a regional stratification as that witnessed among fossil sediments, in spite of the observations above, actually existed. Given the extensiveness of the ocean-floor sample material extracted in the equatorial region of the Atlantic Ocean by Prof. C.W. Correns on board the survey-ship Meteor (of the German Atlantic Expedition), it appeared appropriate to once again examine these questions more closely, and, above all, to attempt to establish continuous stratigraphic units in the recent deep-sea sediments. Pelagic foraminifers, i.e., foraminifers living planktonically in the surface waters of the oceans, were used for these investigations, as they and their calcareous shells represent, so to speak, the main fossil types of today’s deep-sea deposits. In order to be able to compare the compositions of foraminiferal faunas from different sediment types with each other directly, it was necessary not only to classify the individual foraminifer species, but also to ascertain the content of the species as a percentage of the total fauna, by quantitatively counting the ca. 500 foraminifers per sample. This was absolutely necessary for stratigraphic investigation so that the distribution of foraminiferal fauna in both the horizontal and the vertical directions of the ocean-floor could be interpreted precisely. In order to interpret the change in fauna in the vertical direction, the regional distribution on today’s ocean-floor first had to be clarified. As it was a question of pelagic foraminifers, it appeared that a comparison of the distribution of these foraminifers in their environment at 0–100-m water depth (information gained through plankton-net catches of the Meteor expedition biologist) was reasonable, a comparison that could possibly yield information concerning the occurrence of the foraminifers’ shells in deep-sea sediment. These investigations in the surface of the equatorial Atlantic Ocean have proved a marked dependence on the part of the cool-water foraminifers Globigerina bulloides (D’ORB) and Globigerina inflata (D’ORB) upon the cold-water region between Cape Verde and Cape Blanco, on the African coast, as well as upon the relatively cool

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surface currents of the Canary Currents out-runners, and the South Equatorial Current. Their calcareous shells are, correspondingly, more numerous on the ocean floor below these cold surface waters. The warm-water foraminifers, Globigerinoides saculifera (Brady) and Globorotalia menardii (D’Orb), among others, are to be found predominantly in the remaining parts of the ocean, and avoid these cool surface-water zones. Although, it is true, the dissolution of their calcareous shells by ocean water after the animals’ demise plays a major role in the distribution of various foraminifer species on the ocean floor, the percent composition of the foraminiferal fauna on the deepsea bed is, to a great extent, dependent upon the environment of the individual pelagic foraminifers at depths of 0–100 m. Through these comparative investigations, it was possible to interpret the considerable variability in the content of the foraminiferal fauna in the equatorial part of today’s Atlantic Ocean floor, which, in itself, is necessary for the explanation of the fauna change in the deeper strata of ocean deposits – as today’s deep-sea bed’s surface represents, geologically, a horizon. The decisive factors in accounting for the change in foraminifera fauna in the vertical direction found in the floor samples are Globigerina bulloides (D’Orb) and Globigerina inflata (D’Orb), and, above all, the warmwater foraminifer, Globorotalia menardii (D’Orb), which disappear in the lower horizons of the samples, only to reappear in still lower section parts. Through the exact determination of the boundaries between which Globorotalia menardii (D’Orb) disappears and, respectively, reappears, it has been possible to separate a layer free from Globorotalia menardii in the hanging layer and in the underlying bed from one carrying Globorotalia menardii. In this manner, it was for the first time possible to successfully establish continuous layer-profiles based upon the foraminiferal fauna in recent deep-sea sediments irrespective of sediment type, something that has long been known from fossil sediments. Unlike both Globorotalia menardii-containing layers, the Globorotalia menardii-free layer is characterized by a notably larger distribution of the cooler-water pelagic foraminifers Globigerina bulloides (D’Orb) and Globigerina inflata (D’Orb), which indicates a drop in temperature of the surface water in the equatorial Atlantic Ocean, as a result of a climate change. As, according to various observations, there has been no known climatic deterioration since the end of the Dilluvium, this drop in temperature in the surface water of the equatorial Atlantic latitudes was caused by the Ice Age, i.e., the Globorotalia menardii-free layer was deposited during the period of the last Ice Age. The lower Globorotalia menardii-carrying layer belongs accordingly to the most recent interglacial period, and the upper Globorotalia menardii-carrying layer was deposited since the end of the Dilluvium.

The comparison of the percent-composition of the foraminiferal fauna of today’s ocean-floor with the Globorotalia menardii-free layer shows no essential change in the equatorial deep-sea environment of the Atlantic Ocean since the Dilluvium. The surface-current conditions at the end of the last interglacial period were already the same as those today, and the Mid-Atlantic ridge was already present on the ocean floor as a rise. Because the end of the Dilluvium can be chronologically established with relative certainty, the sedimentation-rate of recent ocean sediments can be calculated through the thickness of the upper Globorotalia menardii-carrying layer, which has been deposited since the end of the Dilluvium. This rate amounts to approximately 1 cm in 1,000 years for the equatorial Atlantic Ocean. The average sedimentation-rate for 1,000 years shows a clear decrease from near-coastal Blue Clay over Globigerina Clay to the Red Clay typically found at great depths. However instructive these facts may be, being based on a solid foundation, one must use caution when forming generalizations; in the expansive regions of the Indian and Pacific Oceans, into which much less terrigenous material is deposited than into the narrow Atlantic valley, sedimentation proceeds at a much slower pace (in the southern Indian Ocean, apparently only 0.5 cm per 1,000 years are deposited on average). [For additional information, see below, W. Schott (1938) this issue, p. 322.] These communications are to represent only a short report of the lecture held at the congress of the Geological Association in Frankfurt a. Main. It is superfluous to go into these investigations in further detail here because their results have already been extensively collected in the texts listed below. But even through this brief report, it becomes apparent that the central problems lie in the clarification of the stratigraphic relationships and of the recent marine deposits. Moreover, one appreciates the multitudinous conclusions that can be reached regarding the nature of the origins of recent sediments, conclusions that might possibly be of use in the interpretation of fossil sediments.

References Schott W (1933) Die jüngste Vergangenheit des äquatorialen Atlantischen Ozeans auf Grund von Untersuchungen an Bodenproben der Meteor expedition. Sitzungsber. Abh Naturforsch Ges Rostock (3)4 Schott W (1935a) Die Foraminiferen in dem äquatorialen Teil des Atlantischen Ozeans. – Wiss Ergebnisse d. Deutsch. Atlant. Exp. auf dem Forsehungs- und Vermessungsschiff Meteor 1925–1927. 3, 3 Teil, B. Berlin and Leipzig Schott W (1935b) Die Bodenbedeckung des Indischen und Stillen Ozeans. In: Schott G (ed) Geographie des Indischen und Stillen Ozeans. Hamburg Schott W (1938) Über die Sedimentationsgeschwindigkeit rezenter Tiefseesedimente. Dieses Heft 322

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P.H. Kuenen

No geology without marine geology Geol Rundsch 47:1–10

Received: 8 April 2002 © Springer-Verlag 2002

Abstract A brief review is offered of the many problems where knowledge of the ocean floors and of marine processes in shallow water is indispensable for the further advancement of geology. The subject of turbidity currents is treated in greater detail, to demonstrate the interrelation of several aspects of marine geology with sedimentologic and paleogeographic investigations. It is obvious that the title of this introduction is, on the one hand, an exaggeration and, on the other hand, not a very startling new point of view. All geologists are aware that many parts of our science have something to do with the oceans. Moreover, it could also be said of several other specialities, such as age determinations and paleontology, that they show countless points of contact with general geology. Yet, the importance of marine geology is greater and more universal than many geologists realize. Besides, among the various branches of geology, the investigation of the sea has been much neglected up to a few years ago. And for this reason, a great effort is required to catch up on other kinds of geological investigation. In the short space available these two points cannot be fully developed, but an attempt will be made to illustrate a number of aspects. Any geologist will doubtless be able to supplement these from his/her own experience. I will start with geophysics and take seismology to begin with. Deep-focus earthquakes are limited to the circumference of the Pacific Ocean and the questions arise not only why they are situated there at the oceanic margin, but also why they are absent around the other oceans. In any study of the regional distribution of normal earthquakes there is also much to be learnt from the curious concentration on mid-ocean ridges between non-seismic deep basins. Even more important is the propagation of seismic waves below the sea floor. Recent studies of the dispersion of surface waves by Ewing and Press have brought out marked differences between continental areas and the deep-sea floor, which can only be explained if the granitic W.-C. Dullo (✉) Forschungszentrum GEOMAR, Wischhofstr. 1–3, 24148 Kiel, Germany e-mail: [email protected]

layer is entirely absent from the deep-ocean crust even in the Atlantic. Some oceanic areas are more like continents and, conversely, some basins like the Mediterranean tend to show oceanic structure. Curiously the depth does not appear to be the decisive factor, as one might have expected. Explosion seismology of the sea floor, pioneered by Ewing, has shown during the last years that the sedimentary cover of the ocean floor is on the average only 0.5 km thick. More surprising still, the Mohorovicic discontinuity, which lies 35 km deep under the continents, is shown to occur at only 6 km below the ocean bottom. The granitic layer apparently wedges out below the continental slope and is absent from the true oceans, thus confirming the results of seismic surface wave studies and petrology. The thin granitic layer, postulated until recently for the Atlantic and Indian Oceans, does not exist. The opinion is widely held that the “Moho” discontinuity marks the transition from the rigid crust to the plastic substratum, and the oceanic crust would then be almost frighteningly thin. But it may mark only a chemical boundary, or even a margin below which material of the same chemical composition attains a different mineralogical combination of higher density. In these questions we are touching at the very foundations of our science, also in a more literal sense. Each time certain properties of the sea floor were postulated on theoretical grounds, investigations in-situ have upset the picture. A striking example is the flow of heat from the earth, which was predicted to be low on the deep-sea floor because the granitic layer of the continents was held responsible for most of the heat. Several measurements by Bullard and Revelle are now available and consistently give values equal to the average on the continents. Does this mean that the suboceanic crust is more radioactive, or a better conductor, or much thinner than was formerly supposed? The action of postulated convection currents in the mantle was attributed by some geophysicists to the contrast between radioactively heated continental sections and water-cooled oceanic sections. Obviously this hypothesis must be re-examined in the light of that new discovery. Vening Meinesz suggests (personal communication) that the large oceanic heat

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flow may be a temporary condition connected with a convective overturn in the substratum. With regard to gravity investigations it is well known that the possibility of the equator being an ellipse could only be disproved by gravity measurements in the oceans as carried out by Vening Meinesz. To his work at sea we also owe the remarkable discovery of narrow belts of excessive negative anomalies closely linked to island arcs. The strongly positive anomalies he found in several deepsea basins are likewise of fundamental importance. Both phenomena, together with a general excess of gravity in the oceans, are linked with the hypothesis proposing convection currents in the mantle as tectonic agents or as a force causing continental drift. Local thinning of the granitic crust by stretching is assumed by some (Shurbet et al. 1956) on the basis of gravity measurements. This leads us away from geophysics to tectonic geology, where some major problems are also bound up with the contrast between continental blocks and the deep-sea floor. A question, which has fascinated geologists from the very beginnings of our science, is whether mountain chains end primarily where they abut on a coast, or whether they have been cut off later by faulting. There is much to be said for the idea offered by Hess that the former geosynclinal structure continued on the sea floor, but the lack of sediment left the part forming a deep-sea trough empty. When compressed together with the continental geosyncline the resultant structure failed to rise high above the surroundings because there was no prism of light rock and hence no isostatic uplift. Few geologists still accept Wegener’s hypothesis of continental drift. The arguments against his bold suggestion are partly geological. But they are also derived from the geophysical nature of the deep-sea floor and its thick sedimentary cover denoting great age. However, it should not be forgotten that the questions that Wegener sought to answer, especially those of plant and animal migration, the Permian ice age, and certain homologies on opposite sides of oceans, are now again without answers that are quite satisfactory. Sunken continents, land bridges, or pole wanderings do not offer very adequate solutions. Further exploration of the ocean bed may lead to more promising hypotheses. No less fascinating is the problem of whether in the course of geologic history the continents have grown in area at the cost of the oceans. Many geologists have accepted the view that outward growth by the addition of successive orogenic zones has expanded the continents (e.g., Wilson 1954, pp. 151, 205). But grave objections can be raised. All evidence favors the view that the geosynclines in question originated by the depression of land areas and that if the troughs became deep this was not until an advanced stage of development had been attained. Then, the area of the Precambrian shields is relatively so small that one would have to admit that the assumed growth suddenly became ten times as fast from the Cambrian onwards. Hardly any areas do show a clear outward succession of post-Cambrian orogenic belts. As there are no examples of deep-sea sediments occurring at

the base of geosynclinal prisms there is no good evidence of oceanic areas being incorporated in the continents. I am more inclined to assume that orogenic activity has case-hardened certain parts of pre-existing continental blocks, and that later geosynclines usually avoid orogenic belts. A similar fundamental problem is whether the thickness of the continents has increased by the oft repeated horizontal compression during orogenic activities. Denudation at the surface, possibly assisted by melting at the base and tensile stress, have tended to reduce the thickness again. But, between the early Cambrian and the Cenozoic, transgressions have been repeated time and again and, therefore, the elevation above sea level must have remained roughly the same. The obviously higher stand of the continental blocks at the present time is probably a major, but not an abnormal, regression following the Alpine orogeny. However, as Bucher has pointed out, the amount of denudation is largely controlled by sea level. Therefore, if the amount of water on the Earth is increasing, then the thickness of the continental blocks must also be growing. And, if the amount of water is constant and the continents are growing in area then they must also be increasing in thickness. In this manner, the amount of juvenile water in hot springs and volcanic exhalations becomes of importance. Sedimentation on the deep-sea floor constitutes an opposite process because this material is removed from the continents and allows them to rise isostatically. This, in turn, exposes deeper layers of the crust. Hence, even a petrologist who specializes in crystalline schists has a very real interest in the amount of deep-sea sedimentation because this process brings his kind of rock to the surface. All petrologists are aware of certain marine geological problems in their field of study. The high density of the crust below the deep-sea and the exclusively basaltic composition of truly oceanic volcanoes indicate that the ocean floor has a composition different from the continents. But why then does the andesite line not coincide with the topographic boundary of the Pacific? Is andesite a product of partial refusion of basalt as Hess suggests? Is the diversity of continental magmas due to contamination or to conditions favoring gravitative differentiation? These speculations lead to the origin of granite, the most hotly debated problem of petrogenesis. The question whether granite is absent from the suboceanic crust and from mid-ocean ridges becomes of primary importance to petrologists. Volcanology is not only concerned with the petrological problems just mentioned, but poses its own questions. For instance, it is not known whether submarine eruptions produce volcanic ash. Then, the steep submarine slopes of volcanoes prove that the concave profile of subaerial zones is the result of denudation. The beheaded volcanoes of the Pacific that have sunk away to produce flat-topped seamounts and also the foundations on which atolls have grown, are of importance not only to the coral-reef problem, but also for understanding the properties of the crust. The newest data favor the suggestion that each volcano gradually sinks back into the crust at about

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2 cm per 1,000 years. But as far as we know the volcanic islands of Indonesia and the Mid-Atlantic Ridge do not show this tendency to subside. If this actually proves to be the case, a curious contrast with volcanoes on the floor of basins must exist. Is that connected with the shallow situation of the “Moho” discontinuity? Fluctuations of sea level belong typically to the domain of marine geology, but they tie up with a number of general problems, such as transgressions and regressions, epirogenic movements, and the vexed question of marine and fluviatile terraces. There is a separate branch of geochemistry that I have called geoeconomy, which is concerned with total amounts of substances in atmosphere, igneous rocks, oceans, and the sediments of the continents and those of the deep sea. Besides the question already mentioned of the total amount of free water there are others, of fundamental importance to life on Earth; for instance, whether the available amount of carbon dioxide can change. Will an increase due to volcanic activity result in swifter weathering, as Revelle suggests, and that in turn lead to more calcium carbonate sedimentation in the deep sea? Similar problems exist for chlorine, but here instead of sedimentation we have neutralization by sodium derived from weathering of acid rocks. For the majority of substances the principal factor in its geoeconomy is whether accumulation in sea water or on the sea floor takes place. Geochemistry, therefore, contacts marine geology again and again. This review would be very incomplete if no mention were made to how deep-sea sedimentology has recently acquired basic significance for Quaternary geology. The remarkable sediment cores obtained by the use of Kullenberg’s piston corer reach far into the Pleistocene, some even attaining Tertiary strata. Great advances have already been made towards the establishment of a stratigraphy for the last million years. The analysis of Foraminifera, after the example of Schott’s work on the Meteor samples, demonstrates the climatic variations, and Urey’s 0–18 determinations produce astonishing details of paleotemperatures. Absolute chronology in years is also advancing rapidly although a final test of Milankovitch’s curve cannot yet be made. Unsuspected complications are being encountered, such as the occurrence of gaps in the sedimentary calendar and irregularities when cores are compared with each other. But to find complications piled one over the other is the destiny that geologists share with all investigators of field problems. One can almost envy the physicist and chemist who have such complicated machinery for the study of such simple problems, while we geologists have to probe a whole terrestrial globe and milliards of years of history with a hammer and pocket lens. All the great enigmas and questions I have mentioned are bound up with the contrast between the deep ocean floor and the continental blocks. The difference between these two realms is much greater than between any two parts of the continents. That is why examination of the much neglected ocean bed is more urgently needed than

continued studies on dry land. By showing the contrast of continent to ocean, the Earth offers a challenging opportunity for studying its structure and testing hypotheses developed from data won on land. For quite different reasons investigation of shallow seas is no less urgently required. A high proportion of the rocks exposed on the continents are of sedimentary origin, but an even higher percentage of geologists are occupied with sedimentary rocks because of the economic importance of fossil fuels. And as the great majority of sediments is of shallow marine origin, it follows that stratigraphers and paleontologists, sedimentologists, and most economic geologists are almost exclusively engrossed in the study of marine shallow-water rocks. Even coal geologists are confronted with marine intercalations, especially when their terrain encompasses cyclothems. Geological science has flourished on the application of the maxim that the present is the key to the past. Therefore, one would expect that of all environments on Earth, the shallow seas must have been most intensively studied by geologists to find out about present-day happenings. But, on the contrary, less time has been spent on work at sea than on volcanoes or glaciers. And although abyssal sediments are practically absent among ancient rocks, and fossil beaches are very rare, the lion’s share of this meager interest in the marine environment has been given to the deep sea and to beaches. What we think we know about neritic and bathyal sedimentation is practically all deduced from the study of ancient sediments. It is little enough, and unhappily much of this is not even correct. The fault lies only partly with geologists because the cost of work at sea is prohibitive. Only since a few years has the oil industry awakened to this shortage in knowledge and started to provide funds. Generous assistance is now also being given by several navies and hydrographic services. Important work in shallow seas, thus, has already been accomplished and the remarkable output in the last few years of papers dealing with marine sedimentology testifies to the size and interest of this new field of endeavor. In the foregoing it has merely been pointed out that the field of marine geology is of great extent and that future results will fertilize other specialities in our science. In the second part of this paper, an attempt will be made to offer something more positive by reporting on the results of research in which the author has been personally active, the chapter of turbidity currents. Daly was the first to suggest that, 20 years ago, turbidity currents might have played a geological role. During the low sea levels of the Ice Age storms must have raised unusual amounts of mud on the continental shelves. Water with suspended mud has a higher density than clear water and must therefore flow down submarine slopes. This mechanism must have caused the turbid shelf water of the Pleistocene to flow down the continental slopes and thereby to cut out the submarine canyons. By experiments, the present author showed that the mechanism of turbidity flow is indeed very efficient. There is still no full agreement whether the hypothesis of

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canyon cutting is correct, but it is now generally admitted that turbidity currents have played an important part in producing and maintaining these submarine valleys, especially their lower ends. Stetson pointed out that turbidity currents are possibly of importance in carrying fine sediment to the deep-sea floor. Later, I suggested that this mechanism could also explain the occurrence of deep-sea sands at great distances from the shelf. It is Ewing above all else who, with his collaborators, has applied and extended these ideas. He and others have found strong evidence that fine material is carried for hundreds or even thousands of kilometers by turbidity currents and has leveled off the floor of the deeper basins of the Atlantic and the Gulf of Mexico. Broad strips along the margins of the Pacific show the same features. The only reasonable explanation for the delayed break of submarine cables following earthquakes (Grand Banks 1929; Orléansville 1954) is that of Ewing and Heezen that huge turbidity currents were started. From the timing of the breaks the velocity can be deduced. They found 100 km per hour: a value that, in the opinion of many scientists, is impossibly high for a current. Bottom samples showing recent deposition of a graded bed in the Grand Banks area, however, provide a strong point in favor of such a current. The great distance from the shelf to which the ocean floor has apparently been influenced elsewhere by turbidity flow requires the action to be on a vast scale in size and this naturally means great velocities. Yet a certain conservatism in accepting the explanation is justified. The problem of turbidity currents belonged for 10 years purely to the domain of recent marine geology. But later it became of equal importance for ancient deposits and paleogeography. Without knowing of work on turbidity currents, Migliorini had suggested that the Oligocene Flysch of the northern Apennines, the so-called macigno, had been deposited by re-sedimentation from such currents. Together, he and the author then worked out this hypothesis for sediments showing graded bedding. Again, experiments were the chief tool and these demonstrated that artificial turbidity currents actually do deposit a bed, which at each point shows the coarsest grains at the bottom, gradually becoming finer towards the top. During subsequent fieldwork, the writer had several excellent cooperators and we were able to add much confirmation and detail to this explanation of graded bedding. There is a close relation between many formations variously called flysch and kulm, macigno and marnoso arenacea in a number of geosynclines, and also certain detrital limestones. These formations are characterized by a combination of more than a dozen typical properties. The most important of these are the following. Regular parallel bedding of alternating coarse and fine strata: the former usually muddy sandstones of siltstones with graded bedding, the latter pelagic clays. Then there is ubiquitous striation and fluting of bedding planes below the sands together with load casting combined with a variety of tracks and trails.

Inside the graded beds are seen current ripple with its cross lamination, convolute lamination, shale pebbles. The coarser grains and organic remains tend to be oriented parallel to the other features denoting lineation. Several of these features indicate current directions and these currents are found to be parallel over wide areas and through considerable thicknesses. Slump structures are not infrequent. The negative characteristics are absence of wave ripple mark and all indications of shallow water or emergence, absence of larger-scale current bedding, and scarcity of benthonic fossils in-situ. All these properties are satisfactorily accounted for by the hypothesis of turbidity currents. Little is yet known concerning the depth at which re-sedimentation occurs. In the Ventura Basin, Natland demonstrated with Foraminifera in the pelagic shales that depths varied from a few hundred to 2,000 m. In general, indications point to bathyal depths, and this is confirmed by the minimum distances of transport of many dozens of kilometers, which are common. Together with pupils, the writer has examined current directions over wide areas and this has produced important paleogeographic evidence. Kopstein discovered the orientation of grains in the current direction while investigating the Cambrian of Wales, which outcrops in an area of 15 by 20 km around Harlech. After elimination of the folds, the sedimentary directions were found to be remarkably constant. In the Silurian of Wales to the south, the same direction was obtained. In the Kulm of Sauerland and Harz, Sanders and I found directions, which are in reasonable agreement with what several German geologists had concluded from pebble analyses. The source of sands for the Flysch-like formations of the northern Apennines has always been sought to the west in the Tyrrhenian Sea. Ten Haaf has shown that from near Genoa to east of Rome the currents were directed from the northwest. The only case found up to the present with strongly variable directions is the lower Paleozoic geosyncline of southern Scotland. This confusion may be only apparent and result from tectonic complication. From these constant directions it is found that, in the majority of cases, the currents did not run down the sides of the geosynclinal troughs, but lengthwise. This possibility had hardly been considered up to the present in paleogeographic reconstructions, although obviously there is much in its favor. Nearly all land-locked basins of the present time are being filled from one or both ends. The anticlines bordering a geosyncline cannot deliver much sediment laterally into the trough, but they must tend to direct the transport towards the ends. Large parts of a continent can supply detritus through rivers, which will usually join the sedimentary trough at its end, not in the middle. Recently, a reconnaissance of the Oligocene and Cretaceous Flysch in the Alpes Maritimes was carried out with Fallot. The basement outcrop of Mercantour has always been looked upon as the source of the Flysch graywackes. But close study of pebbles has brought little confirmation and the grain size appears to decrease as

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one approaches the supposed source. Current measurements have now demonstrated that the great bulk of sand and pebbles must have been derived from a southerly source. This holds even for exposures right on the present coast, e.g., at Menton and San Remo. Here the circle can be closed and a return made from paleogeography to marine geology and geophysics. For here we have one of the most striking and direct demonstrations that a deep basin with 2,500 m of water was formerly a land area undergoing denudation from the early Cretaceous to the late Oligocene. This constitutes irrefutable proof of the comparatively recent origin of a deep-sea basin. This Ligurian Sea is a perfectly normal part of the Mediterranean, held by many geologists to be the remains of a primeval sea called Tethys. It is all the more striking to find this basin to be so young because there is a large positive isostatic anomaly, and Petterson and Weibul discovered a thick layer of unconsolidated sediment in the adjoining Tyrrhenian Sea. Subsidence must have been 4,000 m and another 1,500 m is required before isostasy will be regained. What has caused this huge increase in density in or below the crust of the Mediterranean Sea? A downward convection current is theoretically able to cause the sinking, but, as mentioned earlier, seismic evidence favors the absence of a granitic layer. There are other true oceanic areas where formerly land existed according to paleogeographic evidence. One is tempted to speculate on how the granitic crust was either changed to basic rock by the opposite to granitization of foundered by stoping, or re-crystallized to denser minerals, or split by tensional stress and pulled apart by continental drifting. But none of these suggestions is very helpful. Light is thrown on another problem of marine geology by the discovery of subsidence in the Mediterranean. The author agrees with Daly that submarine canyons, in general, have been formed by the action of turbidity currents. Shepard has long held the view that these canyons are formed by the drowning of normal river valleys and Bourcart came to the conclusion that this is accomplished by a down-buckling of the continental margin. For the Rivièra and Corsica, the abnormal topography of the submarine valleys provides strong evidence that in these cases Shepard and Bourcart are right. It is the irony of fate that the study of ancient turbidity currents has now brought significant confirmation of subsidence just there where the rival hypothesis of valley drowning was in need of supporting evidence! A final aspect of the doctrine of turbidity currents is the unexpected help it supplies in certain tectonic problems. Italian geologists, especially Merla, have arrived at the conclusion that the “argille scagliose” of the Apennines are a huge mass of clayey sediment, in which are to be found floating blocks of older rock displaced by gravity sliding and ranging in size up to many dozens of square kilometers. In spite of much evidence in favor of this view it is obviously difficult to find simple proof that is convincing. Now Ten Haaf has succeeded in showing that the remarkably regular and consistent orientation of the current directions in the autochthonous macigno does

not hold for those masses, which have slid. They have been rotated in various directions as much as 90° or even more. This proves in an elegant manner that these “icebergs” of rock have indeed been detached from their original position and that, therefore, the hypothesis of gravity sliding is correct. If the slabs were parts of an overthrust sheet they would not show such variable amounts of rotation. At the same time, the mechanism of sliding is rendered more clear by the observation that such enormous slabs are not broken up or distorted in spite of undergoing such large lateral displacements and rotations. It was emphasized at the start that the thesis of all geology being connected by the action of the marine environment is a strong exaggeration. But the writer hopes to have demonstrated that any geologist who looks further than the head of his hammer or the stage of his microscope will also have to take the wide oceans within the circle of his view.

References Daly RA (1936) Origin of submarine canyons. Am J Sci 31: 402–420 Ericson EB, Ewing M, Heezn BC (1952) Turbidity currents and sediments in the North Atlantic. Bull Am Assoc Petrol Geol 36:489–511 Ewing M, Heezen B (1956) Oceanographic research programs of the Lamont Geological Observatory. Geogr Rev 46:508–535 Ewing M, Press F (1955) Seismic measurements in ocean basins. J Mar Res 14:417–422 Ewing M, Press F (1955) Geophysical contrasts between continents and ocean basins. Crust of the Earth. Geol Soc Am Spec Pap 62:1–6 Gilluly J (1955) Geologic contrasts between continents and ocean basins. Crust of the Earth. Geol Soc Am Spec Pap 62:7–18 Heezen BC, Ewing M (1955) Orléansville earthquake and turbidity currents. Bull Am Assoc Petrol Geol 39:2505–2514 Hess HH (1955) The ocean crust. J Mar Res 14:423–439 Kuenen PH (1953) Origin and classification of submarine canyons. Bull Geol Soc Am 64:1295–1314 Kuenen PH (1954) Recent advances in deep-sea sedimentation. Proc R Soc Am 222:289–295 Kuenen PH (1954) Eniwetok drilling results. Deep-sea Res 1:187–189 Kuenen PH (1956) The difference between sliding and turbidity flow. Deep-sea Res 3:134–139 Kuenen PH (1957) Sole markings of graded graywackes. J Geol 65:231–258 Kuenen PH (1957) Longitudinal filling of oblong sedimentary basins. Verh Kon Nederl Geol Mijnb Gen XVIII:189–195 Kuenen PHH, Ten Haaf E (1956) Graded bedding in limestones. Proc Kon Ned Akad Wet Amsterdam, B 59:314–317 Kuenen PH, Faure-Muret A, Lanteaume M, Fallot P (1957) Observations sur les flyschs des Alpes maritimes francaises et italiennes. Bull Soc Géol Fr 6e(VII):11–26 Menard HW (1955) Deep-sea channels, topography and sedimentation. Bull Am Assoc Petrol Geol 39:236–255 Press F, Ewing M (1955) Earthquake surface waves and crustal structure. Crust of the Earth. Geol Soc Am Spec Pap 62:51–60 Revelle R (1955) On the history of the oceans. J Mar Res 14:446–461 Schubert GL, Worzel JL, Ewing M (1956) Gravity measurements in the Virgin Islands. Bull Geol Soc Am 67:1529–1536 Stetson HC, Smith JF (1938) Behavior of suspension currents and mud slides on the continental slope. Am J Sci 35:1–13 Ten Haaf E (1957) Tectonic utility of oriented resedimentation structures. Geol Mijnb 19:33–35 Wilson JT (1954) The development and structure of the crust, ch 4. In: Kuiper GP (ed) The Earth as a planet. University of Chicago Press, Chicago, pp 138–214

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S. Arrhenius · R. Lachmann

The physical–chemical conditions relating to the formation of salt deposits and their application to geologic problems Geol Rundsch 3:139–157

Translation received: 28 February 2002 © Springer-Verlag 2002

Already today, several years after the completion of the well-known Van’t Hoff studies on the formation of the oceanic salt deposits1, not their experimental results, but their application to geologic conditions require renewed investigations. This need is a result of the increasing unexpected geologic observations, which follow exploration for potash deposits. As is well known, Van’t Hoff based his studies on the deposits of the Zechstein salt profile of Stassfurt from which it was assumed that in its shape and content the original salt sediments of the Zechstein time were preserved. With the expansion of the knowledge derived from mining operations deviations became more obvious, so that the monograph of Beyschlag–Everding, “On the geology of the German Zechstein Salt”, published on the occasion of the 10th Mining Congress of the year 1907, recognized three distinct types of deposits in addition to the Stassfurt deposits themselves. The point of view has been presented that the observed deviations can be derived from purely geologic factors, such as erosion during Zechstein time and later mountain folding of the original Stassfurt type. Soon this contradiction became apparent from considerations of the physical chemistry2, which opposed some of the noted conclusions relating to the composition of the potash deposits and doubts were expressed that the potash deposits may be explained as a result of mechanical processes through mountain building3. It seemed, therefore, opportune to take up several important points relating to the question of salt deposits that express the current differences of opinions that are still unclear and need new solutions from the physical and geologic points of view. In the following, the geological viewpoints will be described that led to agreement between the authors in letters of exchange4. The Translated by Gerald M. Friedman G.M. Friedman (✉) Northeastern Science Foundation Inc., 15 Third Street, P.O. Box 746, Troy, NY 12181-0746, USA e-mail: [email protected]

questions that will be discussed are the temperature of formation of the German potash deposits, the cause of the strong inner deformation of the originally horizontal sedimentary layers, and finally the origin of the peculiar salt domes (ekzemes), which in North Germany, as in other places on Earth, have brought salt masses from great depths to near the surface.

Conditions of sedimentation of the salt deposits The difficulty of temperature determination is based on certain kinds of salt combinations, especially sylvite and kieserite, in addition to rock salt and anhydrite of the German potash deposits, which according to the research of Van’t Hoff can only form at temperatures above 70°. However, the actual climate at the time of formation of the potash deposits at the end of the Paleozoic was especially low. This low-temperature climatic setting applies especially to the area of Germany. The time of the Triassic is well known as one of the most extensive periods of inland glaciation, which is evident from the study of Earth’s history5. Glacial deposits have been found in South Africa, northwest India, and southeast Australia. Local mountain glaciation is known perhaps from Westphalia (Germany), Cameroon, and southern Brazil. If one wishes to explain the undoubted glacial deposits through the movements of the south pole into the middle of today’s Indian Ocean (Oldham, Kreichgauer, and Penck), then the difficulty is the lack of glacial deposits at the location of the former North Pole (Frech, Koken), which must have been in Central America. Here the faunal presence (fusulinids and extensively developed brachiopods) suggest a warm climatic setting. The displacement of the North Pole of 70 to the 170° meridian would allow the equator to cut through the German Zechstein sea, so that the presence of high temperature would gain probability. But even here faunal and geographic reasons suggest a lower temperature and point to one of the present congruent locations of the North Pole.

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The German Zechstein Sea formed in the geographic sense an “inland sea”, which moved across from Russia in a western direction through North Germany to East Anglia (in England). This sea cuts into a large North Atlantic continent, which stretched from western Europe via Greenland to North America. To the south it was washed by a large Mediterranean Sea, which itself was separated from the Zechstein Sea by a peninsula that stretched to the east all the way to Russia. At the northern shores of this Mediterranean Sea (Bellerophon limestones of southern Tyrol, Sosio limes of Sicily) the fauna has a close relationship with Asiatic forms and shows through its rich development a warmer climate, which was governed by marine currents from the southeast. By contrast, the fauna of the German Zechstein is a relict fauna, which existed only under unfavorable conditions and was exposed to the influence of cold marine currents that moved along the eastern margin of the North Atlantic continent and may be responsible for the leanness of the climate. In the same sense may be explained the relationship of the Zechstein fauna with the slightly older animal forms on Spitzbergen. The access to the German Zechstein Sea at the Dwina, an island located opposite, which was settled by a Glossopteris-Gangamopteris fauna, which flourished also at the latitudes of icy terrain. We have, therefore, the right to designate the animal world of the German Zechstein by comparison with the conditions of the well-developed climatic zones as “arctic” or “subarctic”. The average atmospheric temperature from the geologic standpoint was probably below 10 °C. The present annual isotherm of this area is 9 °C. For several reasons we hold the view that the precipitation of the Zechstein salt was from the Zechstein Sea and related to a continental origin (Walther). First there is a spatial identity between the spread of the salt deposits and the well-known spread of marine sediments. Also, except for the fossils (petrifactions) in the salt mud, which are enclosed in the salt deposits, the Zechstein salt is accompanied both above and below by marine sediments, which only to the west are spread out somewhat farther than the saline deposits. There is, therefore, from the geological distribution of the salts, no doubt that the marine origin, based on the well-known theory of Ochsenius, should be doubted. The opponents of this view base themselves on the observation that at the present time no large-scale salt deposits are forming where parts of the sea have become isolated, and that the salt deposits contain no fossils (petrifactions). This point of view may be opposed that in the present distribution of water and land, inland seas at the margin of the sea-washed continents, cold marine currents are not present, so that the geographic conditions for the isolation of large and shallow seas in arid climates do not exist. That such conditions are necessary for the formation of salt deposits of any kind has been emphasized correctly by Walther. The absence of large-scale salt deposits in many geological formations presents evidence

that there was not at all times the possibility for sedimentation, leading to the formation of salt deposits. Accordingly it is not surprising that today, impure, and, as a result of winter erosion, only small salt deposits are formed in terrains of steppes on continents that do not recall the profiles of the German salt deposits. To explain the lack of fossils (petrifactions) in the actual salt one needs to study only the cross section of the Russian Narrows to the sea, which have been interpreted as sufficiently wide for communication to the ocean. Then it is understandable that the precipitation of salt in the Zechstein sea progressed slowly, so that the indigenous organisms of the sea had enough time to move away because of the unfavorable living conditions, or they died out. The lack of planktonic animals is not surprising because they may have been retained in the entrance channel in Russia, or in branches thereof, where they are still unknown. For the apparent disagreement of the chemical nature between the bar theory of Ochsenius and the crystallization scheme of Van’t Hoff there is, we believe as explained below, a satisfactory explanation. Therefore, there is lack of reason to deviate from the old concept of the unity of all salt deposits, which in no way breaks down into individual salt pans; moreover the lack of products of erosion, especially the amount of accumulated salt, against which Walther made the effort to explain the Zechstein salt deposits to be of continental origin. I would like to explain the last objection by means of a few numbers. Assume, approximately, the average amount of anhydrite and gypsum in an undisturbed Zechstein profile to be 50 m and estimate the original distribution of the formation in Germany and its immediate surroundings to be 250,000 km2, so one obtains the amount of 12,500 km3 of calcium sulfates. As the sediments of the Zechstein Sea broke into the North Atlantic continent only shortly before deposition of the salts, as a result of tectonic movements, as Koken assumed, where they were exposed in a relatively small land stripe, so that the derivation of this sediment by evaporation of the sea at an average depth of 500 m can produce only a 200th part of the observed mass. One asks in vain where this relict of flattened Variscian mountains and eruptive rocks and tuffs of the aggregated North Atlantic continent derived additional amounts of dissolved gypsum. One should recognize that if the desert terrain was the source of the dried-up salt of a continental platform transgressed by a shallow sea one should recognize that, even if everywhere the desert terrain was derived from the dried-up salts of a shallow sea that transgressed across the continental platform, before concentration in the direction of the German depression began, then the desert terrain must have stretched across an area of approximately 50 km3! We believe, therefore, that we must maintain our concept that a steady process of precipitation of the Zechstein salt deposits took place in a part of the sea that

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connected with the ocean through encumbered communication as a result of tectonic processes. We want to investigate if the aforementioned salt combinations and mass relations can be explained by application of actual geologic processes as occurred in the past. For sylvite and kieserite to occur next to each other in salt, according to Van’t Hoff and Meyerhoffer, a temperature of at least 72° at the time of formation was necessary. One could use the example of the Medvesees (Lake) in Hungary, where such temperatures at temperate latitudes are known, and an actual measurement of 71° has been made. This fact can only be explained in that saturated salt water is covered by a layer of fresh water, which excludes evaporation and, therefore, also vaporization6. However, one has to find another explanation. Without a doubt, unfortunately, one has to understand the existing quantitative deviations that exist in the ratios of the masses of salt in the ocean and salts in the Stassfurt profile. Looking at the numbers, these deviations may be expressed as follows: in proportion to the rock salt the first precipitated lime salts are at an approximately sixfold quantity, whereas the easily soluble calcium and magnesium salts make up only one-third. Large amounts of magnesium chloride, as well as a sequence of easily soluble rare components of seawater, especially iodine salts, are not even present. Purely geographic factors explain the circumstances. Already in the sequence of lithification of the motherwater there may be an interruption of precipitation, as the eolian sediments are introduced, which together with traces of newly brought-in seawater determine the composition of the salt mud. Secondly, one has to think of a change in climate, such that the humidity of the air prevents further evaporation. It is also possible that some of the easily soluble salts are dissolved and removed by compaction during diagenesis, which will be discussed later. On the other hand, processes of diffusion that affected various levels of concentration in the water of the basin and could have reintroduced the more soluble salts into the ocean through the Russian narrows, could not have played an important role. These movements would have advanced so slowly that even in geologic times at distances of only several kilometers they would not have been noticeable. Several differences in concentration would last only so long until precipitation of the first salts would take place because stirring during sinking of the salt mud obliterates the contribution of diffusion currents. A return diffusion of salts across the barrier would only result in dilution of the water, i.e., a return dissolution could perhaps follow. The few rain drops that fell must have had large effects. In addition, one could explain the fine laminae or beds of many potash-salt deposits with the supposition that stratified layers of different salts reached saturation one after the other and that, therefore, the layered struc-

tures resulted7. The assumption is probable that different salts precipitated penecontemporaneously from a solution at the surface, and that already prior to precipitation a differentiation took place, be it through specific weight, grain size, or friction resistance of the salt mud particles of the mother-water.

Diagenesis of salt rocks From what has been said it must appear that great difficulties are apparent in bringing the present composition of the potash deposits into agreement with their probable mode of formation. Moreover, new difficulties arise in explaining diagenetic changes that the salt deposits have suffered since their formation. This observation is in contrast to mechanically deposited sediments that have retained their parallel layering, even where mountain building has deformed the rocks strongly, and the original layering of the clastic rocks is still recognizable. The extent of the deformation increases, as shown elsewhere8, in Zechstein salts, and especially in easily soluble salts, i.e., carnallite deposits, and one finds here the distorted “strings” of kieserite that miners call “worms”. The opinion was voiced until recently that tectonic forces generate the observed undulations. Everding9 noted that the differences in diagenesis must be sought in the different degrees of plasticity of the salt masses subjected to tectonic pressure. But, according to observations in nature, carnallite, as compared with rock salt, should be the more plastic material. However, experiments of Rinne have taught us that, in reality, pressures on carnallite cause only incomplete diagenesis, whereas rock salt suffers complete plastic diagenesis10. A further objection against the application of these experiments of the observed diagenetic changes in salt deposits noted that the deformation of crystals in rock salt deposits has apparently nothing to do with the deformation of layers. With such bent rock salt knots, as exemplified by the carnallite deposits of Salzdetfurth11, curved sights of equally bent rock salt crystals are not observed. The development of streaks of translation and irregular bordering surfaces of crystals in the salt masses12, whose appearance may be created through mechanical pressure or as a result of encumbered recrystallization, must be separated from the deformation of layers whose cause may be recognized at best as diagenesis of the salts as a result of volume changes. Also, the formation of the so-called conglomeratic carnallite may best be explained by physico-chemical influence. Everding was the first to point to the strange circumstance that, in the great majority of cases, carnallite does not occur in fine alternating layers with rock salt and kieserite, but is present as matrix in tuff-like, bedded, or completely structureless rock, in which small to metersize blocks of rock salt and fragments of kieserite, anhydrite, and salt mud are enclosed.

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It is undoubted that at the first consideration, if one expects masses of tuff one is reminded of the irregular layering of debris flows, or of the erratic sediments of roaring wild brooks. More difficult is the comparison with marine shoreline conglomerates that, however, never attained such huge thickness13. It must also be mentioned that the correlation of observations on insoluble rocks with salts must be made with caution. From direct observations it is hardly possible to determine how rubble of rock salt looks as a recycled of deposit, because erosion of rock salt today leads only to dissolution, or to landslides as a result of undermining. The observations of Kaiser in Cardona14, or the experience in rock salt quarries in which rock salt is obtained through the Sol method, make one thing sure that the mechanical erosion of salt rocks as transported through water or solutions does not involve etching. Eroded and transported salt deposits must at their second depositional site accumulate in the form of a chaos of broken-up angular and partially dissolved cones and edges, if mechanical transport has actually taken place, but they could never assume the shape of well-rounded boulders in the way they are found today in weathered exposures of potash mines. It is also most unlikely that the salt mud should assume the observed solid fabric of boulders shortly after deposition, which is caused by long-lasting loaded mountain pressures. Other objections derived from simple geologic considerations that these deposits relate to the surface are pointed out elsewhere15. Opposing the interpretation of Everding, the proposal was made that the shape of the deposits of the rock salt, which resemble tidal channels of the North Sea tidal setting as well as bedded carbonate deposits, can be explained genetically and that the origin of these deposits is autochthonous. The apparent conglomerate must then be interpreted as concretions of the involved mixtures in a mother-water of magnesium chloride. Because it is evident that all shapes of the potash deposits were the result, to a large extent, of later diagenetic processes, and it is not easy to understand how the movement of waves can separate the different salts, and how the same kinds of crystals are converted to fragments and flakes, so this concept has been abandoned and instead the concept is outlined below, which likewise agrees with the geologic requirement that the solid rock salt and carnallite are autochthonous. It is a sure result of many observations that the salt of the potash deposits can be attributed to a large degree to reciprocal displacement. We recognize here not so much an appearance of plasticity of the crystals in a mechanical sense, but more likely the attribute of soluble bodies, which touch their solution and are removed from their place of origin through recrystallization. This process causes deformation of the layers for which not even high pressures are necessary, provided the effective processes are active continuously16. The best comparison is with the movements of glaciers, as Pfaundler has related with recrystallization many years ago17.

The deformation of the original horizontal layers reach their maximum in isolated salt blocks mined in the northern German lowlands and have been discovered over the last two decades. They represent such a big contrast to the flat twists of the deposits of the German central chain of mountains, and moreover to the North European host Variscan formations, that one does not need the usual tectonic explanation, especially as one compares the occurrence of salt domes in Louisiana, Algeria, Siebenbürgen18, and the sure knowledge obtained with the aid of deep borings in Allertal19, where the relationship is apparent of a salt dome to its source, and the outer form of the salt masses provide an explanation of the origin.

Temperature determination Based on the previous explanations we can combine perceptions to obtain the following genetic view. The potash deposits of the German Zechstein accumulated as a result of evaporation of part of the sea that was in partial communication with the ocean and exposed to an arid continental climate. The composition and temperature of the solution was more or less homogeneous during the processes of lithification. The temperature of the solution approximated that of the atmosphere, which from a geologic point of view was about 10 °C. This assumption is not contradicted by the chemical evidence, rather we believe that we have evidence that the temperature never exceeded 25 °C, maybe it did not reach 20°. According to Van’t Hoff’s data there is no difficulty to infer that today’s potash deposits may have been derived from the crystallization diagram at 4.5 °C. That means that the evaporation during the lowering of the temperature decreases and becomes less, and is not questioned at such a low isotherm. The precipitates of the restricted sea will yield at 10 °C the following salt profile at its depositional site: Region

Composition in quantitative sequence

Region of bischoffite

Bischoffite, reichardite, rock salt, carnallite Carnallite, reichardite, rock salt, kainite Kainite, reichardite, rock salt Rock salt, reichardite, kainite Rock salt, polyhalite Rock salt, gypsum Gypsum

Region of carnallite Region of kainite Region of reichardite Region of polyhalite Region of gypsum Region of basal gypsum

It is most likely, that the process of precipitation was interrupted by one of the noted causes, before the region of bischoffite and partially the carnallite region could form. The potash salts were covered by salt mud and, from the younger salt sequence, they were further covered by the clay of the upper Zechstein and the sandstones of the lower Triassic. Approximately during the middle of Buntsandstein time, the thickness of the overlying beds amounted to 700 m, and the temperature of the salt sediments had

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risen to 32°C20. At this temperature the reichardtite breaks down into kieserite (MgSO4 H2O) and 6 molecules of water. A molecular increase in volume of 11% takes place, followed by a contraction of not less than 62% in the course of a long period of time during the evaporation of the water. It seems apparent that these large-scale volume changes would not take place without major twists, even in the surrounding beds, as a result of ejection of water that stood in contact with the saturated solution. Fractures formed along the joints of the beds of the former reichardtite, which filled for the most part with a solution of carnallite and magnesium chloride. In the solutions, the transformation of gypsum layers must have taken place, whose point of change to anhydrite at a sodium chloride and mother-water saturation solution was at approximately 25°C. The rock salt layers deformed through recrystallization and created undulating shapes, especially in the area of today’s kieserite and polyhalite regions and in the bedded carnallite deposits. The intensity of deformation is dependent on the speed of the processes of transformation and evaporation to the extent that the largest deformations appear as soon as the removal of water affects large masses penecontemporaneously, and the evaporation can not keep up with it. Today, in undisturbed deposits of the kieserite region, the transformation follows a molecule-to-molecule reaction in that the kieserite crystals attach themselves to those already transformed and the ejected crystal water is distilled and slowly evaporated through the fabric of the newly formed fractures that move towards older beds. The second impulse towards transformation was the temperature of 65°C, corresponding to a thickness of the cover beds of approximately 1,500 m during Muschelkalk or Keuper time. Now the gypsum that has not yet been transformed had to give up its water because the transformation to calcium sulfate by itself was at the indicated temperature21. During the transformation, the increase of the molecular volume amounted at first to 12% and subsequent contraction was 24%; this transformation resulted in the so-called annual rings of the anhydrite region. The increase and decrease in volume had naturally to take place at the same rate, but at different times in the compact anhydrite, which was the floor and the ceiling of the older Stassfurt salt sequence. If the inner deformations are only of apparently minor effect, then it is evident that the process of deformation affects primarily inhomogeneous salt rocks, and that first of all the recrystallization of the passively participating salt displays the transformation that has occurred22. It is clear that, today, after the Zechstein formations have moved up again into a higher position, at depths of less than 2,000 m, anhydrite represents the unstable modification of calcium sulfate. A retransformation into gypsum, however, can only occur where the anhydrite is in contact with fresh water, not with salt solution. In in-

tergrowth with rock salt, anhydrite becomes the stable form already at depths of several hundred meters. Corresponding to the theoretical introduction, we observe the following: (1) In the zone of water migration above the salt domes occurs the deposit of gypsum that is near the rock salt (see Everding: zur Geologie der deutschen Zechsteinsalze [Geology of the German Zechstein salts] Abh. d. geol. Landesanst. Neue Folge, Heft 52, Table II, Fig. 4); (2) In the salt mass, the mineral is anhydrite. (3) At the base, the rock salt mass is anhydrite. Here one should find, at least in part, the change back into gypsum because fresh water would circulate in the different joints, at least at some distance. That is how one would explain the Mansfield deposits in which boreholes have shown that the base anhydrite contains gypsum layers. As an example, we have looked at the following borehole, Amsdorf 6, which the directors of the Mansfield mines and quarries have placed at our disposal. Bohrung No. 6 bei Amsdorf. +86,407 m over NN 16.30 m 75.70 m 163.70 m 212.00 m 1,288.90 m 1,291.50 m 1,295.00 m 1,302.00 m 1,303.30 m 1,322.00 m 1,337.00 m 1,378.50 m 1,382.00 m 1,382.54 m 1,383.00 m

Sand with gravel Clay with gravel Buntsandstein Gypsum Older rock salt Anhydrite Stinkstone Stinkstone with gypsum Pure gypsum Anhydrite with stinkstone White crystalline rock salt Anhydrite Zechstein and Fäule Kupferschieferflötz Weissliegendes

Diluvium Tertiary Buntsandstein Upper Zechstein Upper Zechstein Middle Zechstein Middle Zechstein Middle Zechstein Middle Zechstein Middle Zechstein Middle Zechstein Middle Zechstein Lower Zechstein Lower Zechstein Rotliegendes

Because of the strong delay in the ejection of the water from gypsum it seems most probable that the evaporation of the water was not yet completed when, at a further burial of 250 m of sediments, the limit of transformation of kainite to carnallite at 72° was reached. The precipitation of carnallite occurred by consumption of the solutions involved in the previous processes of transformation, which had remained in the fractures and which, like the modern “original solutions”, must have been composed of magnesium chloride. Where it lacked solutions, the transformation of carnallite did not occur, and with a further increase in temperature (up to 83°) a mixture of sylvite and kieserite developed, which is the modern hard salt. The volume increase amounts here to only 1.1%, during the formation of carnallite 5.5%, and the volume decrease after the evaporation of water was 13.5%. The effect of deformation at this time was important because the formation of new potash salt is preceded by a total dissolution, and because the transformation is more enhanced than in the formation of kieserite and anhydrite. Where hard salt formed, the melting away of kainite reached large parts of the deposit. The rock salt banks, originally interbedded with kainite, separated from the melting kainite masses and

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formed the so-called “descending” rock salt, which is characteristic of some hard salt deposits. This observation explains the enrichment of potash deposits in hard salt. In carnallite, the chilling after the kainite melting process seemed to have been discontinuous. To a large part, the structure was completely destroyed and in the groundmass of carnallite, in addition to the rest of the broken-up rock salt deposits and salt-mud pieces, concretions were formed composed of rock salt, kieserite, and anhydrite. We use the term “carnallite mixture” because the concept of conglomerate (Everding’s main salt conglomerate) involves mechanical transportation. It seems apparent that for certain layered carnallite deposits, as found typically in the roof of the conglomerates in Stassfurt, Salzdetfurth, and Wilhelmshall, one can accept an original formation. If this concept fits, then the here-observed deformation of kieserite will point to the strongly flooded magnesium sulfates that were paragenetically removed with carnallite, which in the 25° diagram of Van’t Hoff, does not yet apply. Only at 18° does kieserite disappear23. From this demonstration one may conclude that, with the chemical evidence, the higher temperature boundary for the original precipitation was approximately 20°. Besides sylvite and kieserite, the occurrence of langbeinite showed that at least in some parts of the deposit warming of the temperature by the Earth exceeded 85°. The described processes of transformation are not reversible in the sequence of later removal and cooling of the salt layers. The large masses of removed water are meanwhile evaporated or pressed out of the transformed layers as a solution of magnesium chloride. The strong expansion of the volume during the reverse formation may have been helped because the fractures were compacted, and the transformation was confined to parts of the hanging wall area. Also the formation of gypsum at a depth of 1,300 m, which was discussed earlier, must be included with the phenomena of the formation of the cover. At another place24, evidence was presented that the deformations are older throughout than the mountain building. This observation is easily understandable according to the concept developed here, which places the development of the inner deformations back in the Triassic.

Explanation of the Ekzeme As the critical force in the formation of salt domes we have recognized the upward-drive (buoyancy) of the salt25, i.e., a vertical force that can be recognized as an effect of the Earth’s gravity, which attacks the salt masses in its center of gravity and moves them upward with respect to the surrounding and specifically heavier Earth masses. We have a small expression of isostasy of the crust of the Earth. Buoyancy can only be present if the salt or its cover strata have undergone displacement. The mobility of the salt masses is based on the ease of recrystallization at continuous differences in pressure.

Under less-pressured cover strata, among which a loosening of the fabric of the salt layers occurs, a molecular addition of dissolved material from more strongly pressured regions takes place, which re-precipitates at sites of less pressure to compensate for the tension. The result is a slow movement of salt material from sites of dissolution to sites of precipitation. The differences in pressure are, of course, generated from the outside. The causes may be of tectonic nature or brought about by groundwater. The driving of the salt upwards, as a result of mountain building, can be recognized from suture lines between the different basins of subsidence of north and middle Germany26, which developed an “ekzematic” swelling. The thicknesses of the older rock salt, which is found in the borehole near Unseburge in the Stassfurt saddle ridge, is without doubt explained by such an influence. Similar examples are known from Dorm, under the forest of Hildesheim and in the area between Freden and Eime. The northwest-trending rocks of the ekzemes, which occur north of Hanover, are derived from such deformed saddle ridges as a result of the upward movement of the salt. Near Beienrode and Wunstorf (Sigmundshall) there can be no doubt that the vertical northwest-trending salt pillars may still be designated salt ridges or “rowekzeme” derived from them, because these differences betray only the position, but not the shape of their mode of origin. Kirchmann recently described a second form of tectonically emplaced row exzemes. Such a form was built in the Allertal: not on the saddle ridge, but on a flexure that developed in early Jurassic time at the latest. The age of the exzemes can be determined in many examples through processes of transgression. Especially at times of negative shoreline displacement, in the struggle between the upward drive of the salt and its dissolution through groundwater, the upward drive is a victor, then hills and domes formed in the landscape over the salt, which averages 1 km in diameter. Such hills are known in the coastal plains of the Gulf of Mexico under the name of “isles”. They are also present, even if less evident, in northern Germany near Lüneburg, Segeberg, in the North Sea (Helgoland), and in Posen (domelike rise of ground near Hohensalza, Exin, and Wapno). The example of Helgoland explains how such risen ground above ekzemes may be recognized through transgression of the sea across older cover strata. In Louisiana, marine sediments accumulate directly on ekzeme salt following a minor movement of the shoreline. A similar event happened in the Allertal during the middle Keuper where, today, following a changing history of the salt occurrence, the sediment has remained, in the removed ditch above the salt body. The occurrence in the Allertal is not unique. A transgression of middle Keuper can be proven at Fallersleben and even older (Middle Muschelkalk) is a similar occurrence of an already “scarred” ekzeme in Niederhessen,

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about which a more detailed report will be given in the near future. The actual area of distribution of the salt domes is the Northern German depression, where they commonly occur completely isolated. The difficult question now to be resolved is whether through the concealment of the subsurface these occurrences in their setting can be predetermined tectonically, even though their mode of formation can not be predetermined. The question is not resolved by relating a “Hercynian” line through Lüneburg and Helgoland, a line that in good faith one must accept. By comparison of the borings and exposures obtained through mining in the Bernburg Plateau in the neighborhood of Bleicherode and in the marine setting of Mansfield one can recognize that even without tectonics striking thickness variations of the Zechstein salt deposits may occur. With salt domes in depressions one can explain their inner and outer shape for examples, and in many cases probably also their position, but not through mountainbuilding processes, but instead through the effect of groundwater27, which physically seems explainable. The effect of the upward drive of the salt is, in individual cases, first dependent on the conditions of friction of the rising salt bodies. It is obvious that under conditions of upward convergence of the border surfaces the salt dome is soon forced to stop. This case applies, for instance, to the Fallersleben ekzeme, which at the top is surrounded by cover layers that dip 20–50° and, because gypsum was deposited in Keuper time, has apparently grown only little. In other examples, the salt dome has a vertical, even overturned position in comparison with its surroundings. The borderline of a mature ekzeme is a so-called swanhalf curve, or an S-line, as Posepny28 has described from Siebenbürgen, and as they can be confirmed in the Allertal and near Hanover29. The development of vertical scratches on polished border surfaces, the presence of torn off fragments of adjacent lithologies, the spilling of salt water along the contact, and the deposition of the rock fragments that have been carried along above the indicated border of the salt surface, which has been designated the border of the washing out of the salt bed –- all these features may be compared with the physically completely analogous phenomena of glaciers. As with the glaciers, the salt masses depend on the speed of the movement, and apart from the influence of friction, are a function of the cross section and the length of the stream of salt. In general, an acceleration of movement takes place in the course of geologic time. The speed can be measured in northern Germany on the basis of the thickness of the insoluble separations below the transgressions of the time of the upper Chalk and is estimated at approximately 10–50,000 years. How far the direct measurements of fine details will be used, which Harris30 applied to the ekzemes of Louisiana, must be awaited. The inner structure of ekzemes is governed by the changing conditions of friction of the salt dome in the

various cross sections. Because the differences in the specific weight between cover layers (2.4–2.6) and rock salt (2.16) are only twice as large, compared with rock salt and carnallite deposits (2.03)31, it is easily understandable that the carnallite masses from depth rush ahead in the upward movement. Finally, the speed of upward movement of the levels of recrystallization, that is the level of the varying dissolution of the beds, play an important role32. These differences in the salt layers result in differential streams within the ekzemes in the vertical direction, which can be recognized in the North German potash deposits33 in standing folds on a large scale.

Conclusions Explanation of the inner deformation of the salt deposits 1. The Zechstein salts accumulated in a restricted part of the sea at a temperature below 20°. The average temperature may have been 10°. 2. The deviations from the Van’t Hoff determined sequence of crystallization of the marine salts maybe explained as follows: (i) quantitatively through geologic processes during and at the conclusion of the process of crystallization, and (ii) qualitatively that the salt deposits were covered in the course of the Mesozoic by sediments several kilometers thick and under the influence of the heat from the interior of the Earth; in part, water of crystallization was lost, and in part new mineral combinations came together. 3. The result of the volume changes generated pressure differences; these pressure differences, together with the water released from the salt rocks that was in contact with the crystal mush, yielded by twisting of the beds. Similar processes, not the hypothetical tectonic folding pressures, caused the observed inner deformations of the salt deposits. 4. The strongest changes were observed in today’s carnallite region of the potash deposits. Here the original bedding has been for the most part destroyed, as a result of which Everding’s main salt conglomerate developed. Explanation of the outer deformations of the salt deposits 1. The groundwater causes local dissolution of the salt deposits that, however, at greater depths do not generate pore space as developed in carbonates. Rather, as a result of the pressure differences in these easily displaced salt masses (recrystallization plasticity), the salt masses close resultant pore spaces in place. 2. As part of the continuation of the subterranean dissolution of the salt a decrease in thickness of the salt deposits takes place, where the groundwater attacks the salt. 3. The salt forms rock salt masses in the form of cylindrical bodies (ekzemes), which during the dissolution

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along their margins in their slow rise, raise the overlying layers. At the level of the upper area of maximum dissolution an equilibrium forms, the so-called salt surface, above which the insoluble components of the ekzeme pile up. 4. The formation of the ekzeme is favored through tectonic processes (fractures, flexures), so that the ekzemes commonly occur in rows. 5. As a result of the changing circumstances of inner and outer friction, in addition to the composition of the salt domes of specifically lighter and heavier, as well as more and less soluble kinds of salt, differential movements are generated within the ekzeme. These generate standing folds of, in part, great dimensions in the potash mines.

References 1. Görgey R (1911) Die Entwicklung der Lehre von den Salzlagerstätten (The development of the study of salt deposits). Geol Rundsch II:278–302 2. Erdmann(1908) Die Entstehung der Kalisalzlagerstätten (The origin of potash deposits). Kali p 362 3. Lachmann, Über autoplaste (nicht tektonische) Formelemente im Bau der Salzlagerstätten Norddeutschlands (About nontectonic structures in the development of the salt deposits of North Germany). Z Geol Ges 62:113–116 4. The physical problems are discussed in Arrhenius. Zur Physik der Salzlagerstätten (The physics of salt deposits). Meddel Svensk Akad Nobelinst 2(20) 5. Koken (1907) Indisches Perm und die permische Eiszeit. NeuesJahrb Festband, pp 446–546. Lethaea Palaeozoica 2:453. Compare also the further finds of Dwyka conglomerate by Stutzer (1911) in Katanga. Z Geol Ges 63, Monatsber. pp 626 ff 6. Pompecky (1911) Hohe Temperaturen bei Kalisalzen (High temperatures with potash salt). Refer. Z Prakt Geol p 166 7. Boeke (1908) Über das Kristallisationsschema der Chloride etc. (Relating to the scheme of crystallization of chlorides). Z Kristallogr 45:346, etc. 8. Lachmann (1911) Der Salzauftrieb (Salt bouyancy). Halle, p 53, etc. 9. Zur Geologie der deutschen Zechsteinsalze (Geology of the German Zechstein salts). Abh Geol Landesanst NF Heft 52:49 10. (1907) Über die Umformung von Carnallit (About transformation of Carnallite). Koenen-Festschrift p 369, etc. 11. Salzauftrieb (bouyancy). p 60 12. Rinne (1912) Natürliche Translationen an Steinsalzkristallen (Natural translations of rock salt crystals). Z Krist 50:260

13. The Teutonia Corporation has opened such a carnallite deposit which exceeds 150 m in thickness. The Zechstein conglomerate, however, is a witness of true erosion during Zechstein time. It is not more than a few decimeters thick 14. Kaiser F (1909) Das Steinsalz Vorkommen von Cardona in Katalonien (The rock salt deposit of Cardona in Catalonia). Neues Jahrb Mineral I:14–27 15. Lachmann (1910) Über die Natur des Everding’schen deszendenten Hauptsalz Konglomerats (About the nature of the chief salt conglomerate). Z Geol Ges pp 318–321 16. I have tried to explain elsewhere the thermodynamic principle (Weiteres zur Frage der Autoplastic der Salzgesteine). Additional information on the question of autoplasticity of the salt rocks, Zentralbl Min, etc. 1912, p 42). As Riecke recently emphasized (Zur Erniederung des Schmelzpunktes (Decrease of the melting point) Zentralbl Min etc. 1912, p 97). His equations relate to adiabatic processes, whereas geologic deformations are isothermal 17. Über den weichen Aggregatzustand, Regelation und Rekristallisation (About the soft condition of aggregates, regelation, and recrystallization). Ber Wien Akad W 73, 1876 18. Salzauftrieb (bouyancy), p 18, etc. 19. Kirschmann (1911) Bau des Reihenekzems an der oberen Aller (Development of rows of exzemes at the upper Aller). Geol Rundsch II:110, etc. 20. Even in the Upper Elsass, where Görgey discovered kieserite in the Oligocene rock salt, the temperature of transformation reached 32°. According to Förster temperatures of 42–48° were measured in one of the adits. However, Görgey no longer claims that his discovery was correct (correspondence by letter) 21. Van’t Hoff (1909) Zur Bildung der ozeanischen Salzablagerungen (Formation of marine salt deposits) II:16 22. That is why carnallite meanders in modern rock salt deposits 23. Van’t Hoff, op cit 21, vol I, p 61 24. Van’t Hoff, op cit 21, vol I, p 61 25. Salzauftrieb (bouyancy), see p 126, etc. 26. About our tectonic concepts, see Salzauftrieb (salt bouyancy), p 83, etc. Stille (1911) raised objections (Die Faltung des deutschen Bodens. (The folding of German soil.) Kali 27. Arrhenius, 1.C. p 14, etc. 28. Studien aus dem Salinargebiete Siebenbürgens (Studies from the sites of saline deposits). Jahrb Geologischen Reichsandstalt 1871, XXI:162 29. Details, especially exhaustion and about “scarring” of ekzemes, will be reported soon in greater detail in the journal Kali 30. Econ Geol IV, 1909, p 30, etc. 31. 55% carnallite, 25% rock salt, 20% kieserite 32. For examples from Beienrode and Desdemona in “Salzauftrieb” (bouyancy), see p 74, etc. Fig. 28. Probably the accumulation of carnallite in the adits of Jessenitz and Teutonia has the same origin 33. Salzauftrieb (bouyancy), pp 79–82

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M. Teichmüller · R. Teichmüller

The chemical and structural metamorphosis of coals Geol Rundsch 42:265–296

Translation received: 31 July 2002 © Springer-Verlag 2002

If a sediment is heated or subjected to pressure so that it becomes significantly altered, either chemically or structurally, it is said to have been metamorphosed. As Niggli and his coworkers have shown, glacial ice is, by this definition, metamorphic. The original material, snow, has been fully changed – it has been reordered and recrystallized, like a shale being altered to a crystalline slate. The situation with carbonaceous matter is similar. Coal [Steinkohle] is so different structurally and chemically from peat that it must be termed metamorphic, even when the other rock types adjacent to it show no signs of metamorphism (e.g., the coals of Bohmte in the Wealdean clays of the Lower Saxony Basin). Colloidal carbonaceous material includes a number of complex carbon compounds, and is especially sensitive to increased temperature and pressure. It is apparent that the boundary between diagenesis and metamorphosis is not well defined for carbonaceous material. As a rule, the loss of water from humic matter to become lignite [Braunkohle] is usually considered to be diagenesis. However, as the material is altered from soft lignite [Weichbraunkohle] to the stage of glance lignite [Glanzbraunkohle], there are such marked structural alterations that they need to be described in greater detail.

Translated by William W. Hay

[Steinkohlen]. Microscopically the difference between soft lignite and glance lignite is the most obvious of the entire coalification series: in the soft lignite the structural elements are loosely packed and disordered with reference to the bedding, but in the glance lignite they have been compacted and oriented parallel to the bedding planes. Xylites or woody remains, which in soft lignites are hardly distinguishable from recent wood, have been transformed to compact, thin vitrite bands in glance lignites. In this transformation, the cell lumens, which are empty or filled with water in soft lignites, become completely compressed. One has the impression that the woody materials were, to a large extent, originally soft and that they have been homogenized. At the transition from soft to glance lignite there must have been a high degree of peptization of the humic substances. As this occurred, colloidal humic solutions were produced; these permeated all of the carbonaceous matter and, as the material dried out, become glued together and solidified1. This obvious cementation process has been termed “Vergelung” (M. Teichmüller 1950). Van Krevelen (1951/52) used the term “collinitisation”. The process can be simulated experimentally, as has been shown by, among others, W. Petrascheck (1947) and Dulhunty (1950a). Dulhunty heated soft lignite saturated with water for a lengthy period of time to a temperature of 100 °C under a pressure corresponding to a burial depth of 1400 m. The result was a shiny, hard lignite [glänzende Hartbraunkohle] as the water content of the carbonaceous matter sank to 24% and the volume was reduced to 40% that of the original material. The process is dependant on pressure, temperature and time. The most important factor is temperature. Chemical changes play a lesser role in this stage. H. Stach was able to produce an artificial “Pechkohle” [pitch coal] solely through peptization of a soft lignite treated with alkali and subsequent drying of the watery carbonaceous gel at room

W.W. Hay (✉) GEOMAR Forschungszentrum, Wischhofstr. 1–3, 24148 Kiel, Germany e-mail: [email protected]; [email protected]

1 Saturation of this sort with colloidal humic material occurs locally in peat [Torf] and soft lignite [Weichbraunkohle] (M. Teichmüller 1950). However, there it is restricted to certain of the components or to particular facies types or layers.

1. The alteration of carbonaceous matter in the lignite stage In its structure, soft lignite differs only slightly from peat (Thomson 1950); its water content is still high. By contrast, hard [Hartbraunkohlen] or glance lignites [Glanzbraunkohlen] are often macroscopically and microscopically almost indistinguishable from true coal

S76 Fig. 1 The content of bound water in the glance lignite [Glanzbraunkohlen] seams of the Haushamer syncline of the Bavarian alpine foreland decreases with the age of the seams and the tectonic depth

Fig. 2 Degree of decrease in bound water in coals of Upper Silesia. The individual lines show the gradient of water decrease in the various drill holes and mining sections. Depth differences can be read from the scale in the lower right. The individual curves are ordered according to water content. Thereby it becomes evident that with declining water content the gradients of water loss decrease (after M. Teichmüller and R. Teichmüller 1949). 1 Well Trzebinia, 2 Tenczynek (Glückauf, Kristina), 3 Janina, 4 Well Pogoryce, 5 Jaworzno, 6 Well Koscielsce 2, 7 Well Koscielsce 3, 8 Well Theodor Körner, 9 Fürstengrube 127, 10 Valeska, 11 Gräfin Laura, 12 Castellengo, 13 Abwehr, 14 Wolfgang, 15 Brzezszce, 16 Silesia, 17 Well Katschütz, 18 Gleiwitz

temperature. This product was almost indistinguishable chemically from the original carbonaceous matter. The transformation from soft lignite to glance lignite is, according to H. Stach (1933), primarily a colloid-physical process. The chemical alterations are, as noted, relatively slight: the carbon is only slightly enriched2. The acidity of the humic substances remains (it is evident in the ability of lignites to dissolve alkalis, and is not lost until the coal stage [Steinkohlenstadium] is reached). Since structural changes dominate, the water content of the lignite stage is a far better measure of the degree of incoalat2 According to the structural chemical calculations of van Krevelen (1953), the content of aromatic hydrocarbons should climb rapidly at the expense of non-aromatic hydrocarbons in the glance lignite stage [Glanzbraunkohlenstadium].

ion than the carbon content or content of volatiles. Nevertheless, the dewatering of carbonaceous matter gradually decreases: according to Schmitz (1932, the soft lignite of Cologne) and Edwards (1948, the Australian soft lignites), the water content of fresh moist coal from the mining pits decreases 1% with every 30-m depth, and Schürmann (1927) reported that the water content of the hard lignites of Borneo decreases 1% per 100-m depth. In a similar manner, the bound water content of the pitch coal [Pechkohle] of the alpine foreland decreases 0.5–1% per 100-m depth (see Fig. 1). The dewatering takes place even more slowly in the coal stage [Steinkohlenstadium]. The decrease in water loss with decreasing water content has been demonstrated very clearly through deep drilling in the Upper Silesian coal basin (see Fig. 2).

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Fig. 4 The increasing similarity of chemical composition of different original materials in the course of metamorphism (after van Krevelen 1951/52) [Algen = Alge; Blatthäute + Sporen; Leaf cuticle + spores; Holzgewebe = Wood tissue]

Fig. 3 The decrease of water and volatile components of coals in the individual stages of metamorphism. [Wasser = water; Wassergehalt = water content; der lufttrokenen Kohle = of air dried coal; der grubenfeuchten Kohle = of wet coal from the pit; Gehalt an Flücht. Bestandteilen = Content of volatiles]

As the results of the experiments (discussed above) have shown, the water content of the carbonaceous matter is largely dependant on the temperature, pressure and their duration. The experiments of H. Stach, mentioned above, have also shown that time plays a role in the aging of humus colloids. However, the heating of the carbonaceous matter is more effective than time (Dulhunty 1950a). It leads to a rapid drying of the humic colloids and, at the same time, hydrophilic groups are split off from the humin molecules. Without doubt, pressure also plays a role, because it collapses the pores of the carbonaceous matter, thereby aiding the release of water from the larger capillaries. The process is facilitated when the temperature also increases because the viscosity of the water decreases (Dulhunty 1950a; Fig. 3). In accord with the experimental observations, the water content of lignites decreases in certain of the tectonic zones of compression of the Australian coal fields (Edwards 1948). Also, as Berkowitz and Schein (1952a) have shown, folded glance lignites of Pakistan sometimes have minimal water content, equal to bituminous coals [Fettkohle]. Although these glance lignites have hardly been altered chemically, their structure has been greatly altered by tectonic compression. In other words, the structural metamorphosis outstrips the chemical alteration. Hence, even glance lignites may be termed metamorphic.

2. The transformation of carbonaceous matter in the coal stage [Steinkohlenstadium] a) The chemical metamorphosis Because coaly matter consist of a great variety of original plant materials, each of which has its own incoalation sequence (see Figs. 4, 10), it is necessary to always use the same component of the carbonaceous matter in defining the grade of chemical metamorphism. The material best suited to this purpose is the chemically relatively homogeneous vitrite (Patteisky 1925; W. Petrascheck 1947; M. Teichmüller and R. Teichmüller 1949; van Krevelen 1951/52). The chemical metamorphosis of coal has long been expressed in terms of data on elemental analysis (C, H, O) and quick analyses (bound carbon, volatile components). Recently, it has become common practice to give not only the absolute values of the elemental analyses but also the atomic ratios H/O, H/C, and O/C (Mott 1942; Mackowsky 1949a; van Krevelen 1950; Huck and Karweil 1953a). Thereby one gains a first impression of the changes in the chemical constitution of the carbonaceous matter (van Krevelen 1952). Since publication of the important work on changes in the chemical constitution of the carbonaceous matter in the course of metamorphosis by H. Stach (1933), recent investigators have again begun to characterize incoalation in terms of structural chemistry (van Krevelen 1950, 1952, 1953; Huck and Karweil 1953a). Van Krevelen has devised a new means of characterizing the changes: he uses both chemical and physical methods to examine all of the vitrite without using oxidative, hydrative, or dissolution processes. In so doing, he follows the example of Watermann (cf. Leendertse et al. 1953) who developed this method for the structural analysis of petroleum. Its application to carbonaceous matter assumes that vitrite is a glass-like material, that is,

S78 Fig. 5 A The increase of aromatic-bound carbon, and B the increase in the number of rings per carbon atom in the course of metamorphism (after van Krevelen 1953)

a sort of supercooled liquid. If this is the case, and much evidence supports this idea, it is possible from elemental analysis of the carbonaceous matter and its density to estimate the proportion of aromatic compounds and the average number of rings per carbon atom. Van Krevelen thought that the number of carbon atoms which belong to rings decreases as metamorphism proceeds to highvolatile bituminous coal [Gasflammenkohlen] but then increases sharply to anthracite (see Fig. 5). The content of aromatic carbon, which increases rapidly from soft lignite to glance lignite, increases only slowly in coals to the medium-volatile bituminous [Fettkohle] stage but then increases rapidly in the low-volatile bituminous [Magerkohle] and anthracite stages (Fig. 5). In highly metamorphic anthracites almost all of the carbon is bound in aromatic compounds. The size of the aromatic ring systems which, according to van Krevelen, can be determined from elemental analyses, density, and refraction index, steadily increases during the metamorphic process, being especially rapid in highly metamorphic coals and anthracite. Van Krevelen came to the following view of the process of metamorphosis. In slightly incoaled carbonaceous matter, the relatively small aromatic ring groups are bound to each other by non-aromatic bridges. Because of this, the coal molecules have a three-dimensional structure, as has been assumed for the “micelles” by Bagham et al. (1949). Gradually the bridges are destroyed and, at the same time, the lamellar aromatic complexes become increasingly wider. They grow into layered, honeycomb-like structures. The aromatic lamellae are stacked in parallel sheets, although they do not have a strict regular orientation as in the case of graphite. This stage corresponds to the crystallites with “turbostratal” structure, which Blayden, Gibson and Riley (1944) found by X-ray examination of carbonaceous matter. As the aromatic layers grow larger, the crystals become ever more graphite-like. Huck and Karweil (1953a) consider, on the basis of comparative adsorption and porosity measurements on activated carbons, that there are several original carbonaceous materials. The coal molecules consist of an aromatic compound forming a “nuclear system”, and a nonaromatic “methylene system” which is rich in hydrogen and oxygen. It is suspected that the nuclear system is derived from lignin and the methylene system from degrad-

ed cellulose. The nuclear system remains almost constant in size during the metamorphosis, whilst the methylene system is gradually dismantled. In bituminous coal [Fettkohle] with 90% C, almost all oxygen is in the methylene groups. The metamorphosis of the organic compounds in slightly incoaled carbonaceous matter consists initially of breaking the carbon chains of the methylene system and, from the bituminous coal [Fettkohle] stage on, linkage of the dominant aromatic molecules plays the major role. In principle there are no differences between the concepts of van Krevelen and Huck and Karweil. Although we are just at the beginning of an understanding of the chemical composition of carbonaceous matter, and the observations made to date must be supported by further investigations, it seems that a sure result of recent work is: the chemical metamorphosis of carbonaceous matter is characterized by an increasing aromatization of the humin (ulmin) complexes. Hydrogen- and oxygen-rich molecules having non-aromatic character are degraded. At the same time, condensation processes occur whereby the molecular complexes become more and more integrated. This corresponds to the view of H. Stach (1933). H. Stach came to the conclusion that the nucleus of highmolecular weight humin molecules apparently in “each incoalation condition... is built in the same way” and “the incoalation series is caused by more or less drastic changes of peripheral groups”. The results confirm the conclusions which had been reached in the 1930s through fractional solution experiments (Peters and Cramer 1934), hydration ( Fischer, Sprunk, Eisner, Clarke and Storch 1939), oxidative degradation (Juettner 1937; van Krevelen 1951/52) and thermal degradation (Lowry 1934) on carbonaceous matter. These showed that with increasing incoalation, the degree of condensation and aromatic content increase. The changes are most strongly developed from the bituminous stage [Fettkohlenstadium] on and are especially obvious in the anthracite stage. One can assume that the easily split oxygen- and hydrogen-rich molecule groups escape as volatile components during carbonization heating in a crucible, whereas the stable, condensed aromatic molecule groups remain behind in the coke formed in the crucible (van Krevelen 1953; Huck and Karweil 1953). Insofar as the content of volatile components is a measure of the aromatization of

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Fig. 6 Changes in physical properties of coals in the course of metamorphism (measured against C content; modified after van Krevelen 1953) [Innere Feuchtigkeit = Internal moisture; Benetzungswärme = Heat of wetting; Härte = Hardness; Zermahlbarkeit = Ease of pulverization; wahre Dichte = True density; Kristallitgröße = Crystallite size; Reflexion = Reflectivity; Brechungsindex = Index of refraction; Absorptionsindex = Index of absorption]

coal3, van Krevelen showed in 1953 that one can in fact calculate the content of aromatic carbon (which, according to his method, can be determined from elemental analysis and density) from the content of volatile components. b) The structural metamorphosis The structural changes in coal in the course of metamorphism have been the subject of intensive research during the last decade. New breakthroughs in this area of research have been made especially in England. In 1944, the results of a series of colloid-physical, optical, and X-ray investigations of carbonaceous matter were reported in the “Proceedings of a Conference on the Ultra-fine Structure of Coals and Cokes”. Investigations of the internal surface area and capillary spaces within the carbonaceous matter have proven to be especially important (Fig. 6). It has long been known that the natural water content of air-dried coal from high-volatile sub-bituminous coal [Flammkohle] to the bituminous coal stage [Fettkohlenstadium] sinks from about 5 to 1%, and then rises slightly in anthracite. The same behavior is also shown by the so-called maximal internal moisture, i.e., the maximal artificial water adsorption of the carbonaceous matter (Dunningham 1944; Dulhunty 1947, 1950b). This also reaches a minimum of 2% in bituminous coals [Fettkohle] with 90% carbon content, whereas in high-volatile sub-bituminous coals [Flammkohlen] with 80% C, it is approximately 15% and in anthracite with 95% C it is only 4%. Since the water in air-dried coals is bound by adsorption, the lower water contents indicate a smaller internal surface area in the carbonaceous matter. This can also be calculated from the adsorption of organic liquids, such as methanol, or even better from adsorption of gasses such as argon and nitrogen. Also, the heat which is de3 This measure of incoalation cannot be used for lignites [Braunkohlen] and for water-rich high-volatile sub-bituminous coals [Flammkohlen].

veloped by moistening of carbonaceous matter with liquids or gasses (nitrogen) as a result of the decrease of free surface energy, e.g., the so-called heat of wetting, gives information about the internal surface area (Griffith and Hirst 1944; King and Wilkins 1944; Dressel and Griffith 1949; Berkowitz 1951; Zwietering, Oele and van Krevelen 1951; Lecky, Hall and Anderson 1951; Malherbe 1951). Using argon and nitrogen, Lecky, Malherbe, van Krevelen and coworkers arrived at values of 1–3 m2 of internal surface area per gram of carbonaceous matter. Using methanol, Berkowitz and Schein (1952b) arrived at much larger numbers. Obviously, in the latter case the carbonaceous matter swelled, causing the capillaries to distend. Also, through the use of these methods it became apparent that the internal surface of coals decreases from the high-volatile sub-bituminous stage [Flammkohlenstadium] to the bituminous stage [Fettkohlenstadium], and then increases slightly to the anthracite stage. On the basis of heat of wetting, King and Wilkins (1944), Berkowitz (1951) and others have estimated the mean size of the colloidal units of the coals, the so-called micelles. Berkowitz proposed that they are 120–130 Å. Thus, the coal micelles are not much larger than rubber molecules. According to the view of Bangham, Franklin, Hirst and Maggs (1949) and Berkowitz, the coal micelles are spherical and do not change in size during metamorphosis – the spheres become more tightly packed with incoalation. King and Wilkins, however, assume that the micelles become larger with incoalation, and change form. The micelles are probably relatively loose agglomerations of molecules which have similar composition but become more complex toward the center of the micelles and thus act indifferently with respect to heating and solvents. Microhardness, elastic modulus and solidity of coals, which are important in their mining and pulverization, decrease from high-volatile sub-bituminous coal [Flammkohle] (>40% volatiles) to bituminous coal [Fettkohle] with 20% volatiles, and then increase rapidly (see, among others, van Krevelen 1953). Bangham and Maggs (1944) attribute the solidity of slightly incoaled carbonaceous matter to van der Waals forces and the solidity of anthracite to chemical bonds. Huck and Karweil (1953a) assume that the molecules of slightly incoaled carbonaceous matter are held together by hydrogen bonds: the coal loses solidity in proportion to the loss of these bonds during metamorphosis. In highly incoaled coals, especially anthracite, multiple bond valence forces result from linking of the molecules. In bituminous coal

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[Fettkohle], the hydrogen bonds have been largely eliminated and the molecular links are weak; as a result, the solidity of bituminous coal [Fettkohle] is minimal. The low solidity of bituminous coal [Fettkohle] is apparent from experience in mining (largest occurrences of fine coal!) and in making briquettes without the use of bonding agents. Bituminous coals [Fettkohle] with 20% volatiles are easiest to use for making briquettes because their resistance to deformation is especially low. Accordingly, microtectonic plastic deformation is often observed in the bituminous coal seams of the Ruhr (M. and R. Teichmüller 19544). After it had been determined that bituminous coals [Fettkohle] are characterized by especially low porosity and solidity, the coking properties of bituminous coal were seen in a new light (Hirst 1944; Berkowitz 1949). The smallest colloidal coal particles, the micelles, lose more of their solidity as soon as the atomic groups on their surface are set in motion by heating. The micelles begin to slip, so that the coal appears to melt. As a result of the low porosity of bituminous coal [Fettkohle], the volatiles released by heating are trapped within the pores and expand them so that the bituminous coke swells. In less-metamorphic coals, the oxygen-rich bonds reduce the motility of the micelles, so that in coking the coal remains solid or is only slightly softened. In addition, because of the more open pore structure, the volatiles can easily escape. As a result, the coke made from these coals does not swell. Only small quantities of volatiles are developed from heating highly metamorphic coals and anthracites. As a result of the high solidity of the coal, the volatiles cannot expand the pores. These coals produce only bad coke or only coke powder. The example of coking of glance lignite [Glanzbraunkohle] from Pakistan supports this purely physical explanation of coking behavior (Berkowitz 1950, Berkowitz and Schein 1952a): The coaly material from Sharigh contains 74% C and 55% volatiles – it is thus chemically a lignite [Braunkohle]. Through strong tectonic compression its internal surface (and thereby its water content) has been so much reduced that it corresponds to a coking bituminous coal [Fettkohle]. In fact, this lignite produces a baked coke. Another support for this hypothesis is the experience that many non-baking coals “melt” if they are so rapidly heated that the inner gas pressure overcomes the solidity of the coal. The true density of carbonaceous matter in individual stages of incoalation has been determined using the helium or water replacement methods reported by Franklin (1949), Dulhunty and Penrose (1951) and van Krevelen (1953). The true density declines to bituminous coal [Fettkohle] with 20% volatile content, and then increases rapidly. A further insight into the fine structure of coals has been gained from X-ray analysis. On the basis of Debye4 According to Boddy (1944), coals of all ranks of incoalation can, under sufficient pressure, be deformed. Berkowitz (1951) called attention to the temperature dependence of deformation. This indicates that the intermolecular forces of the carbonaceous matter can not be very large.

Scherrer pictures, Blayden, Gibson and Riley (1944) distinguished crystallites in coal forming a so-called turbostratal system. These are aggregates of flat, honeycomb-shapes molecules having a more or less aromatic character. Although they are stacked in parallel sheets, they are otherwise not regularly arranged. Two types of crystallites have been distinguished: 1. flat aromatic lamellae, which are relatively immobile during heating and represent degraded lignin, and 2. “bitumen” lamellae which, as a result of numerous marginal atomic groups, are not so flat and not so aromatic. They should have a longer c-axis and are mobile during heating. Perhaps these are degraded cellulose. With the loss of volatiles, i.e., with increasing metamorphism, the bitumen lamellae become flatter. This corresponds to an increasing aromatization. Blayden, Gibson and Riley have estimated the size of the crystallites in coal to be 20–30 Å. In the course of metamorphosis the a-axis slowly becomes longer until reaching the low-volatile bituminous coal stage [Eßkohlestadium] then, as a result of loss of the peripheral hydrogen and oxygen atoms, it rapidly expands. In this process the released carbon valence bonds link together so that the crystal lattice becomes very strong. Since Debye-Scherrer observations of coals show only diffuse diffraction patterns which resemble those of liquids, Jagodzinsky (1950/51) finds the estimates of crystallite and axis sizes questionable. Electron diffraction pictures of coals show no sharp interference lines, even though the cathode rays have a shorter wavelength than X-rays and should be able to reveal finer structures (R. Teichmüller and M. Teichmüller). The “crystallites” of coals must therefore be extremely small. In addition, their “turbostratal” arrangement of atoms (discussed above) does not correspond to the order expected in a crystal lattice. This is true also for highly metamorphic anthracites which, therefore, despite many optical similarities (see below), are not yet truly crystalline bodies. A three-dimensional lattice first appears with graphite (Mackowsky 1950/51). Nevertheless, the sheety structure of the coal molecules and molecule complexes becomes better organized with increasing metamorphosis. The anisotropy of coals is related to the increasing organization of the structural elements in a particular plane (usually the bedding plane). Because in reflected light anisotropic effects first become visible with strong anisotropy, it had been assumed, on the basis of observation of polished surfaces, that slightly incoaled carbonaceous matter was optically isotropic (Mackowsky 1950/51) and that the ordering of structural elements in a particular direction did not become evident until the stage of bituminous [Fettkohle] or low-volatile bituminous coal [Eßkohle] had been reached. However, anisotropy is very obvious in thin sections of high-volatile subbituminous coal [Flammkohle] (M. Teichmüller 1952a). M. Teichmüller noted that, even in the glance lignites [Glanzbraunkohlen] of the Alpine foreland, there is illu-

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Fig. 7 The anisotropic vitrite of a glance lignite [Glanzbraunkohle] from upper Bavaria in polished thin section viewed through almost crossed nicols. In this position a parallel structure becomes visible, resembling microschistosity. This structure cannot be seen macroscopically. Magnification 200X

mination and extinction of all of the vitrite as the stage of the petrographic microscope is rotated with crossed nicols. The extinction directions are usually parallel and at right angles to the bedding plane. However, in the case of folded coals they may be at an angle (W. Petrascheck 1947). Sometimes, in strongly folded glance lignites [Glanzbraunkohlen], a sort of microschistosity can be seen (see Fig. 7). In conclusion, the anisotropy of coals is independent of the chemical grade of incoalation and is produced only by the ordering of molecular complexes in response to increased pressure. By contrast, the refractive index and absorption coefficient, and thereby the reflectivity of vitrite in reflected light, are dependent on the chemical structure of the carbonaceous matter (van Krevelen 1953; H. Stach and M. Teichmüller 1953). According to measurements made by Cannon and George (1944) and the calculations (based on reflectivity) of van Krevelen (1953), the refractive index and absorption coefficient become greater as metamorphism proceeds (see Fig. 6). According to van Krevelen, the increase in refractive index is especially marked from the bituminous coal stage [Fettkohlenstadium] onward. In the range of anthracite, the refractive index remains constant. However, the absorption index increases especially sharply in the anthracite stage [Anthrazistadium], although it increased only slightly in lower stages5. Because the reflectivity of vitrite is dependent on the refractive index and the absorption coefficient, it increases most sharply during the course of metamorphism where the refraction and absorption rapidly increase, that is, in the range of bituminous coal [Fettkohle] and lowvolatile bituminous coals [Eßkohle and Magerkohle] and anthracites. The refractive index increases with the atomic density. This increases during the course of aromatiza5 The division of the corresponding curves in Fig. 6 is related to anisotropy, which can first be seen in polished section at the bituminous coal stage [Fettkohlenstadium].

tion through an increase in the number of C=C double bonds. According to electromagnetic theory of light, the capability of absorption of light is dependent on the number of freely vibrating electrons. The vibrations of the electrons are damped by the vibrations of the light, and absorption occurs (Niggli 1924). According to a verbal communication from Prof. van Krevelen, the electrons move more freely with increasing condensation of the aromatic complexes. The increase in the refractive index and absorptivity, and therefore the reflectivity, of the vitrite in the course of metamorphism are ultimately a response to the aromatization and condensation of the humin complexes. Van Krevelen (1953), after careful repetition of the observations, was able to relate the controversial “steps” of Seyler, i.e., the stepwise increases of the reflectivity during the course of incoalation reported by Seyler (1944, 1950), to chemical changes. He related them to increases in size of the aromatic ring systems during metamorphosis. The hypotheses that the reflectivity of coals depends on the density of packing of the micelles (Mackowsky 1952) or directly on the carbon content have not been substantiated. Reflection measurements on artificially sulfurized coals have shown that the reflectivity of vitrite can be very strong in spite of greater porosity and smaller carbon content (H. Stach and M. Teichmüller 1953). This supports the view of van Krevelen that, in the long run, the structural-chemical make up of the coal is the determining factor for reflectivity. Insofar as the chemical structure has not been destroyed through extensive weathering processes, the reflectivity of the vitrite remains an important means of determining the grade of metamorphism. Of course, only major stages of metamorphism can be determined from reflectivity. For more refined subdivision the chemical measures are essential. This is also true even if the reflectivity measurements are made using a photocell (Cannon and George 1944, Dahme and Mackowsky 1950) which – in contrast to the subjective method of the Berek-Photometer ocular – permits objective determination of the brightness differences. An important optical aid in determining the grade of incoalation is finally also the determination of color, reflectance and grinding hardness of exinite, i.e., the spores and cuticle (Böttcher, M. Teichmüller and R. Teichmüller 1949; M. Teichmüller and R. Teichmüller 1950). The colors of exinite become paler with increasing metamorphism until, in the bituminous stage [Fettkohlenstadium] (with a volatile content of about 20% in vitrite), it takes on the color of vitrinite. From this stage of metamorphism exinite can no longer be distinguished from vitrinite. This gradual optical equalization of the individual components of the coal corresponds to their chemical development (Francis 1952; van Krevelen 1951/52). As a sketch by van Krevelen (see Fig. 4) shows, even such different original materials as wood and spores (vitrinite and exinite) have the same H/C:O/C relation when they reach the bituminous stage [Fettkohlenstadium].

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c) Results Figure 6 offers a summary overview of the changes of some physical properties of carbonaceous matter in the course of chemical metamorphosis (measured as carbon content). Not all of the relations between the chemical structure of carbonaceous matter and physical behavior are clear. Van Krevelen (1951/52) interpreted some of these relations as follows. In lignites [Braunkohlen], porosity and internal surface areas are very large because the molecules, having many polar groups with high oxygen content, are very bulky. Such oxygen-rich but at the same time hydrophilic groups (OH-, CO2H groups) are responsible for the ability of lignites to dissolve alkalis. As metamorphism occurs, the oxygen leaves the polar groups as carbonic acid and water. This causes the internal surface of the carbonaceous matter to become smaller, and the true density is reduced as a result of the rapid loss of the relatively heavy oxygen atoms. As a result of the large release of oxygen, the carbonaceous matter begins to take on more and more the character of hydrocarbons and becomes soluble in substances such as phenanthrene. In the bituminous stage [Fettkohlenstadium], the inner surface area reaches a minimum. The same is the case for the true density because, in the bituminous stage [Fettkohlenstadium], the carbonaceous matter contains only a little oxygen but large amounts of hydrogen, which is especially light. Up to this stage of metamorphism the carbonaceous matter is in part still hydroaromatic. Under continuing metamorphism, carbon and hydrogen are split off in the form of methane. In this process ring condensation occurs. At the same time the bonding forces between the macromolecules increase. The carbonaceous matter loses its solubility and plasticity, and can no longer be liquified. As a result of the splitting off of methane from the increasingly rigid molecular structure, the internal surface area increases somewhat again, causing the internal moisture content and heat of wetting to also increase. At the same time the true density increases because the relative carbon content increases as hydrogen is lost. Reaching the anthracite stage, the ring condensation and related processes become important. This survey shows that the changes which carbonaceous matter undergoes during metamorphism is very different in the different stages. Therefore, there is no measure which can be used in all stages of incoalation equally well: the major colloid-physical changes in the lignite stage [Braunkohlenstadium] and also in the highvolatile sub-bituminous coal stages [Flamm- and Gasflammkohlenstadien] are best expressed by the decrease in water content of air-dried coal. It must still be determined whether a chemical indicator, such as perhaps the content of OH groups, can be found for these early stages. As condensation and aromatization of the molecular complexes becomes important, the content of volatiles becomes a useful measure of the degree of incoalation. Water content and volatiles are relatively easy to determine and have been used by practicing geologists for

75 years. Their deeper meaning as a measure of incoalation has only become apparent from the new chemical and physical investigations of the last few years. It should not be supposed that other measures of the degree of incoalation as, for example, the content of carbon and oxygen, the C:H relationship, the content of aromatics, the reflectivity, color of spores, etc., have become superfluous – on the contrary, the more we wish to understand the basic nature of metamorphic processes, the more kinds of measurement and applied methodologies will be needed.

3. The causes of metamorphism a) The factor time W. Fuchs (1938) noted that conversion in a chemical reaction which proceeds without consuming energy goes ever more to completion as more time is available. In a reaction which proceeds only by supplying energy, conversion will not occur without the additional energy, no matter how much time is available. The experiments of H. Stach have shown that lignite colloids [Braukohlenkolloide] age even at room temperature and pressure if enough time is available. The Early Carboniferous lignite of Moscow is an example showing that, without any significant addition of energy but solely through the effect of a long time span, a soft lignite [Weichbraunkohle] will be converted into a hard lignite [Hartbraunkohle]. Conditions are different if energy is added. If the addition of energy is very large as, for example, occurs when there is contact with eruptive volcanic rocks, lignites [Braunkohlen] can be quickly converted into coals [Steinkohlen] or even anthracite, as shown by the Pliocene coals of Palembang on Sumatra. If the addition of energy occurs slowly and takes place over a long period of time, as is the case for most coal deposits, then geological experience dictates that very long periods of time are required. In comparison with some older analogous coal deposits, some of the lignites [Braunkohlen] of the youngest Tertiary which have already been buried to depths of several thousand meters have not achieved the quasi-stationary chemical equilibrium which reigns at these depths. Petrascheck and Wilser (1924) were the first to note this phenomenon. Although lignite [Braunkohle] heated above 100 °C in a drying chamber for a short time gives off large amounts of water, it is hardly altered chemically. By contrast, geological experience indicates that at constant temperature a few million years suffice to transform a lignite [Braunkohle] into coal [Steinkohle] (from geological observations a temperature of 100–150 °C is adequate to produce a coal; Zetzsche 1932; Thieysen 1936; M. Teichmüller and R. Teichmüller 1949). According to R. Schultze (1948), the aromatic compounds in particular require much more time for thermodynamic changes to take place. Thus, time plays a role in metamorphism as long as heat and pressure are

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available to make a reaction possible (it should be remembered that the incoalation process is in itself exothermal). b) The factor pressure Pressure undoubtedly has a strong effect on the structural metamorphism of carbonaceous matter. However, it can not break the chemical bonds. This has been emphasized by Fuchs (1953) and Huck and Karweil (1953). Because of their ring structure the aromatic compounds, which are the main components of coals, are very resistant to pressure (R. Schultze, written communication). Zetzsche (1932) found that the depolymerization of bitumen can at most be delayed by static pressure. Accordingly, attempts at incoalation under pressure succeed only if high temperatures are imposed at the same time (e.g., Bergius 1913). Otherwise the results are essentially negative (cf. Hoffmann 1936, Setcliff and Wilson after Briggs 1934–36). Huck and Karweil (1953a) pointed out that sometimes the change from elastic deformation to plastic deformation results in deformation energy being released as heat from the coaly material. However, according to Kienow (1942, p. 122), the elastic modulus of rocks in slow tectonic processes is only 1/10 as large as that measured in experiments. This means that the temperature increase would be very slight. H. Stach (1933) and Huck and Karweil suggested the possibility that pressure forces the molecules of the carbonaceous matter closer together and thereby facilitates reactions in the solid state. As soon as pressure is transformed into movement frictional heating occurs. This may under circumstances significantly accelerate the incoalation. This is the case, for example, with the Sutan thrust in the Ruhr coal measures near Bochum. There, a reduction of 6–10% in the volatiles of the Sonnenschein coal seam has been determined in the vicinity of the thrust surface over a distance of several kilometers along strike (Böttcher and Teichmüller 1949). However, generally the volatile contents of coals along the Sutan, as along other thrusts in the Ruhr, decrease by only 1–2%. Beneath the Veen thrust at Langerwehe, the deepest coal beds of the Inde depression remain quite poorly incoaled (R. Teichmüller 1950). On the Osning thrust the mylonitized Wealdean coals are essentially briquetted but, despite the intensive mechanical stresses, they are less incoaled than the Wealdean coals in the overlying strata which were almost unaffected by the tectonic activity. It is apparent that the frictional heat was rapidly conducted away, before it could contribute significantly to the metamorphosis of the coals. Additionally, it must be noted that largescale tectonic movements, even in times of orogeny, proceed very slowly. It is not permissible to ascribe a major effect on chemical metamorphosis to the kinetic energy of folding, as some have done (Patteisky 1950). One cannot speak of an acceleration associated with the slowness of tectonic movements. Even in the case of the dif-

ferent rates of plastic deformation of materials, acceleration can be neglected as a factor (personal communication from Dr. Kienow). Pressure has no decisive influence on material metamorphosis. This conclusion seems to be contradicted by the observation that the chemical incoalation in the marginal basins of mountain ranges often increases with the intensity of folding (White 1925). However, one must recall that such marginal basins are asymmetrical, with their greatest depths near the mountains where the coal seams will later be most strongly folded. The intensive chemical metamorphosis can thus be attributed to the stronger subsidence and the associated greater heating (M. Teichmüller and R. Teichmüller 1949; Fig. 7). Accordingly, the metamorphism of coals in the foreland basin of the Appalachians increases much more rapidly from the upper to the lower layers than it does in the horizontal direction, i.e., in the direction of the tangential folding pressure (Reeves 1928). The most strongly folded areas do not show the highest degree of incoalation. On the contrary, there is a close relationship in the foreland basin of the Appalachians between the pre-orogenic depth of burial and the degree of chemical metamorphism (E.T. Haeck 1943). Hickling (1947/48), Jones (1949) and others have shown that in south Wales the influence of the pressure of a hypothetical great thrust on chemical metamorphosis, postulated by Trotter (1947/48), cannot be substantiated. Likewise, the tangential folding pressure in the Carboniferous of the Ruhr cannot, except in isolated cases, have forced chemical metamorphosis of the coals. Patteisky (1950), following the ideas of White (1925), tried to relate the regional decrease in incoalation from southeast to northwest to the decrease in folding intensity. However, this idea is contradicted by the fact that coal seams along the southern margin of the Ruhr coal basin show only a low degree of metamorphism in spite of intensive folding (see Fig. 8). Dubrul (1938) and Legraye (1936, 1942/43) found the same conditions on the southern margin of the Belgian coal measures. Additionally, in the Ruhr coals the metamorphism increases much more rapidly with the stratigraphic age of the deposits than in the horizontal direction. This again shows that the tangential folding pressure – in contrast to the pre-orogenic subsidence depth – has not played an important role in the chemical metamorphism of the Ruhr coals. The most obvious evidence for this condition is the concordance of isovols (lines of equal content of volatiles) and bedding surface contours (Böttcher and Teichmüller 1949) – the isovols have been folded along with the strata. The incoalation is therefore in general older than the folding and, because of this, cannot be a result of the folding and the associated tangential folding pressure. Further, in the Wealdean Basin of Lower Saxony, for which detailed maps of the degree of incoalation now exist (M. Teichmüller and R. Teichmüller1950), no relation between folding pressure and metamorphosis of the coals can be found. Here the slight metamorphism of the coal seams which have been strongly affected by tecton-

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Fig. 8 Regional changes in the chemical metamorphism of coals in the subvariscan Carboniferous (after M. Teichmüller and R. Teichmüller 1949; Dubrul 1931). The numbers show the content of volatiles in the Sonnenschein coal seam. It is evident that the strongly folded southern margin of the productive coal measures are characterized by a relatively slight metamorphism. As a result of the asymmetry of the foreland basin, the subsidence of the coals was strongest a short distance north of the southern margin of the basin before the folding. There the metamorphism is especially advanced. Toward the foreland the degree of incoalation decreases

ics along the Osning thrust,on the one hand and, on the other hand, the anthracitization of the flat-lying Wealdean coals of Bohmte argue against any effect of the tangential folding pressure on chemical metamorphism (Fig. 9). The same is true for the fire slates [Brandschiefer = slate with a high content of carbonaceous matter] in the Lower Devonian of the Münster Eifel (M. Teichmüller and A. Teichmüller 1952). These Devonian deposits in the Rheinische Schiefergebirge are perhaps the best Fig. 9 Chemical metamorphism of the Wealdean coals in the Lower Saxony Basin. The marginal zones of the basin are characterized by low degrees of incoalation. Petroleum and natural gas discoveries until now have been restricted to this low incoalation region [Ölfeld = Oil field; Ölspur = Traces of oil; Erdgas = Natural gas; Isopachyn des Wealden nach SEITZ = Isopachs of the Wealdean after SEITZ]

proof that folding pressure plays only an unimportant role in the chemical metamorphism of carbonaceous matter.

c) The factor temperature Temperature is considered to have a great significance for the metamorphosis of carbonaceous matter, both from the chemical aspect (among others, Zetzsche 1932, as well as R. Schultze 1984; Dulhunty 1950; Dulhunty, Hinder and Penrose 1951; Huck and Karweil 1953) as well as from the geological point of view (Bode 1939; Hickling 1947/48). Hickling has termed coal essentially a geological thermometer. Every artificial heating of coal leads to a loss of volatiles and an enrichment of carbon (the most well-known example is coking). However, the temperatures at which coal begins to lose gas quickly is relatively high (250 °C) compared with the temperatures which in the

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rule are assumed for the natural metamorphism of coal (100–150 °C). Fuchs (1952) is even of the view that the incoalation process requires temperatures of at least 400 °C. The incoalation experiments of Terres (1952) have shown that in the watery-liquid phase, the change from peat or soft lignite [Weichbraunkohle] to glance lignite [Glanzbraunkohle] or into coal proper [Steinkohle] occurs at much lower temperatures than by dry heating in the absence of water: in the first case, the change occurs at 250 °C within a relatively short time, but in the second case changes hardy occur even at a temperature of 350 °C. Terres noted the strongly exothermal nature of the decarboxylation and dehydratization reactions in his experiments. According to Huck and Karweil (1953b), most incoalation reactions, including the splitting off of methane, are exothermal. The time factor should also be taken into consideration in considering natural heat-induced metamorphism. Geologically, the importance of temperature is most clearly seen where the carbonaceous matter is heated by volcanic eruptive rocks., i.e., in contact metamorphism. The metamorphism of the coaly material increases as the eruptive rocks are approached. Often all of the incoalation stages from lignite to anthracite can be observed. The best examples are the Pliocene lignites [Braunkohlen] of Palembang on Sumatra (Kreulen 1935, A.N. Mukherjee 1935, Seyler 1948). In contact metamorphism the chemical change in the carbonaceous matter is dependent on the amount of heat introduced, and thereby the size of the intrusive body. For this reason, the effects of contact metamorphism from intrusive dikes and smaller plutons on coal seams is restricted to the immediate vicinity of the intrusive body. If, however, the pluton reaches a diameter of many kilometers, the heat from it is correspondingly large and can affect a large area. If the metamorphism from contact with volcanic rocks occurs quickly then, according to a communication from Dr. Huck, it can be distinguished from normal geothermal metamorphism because, through rapid heating, the release of CO2 is thermodynamically favored over release of H2O. This is probably also the reason why contact metamorphic coals are shown to be characterized by relatively low carbon contents in Francis’ (1952) incoalation diagram. In the case of the contact metamorphic coals of the Pliocene of Palembang (Sumatra), we found carbon contents to be relatively low in comparison with the content of volatiles. Geothermal metamorphism of carbonaceous matter plays a role when the coal seams subside to considerable depths (2000 to >5000 m) and thereby come into regions of high temperature. From this it follows that the oldest coals in a basin are the most highly incoaled. This observation (Hilt’s rule) is by and large the case, in spite of the minor exceptions which W. Petrascheck (1953) has noted. In sections through many coal basins the isovols, i.e., the lines of equal content of volatiles, more or less follow the bedding. This proves that the metamorphosis of the coals was completed before the folding took place – hence, folding pressure cannot be the cause of the

metamorphism. However, since it was greater than the pressure from the overlying load – otherwise the rocks would not have been folded – it follows that Hilt’s rule reflects the increase in temperature with burial depth rather than the increase in pressure. In the Ruhr coal measures the major anticlines appear to have been initiated as broad swells before the actual folding occurred in the youngest Late Carboniferous; the degree of metamorphism of the coals declines somewhat toward the anticlinal crests (Böttcher and Teichmüller 1949). The situation in the Waldenburger coal measures is similar. There the degree of metamorphism in a single coal seam decreases toward the crest of the swell. For single stratigraphic sections, however, Hilt’s rule is valid (Dantz 1940). Comparison of the isovols of the carbonaceous matter with the depths of pre-orogenic subsidence is interesting. M. Teichmüller and R. Teichmüller (1950) have done this in the region of the Lower Saxony Basin. It was found that the degree of metamorphism and depth of subsidence are not always parallel; in the region of the Bramscher Massif the depth of subsidence is insufficient to produce anthracitization – here additional magmatic heating must be assumed (this conclusion was supported in 1953 by Lotze’s finding of a younger ore formation stage in the region of Osnabrück). In addition to the subsidence depth, the relevant geothermal gradient plays a great role in the metamorphism of carbonaceous matter. This became apparent from the studies of metamorphism in the Devonian of the Rheinische Schiefergebirge. There the fire slates [Brandschiefer] in the region of the Siegerland ore district which, according to Brinkmann (1935), correspond to an ancient rise in the isotherms, have been especially strongly anthracitized (M. Teichmüller and R. Teichmüller). These examples show how the geologic causes can be derived from investigations of incoalation – with the proviso that other factors, such as time, pressure, and temperature, did not influence the metamorphism of the carbonaceous matter. We still need to consider whether other factors may be important in the metamorphosis of coals. d) The importance of radioactive decay The radioactivity of certain minerals incorporated into the coals can undoubtedly affect and accelerate the chemical metamorphism of the carbonaceous matter, given enough time. Tiny particles of uranium ore in the Kamkrish Kolm of Westergotland have sufficed to transform this fire slate [Brandschiefer] to the bituminous stage [Fettkohlenstadium] through radioactive energy (R. Teichmüller 1952). In the Ruhr coals there are occasional reworked zircons; around them, E. Stach (1950) observed small contact halos in which the carbonaceous matter is distinguished by its hardness and reflectivity. However, these are exceptional occurrences: In general, radioactive radiation is only of very minor importance in the metamorphosis of carbonaceous matter.

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e) The importance of catalysts Mackowsky (1948) is of the opinion that the catalytic effect of heavy metals exerts an important influence on the incoalation process. She refers to a “catalytic guiding” of the incoalation. It will be difficult to establish the validity of this hypothesis because of the many different catalysts which occur in nature and the fact that they may interact and even nullify each other (R. Schultze, personal communication). Van Krevelen (1951/52) noted the significance of bacterial enzymes as catalysts in his biochemical study of incoalation. These enzymes undoubtedly play a large role in the decomposition of the original plant material. However, because bacterial activity is almost extinguished at a depth of a few meters in peat (Waksman and Stevens 1930; Baier 1938; Müller and Schwarz 1953), these catalysts must be unimportant even in the lignite stage [Braunkolenstadium]. For the incoalation of coals [Steinkohle], they are in any case of no importance. The bacteria in coals reported by Lieske are surface forms which penetrated into the long-incoaled coal along cracks. Even in the case of the bacterial strain isolated from a dense cannel coal [Kännelkohle] by Schwartz and Müller (1953), it remains uncertain whether they are autochthonous. f) The importance of the original material and of early decomposition for the metamorphosis of carbonaceous matter The original materials which form the carbonaceous matter (wood, spores, cuticle, resin, etc.) differ greatly from one another – only as metamorphism proceeds do these differences decrease (see Fig. 4). For this reason the degree of metamorphism is always measured on one particular component, vitrite. Vitrite is derived from wood and bark, that is, mostly cellulose and lignin. There is no reason to suppose that the relation of cellulose to lignin in the woody tissues of land plants has changed over the course of evolution of the floras. However, it must be borne in mind that the resin content of woods and barks varies, and that corking (suberinization) of bark first appears in higher plants. In Mesozoic and Tertiary coals there are relatively large amounts of resinrich vitrites. This is because since the Permian the resinrich conifers have been most important in producing coals (Gothan 1937). Conifer wood is especially resistant to bacterial decomposition and, since the beginning of the Carboniferous, the broad vitrite strips (accordingly, the larger xylites in soft lignites [Weichbraunkohle]) have been almost exclusively derived from confer wood. This is perhaps related to the greater hydrogen content of Jurassic, Cretaceous and Tertiary vitrites – in contrast to those of the Carboniferous (Francis 1952; cf. Fig. 10). In addition, especially in the Tertiary, the barks are often strongly corked and have a higher suberin content. In the Carboniferous the thicker vitrite occurrences are mostly

derived from the bark of lepidophytes (Raistrick and Marshall 1948; Patteisky 1953) which were not corked. Biological degradation is mostly determined by the nature of the original material, the temperature, the ground water level, the oxygen supply, and the acidity in the peat bog. Everyone who knows bogs knows that these conditions vary greatly from place to place and from time to time. As a result there develop different peat facies, which later become the different bands of coals (H. Potonié 1910; R. Potonié 1924; R. Potonié and R. Bosenick 1933; Thiessen 1937; Jurasky 1940; P.W. Thomson 1950; M. Teichmüller 1950, 1952a). Biological degradation is also of primary importance for the formation of different coal facies (vitrites, clarite, durite, fusite, bogheads, cannel coals) and for their petrographic and chemical differences. The carbon richness of fusites, for example, is a result of the facies and has nothing to do with the metamorphosis of the coal. The metamorphism is impressed on the individual facies types later. Because we restrict studies of incoalation to vitrite, we are largely able to exclude the influence of facies and primary biological degradation. There may have been very different primary conditions for the degradation of woods, as in the case of coal seam vitrites on the one hand and wood fragments sedimented in clay and turned to vitrite on the other. We found no great differences in the elemental composition of vitrites and in the volatile content of the non-coaly strata associated with the high-volatile sub-bituminous coals [Gasflammenkohlen] of the Wealdean (M. Teichmüller and R. Teichmüller). Patteisky (1953) made the same observation in the coal measures of the Ruhr, and recommended that for incoalation studies the more easily isolated vitrites from the shales above the coals be used rather than vitrites from the coal beds themselves. Although different ecological conditions are primarily responsible for producing the different types of coal band and their textural elements, later events, such as a more or less complete cover of the peat by a layer of mud, can lead to a different course of microbiological degradation of the entire peat profile. Many petrographic observations indicate that the woods of the Katharina coal seam in the Ruhr coal measures were degraded under anaerobic conditions after deposition of the overlying marine shale (M. Teichmüller 1952a). This is also the case for other coal beds overlain by marine deposits. Vitrites from such coal seams are often characterized by a relatively high content of hydrogen and a stronger buoyancy during coking (Daub, verbal communication 1947, Mackowsky 1948). It is important to note that in the incoalation profile of a well or pit which penetrates several hundred meters of a coal bed-rich section, the coal seams overlain by marine shales are hardly distinguishable by their content of volatiles or carbon. In slightly incoaled coal beds (high-volatile sub-bituminous coals [Flammkohlen, Gasflammkohlen]), there are sometimes large chemical differences between individual vitrite occurrences. Marshall (1943) found that differences of 6% volatiles and 1% carbon occur. These

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Fig. 10 C–H–O incoalation diagram (after Francis 1952) with incoalation lines for humins, fusite, resin, and pure hydrocarbons. The original chemical composition of weathered coals can be derived using the oxidation lines. Analyses of fresh (filled dots) and weathered (open dots) vitrites of the Wealdean coals of Lower Saxony are shown in Francis’ diagram. Analytical values for fresh Wealdean vitrite lie above the normal humin incoalation band, i.e., they are significantly more hydrogen rich than Carboniferous vitrites having the same C content. 1 Atgeberg, 2 Barsinghausen, 3 Beckendorf, 5 Barbara-Stollen, 6 Dörenberg, 7 Düdinghausen, 8 Duingen, 9 Georg-Schacht, 10 Georg-Stollen, 12 Harrl-Stollen, 13 Hütten-Stollen, 14 Hohewarte-Stollen, 15 Lauenhagen, 16 Limberg, 17 Lohnberg, 18 Neuenkirchner Berg, 19 Notthorn, 20 Kloster Ösede, 21 Probsthagen, 22 Reinsen, 23 Rheine, 24 Rökke, 25 Wellendorf. A Alte Taufe, b Bocketal, c Bohmte, d Brandschütt, e Zeche Friedrich, f Gersberg, g Hilterberg, h Lieth, i Limberg, k Lohnberg, l Meike, m Sehnde, n Strubberg, o Sundern, p Süntelwald [Kohlenwasserstoff - Linie = Hydrocarbon Line; Harz - Linie = Resin Line; Oxydations - Linie = Oxidation Line; Humin - Band = Humin Band; Fusit - Linie = Fusite Line]

variations must be related to the original botanical matter, the age of the buried tree trunks, and to the degradation before and after deposition, although microscopic examination of the material does not allow such relationships to be demonstrated (Marshall 1943). In order to exclude such primary differences in determination of metamorphic grade, it is important to use average values for slightly incoaled vitrites, i.e., it is best to combine as many different vitrite samples as possible into a single analysis. The opinion which is sometimes expressed, that the differences in the primary (biogeochemical) decomposi-

tion plays a decisive role in the course of geochemical metamorphosis of vitrites (Mackowsky 1949b), is contradicted by the observation that all significant incoalation changes in different coal basins follow the same path in both vertical and horizontal directions, and thus can only be explained by metamorphic processes which operate on a large scale. Because the biological degradation processes in bogs change very rapidly in both space and time, one will never find that Hilt’s rule or the regional incoalation changes affecting all of the coal beds in a large coal basin in the same way could be explained by the composition of the flora or its biochemical degradation. Attempts to do this (see Fuchs 1941, 1952, 1953) always meet with repudiation from geologists and biologists. E.T. Heck (1943) and Schwartz and Müller (1953) have already noted this. Also, the thesis has recently set forth from the chemical viewpoint (Fuchs 1952, 1953) that the nature of the biological degradation of peat produces either lignite (aerobic) or coal (anaerobic) is not tenable from the geologic evidence, and will not be further discussed here. It need only be pointed out that transitions from peats to lignites and from lignites to coals have often been found, but a transition from peat to coal has never been observed. Aerobic and anaerobic decomposition has occurred in all bogs throughout all ages. The corresponding degradation products occur in both lignite and coal beds (for example, xylitic lignites [Braunkohlen] or coals with shiny bands [Glanzstreifenkohle] which were originally forest peat and dysodile or boghead coals which were

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originally sapropels). Huck and Karweil (1953) have recently argued against Fuchs’s theory from the chemical standpoint. As an addition it should be noted that there is an occurrence which has long not been taken into account but which is important for understanding exceptions to Hilt’s rule. M. Teichmüller observed both in Cretaceous and Carboniferous coals an occasional “abnormal” chemical composition of vitrites, which was attributable to saturation with bitumen. Bitumen cannot be seen in ordinary light in the microscope because it is absorptively bound and extremely finely distributed. It can be detected only through a relatively small change in the reflection of vitrite, which is only observed with great care. Bitumen is, however, easily detected using ultraviolet light. g) Results It is evident that neither radioactive energy nor catalysts, much less plant evolution and primary degradation can explain the large-scale incoalation changes which are observed in vertical and horizontal directions in all coal basins. Since it has been shown that pressure does not play a major role in the chemical metamorphosis of carbonaceous matter, the sole remaining factor is the temperature which increases with depth. In considering this, the length of time of heating must not be overlooked. This perhaps explains why the low temperatures indicated by geological observations suffice for the metamorphism of coals. These temperature estimates can not yet be brought into agreement with experimental results but, according to the thermodynamic and kinetic calculations of Huck and Karweil (1953b), they are fully capable of producing the observed results.

View to the future In this report we have attempted to summarize the results of the last decade of research in many diverse areas on the problem of metamorphosis of carbonaceous matter. During this period the changes in physical structure have been especially thoroughly studied. The results of these works, coupled with those on elemental analysis, have permitted further insight into the changing chemical constitution of the carbonaceous matter in the course of metamorphism, and the relation between the chemical composition and the physical behavior of the coals. In future geological investigations of the metamorphosis of carbonaceous matter one should take these results into account and differentiate between structural metamorphosis, examined chiefly with physical methods, and chemical metamorphosis, explored principally with chemical methods. Carbonaceous matter reacts more sensitively, both chemically and structurally, to increases in temperature and pressure than many other minerals. Therefore, it is important to the geologist as an indicator in the early

stages of sediment diagenesis and metamorphosis. Although at present the metamorphism of carbonaceous matter does not yield quantitative values for these conditions, this may be possible in the future. The size of the internal surface area and degree of anisotropy of coals may one day be used as a manometer for tectonic pressure, and the degree of aromatization and of condensation may be used as a sort of geological thermometer, as long as one knows the length of time these processes have acted. Regional investigations of the effect of pressure on the structural metamorphosis of coals still need to be done, although the first works in this field by Edwards (1948) and Dulhunty, Hinder and Penrose (1951) in Australia are very promising. Regional investigations of chemical metamorphism have already been carried out in many coal basins. They show that there is a close relation between the maximum depth of burial of the coalbearing sediments and the metamorphism of the coals. Magmatic heating leads to a particularly intense metamorphism of the coals in some areas. Often there is a relation between high incoalation and the occurrence of deeper layers of ore deposits. On the other hand, petroleum deposits, apart form condensate concentrations, are restricted to the realm of low incoalation (carbon ratio theory). The geothermal conclusions resulting from investigation of incoalation have a certain practical importance. It would be desirable to compare the understanding of incoalation with information on the alteration of the adjacent rocks, especially the clay minerals. Such comparative studies are, however, only in their early stages.

Translator’s note The German classification of coals differs from both the UK and US classifications. The German word “Kohle” is much broader than any English equivalent, referring to any solid carbonaceous matter showing some alteration from the original plant material. For accuracy, the German term for particular “coal” types is included in square brackets [] after its English equivalent. The German classification is based on volatile content: Braunkohle (English lignite) has two ranks, Weichbraunkohle (50–60% volatiles) and Hartbraunkohle (47–50% volatiles), and a third form, Glanzbraunkohle, which is a shiny-surface version of Hartbraunkohle. Steinkohle are the coals proper, and seven categories are recognized: Flammkohle (>40% volatiles), Gasflammkohle (35–40% volatiles), Gaskohle (28–35% volatiles), Fettkohle (19–28% volatiles), Eßkohle = Esskohle (14–19% volatiles), Magerkohle (10–14% volatiles), and Anthrazit (<10% volatiles). In English, the first six are varieties of sub-bituminous and bituminous coal, the last corresponds approximately to anthracite but is more inclusive (US anthracite has <8% volatiles).

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S90 – Einige neuere Einsichten, die chemische Struktur in Steinkohlen betreffend. Brennstoff-Chemie, 33:260–268, 13 figs, 3 tables, Essen 1952 – Physikalische Eigenschaften und chemische Struktur der Steinkohle. Brennstoff-Chemie 33:167–182, 26 figs, 8 tables, Essen 1953 Lecky, J.A. Hall, W.K. and Anderson, R.B.: Adsorption of water and methanol on coal. Nature 168:124–125, London 1951 Leendertse, J.J. Tameda, H.J. Smittenberg, J. Vlugter, J.C. Watermann, H.I. van Westen, H.A. and van Nes, K.: Strukturgruppenanalyse von Erdölfraktionen nach der n-dM-Methode. Erdöl und Kohle 6:537–542, 8 figs, 8 tables, Hamburg 1953 Legrave, M.: Étude des charbons du bassin houllier du Nord de la Belgique. Revue Univ. Mines 12, 1936 – Le rôle des failles dans la répartition des qualités des charbons du bassin houllier de Liège. Mém Soc Géol. Belgique 66:205–260, 1942/43 Lehmann, K. and Hoffmann E.: Neue Erkenntnisse über Bildung und Umwandlung der Kohlen. Glückauf 68, p 793, Essen 1932 Lowry, H.H.: The chemical coal. Ind Eng Chemistry 26, 5 figs, 1934. – Thermal decomposition of the “coal hydrocarbon”. Ind Eng Chem 26:321–331, 7 figs, 1934 Mackowsky, M.Th.: Mineralogische Probleme in der Kohlenpetrographie. Glückauf 81–84, 163–165, Essen 1948 – Stand der Untersuchungen und Versuch einer neuen Kohleneinteilung. Brennstoff-Chemie 30, 44–60, Essen 1949a – Neuere Anschauungen über den Inkohlungsvorgang. Fortschr Mineral 28:38–46, 7 figs, 1949b – Gibt es Graphit in Kohle und Koks? Fortschr Mineral 29/30:10–17, 1950/51 – Die Feinstruktur der Kohle. Fortschr Mineral 31:60–61, 1 fig, 1952 Malherbe, P.L.R.: Microstructure of some South African coals. Fuel 30:97–109, 9 figs, 7 tables, London 1951 Marshall, C.E.: The constitution of anthraxylon (vitrain or vitrinite) and its relation to type and rank variation in coal seams. Fuel 22:140–155, 14 figs, 8 tables, London 1943 Meldau, R. and Teichmüller, M.: Übermikroskopische Beobachtungen an schwinggemahlenen Kohlenstäubchen. Öl und Kohle 37:751–755, 17 figs, Berlin 1941 Meyer, H.: Untersuchung über Möglichkeiten, Teerpech bei der Brikettierung von Steinkohlen einzusparen oder durch andere Bindemittel zu ersetzen. Bergbau-Archiv 4:7–54, Essen 1947 Mott, R.A.: The origin and composition of coals. Fuel 21:129–142, 5 figs, London 1942 – Diskussionsbemerkung. In: Proceedings of a Conference on the Ultrafine Structure of Coals and Cokes, 157, London 1944 Müller, A. and Schwartz, W.: Geomikrobiologische Untersuchungen I. Die mikrobiologischen Verhältnisse in einer spät- und post-glazialen Sedimentfolge. Geol Jahrb 67:195–208, Hannover 1953 Mukherjee, A.N.: Ein Beitrag zur Kenntnis der pliozänen Braunkohle des Tandjoeng Kohlenfeldes Palembang, Süd-Sumatra. Dissertation, 52 pp, 40 figs, Würzburg 1935 Niggli, P.: Lehrbuch der Mineralogie, I. 2. Auflage, 712 pp, 553 figs, Berlin 1924 Niggli, P. Bader, H. Haefeli, R. Bucher, E. Neher, J. Eckel, O. and Thams, Ch.: Der Schnee und seine metamorphose. Beitr. z. Geol. d. Schweiz. Geotech. Serie, Hydrologie, Lf. 3, Bern 1939 Oversohl, W.: Beitrag zur Kenntnis der Steinkohle. BrennstoffChemie 31:103–111, Essen 1950 Patteisky, K.: Zusammenhänge zwischen tektonischer Lage und Zusammensetzung der Kohlen des Ostrau-Karwiner Steinkohlenbeckens. Montanistische Rundsch. 1925 – Die Entstehung des Grubengases. Bergbau-Archiv 11/12, 5–24, 12 figs. Essen 1950. – Die Veränderungen der Steinkohlen beim Ablauf der Inkohlung. Brennstoff-Chemie 34:78–82 and 102–108, 16 figs, Essen 1953

Peters, K. and Cremer, W.: Über lösliche Bestandteile der Steinkohle. Z Angew Chem 47:576, 1934 Petrascheck, W.: Die Metamorphose der Kohle und ihr Einfluß auf die sichtbaren Bestandteile derselben. Sitzungsbericht Österr. Akad. Wiss. Math.-naturwiss. Kl. Abt. 1, 156, 7 and 8, 375–444, Vienna 1947 – Die Regel von Hilt. Brennstoff-Chemie 34:194–196, Essen, 1953 Petrascheck, W. and Wilser, B.: Studien der Geochemie des Inkohlungsprozesses. Z Dtsch Geol Ges 76:200, 1924 Potonié, H.: Die Entstehung der Steinkohle und der Kaustobiolithe überhaupt. 5 Aufl. Berlin 1910 Potonié, R.: Einführung in die allgemeine Kohlenpetrographie. Berlin 1924 Potonié, R. and Bosenick, G.: Zur Entstehung der Steinkohle. Mitt Labor Preuß Geol L-A, H 19:75–110, Berlin 1933 Raistrick, A. and Marshall, C.E.: The nature and origin of coal and coal seams. 182 pp, 100 figs, London 1948 Reeves, F.: The carbon ratio theory in the light of Hilt’s law. Bull Am Assoc Petrol Geol. 12:759–823, 1928 Schmitz, H.: Die Abbaumöglichkeit tiefliegender Braunkohlen westlich des Höhenrückens der Ville. Dissertation Tech. Hochschule Aachen, Würzburg 1932 Schürmann, H.M.C.: Über jungtertiäre Braunkohlen in Ost-Borneo. Braunkohle, 609, 1927 Schultze, Gg.R.: Die Diagenese von Kohle und Erdöl als thermodynamisches Problem. Vortrag vor dem Ortsverband Harz der Ges. Dtsch. Chemiker, 5 March 1948 Schwartz, W. and Müller, A.: Geomikrobiologie, Entwicklung und Stand eines neuen Forschungsgebietes. Erdöl und Kohle 6:523–527, Hamburg 1953 Seyler, C.A.: The relevance of coal optical measurements to the structure and petrology of coal. Proceedings of a Conference on the Ultrafine Structure of Coals and Cokes, 270–289, London 1944 – The past and future of coal – the contribution of petrology. Proc. South Wales Inst. Eng. 63, No. 3, 213–243, 19 figs, Cardiff 1948 – Coal petrology. British Coal Utilisation Research-Association Quart. Gaz. 1950, 9–14, 6 figs Stach, E.: Lehrbuch der Kohlenmikroskopie 1. 285 pp, 50 figs. Kettwig 1949 – Vulkanische Aschenregen über dem Steinkohlenmoor. Glückauf 86:41–50, 17 figs, Essen 1950 Stach, H.: Beitrag zur Kenntnis der Entstehung und chemischen Struktur der Glanzbraunkohlen. Brennstoff-Chemie 14:201– 207, Essen 1933 – Experimentelle Beiträge zur Frage der Brikettierbarkeit von Weich- und Hartkohlen und der Quellung und des Zerfalls von Braunkohlenbriketts. Braunkohle, Wärme und Energie 1:35– 44, 9 figs, Düsseldorf 1949 Stach, H. and Teichmüller, M.: Zur Chemie und Petrographie der Ionen-Austauscher aus Braun- und Steinkohlen, BrennstoffChemie 34, Essen 1953 Teichmüller, M.: Zum petrographischen Aufbau und Werdegang der Weichbraunkohle, Geol Jahrb 64:429–488, 5 figs, 6 plates, Hannover/Celle 1950 – Vergleichende mikroskopische Untersuchungen versteinerter Torfe des Ruhrkarbons und der daraus entstandenen Steinkohlen. Compte Rendu 3. Congr. Strat. Géol. Carbonif. Heerlen 1951, 607–613, 1 fig, 5 plates, Maastricht 1952a – Die Anwendung des polierten Dünnschliffs bei der Mikroskopie von Kohlen und versteinerten Torfen. In: Freund, H.: Handbuch der Mikroskopie in der Technik, v. II, pt. 1, Mikroskopie der Steinkohle, des Kokses und der Braunkohle. 237–310, 64 figs. 3 color plates, Frankfurt a. M. 1952b Teichmüller, M. and R.: Inkohlungsfragen im Ruhrkarbon. Z Dtsch Geol Ges 99:40–77, 15 figs, Stuttgart 1949 – Das Inkohlungsbild des Niedersächsischen Wealdenbeckens. Z Dtsch Geol Ges 100:498–517, 8 figs, 5 plates, Stuttgart 1950

S91 – Spuren vorasturischer Bewegungen am Südrand des Ruhrkarbons. Geol Jahrb 65:497–506, 5 figs, 1 table, Hannover/Celle 1950 – Inkohlungsfragen im Osnabrücker Raum. Neues Jahrb Geol Paläontol Monatsh: 69–85, 9 figs, Stuttgart 1951 – Zur Fazies und Metamorphose der “Kohlen” im Devon des Rheinischen Schiefergebirges. Z Dtsch Geol Ges 103:219– 232, 6 figs, 2 plates, Stuttgart 1952 – Zur mikrotektonischen Verformung der Kohle. Geol Jahrb 69:263–286, 11 figs, 4 plates, Hannover 1954 – Zur Metmorphose der Kohle. Compte Rendu 3. Congr. Strat. Géol. Carbonif. Heerlen 1951, 615–628, 10 figs, Maastricht 1952 Terres, E.: Über die Entwässerung und Veredlung von Rohtorf und Rohbraunkohle. Brennstoff-Chemie 33:1–36, 5 figs, 18 tables, Essen 1952 Thiessen, R.: What is coal? Pap. pres. at the 17th meeting Fuel Eng. of Appal. Coals, Cincinnati, Ohio, 1937, 38 pp – Temperature during coal formation. Fuel, 289, London 1936

Thomson, P.W.: Grundsätzliches zur tertiären Pollen- und Sporenmikrostratigraphie auf Grund einer Untersuchung des Hauptflözes der rheinischen Braunkohle in Liblar, Neurath, Fortuna und Brühl. Geol Jahrb 65:113–126, figs, 1 table, Hannover/Celle 1950 Trotter, F.M.: The devolization of coal seams in South Wales. Abstr. Geol. Soc. London, No. 1442, Session 1947/48 Waksman, S.A. and Stevenson, K.R.: Contribution to the chemical composition of peat: The role of microorganisms in peat formation and decomposition. Soil Sci 28:315–340, 1930 White, D.: Progressive regional carbonization of coals. Trans Am Inst Min Met Eng 71:269, 1925 Zetzsche, F.: Untersuchungen über die Membran der Sporen un Pollen. X: Die Inkohlungstemperatur der Steinkohlen. Helv Chim Acta 1932, p 675 Zwietering, P. Oele, A.P. and van Krevelen, W.: Pore structure and internal surface of coal. Fuel 30:203–204, London 1951

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G. de Geer

Geochronology of the last 12,000 years Geol Rundsch 3:457–471

Translation received: 22 May 2002 © Springer-Verlag 2002

Geology is the history of the earth but until now it has been a history without ages in years. Various attempts have been made to estimate the lengths of time involved in individual parts of this history. However, none could be proven to be strictly correct. The outstanding authors of one of our modern teaching books in geology1 state: “The desire to date the major events of the geological past in years increases as the events approach our own time and touch on human history. However, the difficulties of these attempts are huge and the results are of doubtful value. In the best case, they do little more than portray the order of magnitude of distinct periods. Geological processes are very complicated and each single factor involved is variable in itself, so that the connection of such uncertain variables creates a huge uncertainty in the results”. Under these circumstances, it is appropriate to introduce a new and precise method of investigation which enables the establishment of a real geochronology based on counts of annual sediment layers covering the last 12,000 years. The basis for this chronology is provided by late glacial and post-glacial, periodically layered sediments, in which the deposit of each year can be clearly recognised. Initially, we counted the annual layers having regular intervals at a large number of sites along a line profile stretching from the southernmost to the central part of Sweden. This resulted not only in enumeration of the entire sequence of centuries during which the margin of the continental ice sheet retreated for more than 800 km, but also in an estimate of the time span of the post-glacial period since the disappearance of the ice sheet. Lecture presented on the occasion of the geological congress in Stockholm 1910 Translated by Christian Dullo and William W. Hay W.W. Hay (✉) Forschungszentrum GEOMAR, Wischhofstr. 1–3, 24148 Kiel, Germany e-mail: [email protected]

The most important sediment within these post-glacial deposits is a glacio-marine clay, termed “varvig lera”2 in Swedish for its varves or periodic layers which differ in colour and structure. Already during my first geological field work in the year 1878, I was surprised by the regular pattern of these layers, which very much resemble the annual rings of trees. Hence, the year after, I started detailed investigations and measurements of these layers in various regions of Sweden and continued this in the following years. It turned out that these layers were so regular and continuous that no periodicity other than annual could be ascribed to them. This led to my contention in the year 1882 that there is a very close relationship between the periodic layering of clay and the annual retreat of ice on land3. Two years later the investigations had progressed to the point that I considered my idea of the annual nature of the layers had been confirmed, and that I had found a way to correlate the annual layers of different areas by means of diagrams. In a talk given to our Geological Society in Stockholm, I was able to show how a geochronology could be established for the last part of the ice age4. A few months later I achieved correlation of the clay horizons from three different, but not distant localities. In the year 1889 I found and mapped a series of small but characteristic moraines which had previously been overlooked in the area NW of Stockholm. They were arranged in periodic rows at rather regular intervals of 200–300 m. This brought me to consider that these ridges could correspond to stillstands during the ice re1 Th. C. Chamberlain and R.D. Salisbury, Geology Earth History, part 3. London 1906, p. 413) 2 The Swedish word varve (in older days: hvarf) means a circle as well as periodical layering. As there is no international term for this meaning, it seems to be appropriate to introduce varve, pl. –s, as a new technical term. German Warw, pl. –en, French varve, pl. –s. 3 Om en postglacial landsänking i södra och mellersta Sverige. Geol. Fören. Förhandl. part 6, Stockholm 1882, p. 159 4 ibid. part 7, 1884, p. 3. Here presented only briefly and somewhat unclearly. Personal contribution ibid. 1885. p. 512, where the first correlation of 1884 was reported.

S101 Fig. 1 Map showing the late glacial retreat phases in Sweden [Spätglaciale Subepochen des Eisrezessions = Late Glacial Subepochs of the ice retreat; Postglaciale = Post glacial; 3. Finiglaciale = 3 Finiglacial; 2 Gotiglaciale = 2 Gotiglacial; 1 Daniglaciale = 1 Daniglacial; Rezession aufgemessen = Traverse lines along which the ice retreat was measured; Eisgrenzen = Ice edge boundaries]

treat, as should have occurred each winter, and that this could be determined by investigating the succession of annual clay layers between neighbouring moraine ridges5. In the mean time moraines of this type have been found frequently in the lowlands of the country and so I originally intended to continue my chronological studies through detailed mapping of the annual moraines. A series of these characteristic, well-defined small ridges will be visited during the excursion in the vicinity 5 Geol. Fören. Förhandl. part 11. Stockhom 1889, p. 395. A map showing a group of these moraines has been published by the author in “Stockholmstraktens geologi” in the book: Stockholm Sveriges Hufvudsad. Stockholm. E. Beckmanm 1897, part 1, p. 13.

of Stockholm, during which the varved clays will also be shown along with a demonstration of the method used to determine the last glacial retreat. All of the materials, including measurements, maps, and clay samples from various parts of Sweden, are on display in the Geological Institute of the University throughout the congress. The detailed study of eskers, especially around Stockholm and Upsala and also near Dal’s Ed, has clearly shown that they also have a pronounced periodic structure, with coarse-grained gravels in the centre grading into fine-grained gravel and coarse sand towards the south. This led to a new explanation of their origin, as resulting from a superposed sequence of delta deposits formed beneath the ice margin, within the mouths of gla-

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cial tunnels in the retreating land ice. These deposits are probably coeval with the varved clays and the annual moraines6. Finally, in 1904, I was able to make a very good correlation of two clay sections one kilometre apart. I decided to make a serious attempt to follow my old plan to establish a clay chronology. The investigation of 40 localities in the surroundings of Stockholm demonstrated that the correlation of the clay sections was less difficult than originally assumed, and could be achieved at distances of less than one kilometre if the sites for investigation were well chosen. When I discovered this fact, I organised support for my studies by students from the Universities of Stockholm and Upsala, ten from each. After preparatory training, we all started out on a summer morning in the year 1905, each person at a specific part of an approximately 200-km-long line, shown in Fig. 1. The line extended past Stockholm and Upsala, and through the Södermannland-Uppland peninsula from the large Fennoskandic moraines along its southern margin to the river Dalälfven in the north, following the direction of the ice retreat as well as possible. The major part of our work was completed in four days as had been planned. However, the filling of gaps at difficult sites was achieved only after repeated attempts. As one of the results, it should be mentioned that I obtained convincing proof for the assumption that individual varves had a widespread distribution. It turned out that single layers extended more than 50 km and that their volume could be estimated to be millions of cubic metres. Their widespread occurrence and regular structure demonstrated conclusively that they are not the result of local or sporadic events, and that their origin could be the result of no less important and periodic a process than the annual cycle of the climate. It is impossible to suppose that each single layer of the welldefined varves represents a hypothetical undetermined series of years because then it would not record changes as distinct as those of a single year. In fact, it seems to me to be unlikely that the seasonal cycle of the melting of land ice would not leave its imprint on annual sediments in the same way as the annual vegetation periods relate to tree rings. In the following year I continued these investigations on the remaining part of the line with the support of some of the same staff of co-workers. The line extended over a distance of 800 km between Schonen and the last glacial ice stream in south Jämtland, where the final remains of the ice sheet divided into two parts. This investigation was also successful, although some gaps remained. The main thing was that the original plan turned out to be feasible, even under the very different conditions present along this extended line. It was only a question of time and patience to gradually work out the chronological and climatological archives in a desirable way. 6 In the last reference, part I, pp. 14–17, with a map plate 4, and part II, map plate 5, and: Om rullstens-åsarnas bildningssätt. Geol. Fören. Förh. part 19. 1897, p. 366.

When I summarised and completed the work, I noted with great pleasure and satisfaction how efficient and energetic my many young co-workers had been and how perfect and reliable their results were. There were never any gaps, except at those places where the difficulties of the work would have consumed more time than was available. The natural basis for the whole plan of investigation was the following. As the last land ice retreated in Sweden, the lowlands of the country were still below sea level. During the summer of each year, meltwater sank from the surface of the ice through crevasses and drained through subglacial tunnels along the base. The high hydrostatic pressure forced the water to flow outwards, carrying tremendous amounts of moraine material which resulted in fluvioglacial deposits. Where these sedimentloaded streams beneath the ice reached the steep, cliff-like ice edge and discharged into the calm sea at the mouth of the glacier, the current and the load-carrying capacity of the water decreased rapidly. This resulted in the deposition of gravels and coarse-grained material at the inner part of the mouth of the subglacial cave, whereas the mediumsized gravels were deposited at the distal edge and sand material settled on the marginal delta just off the mouth. In the open sea, further from the ice margin, the sands would become finer and finer, and clay layers more frequent until finally sand-free clays dominate (Fig. 2). Hence, each esker centre represents nothing other than the proximal part of an annual deposit in the glacial cave. Compared with a fan, this part would be the grip. The steep ice margin, the glacial cave, and the mouth of the meltwater river retreated each year during the summer melting phase. During winter the ice margin advanced slightly, as indicated by small, distinct winter moraines. Each following summer time brought with it a new retreat of the ice and the formation of a new fan of gravel, sand and clay. This resulted in a shingled arrangement [imbrication] of fans, one on top of the other, the upper one with its northern or proximal end the same distance from the lower one as the ice had retreated and the sea advanced within one year. Since the retreat was frequently very regular, the grips of the fans gradually formed a ridge, producing eskers. However, their periodic structure became more or less obscured due to erosion by waves along the shore during the last uplift. For this reason and because of their thickness, composition of coarse-grained material, and the irregularities within these deposits, the proximal parts of the annual sediments are, as a rule, less suitable for direct chronologic determinations. However, the regular formation of these esker deposits provides a clear indication of the regularity of ice retreat in this area. The most valuable tool for chronological investigations is the fine clay sediment deposited beyond the ice cover. The position of the retreating ice margin during specific years was determined using the following method. Since the well-structured glacio-marine clays originally formed a continuous layer covering the deeper

S103 Fig. 2 Map showing the annual ice retreat in the Stockholm region [Sommerdeltas, glazifluviale Osen = Summer deltas, glacio-fluvial eskers; Wintermoränen = winter moraines; Äquirezessen N-grenzen der Warwen = Isolines of retreat - northern margin of varves; Gemessene Warwenprofile = Measured sections of varves; 0 Eisrand an der Hochschule und am Observatorium von Stockholm = 0 Ice margin at the Hochschule and Observatory of Stockholm]

parts of the older seafloor and were only later eroded from uplifted and exposed areas, the northern edge of the annual layers must have been near the margin of the presently preserved clay deposits. At such sites we investigated railroad cuts or dug new trenches through the lower layers of the clay, where their thickness was about man-high. The objective was to determine which of the clay layers lay directly on the ground moraine which had been covered by ice the previous year. Since these determinations were to be made over short distances of about 1 km, it was only necessary to measure a minimum number of varves in order to be able to correlate to the next exposure to the north. The number of layers missing at the next site corresponds to the number of years when the presence of inland ice prevented the deposition of clay. In order to save time and funds, deep trenches were excavated only where thicker sections of the annual sediments were required, as in close vicinity to eskers or near the mouths of ancient glacial streams. In the trenches, the clay layers were carefully and smoothly prepared as a vertical section using a sharpened bricklayer’s trowel. The boundaries between the annual layers were then marked and numbered with a pencil on a long, narrow strip of paper. The thickness of each layer was then recorded at equal spacing on a diagram which also displays the elevations of the layers at different sites (Fig. 3). In this way it was possible to compare entire series of identical layers from two or more different localities with each other and also to determine the corresponding high and low points in the thickness variability curve. [These data were used] to determine which of the layers occurred at the base at each locality or, in other words, at its northernmost limit. Of course, one has to avoid those sites where the original thickness of the annual layers has been disturbed or obscured by the stranding of icebergs or by slumping. The points of observation were recorded on a map, and the distances between them were divided by the number of years required for the ice to retreat between

them. By this method we were able to determine the annual average rate of the retreat of the ice margin, and to draw lines through the points marking the successive positions of the ice margin within the study area, as substantiated by terminal moraines and lines perpendicular to glacial striations. In this way we achieve not only a reliable chronology for a wide variety of events, but also an albeit complicated but very interesting record of the climatic conditions of the same epoch. It becomes clear that, under otherwise equal conditions, a slower retreat of the ice indicates cooler conditions, a more rapid retreat warmer conditions. Of course, when comparing different areas it is necessary to bear in mind possible differences in thickness of the inland ice, in the motion of the ice, and in the depth of the sea at the ice margin, which controls the formation of icebergs. However, these complications are minor, when comparing adjacent sections of the long, investigated line with one another in order to establish successive changes of the climate. In the future it will undoubtedly be possible to make corrections for more distant comparisons. The line described here, which is the only one investigated so far, documents a relatively slow retreat of the ice in its southern part, south of the large terminal moraines. In the districts of Schonen and Bleking this was about 50 m per year, farther north about a 100 m and slightly more. From this it can be concluded that the corresponding Gotiglacial epoch was relatively cool. The large Fennoskandic moraines indicate a significant deterioration of the climate, sufficient to stop the retreat of the ice margin for few centuries and even allowing for a slight advance. However, after this epoch the major ice retreat began again and continued with impressive rapidity and regularity. The annual retreat varied between 100 and 300 m, very rarely changing for a few years into a slight advance. This seems to be valid for almost the whole of the last part of the ice retreat from the Fennoskandic moraines to the site of the ice divide, or

S104 Fig. 3 Diagrams of varve correlations and ice retreat between points A, B, and C in the map [shown in] Fig. 2.

for the time which I termed the Finiglacial subepoch. A last advance of the ice margin occurred only for a short period just before the end of the Finiglacial subepoch. The timing of the advance is not yet known, although the time span of this entire epoch up to this point has been well determined, when the last remains of the ice sheet divided into two parts along the ice divide, the event which best defines the end of the ice age. With respect to the stillstand of the ice retreat, marked by the large Fennoskandic moraines, it only took a century to build the largest ridge, based on direct measurements. Accordingly, all of the associated small moraines originated within one or two centuries. This rather insignificant interruption of the ice retreat was nevertheless the largest one of the entire time during which the ice retreated in Sweden. That these variations in the rate of retreat were relatively unimportant is a fortunate circumstance for the geochronology. These small-scale interruptions of the ice retreat had no influence on the continuous sedimentation of annual layers beyond the stationary or slightly advanced ice margin, allowing determination of the duration of these variations using the usual methods. When the ice margin retreated again, the clays began to be deposited on the inner margin of the moraines; identical layers were deposited on both sides of the moraines, permitting the correlation to be continued. It is necessary, of course, to measure a section of the annual varves on the external margin of such a stationary ice margin which is large enough to include both the number of varves representing the whole variation and the varves required to establish the correlation with the next locality on the inner ice margin. As already mentioned, the largest and most continuous end moraines of Scandinavia represent not more than a few centuries. The duration of the stationary condition represented by the end moraines of Kalmar has not been directly de-

termined yet at that site. However, it probably corresponds to the time required to form the large marginal delta of Bredakra in Bleking, which took 50 years. Other, smaller terminal moraines mark what are probably even shorter interruptions. Without doubt, these were much shorter than has often been assumed because they are developed only locally, especially in the western part of Sweden, where the ice retreat was slower. The position of the ice margin was clearly indicated there only where large amounts of morainal material were present or where larger glacial rivers created transverse eskers on the ice margin. In no case could such small interruptions of the general ice retreat be of any significance for the chronology, as long as it has not been developed to the smallest detail. One may assume that the gaps, the lengths of which have not been directly determined, may hide unexpected facts. However, I do not believe that there is any danger of this. Fortunately, at the major gaps there are normal well-developed eskers and, if there was normal development of the coarse parts of the annual deposits, then the same must be assumed for the finest facies. Moreover, in such places as could not be linked by direct correlations, there were different sites with long sequences of annual layers corresponding to the gaps and directly showing that the sedimentation of fine material proceeded very regularly. These are the reasons why I believe that interpolations are justified at those sites, providing good preliminary results. This turned out to be true not only for some of the early gaps, which have subsequently been filled, but also for the whole of the first investigated line, where the regularity of the ice retreat was predicted by the regular arrangement of eskers7. The long line of investigation was not extended as far into the eastern district of Schonen as the uplifted marine 7

Geol. Fören. Förh. part 27, p. 221

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clays would have allowed. Here I applied the method of extrapolation. The same was done at the northern end of the line in the immediate vicinity of the ice shed, where the sea had not extended so far into the land. However, I measured a sequence of annual varves at a site in a neighbouring fjord valley, which probably represents the whole retreat up to the ice shed and demonstrates that it will be possible to work out the last part of the Finiglacial subepoch in detail. I believe it is already justified to state that we are not wrong if we determine the whole Gotiglacial subepoch, the time during which the ice retreated from the central part of Schonen via the old Gotia to the Fennoskandic moraines, to be almost but probably not more than 3,000 years. In the same way, the end of the last glacial or the Finiglacial subepoch can be estimated to be 2,000 years long. Hence, both subepochs1)8 of the last ice retreat, the Gotiglacial and the Finiglacial, together comprised about 5,000 years, most probably not more. To obtain a basis for the method applied in these investigations, I started in the year 1904 to map the retreat of the ice in the area around Stockholm in great detail. This work continued, finally resulting in a map, part of which is shown in Fig. 2. Since the other part of the study had been based entirely on a single line, it was important to study the areal distribution of the glacial deposits, and especially to determine how they changed with distance from the eskers and establish their relation to the smaller terminal moraines and the topography. The mapping of the Stockholm area confirmed the concept that each of the moraine lines which had been described corresponds to the northern boundary of a distinct, annual clay varve. Moreover, it could be demonstrated in a convincing way that the greatest thickness of each single clay layer occurred always around that part of the esker which lay at the corresponding ice margin. We produced a series of maps showing the distribution of the sediments for each year. Isopachs, lines connecting points of equal thickness, were shown on these maps. They clearly demonstrate the close relationship between the individual annual centres of the eskers and the equivalent sand and clay layers. They provide proof of the explanation that the esker is a series of successive glacio-fluvial deposits representing the coarse submarginal delta facies of the same annual deposit as is represented by annual varves of sand and clay in the extraglacial facies. For the first time it was possible here to study in detail and for each year the laws governing the distribution of sediment from a glacial river mouth. It turned out, 8 1)The time of the first periods of the last glacial subperiods is not known, which may be appropriately termed Daniglacial, and during which the ice margin retreated from the maximum extension through Denmark and central Schonen. However, based on measurements of annual warves of the drained lake Steenstrup on the island of Fyen in the year 1906, it seems possible to obtain estimates of their time through more measurements in the sediments of the ice-dammed lake in the near future.

however, that the conditions were different from that for an ordinary land river which discharges onto the surface of saline marine waters. In our case the cold, sedimentladen water of the glacial river was obviously heavier than the almost fresh, relatively warm water of the late glacial Baltic sea. This is clearly visible in the currentgenerated coarse-grained [cross-bedded] sand which is intercalated in the layered clays up to a few kilometres off the river mouth, at sites which would have never been reached if the river discharge had flowed at the surface of the sea. This explains also the fact why – as far as I could find out – annual clay layers have been found only in freshwater or brackish environments in Europe and North America. In open marine environments, where also the fossil fauna indicates saltwater conditions, the coarse sediments of the glacial rivers were deposited very close to the shore or the ice margin, and only the finest clays were able to follow the surface current to be deposited far offshore in almost non-layered beds. By exact comparison of all of the clay layers, it was possible to study the influence of storm waves on the rising, shallow seafloor, sometimes resulting in erosion of the layered, late glacial clay and its redeposition as nonstratified post-glacial clay. In addition, we were able to explain the different structure between the clay which was deposited from the water which originated from the annual melting process and the redeposited clays resulting from storm waves which may have occurred at any time of the year. At first, the lack of annual layers in the post-glacial clays of southern Sweden made it impossible to bridge the huge gap between the late-glacial and historical chronologies. However, one of my most energetic and successful co-workers, R. Liden, found periodic and obviously annual layering in post-glacial Fjord deposits along the river Ångermanälfven in Norrland and began to investigate them. Since this work was very difficult during the first years, it occurred to me that the post-glacial deposits of the lake Ragunda, which had been drained completely in the year 1796, may be more suitable for investigation of the post-glacial chronology. I visited the lake in the fall before the congress to check and see whether it offered any possibility of success. Indeed, the lake was so very suitable that I took the decision to stay and, with the support of my wife, I was able to put together a continuous section within three weeks. It started at the base with morainal material overlain by about 400 well-stratified post-glacial clay layers. These were in turn overlain by about 700 slightly less distinct layers of black, banded post-glacial fjord clay. This clay graded upwards into well-defined annual layers of alternating fine, sandy sediment and mud which, with exception of the lower parts, had been deposited in the basin of the ancient Ragunda Lake from the time of its formation when an esker dammed the fjord. Deposition continued until 1796 when the outlet across the esker dam was deliberately breached, draining the lake completely and providing us with a unique profile which most likely includes the whole of post-glacial time.

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We measured a thickness of 6 m of late glacial sediments in the lower part of the unusually well exposed, undisturbed main section. These are overlain by a completely undisturbed sequence of 13 m of post-glacial sediments. In the overlying 2.5 m of the section we have only counted the layers; the measurements have not been completed because these layers may not be undisturbed and they are partly obscured due to weathering. This was even more the case for the remaining few metres up to the seafloor of 1796. Nevertheless, the present extrapolation leads to 7,000 years for the whole postglacial sequence. We expect this result to be correct in the main, although it must be regarded as preliminary. New measurements and extrapolations are needed for validation. One way to achieve this is through a more detailed analysis of the upper layers of the deposits. Although they are too weathered to be able to count directly, they doubtless represent the same order of magnitude of sedimentation as the normal conditions in this area represented by the lower, directly measured part of the profile. We were able to correlate the layers of the main section at Ragunda to a large extent with equivalent layers at two different sites about 2 km distant. There we found the same continuity and perfect preservation of the layers clearly representing annual sediment deposits. The main standard profile was visited by participants of the congress excursion to Spitzbergen prior to meeting in Stockholm. It will undoubtedly be possible to make a better determination of the time span required for deposition of the upper weathered layers, by seeking out and measuring other sections which are not so weathered. As soon as possible we will check our results through continued mapping and measuring.

In any case we may conclude that the method described here for producing an exact geochronology can be used for at least late Quaternary time (late glacial and post-glacial) without any fundamental problems. Using this method we have established a numerical time scale for this period. With some additional measurements along the first investigated line and a survey of a second line it will be possible to exclude local influences and to determine at least the major changes of climatic parameters, particularly the temperature, which caused the retreat of the inland ice. Such a climatic curve for northern Europe will provide for comparison and correlation with similar curves for other previously glaciated areas, especially North America. In this way we will be able to recognise whether the frequently discussed glaciations of the ice age in different parts of the earth occurred simultaneously and can be ascribed to global climatic causes, or whether they are only of local origin. No matter how the comparison may turn out, the natural time scale will gradually provide us with data which will not only be important for understanding the development of prehistoric man but also for the modern fauna and flora and to understand the laws which govern their migration. This time scale will also be important for physiography in general, as it will enable us to determine the rates of such processes as weathering, talus formation, erosion, deposition, and uplift in much greater detail and more reliably than has been possible as long as we could build only on the much shorter and direct experience of man.

Translator’s comment Square brackets [] indicate additions to the original text used to facilitate language flow and clarity.

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H. Cloos

On experimental tectonics (with 14 figures) V. Comparative analysis of three types of displacement Geol Rundsch 21:353–367 Translation received: 8 April 2002 © Springer-Verlag 2002

Whereas an experiment in physics or chemistry is an artificially induced natural process, a geodynamic experiment can be considered natural only if it is regarded on its own scale, and no relationship to larger, real nature is implied or inferred. If we nevertheless wish to establish such a relationship (and only then does our experiment acquire geologic meaning), then two tasks besides performing and analyzing the experiment become evident: examining a comparable natural object, and equating this object with the experiment. The geodynamic experiment is therefore similar to technical experiments, especially those conducted in the ship-building and aviation industries (see J. Königsberger’s article on orogenesis in Handwörterbuch der Naturwissenschaften, 1st edn., vol. 4, p. 654). In my first essays, I considered all three tasks {i.e., performing and analyzing the experiment, examining a comparable natural object, equating this object with the experiment; see translator’s comments for the use of decorative/square brackets}. To facilitate the further development of experimental techniques, however, I find it necessary to first examine the artificial kinematics in greater detail, and thus to consider the experiment on its own1 {i.e., on its own scale, without reference to natural examples}. I recently began this investigation with the mechanical analysis of a normal fault (IV, p. 743). Below, we shall examine a thrust fault and a strike-slip fault (referred to as experiments II and III) and compare the results of these experiments with those of the aforementioned normal-fault experiment (referred to as experiment I). Cbl. f. Mineralogie, etc., Section B, 1928, p. 609; II. Natur und Museum, 1929, p. 225; III. Natur und Museum, 1930, p. 258; IV. Die Naturwissenschaften, 1930, p. 741. Translated by Mark Handy M. Handy (✉) FU Berlin, FB Geowissenschaften, Malteser Str. 74–100, 12249 Berlin, Germany e-mail: [email protected]

Experimental material Semi-liquid clay was used as experimental material. Common, so-called plastic clay is an inhomogeneous suspension of clay flakes in water, and in a physical or mechanical sense it is therefore neither more nor less plastic than moist sand. Clay plasticity is actually due to the ability of the tiniest, water-lubricated particles to glide over and past one another. It is this characteristic which renders clay so similar to large geological masses and so suitable for simulating their movements. When subjected to an externally imposed load, plastic clay is deformed and segmented by fractures. Joints and displacement fractures2 form, otherwise known as extensional fractures and shear fractures. I have described how one can induce one or the other of these fractures by spreading water on the clay, thereby varying the clay’s capillary surface tension. In cases in which both extensional and shear fractures form, the extensional fractures form first. As in geological bodies, the tensile strength of clay is less than its compressive strength. According to my measurements so far, the time over which clay remains plastic is independent of its viscosity, which is itself a function of water content. I have marked circles onto clays of different viscosity and deformed the clay so that these circles became ellipses. The first shear fractures formed when the ratio of the long axes of the ellipses to the diameters of the undeformed circles was 1.2. The shear fractures became numerous and easy to identify at axial ratios of 1.14 to 1.17. At this stage, the three axes of the strain ellipsoid have the following values (translator’s comment: note that the deformation was plane strain): Long axis

Intermediate axis

Short axis

1.17 1.16 1.14

1 1 1

0.89 0.89 0.88

1 2

See, however, afterword, p. 29. L. Prandt (1914): Enz. d. math. Wiss., IV, 5, p. 718

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The reasonable expectation that clay with a very low viscosity would not develop fractures, or would develop these features only late in the deformation, could not be confirmed. Even clay flowing under its own weight down an inclined table surface disintegrated into sharply edged, elongate blocks, and countless tiny cracks opened up in the presence of water. This demonstrates the potential for using clay experiments to study glacial flow and the formation of cracks in glaciers. In experiments so far, I found that extensional fractures opened when the following axial ratios of the strain ellipsoid were attained: Long axis

Intermediate axis

Short axis

1.13 1.06

1 1

0.9 0.96

The greatest value of the long axis at the onset of extensional fracturing (1.13) is therefore still less than the smallest value of the long axis at the onset of shear fracturing (1.14). Moreover, variations in the lengths of the long and short axes are probably attributable primarily to the difficulty of determining exactly when the first fractures open. In the future, these measurements will be refined and carried out before each experiment. In order to compare experimental with geologic conditions, I have also begun to measure the strength of clay in the manner usually employed for rocks. For the time being, I have restricted myself to measuring the most easily measured kind of strength, the compressive strength. Using a metal mould, I prepare a clay cube of 7 cm per side length (about 50 cm2 surface area per face) and subject this cube to an increasing load. To do this, I place the cube on a flat surface and cover its top surface with a flat, metal plate which overlaps the cube’s upper surface by 1 cm on each side (i.e., the plate is 9 cm to a side). I then place a glass beaker on top of this plate and fill it with water until the first fractures become visible in the cube. At this instant, the combined weight of the metal plate, glass, and water is determined and this weight is divided by 50. In this way, I determine the pressure (i.e., the vertical stress) in grams per square centimeter. Of course, the values obtained depend only on the viscosity (the water content) of the clay. I found: 32.30... 12 g/cm2 We compare this value with an average strength for most common rocks of about 2,000 kg/cm2. From case to case (i.e., depending on the rock type with which the clay is compared), our clay is about 65,000, 60,000, and 170,000 times weaker than a rock! The clay cube used in this experiment is roughly proportional in size to a piece of rock which is that many times bigger. The scale of the experimental tectonic structure is about 1:65,000. The system of fractures in the sides of my cube are similar to those produced by Daubrée on a prism of wax, and confirms that these fractures are shear fractures (Figs. 1, 2, 3). If we moisten a side of a cube, then we also obtain vertical fractures oriented parallel to the sides of the cube. These are extensional fractures associated with the shear fractures (Fig. 1).

Figs. 1–3 Pressed clay cube. 1 (top) with extensional fractures parallel to the compressional direction, 2 and 3 with diagonal shear fractures and displacements

Configuration and evaluation of the experiments In both the next experiments (experiments II and III), one part of the experimental clay body is moved past the other part along a zone of partitioning (i.e., a discontinuity in a base plate underlying the clay body), in the first case vertically (Fig. 4), in the second case horizontally (Fig. 5). We can therefore observe two movements which differ mainly in their displacement direction with respect to the gravitational field, although they also differ somewhat in the manner and direction with which the force which induces motion is transmitted to the moveable part of the clay body. Accordingly, the features of those structures which are not affected by the force of gravity are very similar. The effect of gravity and absolute orientation {i.e., the effect of varying the displacement direction with respect to the gravitational field} becomes clear. The vertical displacement was induced with the aid of a vertical screw-jack which is fixed within and under the base plate of the experimental table {i.e., the plate upon which the clay body rests}. In Figs. 4 and 5, this configuration is shown in side view (profile). The horizontal

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Fig. 4a–e Vertical displacement seen from one side (5 of 12 stages)

Fig. 5 Horizontal displacement seen from above (6 of 10 stages)

displacement is viewed directly from above (map view). The displaced half of the experimental clay body was supported by, and moved on a metal plate. The amount of displacement was measured and photographed. I avoided the formation of extensional fractures because they interrupt the material’s continuity and render the movement uneven. These fractures are easily drawn onto the pictures (of the experiments) because they always form at right angles to the long axis of the strain ellipse. The data evaluation is carried out immediately on the negatives (well-developed but not over-developed film packs with the dimensions 8×14 and 13×18 cm, exposed with artificial light every 45 s at the smallest aperture setting). For ease of illustration, I use a drawing table with translucent glass illuminated from below. We investigate the structures, the deformation and the nature of the movement {i.e., the kinematics}.

Structural state The structural state in both experiments is very similar, especially at the outset. In none of the experiments did we observe fractures which open parallel to the bulk displacement direction and which separate the displaced from the undisplaced halves of the clay body. Instead, a system of closely spaced, parallel fractures forms above and along the displacement zone boundary {i.e., the shear zone boundary}. These fractures are oriented at a low, acute angle to the displacement boundary and are staggered {en échelon} along this boundary. I have often described and interpreted these natural and experimental phenomena, referring to them as splay cracks [Fiederklüfte]. These open splay cracks (F-cracks) can be placed in the same category as similarly oriented – albeit with a larger acute angle {with respect to the shear zone

S114 Fig. 6 Evolution of the main displacement surface in Fig. 4 during stages 3 to 12 {numbers indicate progressive development of fracture surfaces during stages 3 to 12}

boundary} extensional fractures. The individual splaycrack surfaces accommodate small displacements in the same direction as that of the overall displacement. The minor displacements along these splay cracks increase with increasing overall displacement and, measured approximately, they sum up to equal the total displacement in the experiment. The individual displacements {along each splay crack}, however, are not equal. In general, the amount of displacement increases from both sides {of the clay body} towards the displacement boundary. With continued displacement, a few crack surfaces accommodate an increasing proportion of the bulk displacement while propagating in the long direction {i.e., in a direction parallel to the zone separating displaced and undisplaced halves of the clay body} until, during the final stages of the experiment, they accommodate all of the bulk displacement. Initially, the angle of the fractures with the displacement boundary is 11 to 12°. This angle changes little during subsequent time. Only in the upper part of the vertical displacement near the surface do the shear fractures rotate clockwise during the final stages of deformation. This rotation {of the shear surfaces} is associated with the {downward} movement of clay from the upper to the lower {displaced} block {i.e., subparallel to the normal fault} (Fig. 6). In addition to this first system of fractures oriented at acute angles to the shearing plane, a second system develops at high angles to this plane. At the onset of deformation, this second fracture system is as well developed as the first, but it diminishes with continued deformation until it accommodates only minor displacements. Initially, this second fracture system locally overprints the first system, before eventually being overwhelmed, truncated, bent and finally deactivated by the latter. The displacement along these surfaces is directed at high angles {i.e., antithetic} to the bulk displacement direction. In the vertical displacement experiment, these displacements even propagate obliquely upwards from the downward-moving half to the immobile half of the clay block. As we shall see, this {antithetic} movement is only apparently contradictory. The angle between the fracture surfaces of the two systems is initially 63–64°, but increases from 70–80° in one case to as much as 89° with progressive rotation of the second fracture system.

Fig. 7 Normal, synthetic faults with glide striations

Fig. 8 Normal, antithetic faults with glide striations

Apart from these two fracture systems, the first type of experiment (experiment I) shows two paired and equally well-developed systems with a similar relative orientation at the upper margin of the upper block. Their attitude with respect to the vertical is so different, however, that these surfaces appear to be normal faults, geologically speaking. Depending on whether the left or right system (as viewed from our vantage point) predominates, many of these join into synthetic steps looking down the mountain {i.e., left-stepping} or antithetic steps looking up the mountain {i.e., right-stepping}. We see both types in Figs. 7 and 8 (twin experiments), in detail and in perspective. In Fig. 7, steep synthetic displacement surfaces predominate on the left, and flat antithetic displacement surfaces on the right. In Fig. 8, only antithetic surfaces occur. From left to right along the arc of the bent clay tablet, these surfaces become flatter-dipping “into the mountain”. All surfaces are well lineated in the direction of displacement (steepest dip). To compare, we now consider the structures formed during normal faulting (experiment I in IV, p. 744). In accordance with the different principal movement direction (i.e., kinematics), the absolute orientation of these structural elements is different and more complicated. During experiments II and III the bulk displacement

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remains uniform and constant because it is parallel to (experiment II) or opposite to (experiment III) the force of gravity, whereas the displacement in experiment I comprises a primary horizontal movement and a secondary, vertical, gravity-induced movement. The horizontal displacement predominates at the outset but is replaced by the vertical displacement during the end stages of movement. The resulting bulk displacement is therefore irregular and arcuate. The structures in experiment I are predominantly normal faults. Steep or overturned thrust faults are rare and occur only occasionally along the upper, laterally moving margin during the final stage of the experiment, that is, opposite to the order of appearance in experiment II. These contrasts (in the fault kinematics of the different experiments) are so pronounced as to be easily recognizable in large, natural examples.

Structural style We can understand the surfaces and displacements of all three experiments if we consider their relationship to the strain directions (Figs. 9 and 10). The local direction and magnitude of strain can be determined easily and precisely enough from the orientation and relative lengths of the long axis of the strain ellipse (IV, p. 746). Its distribution {i.e., the strain distribution} is very simple. Extension affects both blocks {i.e., both halves of the clay body} at a considerable distance from their mutual boundary and can be traced, symmetrically with respect to this boundary, diagonally across both blocks. An important difference between the two experimental configurations becomes apparent, in that the strain axes in the horizontal displacement experiment {strike-slip, experiment III} are almost straight, whereas in the vertical displacement experiment they {the strain axes} are slightly convex towards the upper part of the falling block. This is also found in my model of a normal fault (IV, Fig. 10) and is apparently due to a low-lying obstacle {asperity} around which the substance {clay} flows. Another difference is evident in the vertical displacement experiment between the lower and upper parts {of the blocks}. This accords with the fact that only one of blocks moves upwards during the experiment. The zone of strain {i.e., the shear zone} is narrower and affects a proportionately smaller volume of material {in the lower block} than in the upper block. The structures and kinematics of the experiment are readily apparent from the configuration and distribution of the strains. The main displacements lie on the left diagonal of the strain ellipses, the subordinate displacements on the right diagonal3. They {i.e., the displacements} form acute angles symmetrically disposed on either side of the short axes of the ellipses, and coincide with the two planes of maximum shear stress. All displacements occur in the direc3 “Left” and “right” refer, respectively, to the positions viewed in a clockwise sense “before” and “after” the small axes of an ellipse.

Fig. 9 Direction and magnitude of stretches in experiment II (Fig. 4, stage 10). The short, thick lines show the orientation and relative length of the long axes of the strain ellipse

Fig. 10 Direction and magnitude of strain in experiment III (Fig. 5)

tion most suitable for elongation of the previously formed strain ellipses. The inequality of the two {fracture} systems stems from the asymmetry of the ellipses with respect to the movement direction. Movements are favored which lie close to the bulk displacement {direction} and those surfaces which accommodate such displacement. Conversely, one may wonder why displacements occur in directions oblique to that of the main, bulk displacement. Even these, however, become understandable when the true movements are considered (see below). The occurrence of two, paired {displacement} systems at the upper margin of the hanging-wall block in

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experiment II can be explained by the occurrence of stretches in this region which are gently inclined toward the lower block. The deformation pattern of the normal fault (experiment I) which we again use for comparison (IV, Figs. 10 and 12) differs in the considerably flatter inclination of its long axes and in the greater width of the deformed zone. Only in the final stages {i.e., at high bulk strains} does the deformation localize in the immediate vicinity of the main fault plane.

The true movements of particles The displacements on thrust surfaces only allow one to determine the relative movement of a small block with respect to an adjacent block. The deformation picture, on the other hand, shows the relative change of distances separating adjacent particles. Movements relative to a point outside of the deforming system, that is, true and absolute movements, are not apparent in the pictures. To become acquainted with them, we will compare the various movement stages by covering up the stationary parts of the picture and tracing the changing positions of the mobile parts of the picture from point to point (Figs. 11, 12, 13, 14). To this end, it is not sufficient to follow the bending of a layer or of another reference line from the original {undeformed} state in the way that one could with originally horizontal strata in a geological profile. Instead, it {the mobile part of the deformation pictures} must be followed point by point, because the lines therein change not only in form but also in length, and their points both converge and diverge. In this way, pictures like those in Fig. 11a–e are produced which depict both the movement of a layer, which resembles a movement front, and the trajectories of its material points. Comparing these pictures reveals some significant differences. The horizontal displacement (Fig. 11e) proves to be the simplest; the particle trajectories are parallel and almost straight. In the vicinity of the vertical displacement (Fig. 11c, d), this {movement pattern} pertains only to the outermost parts of the downward-moving block. In the border domain and on the stationary, adjacent block, the trajectories are strongly arcuate, with the convex sides {of the trajectories} facing in the direction of the lower, hanging-wall block. The material in the foot-wall block moves obliquely downward, while in the lower, hanging-wall block, the material is displaced downwards towards the rigid base plate and is flattened. In the movement picture of the normal fault (Fig. 11a, b, experiment in IV, Fig. 9a–c), the horizontal component of displacement is greatest. This horizontal component even exceeds the vertical component in the distal parts of the blocks. In these areas, broad masses flow almost entirely horizontally. By contrast, in the downward-moving block {i.e., the hanging wall} the material flows downward at a 45° angle to the horizontal. A prominent movement surface {i.e., a fault} opens up, guiding this {oblique} movement (Fig. 11b).

Fig. 11 Trajectories of true motion in experiments I–III. Ia is the right side, Ib is the left side of the normal fault; IIc and d are the upper and lower parts of the vertical displacement, respectively; III is the horizontal (strike-slip) displacement

These movement pictures can be understood as the combined product of the experimental configurations, the orientation of the moving base plate, and the unequal positions of the test materials. The movement pictures engender deformation pictures when we identify the lines along which neighboring points move furthest apart or closest together. These lines define the long and short axes of the {strain} ellipse. The deformation pictures in turn show us the structures, and so bring us full circle back to the beginning of our investigation. Yet, our movement pictures teach us something more. They teach us how to distinguish apparent and real movements in a structural map and how to relate local movements to general {bulk or regional} movements, even though we rarely, if ever, directly see the latter. These significant possibilities can be illustrated with the following three examples. In a structural map, we observed low-angle thrust faults which were inclined toward the foot-wall block and therefore appeared to be paradoxical. An analysis of the true movement reveals no trace of this {paradox}. It teaches us that the only real movements are those which

S117 Fig. 12 Successive positions (numbered 3 to 11) of a thrust surface in Fig. 4 and of a point (a) on and along this surface. (a) is divided into (d1) beneath and (d2) above the thrust surface

right and Fig. 8) have a low-angle, sometimes even horizontal orientation. An analysis of the true movements reveals no such discrepancy {i.e., does not reflect a discrepancy between orientations of apparent and true movements}. In both places (Fig. 11c, upper left), the material flows obliquely downward and with increasing steepness. The true movement diverges from both apparent movements by about the same amount.

Summary

Fig. 13 Schematically enlarged part of Fig. 12 showing the downward movement of the same thrust surface during stages 3 to 8, and the movement of adjacent material both relative to the surfaces and to the observer Fig. 14 Division and displacement of a point mass (labeled 3) moving together with (left) and relative to (right) a thrust surface

coincide with the main {principal} movement planes. Those lateral thrusts are apparent movements which are engendered when two points on either side of a rotating shear surface do not move parallel to each other, but diverge along lines which form a very small angle. This is shown in Figs. 12 and 13, together with its relationship {i.e., the relationship of these apparent movements} to the slight rotation of the intervening thrust surfaces. A similar situation pertained to the two points on either side of a main thrust surface in Fig. 14. One of these points advanced more slowly than the other one, such that they eventually came to rest with one just above the other. This in no way corresponds to a “thrust” as identified in outcrop by a structural geologist, that is, as an upward movement opposed to gravity which develops in response to forces directed obliquely to the surface. Apparent and true movements differ most conspicuously in the case of “antithetic” faults. This can be seen on a small scale in experiment I (IV, p. 745, Fig. 9a–c) but also applies on larger scales in experiment II; Figs. 7 and 8 of this paper reveal relative movements which differ by almost 90° within the same tectonic framework. The synthetic surfaces (Fig. 7) seem to be oriented almost vertically whereas the antithetic surfaces (Fig. 7,

I now summarize and, in so doing, make use of geological language. When subjected to a load, the experimental material behaves plastically for only a short time. Its brittle threshold {i.e., the transition from ductile flow to localized displacement along discrete surfaces} is independent of viscosity and is first reached at extensions of 1 to 1.06 (in tension) and at shortening values of 1 to 1.13 (in compression). By contrast, the compressional strength varies with viscosity and ranges from 32 to 12 g/cm2 in our experiments. This strength is on the order of 50,000 to 200,000 times smaller than the compressional strength of the most common rocks. The fractures which open in rock cubes undergoing compressional strength tests are extensional and shear fractures. The former are oriented parallel to the loading direction, the latter diagonally to this direction. In tests on clay, these fractures can be opened and identified by wetting the clay surface. An experimentally induced, vertical displacement induces flexural bending of the layers and engenders two systems of fault surfaces: a main system {of normal faults} dipping steeply toward and under the overriding {hanging wall} block which evolved into synthetic, slightly overturned steps with different heights (steep thrusts or reverse faults); a subsidiary system of faults accommodating horizontal displacement or low-angle thrusts running from the lower to the upper block {i.e., synthetic, low-angle thrusts}. Extensional cracks dip toward and under the hanging-wall block and are staggered above one another {in an en-échelon configuration}. Small conjugate, synthetic and antithetic faults form near the surface of the upper {hanging-wall} block. Other than these faults, there were no other normal faults inclined from the hanging wall to the foot wall. The absence of such faults, together with the orientation of all other elements, at first sight distinguishes the vertical displacement from a normal fault involving lateral spreading (IV, Figs. 6, 7, 8, 9, 10, 11, 12). The map view of a strike-slip fault looks like the profile view of a vertical experiment {fault}. The master fault splays laterally into a staggered {en-échelon} system of auxiliary faults which have the same sense of displacement. Subsidiary faults are suppressed. The locally measurable displacements should be interpreted as apparent rather than real displacements. They are relative displacements in the sense that the displaced bodies within the system have moved together

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with the faults separating them as well as with the entire mass. The minor, local displacements are parts of a larger movement picture and their nature, orientation and kinematics can be understood only in this broader context. In light of the similarity with many tectonic structures, it is advisable to interpret the movement of small faults only as part of the larger-scale motion of bodies in space. It should be noted that experiments like those shown here do not do justice to what really happens in nature, but only to what can possibly happen {italics are translator’s}. Rather than simulate a specific case, they illustrate ideal circumstances.

Afterword Several people have recently pointed out to me that in order to render my experiments more understandable, it is necessary to not leave the reader to make comparisons {of my experiments} with natural structures all on his own. In one instance, my experiments were even labeled unrealistic. I would like to follow this advice elsewhere. Already at this point, however, a short comment regarding this point seems appropriate. It is revealing that my experiments receive acclaim not from those colleagues who derive their ideas about tectonic structures from mapping, but rather from those who have sketched and measured rock quarries, open-pit mines and drill holes. In my experience, the better and more detailed our knowledge of a geological structure, the closer the resemblance {of nature} with my appropriately conducted experiments. These {experiments} are superior to nature not only in the visualization of the structural evolution but also in the perfection of the exposures. In any case, the final statement {paragraph} of this paper remains valid.

Translator’s comments This paper is one of the first reports of an attempt to scale deformation experiments on a rock-analogue material (clay) and to conduct detailed kinematic and strain analyses of the three end-member types of faulting (thrust, normal, and strike-slip). Given the novelty of this

paper in its time, one may ask why it was (and is) not cited more often. While novelty itself may be one reason, part of the answer has to lie in the inaccessible nature of the text. Cloos has left the reader (and translator) with a difficult job. Cloos frequently switches from the present to the past tense, on some occasions even to the future tense. He uses active and passive verb forms interchangeably. He also shifts between the first person singular, the first person plural (the royal “we”) and the third person singular (the omniscient “one”) for no apparent reason. His liberal use of pronouns when referring to nouns in preceding sentences is ambiguous. This grammatical and semantic confusion probably reflects the lack of an established peer-review policy in those former days, combined with a tendency for senior scientists to write epically and polemically rather than succinctly. Cloos certainly felt a need to relate geology and the experience of being a geologist to the general public. Anyone who has read his book “Gespräch mit der Erde” (1947, Piper Verlag, München) can attest to Cloos’s literary vein and his penchant for philosophy. Some of these elements come across, if only between the lines, in his original text. In translating this paper, I preserved Cloos’s syntax as far as possible without sacrificing clarity. Mixed tenses and declinations are the author’s. In eliminating singlesentence paragraphs and restricting the use of semicolons, I obviously observed the rules of English rather than German. For the sake of clarity, I broke up several long German sentences into shorter English sentences. I tried to enhance the readability of the text by using English idioms for those phrases which do not translate literally and clearly from idiomatic German. Where a literal translation was not clear, I followed it with a looser translation or with added text between decorative brackets {like this}. Only where the original text is worded very ambiguously, did I take the liberty of completely rephrasing the German sentence in English. Where the English translation is unavoidably vague, however, I have left the original German word in square brackets, e.g., splay cracks [Fiederklüfte]. To really understand any translated text, however, the reader must read and engage also the original text on his/her own terms. Acknowledgements In reading my translation, Onno Oncken clarified a few important nuances in the original text which only a German-born scientist can detect.

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C. W. Correns

Fluid inclusions with gas bubbles as geothermometers Geol Rundsch 42:19–34

Translation received: 6 January 2000 © Springer-Verlag 2002

Abstract Two types of fluid inclusions can be distinguished. The first is based on the assumption of Sorby (1858) that a homogeneous phase, such as water, salt solution, or CO2, is entrapped, meaning that the bubbles result from the gas of the enclosed fluid. The second type includes foreign gas entrapped with the fluid. “Sorby”type inclusions can be used as thermometers if either the formation pressure is known, or the pressure impact has been shown to be unimportant. It is only possible to neglect pressure in cases where the degree of filling is high enough that bubbles vanish at low temperatures. If, during entrapment, the fluid included dissolved foreign gas that was released during cooling, it is even more dangerous to equate filling with formation temperatures. Compared with Sorby-type inclusions, even less information is available about the expected large-pressure impact. If foreign gas was entrapped as bubbles, the filling temperature may significantly deviate from the formation temperature and may even increase at first during heating. Such non-Sorby-type inclusions can be identified by measuring the degree of filling and comparing the related filling temperature with that of water and CO2, respectively, at a similar degree of filling. The question of the composition of the inclusions is important not only for determining temperatures, but also for solving questions about the formation and alteration of rocks. Attention is drawn to the method of Brewster (1826), who determined the refractive index by using the total reflection. All these remarks are valid for both primary and secondary inclusions. The decrepitation method is not an appropriate means to distinguish primary from secondary Lecture at the annual meeting of Geologische Vereinigung held in Mainz, 1953 Translated by Gernold Zulauf G. Zulauf (✉) Institut für Geologie und Mineralogie, Universität Erlangen-Nürnberg, Schloßgarten 5, 91054 Erlangen, Germany e-mail: [email protected]

inclusions. Further, it is not suited to determine the type of inclusion, or the degree of filling. Fluid inclusions with gas bubbles have been used as geothermometers for several years. Thus, it is necessary to test this method in some detail. Different opinions about this “geothermometer” have resulted from evaluations on fluid inclusions carried out several times during the last 100 years. In the present paper, current and new studies will be evaluated and a few new observations and instructions are presented. The discovery of fluid inclusions in crystals is relatively old. The nine epigrams of Claudian, a contemporary of the holy Augustin, gave the earliest observations of fluid inclusions. Claudian summarized as follows: De crystallo, cui aqua inerat [On the rock crystal that includes water] (1824). Modern scientific studies of fluid inclusions began during the early 19th century. The famous English chemist, Sir Humphrey Davy, investigated the chemical composition of such inclusions in 1822. Sir David Brewster is known from the history of crystal optics. From 1823 onwards, he described inclusions with bubbles from several minerals including those with two different mobile fluids (Brewster 1823; Fig. 1). In 1858, H.C. Sorby explained the use of fluid inclusions as thermometers and provided a highly sophisticated and critical evaluation that is still worth reading. Sorby (1858) started from the principle that a homogeneous fluid, e.g. water or a diluted salt solution, had been entrapped in the crystal. As the system cools, the water will shrink yielding a vapor bubble. During reheating of the inclusion, the bubble will disappear at the entrapment temperature. Taking into account the relation between the volume of the gas bubble and the bulk volume of the inclusion, as well as the expansion coefficient of water, Sorby (1858) calculated the temperature at which the vapor bubble should vanish. To conveniently determine the exact entrapment temperature, particularly of fluid inclusions with irregular shapes, a heating stage should be used that is fixed at the microscope. Sorby’s paper was very stimulating. Nine years later, Vogelsang noticed that, in his textbook, Philosophie der Geologie, “Für die Bildungsweise der einzelnen

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Fig. 1 Inclusion with two fluids. The less and more expanding fluid is shaded and stippled, respectively. Gas is depicted without a pattern. (after Brewster 1826)

kristallinischen Bestandteile sind ohne Zweifel die darin enthaltenen Einschlüsse von ganz besonderer Wichtigkeit, und seit den geistreichen Schlußfolgerungen Sorby’s haben sie eigentlich bisher den Hauptgegenstand der mikroskopischen Gesteinsstudien gebildet.” However, contradiction occurred after. Reasonable objections could be found in the textbook, Lehrbuch der Petrographie, of Zirkel (1893). He devoted 15 pages to questions on fluid inclusions, and rejected the method. Subsequently, only a few papers on inclusions occurred, like that of Specia about inclusions in anhydrite and calcite, followed by the theoretical work of Scharizer (1920), Nacken (1921), and Holden (1924). The latter papers were stimulated by the work of Johnsen (1919). However, new observations on fluid inclusions were largely lacking at this time. In 1924, Wülfing devoted 20 pages to fluid inclusions in Rosenbusch–Wülfing (1921). In 1930, the literature on fluid inclusions was reviewed by Seifert (1930). The use of fluid inclusions has only been revived over the last few years, particularly through the decrepitation method of Scott (1948). Recent critical expositions have come, for example, from Ingerson (1947), Bailey (1949), Kennedy (1950; with a discussion by Smith), and Stephenson (1952). First, we will explore the theory that inclusions with homogeneous fluids are free from gas, i.e., pure water or a diluted solution of salt, as has been suggested by Sorby. We further assume that the “Sorby” inclusions were formed as primary inclusions that were stable after entrapment. In the second part, the inclusions will be considered that do not reflect the above conditions. These inclusions are probably frequent in nature. First of all, we will consider a hollow space filled with water at T greater than room temperature. The water shrinks when it cools. At room temperature, the hollow space is filled with water and a bubble consisting of H2O vapor. The dimension of the bubble depends on the filling temperature. So far, all seems to be quite easy. However, Sorby already considered the role of pressure to be important. We are only able to determine the temperature at which the bubble will disappear. The pressure, on the other hand, is not known. It seems necessary to calculate, or at least estimate, this filling pressure. Moreover, we have to consider the critical temperature of water at T=374 °C, above which the conditions are still more complicated. Thus, the dependence of water volume (vol) from temperature, T, and pressure, P, is required. Figure 2 shows a scheme of a P–T–vol diagram of water. In the center of

Fig. 2 Block diagram showing the pressure–temperature–volume diagram of water as solid lines in the center of the cube. Projections to the side planes are depicted with dashed lines

the cube it is depicted with solid lines. The projection onto the P–vol, T–vol, and P–T plane is shown with dashed lines at the front, upper, and right-hand side, respectively. As numerical data are difficult to read in such types of 3D graphs, we will use the following projections. Figure 3 shows the projection onto the T–vol plane including the isobars. The specific volume, i.e., the volume per gram, is indicated along the abscissa. As the specific gravity of water is 1 at 4 °C, the quotient of 1/specific volume yields the volume of aqueous fluid in 1 cm3. This is the “degree of filling” or the liquid–vapor ratio, respectively. The degree of filling at 20 °C is not very different from that at 4 °C. Given a hollow space, two-thirds of which is filled with water and one-third with vapor, during heating the water will expand until the two-phase line at ca. 320 °C is reached at a pressure of ca. 120 Atm. At this “filling temperature” the hollow space is filled. Further heating will lead to further pressure increases as indicated by the isobars in Fig. 3. On the other hand, an inclusion can be entrapped at high pressure and temperature. This inclusion is filled until the two-phase line is reached during cooling. If the water pressure exceeds the strength of the inclusion wall because of further heating, the boiler will burst. The decrepitation method is based on this feature. Decrepitation of an inclusion at a certain filling temperature is largely dependent on the strength of the wall. The strength of the wall is probably not the same for all inclusions, even if the mineral has been crushed. It is further dependent on further conditions such as the lattice defects of the crystal. The strength of the wall has nothing to do with the entrapment pressure. Secondly, the decrepitation of the inclusion will depend on if the pressure-increase during heating is fast or slow. This has been particularly emphasized by Kennedy (1950). It is apparent from Fig. 3 that, in the left area, which shows a high degree of filling, the increase in pressure is fast, whereas in the right of the figure it is slower. This is more obvious from the P–T diagram of water (Fig. 4). To better

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Fig. 4 P–T diagram of water

Fig. 3 Temperature–volume diagram of water

understand this diagram, it should be noticed that the two-phase plane (liquid + vapor) occurs as a line. The higher the difference in pressure increase along the twophase line from that of the isochore, the higher the probability that the inclusion will decrepitate at the filling temperature. The smoother the transition, the higher the dependence from the strength of the wall of the inclusion; thus, the determination of the filling temperature will be less reliable. We consider an inclusion that is filled twothirds with water (specific volume =1.5) at room temperature. If this inclusion is heated, it will be filled at a pressure and temperature where the 1.5 isochore branches off and turns upwards from the two-phase line. The pressure increase because of further heating is remarkable in this case. At a low degree of filling(low water–vapor ratio), on the right-hand-side of the figure, the pressure increase slows down. In cases where the inclusions are filled onefifth of water (specific volume =5), the pressure increase is less than that along the two-phase line. The critical point of water at 374 °C corresponds to a degree of filling of one-third. Inclusions with a higher degree of filling contain water at the filling temperature, whereas those with a lower degree of filling contain gas. This is the reason for the large difference in temperature with pressure. By measuring or estimating the degree of filling it is possible to determine the particular field. Thus, there is a fundamental problem to precisely ascertain the filling temperature using the decrepitation method. It should be emphasized that this problem is not related to the difficulties arising from the Sorby method, i.e., that the pressure during entrapment of the inclusion is not identical with the pressure related to the filling temperature. The differences in temperatures at different formation pressures can

be taken from Fig. 4. In our example of an inclusion, filled two-thirds with water (specific volume =1.5), the inclusion will be filled at 120 atm and 320 °C. A formation pressure of 400 and 800 atm would correspond to a formation temperature of 350 and 390 °C, respectively. It is obvious that, in this case, the error is larger the lower the degree of filling. Kennedy (1950), for example, gives a diagram that shows the change in filling temperature with pressure. As has already carried out by Sorby, it is possible to estimate the formation pressure by taking into account the column of rocks resting above. Johnsen (1920) and Nacken (1921) added the geotherm to the diagrams. Smith (1953) has recently depicted different types of “Geothermobaren”. However, such estimates imply a large uncertainty. If the bubbles disappear close to, or above the critical temperature, these inclusions cannot be used to determine the formation temperature. In such cases, the isochores are too close together, resulting in a pressure estimate that is not reliable. Compared with the impact of the pressure and the uncertainty close to the critical point of water, other sources of error, e.g., the expansion of the surrounding crystal because of heating, are not very important, at least in cases of primary and consistent aqueous inclusions. If a homogeneous salt solution is enclosed instead of water, the conditions will not markedly change until T=100 °C. The critical temperature of water is higher if KCl and NaCl are dissolved (diagram in D’ans-Lax 1943, p. 827). No measurements are available for the region in between. Such measurements should be carried out to constrain the impact of dissolved salt on the filling temperature. There are further types of inclusions, such as those with CO2. Simmler (1858) was the first who supposed fluid CO2 to be involved when regarding the description of Brewster. Also, in this case we assume pure CO2 to be present without any additive. As the critical point of CO2 has been fixed at 31 °C, the bubbles should disappear at this temperature. Thus, the determination of the formation temperature of CO2-bearing fluids is more difficult compared with aqueous fluids. This is also obvious from the P–T diagram (Fig. 5) where the degrees of filling are depicted for 0 °C. The application of the decrepitation method is less successful in cases of CO2-bearing inclu-

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Fig. 5 P–T diagram of carbonic acid

sions. Estimates on the impact of pressure at filling temperatures of more than 20 °C are possible if the degree of filling has been measured or estimated by direct observations. This is necessary to distinguish the area left or right of the two-phase line. Inclusions with fluid CO2 occur in halite (Knistersalz) of the Werra potassium salt district, e.g., in the Sachsen-Weimar mine. At room temperature, they are filled with a fluid of low refraction index (n=1.19). At lower temperatures, a gas bubble will appear. The observed filling temperature is 11 °C. The inclusions suffer a pressure of ca. 46 atm (Fig. 5). If the crystal is dissolving in water, this pressure becomes apparent by the fact that the crystal will move rapidly. As yet, we have assumed homogeneous fluids to be entrapped during crystal growth that consists either of pure water, water with minor amount of dissolved salt, or fluid CO2. Therefore, the gas bubbles consist of water vapor or, in the case of fluid CO2, of CO2 gas. We have to test these requirements starting with the question of if foreign gas from the crystal can be involved together with the fluid. Two cases have to be distinguished. (1) Foreign gas and fluid, e.g., water, can be enclosed within a homogeneous solution. Subsequently a bubble of the foreign gas can develop during cooling. (2) A gas bubble is enclosed together with the solution. In both cases it is important to note that the solubility of gas in a fluid decreases with increasing temperature, but increases with increasing pressure. Thus, it is perfectly possible that, at first, the volume of the gas bubble increases because of heating. This feature must not be related to leakage of the inclusion and associated fluid escape, as has been assumed by Ingerson (1947). In cases of a leakage, the gas should escape at first. Unfortunately, only a few details exist concerning this problem. Concerning the solubility of CO2 in H2O, only values have been found that are below 100 °C. Moreover, the values of D’ans-Lax and of Wiebe-Gaddy (1939) are not compatible. Therefore, I do without a diagram to present the data. One example is as follows (all data after Wiebe-Gaddy). At T=100 °C and P=200 atm, 25.7 cm3 CO2 is dissolved in 1 kg water, whereas at 18 °C

and 25 atm, only 19.51 cm3 CO2 is dissolved. We are dealing with a gas bubble resulting from a homogenous solution because of cooling. This solution, however, does not obey the laws derived for pure water or for dilute salt solutions. One objection could be that the above-mentioned pressure drops do not occur because the system is enclosed within a tight container, the walls of which are virtually rigid and impermeable. However, during cooling of pure water, a large drop in pressure can occur as depicted in Figs. 3 and 4. The hypothetical inclusion, mentioned above, could have been developed, for example, at T=125 °C and P=500 atm. If pure water is enclosed at T=100 °C, the inclusion would suffer a pressure of 25 atm. In cases of CO2-bearing inclusions, the numbers are somewhat different, but are similar according to size. However, compared with pure water, the filling temperature determined could deviate even more from the formation temperature because of the increased pressure impact. Thus, if all inclusions, or inclusions of a growth zone of a fluorite crystal (Twenhofel 1947) fill simultaneously, it is not justified to speak about “Sorby” inclusions. Inclusions with dissolved gas are also possible. The only quantitative data on CO2 content of aqueous inclusions, known by myself, are from Königsberger and Müller (1906). They found 40–50 cm3 CO2 related to 1 g H2O. The closing temperature ranged from 200 to 230 °C. At 250 °C, the inclusions decrepitated. According to the available data, 40 cm3 CO2 is dissolved in 1 g H20. Thus, it is possible that 40–50 cm3 CO2 is enclosed at high pressures at T>220 °C. Moreover, because of water cooling to room temperature, the pressure increase was strong enough to produce a gas bubble (Fig. 4, left area). This view is supported by the fact that the inclusions decrepitated at T=250 °C. At this temperature, the fluids were affected by a strong pressure increase because of the increase in temperature. Higher amounts of CO2 may occur within inclusions that contain two different fluids. Solubility or miscibility of CO2 in water is possible only to a relatively low degree. General considerations on such systems have been described by Nacken (1921). However, experimental data, which would apply to such types of inclusions, are lacking. In such a system one could overlook the conditions under which homogeneous gas solutions and inhomogeneous mixtures of gas and solutions are entrapped. The inclusion of gas bubbles besides the solution is probably possible in nature. It should also be possible to simulate it experimentally. In cases of cultivated crystals, e.g., sodium chlorate, fluid inclusions with air bubbles are frequent. The filling temperature of the inclusions (formed at 20 °C) is a function of the size of the enclosed air bubble and ranges from 55 to 135 °C. I mentioned this topic in 1950 (Correns 1950) during the meeting of the “Deutsche Mineralogische Gesellschaft” in Göttingen. Solutions are frequently supersaturated with dissolved gas, in the case of NaClO3 with air. The face of a growing crystal may act as a germ and supersaturation will disappear. It is difficult to produce solutions that are

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Fig. 6 T–vol diagram of water for the relation bubble volume/bulk volume in percent (up to 35%)

Fig. 7 Drawing of Brewster (1826) to explain how the refractive index can be determined by using the total reflection

free from gas. Inclusions of such solutions do not show bubbles at the formation temperature. How is it possible to distinguish between inclusions of foreign gas and those that have developed according to Sorby’s view? Incorporated gases are particularly possible where bubbles disappear at different temperatures in one and the same crystal. A reliable, distinctive factor considered so far is characterized as follows. Inclusions with salt solutions or with pure water can be used to calculate the filling temperature from the volume of both the entire inclusion and the bubble. Inclusions with foreign gas, on the other hand, obey other laws that have not been derived as yet. The calculation can be avoided by using the diagram of Fig. 6. The volume of the bubble is depicted along the abscissa as percent of the entire volume of the inclusion. The theoretical closing temperature is shown on the ordinate. Such a diagram can be produced at any extension, taking into account the specific volume of water (e.g., D’ans-Lax 1943, p. 1064). At temperatures below 100 °C, the closing line, which is analogous to the two-phase line of Fig. 3, is not much different for salt solutions. Thus, wherever possible, one should determine the volume of both the bubble and the entire inclusion besides the temperature at which the bubble disappears. By such observations Sorby inclusions can be distinguished from other inclusions. One could guess that the shape of the inclusions yields information about their origin. It seems likely that irregularly shaped or circular inclusions reflect gas bubbles, whereas regularly shaped inclusions, which virtually can be treated as negative crystals, result from homogeneous fluids. Unfortunately this assumption is not correct. The inclusions of gas bubbles in NaClO3 show both very regular and irregular shapes. According to our knowledge, it is highly probable that the origin of hydrothermal, pneumatolytic, and many magmatic formations are markedly controlled by gas phases. We should expect that gas is involved either in solution or as a bubble; Sorby inclusions occur less frequent. Information about the content of the inclusion can be obtained by comparing the filling temperature with the bub-

ble volume. Although, even in recent times, inclusions are frequently applied as geothermometers, such types of observations are largely lacking. What about the assumption that water, salt solution, and CO2 are the only filling materials? Since Davy (1822), water and salt have been detected, analogous to the observations by Sorby. Vogelsang and Geisler (1869) determined CO2 besides H2O by using spectroscopy. In view of the means available at that time, this was not completely possible. Pfaff (1871) detected water and NaCl chemically by using a self-made apparatus. In smoky quartz from Brancheville, Connecticut, Wright (1881) detected 98.33 CO2, 1.67 N, and traces of H2S, SO2, NH3, and F; Cl was questionable. As has been mentioned above, Königsberger and Müller (1906) carried out a quantitative analysis of inclusions of quartz from Bächistock (at the southeastern margin of the Aare massif). Apart from Cl, SO4, and locked carbonic acid, they found 9.5 wt% free CO2. The cations were Na, K, Li, and Ca. Newhouse (1932) presented a review paper of the older literature and on the significant investigations carried out by himself. It is important to note that the investigated ores, galena, and sphalerite, contain only Na and Cl, whereas K, SO4, and H2S are lacking. Moreover, he was not able to detect locked carbonic acid. There was no possibility to prove the presence of free carbonic acid. Faber (1941) published results of extended studies on fluids in volcanic rocks. However, the content of CO2 and CO3 was not addressed. Based on these few incomplete investigations, we can estimate the salt content in aqueous solution to be 10–15%. The large uncertainty of such an estimate is obvious by the fact that small cubic crystals may be present within the inclusions. Even these inclusions have been applied as thermometers. Given that cubic crystals consist of NaCl, and the saturated solution of NaCl in water was entrapped, Lindgren and Whitehead (1914) calculated a formation temperature of more than 500 °C. This, of course, is a minimum temperature because the solution had not been saturated. It was shown by Bowen (1928) that the formation temperature could drop to 210 °C if the enclosed cubes consisted of KCl instead of NaCl. In cases where the composition of the solutions and crystals can be

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determined with low uncertainty, it is possible to calculate only a minimum temperature because the composition of the original solution – if saturated or to what degree it is subsaturated – is not known exactly. Moreover, the pressure at the formation site should also be considered. If the formation temperature of such enriched solutions has to be determined by observing the moment when the bubble disappears, the volume change because of crystallization and dissolution, as far as is known, must be considered. Apart from aqueous solutions, hydrocarbon has also been found in inclusions of quartz (Reese 1898; Bastin 1931) and fluorite (Grogan and Shrode 1952). Also, fluid CO2 has not been unchallenged. von Nordenskjöld (1886), for example, assumed the fluids in Brazilian topaz to consist of hydrocarbon. Brewster considered such possibilities as well. Brewster, in 1826, suggested a relatively simple tool for determining the composition of fluids in inclusions. The refraction index can be determined by means of total reflection, given that a plane boundary of the inclusion is available (Fig. 7). It is surprising that this likely method was only rediscovered recently by Stegmüller (1952) after a time span of 126 years, although Zirkel, for example, had addressed this method in his textbook and the refraction indices of Brewster are listed in Rosenbusch–Wülfing. Even more amazing are the results of Brewster. When studying inclusions that contained two fluids, he found that the more dense of the two had a refractive index below that of water, i.e., 1.2946. The less dense fluid had a refractive index of 1.2106 in topaz and 1.1311 in a Siberian amethyst. In fluorite of Weardale, Stegmüller (1952) determined n=1.3501, which obviously reflects a salt solution. Within another type, he found n=1.049, which is typical for a gas. When proving this method by applying it to NaClO3 crystals and leach brine, we found the universal stage to be appropriate for determining the refractive index correct to three decimal places. We are trying to investigate the inclusions with two fluids as well. If inclusions are used to calculate the formation temperature, the composition of the inclusions should be determined. Altogether, it seems to be very important to study the composition of the inclusions. Only in such cases where the composition of the inclusions is known, including the easily volatilized components, is it possible to draw conclusions about the formation conditions. Based on the few existing data, it seems premature to derive general rules concerning, for example, the igneous origin of granite as has been tried by Deicha (1952). Much more work needs to be done concerning this topic. It needs to be further considered if the inclusions are a primary type, which developed during crystal growth, or of secondary type, which invaded a pre-existing crystal. This question is important when using the inclusions as geothermometers and as geochemical indicators. Moreover, it is possible that primary inclusions may have been subsequently altered. In his textbook mentioned above, Vogelsang (1867) supposed that inclusions had not been completely filled by secondary injection. Julien (1879) showed that fluid inclusions were restricted to fractures of fibrolite gneiss from New-Rochelle (New York). The

planes with inclusions were parallel to those planes along which the fibrolite needles are broken. Lämmlein (1929) focused on secondary fluid inclusions of minerals and considered the previous workers mentioned above as well as further ones. He was also able to produce types of secondary fluid inclusions that caused fractures in halite, saltpeter, and alum, and filled them with solution and water, where necessary, to seal the fractures. In these cases, visible fractures are not absolutely required. How can we distinguish primary and secondary inclusions? Grogan and Shrode (1952) suggested the use of the term “subsequent” instead of “secondary”. However, the term secondary is so common in the literature that new terminology would led to confusion. It is common sense that bands of inclusions that cut through several grains are of secondary origin. If inclusions are restricted to planes that cross each other, again a secondary origin is likely. However, this does not mean that inclusions of non-crossing planes are of a primary type. In this context one should consider the observations of von Engelhardt (1944). In a porphyry quartz of Stolberg, Harz, he measured the orientation of 131 bands of bubbles with respect to the c axis of the quartz. Although the planes slightly bend from their orientation in relation to the c axis it is obvious that fluid entrapment occurred preferentially along the rhombohedral and prism planes. As the planes bend, they should result in fracturing. However, Engelhardt could demonstrate that mechanically induced fractures of the Stolberg quartz crystals were not restricted to the prism planes. Either the bubble bands reflect the anisotropy of high quartz, or the fractures developed during the change from high to low quartz, as has been proposed by Lämmlein (1929). A lack of a preferred arrangement of the inclusions along a visible or assumed fracture is not a safe indication for the presence of primary inclusions. By using alum, G. Friedel (1926) could demonstrate that fluid inclusions may be entrapped in crystals of a bore hole that was flushed with water. Drescher-Kaden (1948) describes the formation of inclusions with bubbles caused by the impact of water on a halite crystal. These features may result from very fine fissures. However, the inclusions could also invade the crystal along lattice defect boundaries, particularly in cases of a coarse mosaic structure. Hollow spaces, on the other hand, can also develop by reactions in intact crystals, as has been experimentally demonstrated by Mollwo (1941). The effect of bromine vapor on a crystal of potassium bromide has been studied. The crystal included some KNO3 and KNO2. At 690 °C, the following reaction occurred: 2KNO2 + Br = KBr + KNO3 + NO. NO gas was present in cubic hollows with a pressure of some atmospheres. Along fractures or lattice defect boundaries, gas or fluid could either escape or could be added to existing inclusions. Literature on these topics has been provided by Kennedy (1950). He describes the unpublished research of Grunig. It could be shown that the bubble volume of inclusions of fluorite was reduced after treating it with water under pressure. It is important to distinguish primary and secondary inclusions because of the fallacy in determining the tem-

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perature and chemical environment during mineral growth. Secondary inclusions further allow us to reconstruct parts of the history of a crystal. As has been shown by Tuttle (1949), the presence and attitude of secondary inclusions can also be used by structural geologists to answer questions in tectonics. Grübelin (1948) drew attention to the importance of inclusions to discern jewels, particularly artificial types. The previous discussion has shown the uncertainties when using gas bubbles as geothermometers. If the bubble volume is small and the inclusion is of the Sorby type, quite safe results can be achieved by using optical methods. In this case, the application of the decrepitation method is not recommended. This method has the advantage that opaque minerals can be investigated as well. However, there is also a large disadvantage. In cases where only one type of fluid is present, the chemistry of the content of the inclusion could perhaps be determined analytically. However, the type of degree of filling is not known, and it is not possible to distinguish primary from secondary inclusions, or even from solid inclusions that also may cause explosions. Acknowledgements Thanks to Privatdozent Dr K. Jasmund for drawing Fig. 2 and for carrying out the calculations for Figs. 3, 4 and 5.

References Bailey SW (1949) Liquid inclusions in granite thermometry. J Geol 57:305 Bastin ES (1931) The fluorspar deposits of Hardin and Pope Counties Illinois. Illinois State Geol Surv Bull 58:64 Bowen NL (1928) Geologic thermometry in Fairbanks. Laboratory investigation of ores, ch X, Geophys Lab Pap no 671, Washington, DC, pp 172–199 Brewster D (1823) On the existence of two new fluids in the cavities of minerals, which are immiscible, and posses remarkable physical properties. Trans R Soc Edinb 10:1 Brewster D (1826) On the refractive power of the two new fluids in minerals, with additional observations on the nature and properties of these substances. Trans R Soc Edinb 10:407 Claudii C (1824) Opera omnia recensuit NL Artaud, vol II, part 1. Paris Correns CW (1950) Wie weit können FIüssigkeitseinschlüsse mit Gasblasen in Kristallen als geologische Thermorneter dienen? Nachr Akad Wiss Göttingen, Math-Phys Klasse, Math-PhysChem Abt D’ans-Lax (1943) Taschenbuch für Chemiker und Physiker. Springer, Berlin Heidelberg New York Davy H (1822) Zitiert nach Zirkel. Deicha GA (1952) Flüssige Einschlüsse im Granit und seiner Ganggefolgschaft und deren Bedeutung. N Jahrb Miner Monatsh 5:145–154 Drescher-Kaden FK (1948) Die Feldspat–Quarz–Reaktionsgefüge der Granite und Gneise. Springer, Berlin Heidelberg New York Faber H (1941) On the salt-solutions in microscopic cavities in granites. Danmarks Geologiske Undersøgelse II. Raekke no 67 Friedel G (1926) Le ons de cristallographie. Paris Grogan RM, Shrode RS (1952) Formation temperatures of southern Illinois bedded fluorite as determined from fluid inclusions. Am Mineral 37:555 Grübelin CG (1948) Die diagnostische Bedeutung der Einschlüsse in Edelsteinen. Schweiz. Mineral Petrol Mitt 28:1 Holden EF (1924) The cause of color in rose quartz. Am Mineral 9(75–88):101–108

Ingerson E (1947) Liquid inclusions in geologic thermometry. Am Mineral 32:375 Johnsen A (1919) Mineralogie im Dienste der Geologie. Die Naturwissenschaften 7:665–670, 690–694 Johnsen A (1920) Über die Paragenese von α-Quarz und Kohlensäure. Sitzungsber Bayr Akad Wiss, Math-Phys Klasse, p 321 Julien (1879) Zitiert nach Zirkel Kennedy GC (1950) “Pneumatolysis” and the liquid inclusion method of geologic thermometry. Econ Geol 45:532 Königsberger J, Müller WJ (1906) Über die Flüssigkeitseinschlüsse im Quarz Apiner Mineralklüfte. Zentralbl Mineral Usw, pp 72–77 Lämmlein G (1929) Sekundäre Flüssigkeitseinschlüsse in Mineralien. Z Krist 71:237–256 Lindgren W, Whitehead WL (1914) A deposit of Jamesonit near Zimapan, Mexico. Econ Geol 9:435–462 Mollwo E (1941) Über die Ausscheidung von Gasen in Alkalihalogenidkristallen. Nachr Akad Wiss Göttingen, Math-Phys Klasse, p 51 Nacken R (1921) Welche Folgerungen ergeben sich aus dem Auftreten von Flüssigkeitseinschlüssen in Mineralien? Zentralbl Mineral Usw, pp 12–20, 35–43 Newhouse WL (1932) The composition of vein solutions as shown by liquid inclusions in minerals. Econ Geol 27:419 Pfaff FR (1871) Über den Gehalt der Gesteine an mechanisch eingeschlossenem Wasser und Kochsalz. Annalen Physik Chemie 5, Reihe 23(8):610 Reese CL (1898) Petroleum inclusions in quartz crystals. J Am Chem Soc 20:795–797 Rosenbusch H, Wülfllng EA (1921) Mikroskopische Physiographie der petrographisch wichtigen Mineralien, vol 1. HäIfte: Untersuchungssmethoden. Schweizerbartsche Verlagsbuchhandlung, Stuttgart Scharizer R (1920) Zur Frage der Bildung der Einschlüsse von flüssigem Kohlendioxyd in Mineralien. Zentralbl Mineral Usw, pp 143–148 Scott HS (1948) The decrepitation method applied to minerals with fluid inclusions. Econ Geol 43:637 Seifert H (1930) Geologische thermometer. Fortschr Mineral 14:167 Simmler RT (1858) Zitiert nach Zirkel Smith FG (1953) Review of physico-chemical data on the state of supercritical fluids. Econ Geol 48:14 Sorby HCL (1858) On the microscopical structure of crystals indicating the origin of minerals and rocks. Q J Geol Soc Lond 14:453–500 Stegmüller L (1952) Bestimmung der optischen Natur durchsichtiger Einschlußkörper, entwickelt am Fluorit. Heidelb Beitr Mineral Petrol 3:186–192 Stephenson THE (1952) Sources of error in the decrepitation method of study. Econ Geol 47:743 Tuttle OF (1949) Structural petrology of planes of liquid inclusions. J Geol 57:331 Twenhofel WS (1947) The temperature of crystallisation of a fluoride crystal from Luna County, New Mexico. Econ Geol 42:78 Vogelsang H (1867) Philosophie der geologie. Bonn Vogelsang H, Geissler H (1869) Über die Natur der Flüssigkeitseinschlüsse in gewissen Mineralien. Annalen Physik Chemie 5, Reihe 17:56 von Engelhardt W (1944) Die Anisotropie der Teilbarkeit des Quarzes. Nachr Akad Wiss Göttingen, Math-Phys Klasse, p 43 von Nordenskiöld N (1886) Vorläufige Mitteilungen über erneuerte Untersuchungen der Flüssigkeitseinschlüsse im brasilianischen Topas. N Jahrb Mineral 1:242 Wiebe R, Gaddy L (1939) The solubility of CO2 in water at 50, 75 and 100°, at pressures to 700 atmospheres. J Am Chem Soc 61:315–318 Wright AW (1881) The gaseous substances contained in the smoky quartz of Brancheville, Conn. Am J Sci 21(123):209 Zirkel F (1893) Lehrbuch der Petrographie, vol I(2A). Leipzig

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E. Wiechert

Investigating the Earth’s crust with the help of explosions (belongs to Research on explosions, supported by the Notgemeinschaft der deutschen Wissenschaft) Geol Rundsch 17:339–346 Translation received: 14 February 2002 © Springer-Verlag 2002

Seismology has succeeded to gain information about the nature of the deep Earth interior – the Earth has been made transparent. One could imagine that, by using the same methods, we could easily define the nature of the Earth’s crust [under our feet]. Two difficulties are encountered. First, the Earth’s crust is more complex than the deep interior. For the Earth as a whole, seismology has encountered primarily two boundaries, one in about 1,200 km, the other in about 2,900 km depth, and these divide the Earth into three parts: the rock mantle [crust and outer mantle], an intermediate layer [inner mantle], and the metal core. Much more complicated is the outermost Earth crust which surrounds the Earth like a relatively thin skin of about 100 to 200 m thickness. Already by their external [appearance], land and sea, mountains and lowlands strongly indicate their non-uniform composition, and geological and geophysical exposures support this interpretation. The second factor which creates problems for seismic investigations of the Earth’s crust is that natural earthquakes are relatively very rare. It is therefore impossible to operate sufficiently large numbers of observatories and to track enough earthquakes to define the details of the nature of the Earth’s crust. I recognised these difficulties already at the beginning of my seismic work. In 1906, therefore, I constructed a seismometer with a magnification of 50,000 but was very disappointed when using it to observe cannon shots from the artillery range in Meppen and on the island of Helgoland – I had to re-

The oral presentation which was planned for the natural sciences Naturforscher Meeting in Düsseldorf in September 1926 was not presented in one talk but was divided into two parts, one for the geophysics division, one for the geology division. Details were presented during discussion. Translated by Ernst Flüh E. Flüh (✉) Forschungszentrum GEOMAR, Wischhofstr. 1–3, 24148 Kiel, Germany e-mail: [email protected]

cognise that the means at my disposal were insufficient for investigating the Earth’s crust. Later, one of my students, L. Mintrop, who joined me from the mining community and who used the highly sensitive instruments during his Ph.D. study, had the glorious idea that seismic methods could – with suitable installation and orientation – serve to investigate the upper layers of the Earth’s crust, this being important for practical mining [purposes]. It is known that Dr. Mintrop has been very successful. Especially it became possible to determine the extent and depth of salt bodies, to which oil occurrences are often associated. The success of Mintrop and my own considerations led me to return to the questions of “small seismology” or, as one could also call it, “experimental seismology”. I now knew that it would be necessary to use a much higher sensitivity of instruments than I had previously thought. Based on experience gained in the meantime, however, this did not deter me any longer. The wonderful successes which had been gained through co-operation between geophysics and geology, especially with gravity as the leading field, provided new stimulus. Scientific considerations were supplemented by the thought that this work could be valuable for economic aspects. I had to expect that time-consuming and cost-intensive work would be necessary, but I found kind support from the “Notgemeinschaft of German Science” and its leader, State Minister Dr. F. Schmidt-Ott. We succeeded to install in Göttingen a seismometer with an amplification of 2 million which, despite the ambient ground noise always present at such amplification, proved to work excellently. Less pleasing is that the highly frequented Herzberger country road is located 100 m from the [so-called] earthquake house, and each passing vehicle generates such strong disturbance that observation with a highly sensitive seismometer is impossible. When we are just about to perform an observation, it is generally possible to delay horse-drawn wagons by means of kind words or money. Cars are worse, however, because these usually do not care about our needs. We then have to rely on the help of the police,

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Fig. 1 Seismometer graphs, recorded in Göttingen. Travel time graph of longitudinal waves in the vicinity of Göttingen. The seismometer graphs are reproduced at 1/8 of their original size. Graph – location of explosion – date – charge size – distance – instrument – period – amplification cap of 5 3/4 s

who will block the road for a short time during particularly important explosions. Luckily, the local authorities have now decided to build a new road which will take over the car traffic from the highly inconvenient Herzberger Landstraße but, unfortunately, the new road will be completed only in two years and, until then, much has to be accomplished – we should not wait! A single observatory in Göttingen is obviously not enough. Therefore, portable field seismometers were built, too. For these, an amplification of 0.8 million was achieved. For observations with our highly sensitive seismometer, quarry blasts alone are relevant for what I wish to say today. We are very grateful to the quarry administrations for having so obligingly authorised and supported our observational collaboration. For a start, we were supported by the Hermann Wegener company (Hannover), which owns a number of quarries in the immediate and wider vicinity of Göttingen; then, the companies Basaltwerk Sodensberg bei Hammelburg, Hartbasaltwerk am Billstein, Kieswerke der Provinz Schleswig-Holstein, Abteilung Basaltwerk Dransfeld, Bartels & Avenarius, Gudensberg, and Kasseler Basaltindustrie. To begin with, may I ask [you] to look at the two curves I and II of the figure. These are illustrations of two recordings made in Göttingen, of one and the same explosion but with different instruments. The explosion was at a distance of 112.4 km (Seiferts in the Rhön). One

instrument had a strong amplification and short [instrument-specific oscillation] period, the other a weaker amplification and longer [instrument-specific oscillation] period: 2-million-fold and 1/10 s versus 70,000-fold and 1.4 s. Arrivals of the longitudinal waves in the beginning and of the transversal waves towards the end are clearly visible in both records but the instrument with the stronger amplification is superior because it shows much more detail. Both the longitudinal and the traversal waves are separated into groups, a few events stand out, and this record also shows a clear precursor before the first strong arrival. The longer [instrument-specific oscillation] period of the second instrument causes that ambient noise, which is always present, is more noticeable, and that the longer earthquake periods suppress the shorter ones. There where the 2-million seismometer shows the precursor so nicely, only waves of ambient noise are to be seen. The comparison of the curves shows clearly that enhancing sensitivity by increasing the [instrument-specific oscillation] period is disadvantageous; we have no option but to attempt to increase sensitivity through an increase in amplification instead. One can see how well the 2-million amplification still works – thanks to this, the precursor is detected. I emphasise all this, because an outsider may feel that our “million-ambition” is exaggerated. This is not the case – it is needed indeed. Now I ask [you] to look at the travel time curve of the longitudinal waves which we have obtained so far (Fig. 1). Each circle indicates one recording, be it with the 2-million instrument in Göttingen or with a field instrument outside Göttingen. The illustration shows something which, I must admit, initially surprised me. The travel time curve is apparently straight from 16 km

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to more than 200 km. I do not wish to overemphasise the last observation point at a distance of 215 km, because it resulted from a rather small explosion (in Jüterbog, 250 kg) which was just about noticeable in Göttingen. So, it could be possible that there was an earlier arrival which could not be fully detected in the record any longer. However, the next shorter distance, 160.4 km, corresponds to a well-observed explosion of 3,500 kg (Morlesan near Bad Kissingen) recorded in Göttingen. Thus, the nearly straight course of the travel time curve is confirmed up to at least 160 km. What does this mean? According to general theory for ray propagation in the Earth’s crust, the tangent at each point along the travel time curve represents the velocity which a ray returning to the Earth’s surface at the corresponding distance had at its deepest point. It thus follows, from the linearity of the travel time curve (i.e. the near-identical directions of the tangents), that in the whole study area, from about the Main to the Harz and from Kassel to probably Jüterbog near Berlin, the earthquake waves recorded passed at depth through a layer which everywhere has roughly the same elastic properties. For this layer a travel velocity of 5.98 km/s was determined. How deep is this layer beneath the surface? I regret to say that there are as yet no observations which would allow a definite answer to this question. From observations near Göttingen I can only infer that here the depth is in any case not much greater than 2 km, and from other indications I suspect that it is not very much less. Curve III demonstrates how to proceed to determine depth. It shows the beginning of a recording in Göttingen, which belongs to an explosion at 16 km distance (“Hohen Hagen”, 900 kg explosion). One can recognise two clear arrivals of longitudinal waves in the beginning. The first arrival corresponds to one of the [observation] points in the figure of the travel time curve. These waves must therefore have penetrated to the uniform layer. The waves of the second arrival have travelled at reduced velocity in the layer above. If we had, in this case, additional observations between the location of the explosion and that of the observation site, such that the travel time curves for the arrivals could be specified from the epicentre onwards, we would be able to determine the depths of these layers. One could use an approach similar to that for depth determination from large-scale seismics in the Earth. Mr. H. Mothes, who will talk after me, will show that depth determinations are also possible by means of reflected waves. In the Alps he succeeded to measure the thickness of glacial ice with seismic instruments using explosions. It is well known that echosounding is an analogous method for [measuring] water depth. I have asked my colleague from geology at Göttingen University, Prof. H. Stille, for advice on how to interpret the uniform layer geologically. He believes that it is most probably the Variscan basement, which once was flattened and subsequently covered by sediment. Once we have more depth determinations, it will be possible to test this view, because the Variscan basement outcrops at

several locations. It will be the task of experimental seismics to determine the depth of the top basement by systematic depth soundings. From the linearity of the travel time curve, I inferred the regularity of a wave guiding layer – the region of observations. Those acquainted with large-scale seismics will perhaps have other ideas about this linearity. According to theory for earthquake waves, the travel time curve should be curved even for a uniform and regular horizontal layering, if the velocity of the waves changes with depth, for example, because of an increase in pressure and temperature. Indeed, seismics of the Earth show this for the rock mantle. Here the velocity nearly doubles from the upper to the lower boundary. Should not a corresponding change of velocity, and thus curvature of the travel time curve be assumed for the uniform layer? The answer is that we are not justified in inferring a noticeable curvature of the travel time curve by analogy. If we were to assume a similar behaviour for the uniform layer as the one [documented] for the rock mantle, an increase in velocity of about 1/10% per km depth would have to occur. The radius of the curvature of rays within the uniform layer would be about 1,000 km, and the rays would thus show very little curvature. For the travel time curve in our presentation, the curvature would be so small that the difference between a straight line and a curve would be 1/100 s, i.e. within the error margins of our observations. It follows, therefore, that a noticeable curvature of the travel time curve, caused by changes in the properties of the uniform layer with depth, can be expected only if the change in these properties was substantially greater (factor 10) than in the rock mantle. For completeness sake, it should be stressed that, strictly speaking, the simple theory of ray propagation cannot be applied here because, on account of the relatively large wavelength of the elastic vibrations, diffraction will certainly contribute in this case. Diffraction has proved to be highly significant also for the propagation of waves through the Earth. Nevertheless, what I have said regarding the travel time curve is essentially not influenced by this inaccuracy of the theory. I remind [you] of the small precursor tremor which is shown in the record of the 2-million seismometer for the explosion at Seiferts (curve I in figure). Such precursors appear also in the other recordings made to date over larger distances (exceeding 100 km). This suggests a layering of the Earth’s crust at deeper depths, which forces some earthquake waves to take deeper routes. This applies also to some of the later arrivals in the earthquake illustrations. The observations which I have at my disposal are still so limited that for the time being I do not wish to be more specific. The linear line shown by the travel time curve from 16 km onwards does not go through the origin for the co-ordinates distance and time but lies about 1 s late compared to the distance axis. This indicates that the uniform layer (the basement) is at some depth below surface. This leads to a remarkable conclusion. In largescale seismics, seismics of the Earth’s body and earth-

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quake waves, we talk about “direct waves” and “reflections”. Waves which travel from the epicentre to greater depths and then return to the Earth’s surface are reflected here, travel again to greater depths, return to the surface, and so on. Those waves which travel from the epicentre to the observatory without reaching the surface in between are called “direct waves”. The terms “first reflection”, “second reflection”, etc. indicate waves which have reached the surface between the epicentre and the station once, twice, etc., and are reflected there. Waves which have changed character during reflection (from longitudinal to transversal or vice versa) are called “converted waves”. The first reflection is seen often, the second less often, and the third only seldom, because each reflection causes disturbances. Reflections are to be expected for our experimental seismics, too, and indeed they are clearly visible for longitudinal as well as for transversal waves in the records. If we were to assume, for the explosion near Seiferts, a uniform nature of the Earth’s crust between the epicentre and the station (Seiferts and Göttingen [respectively]), we would expect (because of the above-mentioned delay of the travel time line) that, for the longitudinal waves, the reflections should follow the direct waves at 1, 2, etc. seconds. For the transversal waves, almost double the time delay would be expected. Looking at the record of the 2-million seismometer, for example, at the transversal waves at the end of curve I, a distinct subdivision into groups is evident, whereby we find two groups with the expected separation of 2 s. Therefore, it is reasonable to imply the [occurrence of] direct wave and first reflection in this case. Despite the strength of the first reflection, however, there is no indication whatsoever of a second reflection. Various explanations are possible [in this respect]. A geographic map showing the area between Seiferts and Göttingen indicates that the Werra River bed is situated precisely at the sites of the second

reflection (at 1/3 and 2/3 of the distance). Although the incision of the Werra River valley is not very large, relatively small disturbances of the land surface can affect the dispersal of seismic waves. Another possible explanation would be peculiarities in the structure of the Earth’s crust at the reflection sites. Additional investigations using experimental seismics could be informative [in this respect]. That is precisely why I brought up the matter, and I give even more freedom to thoughts – it seems to be a desirable and accessible goal of experimental seismics to explain each wiggle and wave of seismogrammes and to render these instrumental in unravelling the nature of the Earth’s crust. Ladies and gentlemen, I regret that I could contribute so little today. Over and over again, I had to acknowledge the meagreness of the observations, to leave unanswered obvious questions. I ask you to keep in mind that, despite all our efforts, we are still at the very beginning of the investigations. We are still fighting for the suitable design of instruments and methods. We gain the necessary information step by step only from our work itself. Consider how much manpower a single borehole of 1- or 2-km depth requires; remember the extraordinary profusion of single contributions upon which the noble edifice of geology rests! I consider my task for today as being fulfilled if my audience accepts that this is a promising method for research. In my imagination I foresee seismic exploration becoming a tool which will lead geology and geophysics to new and great successes. We as beginners have to be satisfied to carry out the troublesome but promising preparatory work.

Translator’ comments Square brackets [] indicate additions to the original text used to facilitate language flow and clarity.

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B. Gutenberg

The structure of the Earth’s crust in Europe Geol Rundsch 19:433–439

Translation received: 28 February 2002 © Springer-Verlag 2002

Similarly to the way light rays shining through a body give us information about its properties, in particular about material discontinuities, we can use recordings of elastic waves, which have been excited by earthquakes or artificial vibrations, to infer the properties of those parts of the Earth these waves have passed through. The farther the observation point is from the source of energy, the deeper the layers the waves have propagated through, disregarding here “surface waves”. For example, the recordings of small explosions at a distance of few tens to several hundreds of metres from the explosion point help to constrain the structure of the uppermost layers, which are of relevance to the mining industry. If, however, we wish to investigate the structure of the Earth’s crust between ~3 and 60 km depths, we need to use strong explosions or earthquakes and analyse recordings at distances of a few to several hundred kilometres. If the Earth were a homogeneous sphere, the waves would propagate with constant velocity on the chords earthquake focus – observation point, i.e. near the focus of an explosive source, the waves should arrive at the Earth’s surface according to the distance of the observation point, since for small distances chord and arc are equal. The next approximation, entirely sufficient for our purpose, is that the Earth is composed of several layers, in each of which the velocity is constant. In reality, it increases somewhat with depth, but the effect of this increase is smaller than the observational uncertainty, as has often been demonstrated. In the more general case of earthquakes, elastic waves emanate from the earthquake focus (H, Fig. 1), propagate along the dashed lines, and cause the large arrivals a in the earthquake diagram. Except in the immediate vicinity of the focus (effect of foTranslated by Frederik Tilmann F. Tilmann (✉) Forschungszentrum GEOMAR, Wischhofstr. 1–3, 24148 Kiel, Germany e-mail: [email protected]

cal depth), the arrivals must be on a straight line from which we can immediately read off the wave velocity in layer I. Other waves c (continuous line) penetrate layer II, are refracted according to the refraction law of opticsi and finally arrive at the surface. These arrivals c are approximately on a straight line, too, but they initially arrive later than a; because the velocity in layer II is higher, the increase in distance travelled for larger focal distances is overcompensated by the higher velocity in the deeper layer, if the increment in velocity is sufficiently large. For large distances, the arrival c can thus come before a. A similar explanation applies to a further layer boundary, which causes arrival b; b can arrive before c, if the change in velocity at the deeper layer boundary is particularly large. An analysis of the recordings at neighbouring stations can show how the different arrivals are related. – Three such arrivals, called P, P*, and P, can now be identified for earthquakes located in Europe. Figure 2 shows two recordings of the earthquake of 16 November 1911 (“Schwäbische Alm” – Swabia). In both cases a strong arrival annotated P can be identified, corresponding to arrival a in Fig. 1. Furthermore, it can be observed – that arrival P arrives earlier with respect to P for stations situated at greater distances from the earthquake focus. The recording in Göttingen also exhibits the P* arrival, corresponding to arrival c in Fig. 1. A detailed analysis, based on many records of this earthquake as well as those of another earthquake at the same location in July 1913, indicated that the focal depth of both earthquakes – is ~30 km, that the (longitudinal) wave P is propagating with a velocity of 5.5–5.6 km/s within the uppermost layer, that P* originates from a layer boundary near the focal depth, i.e. at around 30 km depth, and that there the compressional wave velocity increases to 6 1/4 km/s, whereas P has penetrated an additional layer boundary at ~40–50 km depth where the velocity increases from 6 1/4 to 8 km/s. Because of this large velocity difference, the wave designated by P arrives much earlier than the – direct wave P for large distances from the earthquake focus.

S141 Fig. 1 Schematic display of the travel paths of earthquake waves for the case of several layers. Above Appearance of recordings at various distances from earthquake focus H

Fig. 2 First part of recordings of the 16 November 1911 earthquake in southern Germany: a in Neuchâtel (225 km epicentral distance), b in Göttingen (365 km epicentral distance)

Almost the same results were obtained by V. Conrad for an earthquake in Tauern1. For the same distance, the time differences between the three arrivals are approximately the same as for the earthquake in southern Germany, which indicates that the focal depth and the layering in Tauern and surrounding areas at depths exceeding a few kilometres was about the same as that in southern Germany. It should be mentioned in passing that the ar– rivals P, P*, and P are generally recorded at the same time in Japan as in Germany, such that the focal depth is mostly around 30 km there, too, and layer boundaries are at 20–30 km and at 45 km depth. K. Suda observed different values only near the Pacific coast, leading him to conclude that the layer boundary was shallower there, and hence the layer thickness smaller. In Europe we can further consider A. Mohorovicˆić’s analysis of the Kulpatal (Kulpa Valley) earthquake, for which he, for the first time ever, could distinguish P and S waves and identify the layer boundary which he inferred to be at 57 km depth at the time. S. Mohorovicˆić obtained similar results, too. Finally, the investigations of A. de Quervain 1 Note added in proof: likewise for an earthquake near Vienna (presentation at the Naturforscherversammlung, Hamburg, 1928)

of earthquakes in the Alps have shown that the lower boundary is at a similar depth there as in the rest of Europe. There is still a lack of investigations of the intermediate boundaries. The P* waves were first identified by Gutenberg, and their interpretation was provided by V. Conrad and confirmed by H. Jeffreys, who determined even smaller layer thicknesses. Somewhat surprising was E. Wiechert’s observation that in the wider surroundings of Göttingen, at least in the regions Kassel-Main-Rhön-Jüterbog, seismic wave velocities are 5.9–6.0 km/s even in the upper layers, compared to 5.5 km/s in southern Germany. Furthermore, an explosion record (reproduced in this journal, vol. 17, p. 341) exhibits an arrival which can be interpreted only by assuming that the increase in velocity occurs at shallower depth in the aforementioned area near Göttingen than in southern Germany. Therefore, we have to conclude that there is a difference between the layering near Göttingen (and presumably in northern Germany) and in southern Europe. Because both regions, or materials with rigidity coefficientsii differing by 10%, are unlikely to blend into each other in a continuous manner, we can expect a transitionary zone with vertical dislocations or faults reaching large depths. Such a zone

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Fig. 3 Decrease in wave amplitudes for the 16 November 1911 earthquake in southern Germany. a P waves (propagation mainly – below 50 km depth), b P waves (propagation mainly at 30 km depth), c surface waves (propagation mainly in the uppermost 10 km). Hg Helgoland; Py Puy de Dome; Ma Marseille; Tr Triest; Je Jena; Gz Graz

can be recognised in the seismic data because near it waves are more strongly attenuated, i.e. the observed displacements should decrease strongly within the zone. As example (Fig. 3), we show the 1911 earthquake in southern Germany; the 1913 earthquake as well as the explosion in Oppau show a similar pattern. Figure 3a shows the amplitudes of P waves, which predominantly propagate below 45 km depth. No differences in propagation which exceed uncertainties (e.g. due to variable site conditions) can be identified between the various directions. A different pattern is apparent in Fig. 3b which – displays the amplitudes of P waves which have propagated predominantly above 30 km. Here we find – exactly as in the other two cases mentioned – a strong inward deflection of the contours in a zone which extends approximately between Karlsruhe and Frankfurt in eastwest direction, and then turns towards the south-east. Accordingly, this is the place where we have to look for the transition between the high velocity region in the north and the low velocity region in the south. Lastly, if we consider the amplitude maxima of the surface waves which propagate predominantly in the uppermost 5 km, we obtain a different pattern once again (Fig. 3c). These waves propagate most easily from the focus towards ENE and WSW, whereas they attenuate more strongly in the perpendicular direction. The directions observed here agree very well with those found by Kossmat for the strike of the Variscides. Summarising out results, we obtain the NS cross section through Europe shown very schematically in Fig. 4. The plane at ~60 km depth drawn in the figure is characterised by a sudden onset of near-constant seismic wave velocities (over a few kilometres depth) or even slightly decreasing velocities. Possibly, this is the boundary between amorphous and crystalline material. It should further be pointed out that all focal depth determinations

Fig. 4 Schematic cross section through the crust in central Europe, approximately along 10°E. H earthquake foci. Labels are the velocities of longitudinal waves

have since resulted in a depth of about 30 km, suggesting that the stresses present in the Earth’s crust are released particularly easily in layer boundaries located approximately within this plane, where ruptures occur more easily than within the blocksiii. The earthquake hazard is particularly large in places where vertical dislocations (faults) cut through this layer boundary in an area of relatively high stress. A rupture can initiate within the layer boundary at 30 km depth in such a region, propagate in various directions, but again particularly easily in planes affected by dislocationsiv, and eventually reach the Earth’s surface, causing visible changes there. Finally, there is a compilation of seismic wave velocities V at various depths, together with the elastic moduli Ev which result from a density of 2.7 at the surface and 2.9 at depth, assuming a Poisson ratio of 0.28, as is commonly found in the Earth’s crust; some corresponding laboratory measurements of E are also shown. However, it cannot be excluded, as pointed out by R.A. Daly, that the laboratory values obtained at high pressure are too

S143 Southern Germany, uppermost layer Northern Germany, uppermost layer Europe, intermediate layer Europe, lower layer

V=5.5 km/s

E=ca. 6 1/2×1011 CGS

References

V=6.0 km/s

E=ca. 7 3/4×1011

V=6.3 km/s

E=ca. 9×1011

V=8.0 km/s

E=ca. 15×1011

Conrad V (1925) Laufzeitkurven der Tauernbebens vom 28. Nov. 1923. Mitt Erdbebenkomm, Wien, N F 59 Daly RA (1928) Am J Sci 15:108; Gerlands Beitr Geophys 19:194 Gutenberg B(1927) Der Aufbau der Erdkruste. Z Geophys 3:371 Gutenberg B (1927) Die Herdtiefe der süddeutschen Beben 1911 und 1913. Gerlands Beitr Geophys 18:379 Gutenberg B(1915) Die mitteleuropäischen Beben vom 16. Nov. 1911 und 20. Juli 1913. Veröff Zentralbüro der Int Seismol Assoc, Straßburg Inglada V (1927) Über die Berechnung der Herdtiefe. Z Geophys 3:317 Jeffreys H (1927) On near earthquakes. Gerlands Beitr Geophys 17:417 Mohorovicic A Das Beben vom 8. Okt. 1909. Jahrb Meteorol Observat Zagreb 9, T. IV, S. 1. Mohorovicic S (1914) Die reduzierte Laufzeitkurve. Gerlands Beitr Geophys 13:217 Wiechert E (1926) Untersuchung der Erdrinde mit Hilfe von Sprengungen. Geol. Rundsch 17:339

Observed in the laboratory: Washington granite 2000 atm. pressure Westerly granite 2000 atm. pressure Stone-Mt. granite 2000 atm. pressure Feldspar (oligoclase) 2000 atm. pressure Basalt 2000 atm. pressure Basalt 10000 atm. pressure Augite 2000 atm. pressure Dunite 2000 atm. pressure Dunite 10000 atm. pressure

E=6.0×1011 E=6.9×1011 E=7.0×1011 E=9.1×1011 E=5.7×1011 E=8.1×1011 E=13.3×1011 E=16.5×1011 E=17.5×1011

small. Daly assumed that the uppermost layer consists of granite with α-quartz, the following one of grantite with β-quartz, and the lowermost one of material similar to flood basaltsvi, but others suggested peridotite or dunitelike rocks beneath 50 km depth. 2000 atm. pressure corresponds to ~7 km depth, 10000 atm. to ~36 km. The observed values often differ markedly between different pieces of the same rock type.

Translator’s comments i ii iii

iv

v

i.e. Snell’s law. Also known as shear modulus (the German word is “Righeitskoeffizient”) The German word is “Scholle”, which is not really equivalent to “block”. However, dictionary translations of “Scholle” are even less suitable. From the context is seems fairly clear that Gutenberg is simply referring to fault planes but the translation is close to the German wording. Probably the elastic modulus referred to is Young’s modulus. To convert the units in the table into SI units, use the relation 1011 CGS10 GPa

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