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GEOLOGICAL SOCIETY M E M O I R No. 2 Falcon & K e n t : Geological results of petroleum exploration in Britain 1945-1957
Corrigenda P a g e 1 O, F i g . 4. The Purbeck Cinder Bed at Brightling No. 1 borehole should be shown as 5 feet thick at depth 100 to 105 feet. P l a t e V.
Depth given at Kelham borehole should read --1470 feet.
T a b l e II. Plungar No. 1 borehole : Top of Millstone Grit should read 2864 feet, as in Fig. 23, p. 41. Ruskington No. 1 borehole : Delete the figure 3277 quoted for top of Millstone Grit; insert 3277 in Carboniferous Limestone column. Widmerpool No. 1 borehole : Figure for top of Lower Carboniferous should read 4550 feet, as in Fig. 9, p. 19. T a b l e I I I . Kirkleatham No. 1 and No. 2 boreholes should be shown as reaching Millstone Grit and Carboniferous Limestone (Yoredale Series) respectively beneath the Permian, as in Fig. 15. Kirkleatham No. 1 borehole : Delete ? 3154 in Coal Measures column ; insert ? 3154 in Millstone Grit column. Kirkleatham No. 2 borehole : Delete ? 2897 in Coal Measures column; insert ? 2897 in Carboniferous Limestone column. In last column (' completed in '), for ' Carboniferous ' read ' Carboniferous Limestone (Yoredale Series) '
GEOLOGICAL SOCIETY OF L O N D O N MEMOIR No. 2
GEOLOGICAL RESULTS OF PETROLEUM EXPLORATION IN BRITAIN I 9 4 5 - I 9 5 7
BY N O R M A N LESLIE FALCON, M.A.F.1K.S. (CHIEF GEOLOGIST, THE BRITISH PETROLEUM COMPANY LIMITED)
AND
PERCY E D W A R D KENT,
D.Sc.,
Ph.D.
(GEOLOGICAL ADVISER, BP EXPLORATXON [CANADA])
LONDON 4- AUGUST, I960
LIST PLATE
I, FIG. 1. 2.
II.
OF
PLATES
H y p o t h e t i c a l section through Kingsclere a n d Faringdon borings.
(By R. G. W. BRU~STRO~)
I n t e r p r e t a t i v e section t h r o u g h Fordon No. 1. Based on seismic reflection a n d drilling results, taking into account the probability of faulting of the t y p e exposed in the H o w a r d i a n Hills Jurassic outcrop. Borehole sections in West Yorkshire.
(By A. P. TERRIS)
III.
Borehole sections in the Carboniferous rocks of Scotland.
IV.
Type column of the Upper Carboniferous succession in the E a k r i n g area, showing lithological marker beds. (By M. W. STI~O~C)
V.
Structure contour m a p of the Top H a r d (Barnsley) Seam in the Nottinghamshire a n d Derbyshire Coalfield. Scale : 1 inch to 2 miles.
LIST OF TABLES D a t a from exploration wells, 1945-1957, m - TABLE I. II.
Southern E n g l a n d a n d the South Midlands The E a s t Midlands
III.
E a s t a n d West Yorkshire
IV.
Lancashire and t h e West Midlands
V.
Scotland
LIST
OF
FIGURES
IN
THE
TEXT
Page Fig. 1. 2.
General m a p of areas explored to t h e end of 1957
6
A r r e t o n : g r a v i t y residuals a n d reflection contours .
8
A s h d o w n : seismic i n t e r p r e t a t i o n of s t r u c t u r e after drilling. sea,level
Depths shown are of Great Oolite below 9
4.
Mesozoic borehole sections in s o u t h e r n E n g l a n d
10
5.
F a r i n g d o n area : g r a v i t y residuals a n d seismic refraction s t r u c t u r e
14
6.
Stratigraphical columns of F a r i n g d o n , Kingsclere a n d Willesden borings
15
7.
E a s t Midlands borehole localities, showing variation in t h e Millstone Grit sands
17
8.
Limits of t h e W i d m e r p o o l Lower Carboniferous gulf
18
9,
Stratigraphical columns in t he W i d m e r p o o l gulf, South N o t t i n g h a m s h i r e
.
.
.
.
19
10.
Millstone Grit correlation b e t w e e n t h e Huddersfleld area a n d boreholes a t Trumfleet, Belton a n d Corringham
21
11.
Igneous rock distribution in the E a s t Midlands Carboniferous rocks .
22
12.
Location m a p of igneous rocks in K e l h a m Hills oilfleld
23
13.
A. Sections t h r o u g h c o n t e m p o r a n e o u s igneous lenses, K e l h a m Hills oilfield, showing non-displacive relationships. B. Sections t h r o u g h intrusive igneous lenses, showing displacement of Coal Measures a n d P e r m i a n rocks .
24
14. 15.
H y p o t h e t i c a l m a p of t h e s u b - P e r m i a n floor in E a s t Yorkshire .
27 28
16.
Mesozoic sections in E a s t Yorkshire
29
17.
Permo-Triassic sections in E a s t Yorkshire
30
18.
Borehole sections in t h e F o r m b y area
33
19.
Comparative sections t h r o u g h t h e F o r m b y a n d Clitheroe areas
35
20.
Geological m a p of t h e F o r m b y area, showing post-Triassic faults. (By R. G. W. BRVNSTROM)
36
21.
S t r u c t u r a l section t h r o u g h U p h o l l a n d No. 1 boring
37
22.
Borehole sections in t h e Carboniferous rocks of Lancashire. (By A. P. TERRIS)
38
23.
Millstone Grit succession at P l u n g a r
41
24.
S t ru c t ure contour m a p of t h e P l u n g a r oilfield .
42
25.
S t ru c t ure contour maps of the E g m a n t o n oilfield, showing contrasting s t r u c t u r e at different horizons
44
26.
Cross-section of t h e E g m a n t o n oflfield. (By K. H. ROBERTS)
45
F o r d o n : seismic reflection contours on P e r m i a n limestone, a n d shallow borehole locations .
GEOLOGICAL RESULTS OF PETROLEUM EXPLORATION IN BRITAIN 1945-1957 CONTENTS Page
I.
INTRODUCTION
5
.
i i . GE~ER.~ EX~01CATION (a) Southern. England (i) Dorset and the" Hampshire basra (ii) The Isle of Wight (Arreton) (iii) The Wealden area (b) South Midlands 9 . (c) East Midlands . (i) Outline of operations (ii) Stratigraphy . (iii) Igneous rocks in the" Upper Carboniferous (d) East Yorkshire . (i) Fordon and Lockton (ii) Eskdale, Robin Hood's Bay a f l ( i Redear (e) West Yorkshire (f) Lancashire (i) Formby area . (ii) Upholland (g) The Midland Valley of Scotland
III.
ESTABLISHED
(a) General (b) The Plungar oilfield, Leicestershire (c) The Egmanton oilfield
7 7 7 8 9 14 16 16 20 23 26 26 28 32 34 34 37 39
OILFIELDS
IV. POSTSCRIPT :NOTE (dated 5 January, 1959): More recent borings in southern England .
Page 40 40 40 43
46
V. APPENDIX: Lithological and faunal markers useful for well correlation in the Upper Carboniferous of the East]Midlands, summarized from unpublished reports by T. M. W. STRONG
50
.
VI. LIST OF REFEREI~CES
55
SUMMARY
The main geological results of exploration by the British Petroleum Company Limited since 1945 are outlined, and the general basis of operations described. In the south of England new data emphasize the progressive development of the Wealden area as a Jurassic depositional basin, on a surface of mainly Devonian and Carboniferous rocks. In the East Midlands and West Yorkshire more information on the relation of Carboniferous basins is now available, and extensive occurrences of contemporary and intrusive basic igneous rocks are described. In East Yorkshire a south-easterly extension of the Permian potash basin has been proved. Post-Permian formations tend to thicken eastwards from outcrop and also inland (westwards) from the coast. The Permo-Triassic rocks of the Formby area (Lancashire) have been found to lie in a deep valley cut into Carboniferous rocks, and stratigraphic thickness variations demonstrate intra-Triassic fault movements. Further oilfields have been developed at Plungar and Egrnanton in the East Midlands, and three additional discoveries await evaluation. I. INTRODUCTION I n 1937 t h e Geological S o c i e t y r e c e i v e d f r o m G. M. Lees a n d P. T. Cox a d e s c r i p t i o n of t h e b a s i s o f t h e s e a r c h for oil i n B r i t a i n , a n d i n 1945 t h i s was followed b y a r e p o r t o f t h e d i s c o v e r y o f f o u r oilfields, w i t h geological i n f o r m a t i o n of g r e a t r e g i o n a l s i g n i f i c a n c e (Lees & T a i t t 1946). T h e s u c c e e d i n g t w e l v e y e a r s h a v e seen t h e s e a r c h c o n t i n u e d b y t h e B r i t i s h P e t r o l e u m C o m p a n y L i m i t e d w i t h t h e d i s c o v e r y of two m o r e fields.
T h e a c c o u n t w h i c h follows s u m m a r i z e s t h e m o r e i m p o r t a n t i n f o r m a t i o n o b t a i n e d i n t h i s
t h i r d stage. D u r i n g t h e p e r i o d i n q u e s t i o n t h e b a s i s o f e x p l o r a t i o n h a s b e e n b r o a d e n e d to i n c l u d e s e a r c h for n a t u r a l gas on b e h a l f of t h e Gas C o u n c i l a n d i n c o n j u n c t i o n w i t h I m p e r i a l C h e m i c a l I n d u s t r i e s .
These organiza-
t i o n s h a v e p e r m i t t e d t h e i n c l u s i o n h e r e of i n f o r m a t i o n f r o m t h e j o i n t o p e r a t i o n s . The only significant changes in exploration techniques during the last twelve years have been an i n c r e a s i n g use o f m o d e r n r e f l e c t i o n s e i s m i c w o r k a n d of t h e v a r i o u s m e t h o d s o f electric logging.
The
GEOLOGICAL RESULTS OF PETROLEUM EXPLORATION IN BRITAIN 1945-1957 CONTENTS Page
I.
INTRODUCTION
5
.
i i . GE~ER.~ EX~01CATION (a) Southern. England (i) Dorset and the" Hampshire basra (ii) The Isle of Wight (Arreton) (iii) The Wealden area (b) South Midlands 9 . (c) East Midlands . (i) Outline of operations (ii) Stratigraphy . (iii) Igneous rocks in the" Upper Carboniferous (d) East Yorkshire . (i) Fordon and Lockton (ii) Eskdale, Robin Hood's Bay a f l ( i Redear (e) West Yorkshire (f) Lancashire (i) Formby area . (ii) Upholland (g) The Midland Valley of Scotland
III.
ESTABLISHED
(a) General (b) The Plungar oilfield, Leicestershire (c) The Egmanton oilfield
7 7 7 8 9 14 16 16 20 23 26 26 28 32 34 34 37 39
OILFIELDS
IV. POSTSCRIPT :NOTE (dated 5 January, 1959): More recent borings in southern England .
Page 40 40 40 43
46
V. APPENDIX: Lithological and faunal markers useful for well correlation in the Upper Carboniferous of the East]Midlands, summarized from unpublished reports by T. M. W. STRONG
50
.
VI. LIST OF REFEREI~CES
55
SUMMARY
The main geological results of exploration by the British Petroleum Company Limited since 1945 are outlined, and the general basis of operations described. In the south of England new data emphasize the progressive development of the Wealden area as a Jurassic depositional basin, on a surface of mainly Devonian and Carboniferous rocks. In the East Midlands and West Yorkshire more information on the relation of Carboniferous basins is now available, and extensive occurrences of contemporary and intrusive basic igneous rocks are described. In East Yorkshire a south-easterly extension of the Permian potash basin has been proved. Post-Permian formations tend to thicken eastwards from outcrop and also inland (westwards) from the coast. The Permo-Triassic rocks of the Formby area (Lancashire) have been found to lie in a deep valley cut into Carboniferous rocks, and stratigraphic thickness variations demonstrate intra-Triassic fault movements. Further oilfields have been developed at Plungar and Egrnanton in the East Midlands, and three additional discoveries await evaluation. I. INTRODUCTION I n 1937 t h e Geological S o c i e t y r e c e i v e d f r o m G. M. Lees a n d P. T. Cox a d e s c r i p t i o n of t h e b a s i s o f t h e s e a r c h for oil i n B r i t a i n , a n d i n 1945 t h i s was followed b y a r e p o r t o f t h e d i s c o v e r y o f f o u r oilfields, w i t h geological i n f o r m a t i o n of g r e a t r e g i o n a l s i g n i f i c a n c e (Lees & T a i t t 1946). T h e s u c c e e d i n g t w e l v e y e a r s h a v e seen t h e s e a r c h c o n t i n u e d b y t h e B r i t i s h P e t r o l e u m C o m p a n y L i m i t e d w i t h t h e d i s c o v e r y of two m o r e fields.
T h e a c c o u n t w h i c h follows s u m m a r i z e s t h e m o r e i m p o r t a n t i n f o r m a t i o n o b t a i n e d i n t h i s
t h i r d stage. D u r i n g t h e p e r i o d i n q u e s t i o n t h e b a s i s o f e x p l o r a t i o n h a s b e e n b r o a d e n e d to i n c l u d e s e a r c h for n a t u r a l gas on b e h a l f of t h e Gas C o u n c i l a n d i n c o n j u n c t i o n w i t h I m p e r i a l C h e m i c a l I n d u s t r i e s .
These organiza-
t i o n s h a v e p e r m i t t e d t h e i n c l u s i o n h e r e of i n f o r m a t i o n f r o m t h e j o i n t o p e r a t i o n s . The only significant changes in exploration techniques during the last twelve years have been an i n c r e a s i n g use o f m o d e r n r e f l e c t i o n s e i s m i c w o r k a n d of t h e v a r i o u s m e t h o d s o f electric logging.
The
6
FALCON
AND
KENT
CARBONIFEROUS PROSPECTS ScoTLAND Oil & Gas shows in outcropping rocks & in workings & borings of oil shale field. Oil show in D'Arcy ~ 1 drilled after f914-1918 war & in N°-I & N.°5 at Cousland. N° of Test Boreholes : 8. Total footage:20,270 feet. Small 9asfield in Lower Carboniferous at Cousland.
GLASGOW •
\ CARBONIFEROUS //
PROSPECTS
N. E. FNG,LAND
//
Oil or Gas accumulations possible in Carboniferous & older rocks. C)ccasional gas in coal-mines & some oil reported in a borehole near Richmond. No wells drilled to date f o r oif or gas.
/ CARLISLE
Kirkteatham Robin Hoods Bay
CARBONIFEROUS
~PROSPECTS
N.W. ENGLANO
Strong Oil seepages in Peat. near Formby. Small oilfield in Tries rocks near surface. N9 of shallow Boreholes; 75. Total footage; 26,964 feet.(including producing wells.) N° of Deep Boreholes; 8.Total footage 35,790 feet. ~ _ Ftea
~
PERMIAN PROSPECTS
Evidence of Oil 8, Gas in boreholes & outcropping rocks. Oil & Gas fields in Germany, N9 of Boreholes: 11. Total footage 36,504 feet. Eskdale N° 2 Gas in Upper Permian Limestone N°10 - " Lower " " N9 of shallow Boreholes; 3. Total footage; 2,873 feet. CARBONIFEROUS
PROSPECTS
MIDLANDS
Oil in Carboniferous rocks, in outcrop, boreholes & mines - . Limestone in Hardstoft N91 • Plunger N°2 ;~)~/) OIL F IELD$ IN EAKRING AREA .on//J 60iifields. N9 of Borehotes: 412. Total footageiI,034,613 feet. ~'t/o/n f Producing Horizon is the Millstone Grit Series. -~' o ~ N'.O of Shallow Bar.holes: 14. Total
~,
Stoke
21,367Feet,
_ f~;~C'~'k?'~footaqe:
BIRMINGHAM
PALAEOZOIC PROSPECTS Oil accumulationspossiblein Car~)oniferous & older rocks Occasional shows of gas in boreholes. NOof boreholes;2. Total footage: 5,8ti feet
/
__
A.s.hdo.wj, .m.
Bri~
Herr&n(
-~'ceo~"r) Down MESOZOIC PROSPECTS Oil impregnated sandstones, etc., of Jurassic & Cretaceous age outcropping along coast. Gas at Heathf/e/d (Sussex). N9 of Deep Boreholes:14. Total footage;48.221 feet. N9 of Shallow Information Boreholes; 30. Total 8,508 feet SCALE " Scale ~ Mites 0 5 I i i i i I i i ~ $ J
Fla. l.--General
map
of areas explored
to the end of 1957.
former has been particularly useful in the exploration of the East Midlands concealed coalfield area, and the latter in the development drilling of the newly discovered oilfields. In particular, the use of gamma-ray logging has been of considerable help in the correlation of marine bands in the East Midlands area. Other Publications.--Since the publication by Lees & Taitt (1946) the British Petroleum Company has released a considerable amount of data on additional wells. Summary accounts have been published
ON PETROLEUM
EXPLORATION
IN
BRITAIN
1945-1957
of several borings in Nottinghamshire (Edwards 1951), of three borings in the Market Drayton area of Staffordshire (Wills 1956) and of borings in Dorset at Chaldon Down and Broadbench (Arkell 1947B). More detailed accounts have been published of the Permo-Triassic and Carboniferous sequence of Forn~lby, Lancashire, of the Mesozoic rocks down to basement at North Creake, Norfolk (Kent 1947, 1948) and of the Whittington (Derbyshire), H a y t o n (Yorkshire), Farleys Wood (Nottinghamshire) and Spital (Lincolnshire) borings marginal to the Yorkshire Coalfield (Wilcockson 1950). This information is not repeated in the description below. The Gun Hill (Staffordshire) boring briefly described by Lees & Taitt has been discussed in detail by Hudson & Cotton (1944) and the Kingsclere (Berkshire) boring described more fully by Arkell (1947A). F. H. Stewart has published a series of papers on the Permian evaporites of the Eskdale area (1954) ; F. W. Anderson (1939) has worked on the ostracod faunas of sections in southern England, and M. W. Strong (1956) has described iron-precipitating bacteria in the Permian salt from several borings in Yorkshire. More recently (1958) the British Petroleum Company has issued for limited distribution an account by Taitt & K e n t of the Portsdown and Henfield borings, which provide standard reference sections in the south. II. GENERAL EXPLORATION (a) Southern England (Table I) (i) Dorset and the Hampshire Basin The extent of oil shows at outcrop in Dorset marginal to the Hampshire basin has continued to a t t r a c t our interest. The borehole at Poxwell originally proved the complexity of the movements in pre-Albian times (Taitt & Kent 1939), and holes drilled through the Chalk at Chaldon Down, north of Lulworth, passed directly from Albian to Kimmeridge Clay, showing t h a t strong local pre-Albian uplift continued eastwards from outcrop (Arkell 1947B). Telluric surveys carried out over this area showed a number of anomalies but their interpretation was uncertain, and seismic and gravity surveys south of the Tertiary syncline of Wareham failed to give clear-cut results beneath the Chalk blanket. The next stage, in progress at the time of writing, has included further investigation of outcropping structures in Dorset and seismic work in the less strongly disturbed area north of the Ballard Down fault in Dorset and in the T e r t i a r y basin in Hampshire. The first of the outcropping structures to be drilled was the fold at Chaldon Herring, which had a superficial appearance of simplicity (Arkell 1947B). Four boreholes in a N.-S. line across the culmination proved it to be a structure of Poxwell type, flanked by a fault with a large pre-Albian throw, with the additional complication t h a t the fault plane had been sharply distorted by the final phase of folding. An account by M. R. House is in the press. F u r t h e r operations on outcropping structures are planned on the Weymouth anticline near Langton Herring (see Postscript Note, p. 49) and also at Broadbench, where an earlier hole found a minor oil show in the Corallian. Within the Tertiary outcrop two areas have received detailed attention by seismic reflection survey. The first is near Wareham, where gravity and seismic refraction survey had proved an anomaly. The second is the l%ingwood gravity high in Hampshire (White 1949), where reflection survey has detailed a subcircular crest maximum in the Jurassic ; the shape and size of this structure suggest t h a t it could be an uplift caused by a local intrusion of Triassic salt at depth, analogous to the domal uplift of Compton Valence (Falcon & K e n t 1950) 1. 1 Since this account was prepared, drilling of Fordingbridge No. 1 has shown that this structure is pre-Albian, like those of Dorset, for Gault rests directly on Kimmeridge Clay, with elimination of the thick Portland, Purbeck, Wealden and Lower Greensand (see Postscript :Note). Also, a test well drilling near Bere Regis, north-west of Wareham, at the time of going to press, located on ~, seismic reflection high, has proved Oxford Clay immediately below the Gault.
ON PETROLEUM
EXPLORATION
IN
BRITAIN
1945-1957
of several borings in Nottinghamshire (Edwards 1951), of three borings in the Market Drayton area of Staffordshire (Wills 1956) and of borings in Dorset at Chaldon Down and Broadbench (Arkell 1947B). More detailed accounts have been published of the Permo-Triassic and Carboniferous sequence of Forn~lby, Lancashire, of the Mesozoic rocks down to basement at North Creake, Norfolk (Kent 1947, 1948) and of the Whittington (Derbyshire), H a y t o n (Yorkshire), Farleys Wood (Nottinghamshire) and Spital (Lincolnshire) borings marginal to the Yorkshire Coalfield (Wilcockson 1950). This information is not repeated in the description below. The Gun Hill (Staffordshire) boring briefly described by Lees & Taitt has been discussed in detail by Hudson & Cotton (1944) and the Kingsclere (Berkshire) boring described more fully by Arkell (1947A). F. H. Stewart has published a series of papers on the Permian evaporites of the Eskdale area (1954) ; F. W. Anderson (1939) has worked on the ostracod faunas of sections in southern England, and M. W. Strong (1956) has described iron-precipitating bacteria in the Permian salt from several borings in Yorkshire. More recently (1958) the British Petroleum Company has issued for limited distribution an account by Taitt & K e n t of the Portsdown and Henfield borings, which provide standard reference sections in the south. II. GENERAL EXPLORATION (a) Southern England (Table I) (i) Dorset and the Hampshire Basin The extent of oil shows at outcrop in Dorset marginal to the Hampshire basin has continued to a t t r a c t our interest. The borehole at Poxwell originally proved the complexity of the movements in pre-Albian times (Taitt & Kent 1939), and holes drilled through the Chalk at Chaldon Down, north of Lulworth, passed directly from Albian to Kimmeridge Clay, showing t h a t strong local pre-Albian uplift continued eastwards from outcrop (Arkell 1947B). Telluric surveys carried out over this area showed a number of anomalies but their interpretation was uncertain, and seismic and gravity surveys south of the Tertiary syncline of Wareham failed to give clear-cut results beneath the Chalk blanket. The next stage, in progress at the time of writing, has included further investigation of outcropping structures in Dorset and seismic work in the less strongly disturbed area north of the Ballard Down fault in Dorset and in the T e r t i a r y basin in Hampshire. The first of the outcropping structures to be drilled was the fold at Chaldon Herring, which had a superficial appearance of simplicity (Arkell 1947B). Four boreholes in a N.-S. line across the culmination proved it to be a structure of Poxwell type, flanked by a fault with a large pre-Albian throw, with the additional complication t h a t the fault plane had been sharply distorted by the final phase of folding. An account by M. R. House is in the press. F u r t h e r operations on outcropping structures are planned on the Weymouth anticline near Langton Herring (see Postscript Note, p. 49) and also at Broadbench, where an earlier hole found a minor oil show in the Corallian. Within the Tertiary outcrop two areas have received detailed attention by seismic reflection survey. The first is near Wareham, where gravity and seismic refraction survey had proved an anomaly. The second is the l%ingwood gravity high in Hampshire (White 1949), where reflection survey has detailed a subcircular crest maximum in the Jurassic ; the shape and size of this structure suggest t h a t it could be an uplift caused by a local intrusion of Triassic salt at depth, analogous to the domal uplift of Compton Valence (Falcon & K e n t 1950) 1. 1 Since this account was prepared, drilling of Fordingbridge No. 1 has shown that this structure is pre-Albian, like those of Dorset, for Gault rests directly on Kimmeridge Clay, with elimination of the thick Portland, Purbeck, Wealden and Lower Greensand (see Postscript :Note). Also, a test well drilling near Bere Regis, north-west of Wareham, at the time of going to press, located on ~, seismic reflection high, has proved Oxford Clay immediately below the Gault.
FALCON AND K E N T
(ii) The Isle of Wight (Arreton) The results of the pre-war deep test borings in the Wealden region indicated that most of the folds were Tertiary structures, developed too late to act as traps for oil migrating towards the edge of the Wessex basin. Interest therefore moved to the marginal parts, and discovery of a regional gravity rise from the mainland across the Isle of Wight (White 1949) led to a search for a suitable structural target in the southern part of the island on the hypothesis that the gravity rise indicated the flank of the Jurassic basin. Both the Sandown and Brighstone folds have their culminations off-shore and were therefore impracticable for drilling, but a third dome was found between them at Arreton, nearly in the centre of the island, at a locality indicated by surface geology and a local gravity high subsequently detailed by reflection survey (Fig. 2).
k )~,' NEWPORT
-11r-
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l
SURFACE AXIS DiPS
}
F r o . 2 . - - A r r e t o n : g r a v i t y r e s i d u a l s a n d reflection c o n t o u r s .
The geophysical work confirmed the line of the axis as determined by Osborne White (1921), recently questioned by Whitten (1957) on a basis of a stereographic analysis of published dip data. The mathematical study in this case appears to have given misleading results. The deep test located on this dome started in Ferruginous Sands (Aptian) and passed through a normal succession down to the Inferior Oolite, in which drilling stopped at 5161 feet (Fig. 4). The Wealden 2 and Purbeck are more like the East Dorset development than the Portsdown, with thicknesses of 2010 feet and 343 feet respectively ; below this the Corallian correlates closely with West Dorset, but otherwise thicknesses and facies are much as at Portsdown, although the Kellaways beds (developed as fossfliferous fine muddy sandstone) reach the notable thickness of 99 feet. The Great Oolite series is developed as limestones more muddy than either Portsdown or Henfield ; the Fuller's Earth is distinct but includes in the lower part limestones which are continuous with the Inferior Oolite. The Upper Inferior Oolite is mainly of ferruginous limestones ; below this, limestones with blue cherts can be correlated with the Middle Inferior Oolite of Portsdown, and the well ended in sandy and ]imonitic limestones probably of Lower Inferior Oolite age. The series is thus of normal thickness, and the Mesozoic basin must extend well to the south of Arreton, so that the regional gravity feature has to be explained by deeper-seated density changes. The occurrences ~In F i g . 4 (p. 10) t h e t o p o f t h e W e a l d e n i s s h o w n a t 280 f e e t , b u t in T a b l e I it is s h o w n a t 210 feet. I t is n o t c e r t a i n w h e t h e r t h e c l a y b e t w e e n t h e s e d e p t h s is W e a l d e n Clay or A t h e r f i e l d C l a y (i.e. b a s a l L o w e r G r e e n s a n d representative). " 9"
ON PETROLEUM EXPLORATION IN BRITAIN
1945-1957
of derived Kimmeridge and other Jurassic rocks in the Cretaceous in the Isle of Wight, however, imply nearby pre-Cretaceous uplift by an amount greater than the thickness of the Wealden--perhaps through pre-Albian movement in continuation of the complexities of the Isle of Purbeck. Marginal basin conditions are in any event not available on the Isle of Wight, and suitable oil traps are not likely to be found until the detailed structure of the concealed Jurassic can be worked out. (iii) The Wealden Area
(a) Outline of Operations.--The pre-war recession of interest in the oil prospects of southern England followed a series of six unsuccessful deep borings, four by British Petroleum and two by other companies. Five of these had penetrated the complete Jurassic succession, three of the easterly borings (I-Ienfield, Penshurst and Grove Hill) reaching the Palaeozoic floor. With development of interest in gas prospects the Wealden area was again considered, with gas shows at Heathfield (in the Purbeck) and Henfield (in Great Oolite) as incentives.
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The Ashdown structure called for first attention on account of its size and proximity to Heathfield, and preliminary detailing of the crestal part was carried out by shallow boring and by seismic reflection survey. The shallow boring met with difficulty from the absence of reliable markers in the Lower Wealden and Upper Purbeck, but confirmed in general an earlier interpretation of the surface structure by A. H. Taitt and by the Rev. J. W. Reeves (1948). A site for the first test hole was chosen on the eastward part of the surface crest, on the outskirts of Crowborough, finding gas in small quantities only in the Portland and Corallian and an oil show in the Kellaways. This result was considered to justify another borehole at a structurally higher elevation and a short seismic programme was carried out before selecting a location. The seismic work gave rather discontinuous results, but tended to show a southward and eastward displacement of the crest at depth. The second boring was therefore located one mile to the southeast in the expectation, subsequently confirmed by drilling, t h a t there would be a rise in this direction in the Corallian. The second borehole was taken to the pre-Jurassic floor and found an encouraging oil show in sandy Lower Lias, b u t it was not considered to justify further development in an area with many surface obstructions. The final seismic interpretation of the structure (after drilling) is shown in Fig. 3. 8 Gas has been produced at Heathfield for many years, and two projects were u n d e r t a k e n - - a n additional boring to the Portland a t Heathfield itself, and a test of the whole of the Jurassic on the more northerly a This m a p is so different f r o m t h e s u r f a c e e v i d e n c e t h a t t h e c o n t o u r s m u s t n o t b e a c c e p t e d u n c r i t i c a l l y .
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ON PETROLEUM
EXPLORATION
IN
BRITAIN
1945-1957
11
Purbeck outcrop near Brightling, the highest structural culmination of the Weald. The latter location was based on detailed mapping by F. I-Iowitt on behalf of Gypsum Mines Ltd. The Heathfield test produced gas, but not in quantities large enough to warrant further development. The Brightling hole found gas and water in the Portland Beds and gas with a little oil in the Kellaways, but all the shows were below the commercial level. It revealed the notable feature of a reversed fault repeating part of the Upper, the Middle and most of the Lower Lias, a throw of about 500 feet, clearly established by ammonite evidence. In the following account the recent results (Fig. 4) are compared with the standard sections at Portsdown and Henfield (Taitt & Kent 1958). A summary of a boring drilled at Shalford (near Guildford) since this paper was prepared, is given in the Postscript Note (p. 47). (b) Stratigraphy : the Palaeozoic Floor. The pre-Jurassie rocks at Henfield were described by J. Pringle and Dr. C. J. Stubblefield (in Lees & Cox 1937, pp. 188-90), who found evidence of a Lower Carboniferous age in the lower part and tentatively ascribed the whole 215 feet to the Carboniferous. There were some grounds for assigning some of the higher part to the Upper Carboniferous and Taitt & Kent (1958, p. 28) have so taken the uppermost 170 feet, and they have speculated that the Upper Carboniferous at about 5060 feet rested unconformably on Lower Carboniferous. Dr. Stubblefield, however, informs us that he is unable to accept an Upper Carboniferous age for the fossils occurring at 4997 feet. Carboniferous rocks consisting mainly of limestones with red marl partings were found beneath the Lias at Warlingham (Geological Survey 1958, pp. 29-30) and at Penshurst. The beds beneath the Jurassic at Ashdown No. 2 (Crowborough) may be of the same age as the upper beds at Henfield, although neither earlier Carboniferous nor Devonian ages can certainly be excluded. They consist of purplish red and brownish red soft silty mudstone and sandstones, with oehreous mottling and ochreous calcareous concretions, and a single one-foot band of pale grey fine-grained limestone near the top. The dip varies from horizontal to 6~ ; the uppermost part is shattered with horizontal slickensides. The presence of bedded limestone (which was cored) is a distinction from any normal Trias, and the general facies might be matched in the Carboniferous at Henfield or in the Devonian at Willesden. Farther south-east the Brightling boring passed directly from Lower Lias into Devonian, apparently the first record of this formation in South,East England away from the London platform. It was described by Mr. A. P. Terris as a monotonous series of choco]ate-coloured mudstones and shales, with occasional greenish grey and brown micaceous sandstones. The uppermost part is shattered, with dips up to 50 ~ ; lower down the beds show a uniform 25 ~ to 30 ~ The higher beds yielded only fragmentary plants and "fucoids", but a core of soft mudstones at the final depth (4940 feet) yielded fossils identified as Actinopterella, Paracyclas, Palaeoneilo, Pterinea, Tentaculites and Chonetes cf. sarcinulatus (Sehlotheim) by Dr. Stubblefield, who remarks that they are certainly Devonian and probably indicate a Lower Devonian age. To the extent that these various soundings can be taken as regionally reliable, they indicate that the Weald is mainly underlain by folded Devonian and Carboniferous rocks. The strike of the folding in the Kent Coalfield is Charnoid but farther west a Variscan trend seems more probable, although seismic reflection work in the Crowborough area suggested a Charnoid strike. The gravity low in the South Croydon area (Falcon & Tarrant 1951, pl. xiii, confirmed by a more detailed unpublished survey by A. J. King) has a Variscan strike. Trias is known only in the west, at Portsdown and Kingsclere, where the borings penetrated a few tens of feet of normal Keuper Marl beneath Rhaetic. Professor W. B. R. King (1954)has suggested that the main basin lay west of the Isle of Wight, and with indications of Rhaetic at Penshurst (Gulf Off Company's boring) it may be supposed that a lobe of this basin extended eastwards towards these localities near the line of the Wealden axis. It is, of course, possible that the New Red rocks contribute
12
FALCON AND KENT
importantly to the Hampshire basin gravity picture, that the pronounced low 10 miles south-east of Salisbury (White 1949) is due to a New Red basin, and that the southerly gravity rise in the Isle of Wight is due to a decrease in the thickness of New Red in that direction [see section II, (a), (ii), above]. The Rhaetic of Portsdown is in a littoral facies, with white limestones above, greenish limestones and shales (Cotham Beds?) in the middle part, and black shales and sandstones with the normal Westbury Beds fauna below. Henfield had no Rhaetic, and Brightling (also near the South Downs) was similar, but Penshurst near the centre of the Wealden trough has a possible Rhaetic representative as the first member of the Mesozoic transgression, in a facies much like the WestburyBeds of Portsdown. At Ashdown white and greenish limestones with one red bed are somewhat like the Cotham facies, but limestones below are of Liassic type. The Lower Lias measures 802 feet at Portsdown, 390 feet at Henfield, 840 feet at Ashdown, and 412 feet (allowing for faulting) at Brightling. At Portsdown and Ashdown the series may well be virtually complete. The thinning towards the east and south-east appears to be by overlap of the lower beds, with the ibex Zone identified about 100 feet above the base at Henfield and the oxynotum Zone about 250 feet up at Brightling. Eastwards the overlap carries only the highest zone as far as the Kent Coalfield ; southwards it is probably related to the Paris Plage ridge. Two lithological abnormalities call for mention. One is a marked eastward increase in sandiness, sandy limestones appearing at Ashdown in the middle and lower parts of the Lower Lias and increasing to Brightling, where sandy beds occur at intervals through the lower third of the formation. The other is the occurrence of three or more thin reddish brown mudstone bands associated with Crucilobiceras (approximately oxynotum Zone) interbedded with the normal grey beds; these may demonstrate the effect of material derived from the exposed Palaeozoic floor to the east of the basin, and suggest a minor regression at a level where non-sequences are indicated elsewhere in England. The Middle Lias is represented throughout the area by an eastward-thinning sandy group, with silty and sandy limestones in the upper part. Evidence of the margaritatus Zone has been obtained at Portsdown, Henfield 4 and Brightling, but it is not certain that the spinatum Zone (the Marlstone of the Midlands)is represented (compare Ager 1954, 1956). The Upper Lias 5 at Portsdown and Henfield was in the Dorset facies--developed as "passage beds " sandstones and siltstones, almost entirely of Aalenian date. Eastwards the later sandy beds became reduced, while the earlier more shaly beds thickened, and fossil identifications by Mr. R. V. Melville show that this is transitional to the development of East Kent, where Whitbyan shales are the only Upper Lias representative. At Brightling, in fact, in a moderately sandy sequence, Hildoceras (bifrons Zone) was obtained 43 feet below the top, and Tiltoniceras (early tenuicostatum Zone) 111 feet lower down, just above the base. The deep oil borings proved a thick Inferior Oolite development in southern England for the first time, with a general arrangement in the west (Kingsclere and Portsdown) much like that of the Cotswolds. The additional sinkings have shown that this limestone facies extends across the Weald, maintaining a thickness of 300 to 400 feet as far east as Brightling. All three main subdivisions appear to be represented, as a normal sequence of sandy, raggy and rubbly limestones. A notable feature is a basal oolitic haematitie ironstone, measuring 70 and 43 feet respectively at Ashdown 1 and 2, and 39 feet (including some green chamosite ore) at Brightling. This is another instance of ironstone development at the base of the Inferior Oolite (comparable with the l~orthampton Ironstone and a similar bed at Kingsclere) but the age is not precisely known. Within the area so far drilled there is no indication of overlap by the upper beds (the Vesulian transgression), although this is well advanced in the Kent Coalfield. 4 The interval 4092--4388 feet of Herdleld :No. 1 was called "Passage Beds a n d U p p e r Lias" in fig. 8 of Taitt & K e n t (1958). The margaritatus Zone was p r o v e d at 4398 feet. 5 The 250 feet of silty clays occurring above 5380 feet in P o r t s d o w n No. 1 were called " P a s s a g e Beds a n d U p p e r L i a s " in fig. 8 of T a i t t & K e n t (1958).
O N PETi~OLEUM EXPLOi%ATION IN Bi~ITAIN
1945-1957
13
The Fuller's E a r t h persists across the area as 80 to 100 feet of grey marls and rubbly limestones ; at Portsdown it yielded the ammonite Siemiradzkia and at Ashdown brachiopods confirmed its horizon. The Great Oolite is developed as 150 to 200 feet of fairly uniform oolite with muddy dark beds of Forest Marble facies above ; a few feet of limestone at the top has been tentatively ascribed to the Cornbrash but its identity is unconfirmed except at Portsdown and Henfield, where the faunas indicated Lower and Upper subdivisions respectively. The Kellaways Beds maintain the normal facies (sandstone and sandy siltstone above, shales below) eastward from Portsdown across the Weald. The thickness diminishes slightly from about 30 feet in the west; except for the characteristic Ostrea alimena d'Orbigny few fossils have been found. The Oxford Clay shows the normal facies for southern England ; it measures 444 feet at Portsdown, but in the Weald shows a northerly element of thinning from 525 feet at Henfield and 377 feet at Brightling to 260 feet at Ashdown and 249 feet at Penshurst. Little coring has been carried out but there is no evidence t h a t the zonal sequence is other than normal. The Corallian beds were found to be incomplete and thin (111 feet) at Portsdown, with the middle part missing. They expand again to Henfield (299 feet), where the equivalents of each of the Dorset subdivisions are recognizable, increase to 480 feet at Ashdown but decrease south-eastwards to 301 feet at Brightling. Ashdown is probably the thickest development so far known in Britain, and with the previously known thick development at Brabourne shows the Weald to have been relatively synclinal in the Corallian, with moderate thinning towards the South Downs. Arkell (1933, pp. 436-7) has commented on the thick limestone development marginal to the London land-mass in K e n t ; the Geological Survey found t h a t the facies at Warlingham, Surrey, is similar (with 148 feet of coral limestone) and there is a moderate development of limestone (about one-third of the thickness) at Brightling. West and southwards the expansion is associated with a great increase in the proportion of argillaceous material, which at Ashdown amounts to more t h a n four-fifths of the total. I n such an argillaceous development lithology is an uncertain guide to correlation, but the upper and lower limits are moderately well controlled by ammonite evidence. Faunal data otherwise are scanty in the absence of cores, but the " Trigonia clavellata Beds " known at Henfield may be indicated also at Brightling by the index fossil in the corresponding position. From the Kimmeridge Clay upwards the succession in the Weald is fairly well known, facies changes are small and the interest of the new borings lies mainly in thickness variation. Portsdown and Henfield each have about 1100 feet of Kimmeridge Clay, but there is an expansion into the centre of the Weald matching t h a t of East Dorset (Arkell 1947B), since the Ashdown borings proved thicknesses of 1773 and 1660 feet respectively. Brightling shows a more normal measurement (1136 feet). I n the west and centre of the Weald the sequence is argillaceous except for a persistent limestone group a little above the middle ; this is known to be about 100 feet above the Saccocoma band at Henfield. At Ashdown the index of the highest zone, Pavlovia, shows the sequence to be complete. At Brightling the Lower Kimmeridge Clay shows the sandy, calcareous development already known in East Kent, with Rasenia near the base as at Penshurst, and a shell-bed just below which may be the Ostrea delta bed. There is a lithological gradation from the Kimmeridge into the sandy Portland development in all our borings, but ammonites have been found at Portsdown, Henfield and Ashdown to locate the boundary. At the Portsdown, Henfield and Pevensey borings the Lower Portland fauna was found to within a few inches of the overlying Purbeck ; at Ashdown the beds are similarly dated as probably Lower Portland from a specimen of Crendonites?, and there seems, in fact, no evidence of the occurrence of Upper :Portland anywhere in the Wealden area, there being a non-sequence at the base of the Purbeck. The Purbeck beds proved show no variations from the regional trends already known (Arkell 1933, pp. 537-9), with the persistent Middle Purbeck " Cinder B e d " and the basal anhydrite, and the small
14
FALOOI~
Al~D
KENT
thicknesses of Wealden beds penetrated call for no special comment. The contrast in thickness between Penshurst, near the centre of the Weald, and Henfield and Grove Hill in the south has already led to recognition of an intra-Jurassic swell along the Channel coast in line with the Paris Plage ridge (Kent 1949; King 1949, 1954). The Ashdown and Brightling sections fit into the same pattern, and emphasize the regional nature of the thickness changes. It is clear that the Wealden basin was undergoing differential subsidence in the Lias, Middle Jurassic, Corallian and Kimmeridge, with thicknesses up to 50% greater in the middle than in the south, and of course all subdivisions thinning out to the north. It also appears probable that the contrast arose not by differential subsidence alone, but that in the Lias there was transgression with overlap by higher zones southwards on to a sloping shore--a shore of red beds which gave rise to occasional coloure.d intercalations in the marine series. These conclusions would need to be modified in detail if there were evidence that the individual anticlines had undergone differential movement in Jurassic times, but both stratigraphical and structural indications are that they are post-Jurassic features, although it should be noted that information is mainly available from structural highs. The Weald is thus made up of a group of irregular subparallel folds, probably much faulted, developed in a Jurassic trough which may in turn overlie a broad syncline or synclinorium of Carboniferous age, downpitch of which the Kent Coalfield is developed at the intersection with broad gentle folding of Charnian trend. \ ".
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(b) South Midlands (Table I) M. Lees advanced the view that foreland folds in advance of the Variscan front could provide oil prospects in the southern Midlands, and extensive magnetic and gravity surveys and more limited seismic surveys were carried out to investigate underground conditions. The main results of the magnetic and gravity work have already been presented to this Society (FMcon & Tarrant 1951). Two borings have been made, the first at Willesden, North London, to investigate the circumstances of an oil and gas show reported in an earlier water well ; the second at Faringdon, Berkshire, to check underground stratigraphical conditions on a seismic high with a NW.-SE. trend before undertaking more detailed seismic surveys (Fig. 5). Paringdon
and
Willesden.--G.
ON P E T R O L E U M
EXPLORATION
1945-1957
IN BRITAIN
15
The Willesden boring started in London Clay, reached the Chalk at 196, Upper Greensand at 800 and the Palaeozoic at 1010 feet. As in the original water well, the Palaeozoic rocks proved to be Upper Devonian, dipping at about 15 ~ but although they were predominantly red mudstone and marl with very occasional thin limestones they yielded a rich marine fauna. Dr. Stubblefield (1947) commented briefly on the lithology and on the fossils collected by the late A. G. Davis and by Geological Survey officers from the ~mBR ~
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cored sections between 1020 and 1176 feet, also between 1400 and 1611 feet. He subsequently reported
Productella subaculeata (Murchison), Schizophoria striatula (Schlotheim) and Cyrtospirifer verneuili (Murchison) from limestones at 1624 feet and Camarotoechia ferquensis (Gosselet) from similar sediments at 1630 feet.
Below this depth coring was intermittent. The late Stanley Smith named the corals Alveolites suborbicularis? Lamarck, Thamnopora cervicornis (de Blainville) and a stromatoporoid from a short limestone core at 1719 feet. The hole was continued to 2680 feet in beds becoming generally greyer
16
FALCON
AND
KENT
and more sandy below but with a similar fauna ; dips decreased to about 10 ~ in the neighbourhood of 2000 feet. Dr. Stubblefield noted t h a t Tentaculites, plentiful in the limestone bands between 1410 and 1595 feet, was also recognized in thin limestones at 2230 feet. Cyrtospirifer verneuili found at 1410 feet, 1496 feet, 1624 feet and elsewhere was also recorded from 2446 feet associated with Atrypa. From the nature of the fossils the facies was deemed to be marine throughout, though the uppermost 160 feet appeared to be shallower water with deposits rich in Lingula with few associated lamellibranchs and fishes. No indications of oil were found. The Faringdon (Shellingford) test well in Berkshire started at the top of the Corallian limestones, and proved a Jurassic sequence intermediate between the South Cotswolds and Kingsclere (Fig. 6). The Oxford Clay measures 418 feet, the Kellaways 30 feet (both reduced as compared with the Swindon boring) ; the Great Oolite Series (180 feet) is in the Oxfordshire facies with a thin (10 feet) representative of the Fuller's E a r t h at the base. Sixty-five feet of limestones are ascribed to the Inferior Oolite, but this may include some early Bathonian (Chipping Norton Limestone) above. The Lias measures 655 feet, with typical green oolitic "Marlstone " 75 to 95 feet down from the top (the base of the Middle Lias is arbitrarily placed 30 feet below this in the absence of cores), and includes 20 feet of " H y d r a u l i c Limestones " close to the base. The Rhaetic totals 60 feet, with 20 feet o f " White Lias " at the top separated by 30 feet of green and brown shales and limestones (Cotham Beds) from 10 feet of Black Shales ; at 1525 feet it rests on normal Keuper Marl which extends to 2080 feet. This sequence is very markedly thinner t h a n the Jurassic of Kingsclere (Fig. 6), and Arkell (1947A) has suggested t h a t a sudden thinning over a fault or monocline immediately north of the Kingsclere fold may be the feature controlling sedimentation on the edge of the shelf. The Keuper Marl at Faringdon is separated from the Palaeozoic floor by 70 feet of conglomerates, the upper 40 feet with a red shale matrix, comparable with the " conglomeratic g r i t " of the basal Keuper in the Burford borings, the remainder with a red and purple fine sandstone matrix. A dip-meter survey later showed both groups to be practically horizontal ; hence they are probably post-Variscan, but may be either Keuper or Upper Coal Measures, or both. Beneath this level 981 feet of steeply dipping Palaeozoic rocks were penetrated (Falcon 1955). The sequence is one of indurated sandstones, shales and bedded siltstones forming a uniform series. Grey silts with plant fragments yielded Pachytheca to Dr. Stubblefield, the only evidence of date. Pachytheca ranges from the Silurian to Middle Old Red Sandstone, and a Downtonian age is considered most likely for this series. Dips varied from 45 ~ to vertical, and the locality must be either within the Variscan front or in a sharp fold in the foreland. A section by R. G. W. Brunstrom is appended (P1. I, fig. 1). The tectonic and stratigraphical facies of this Palaeozoic sequence are too unpromising for oil exploration, and further geophysical work in the region is considered unjustified. The structural foreland to the north, however, still has prospects, and a boring at Noke on the Islip anticline has been projected as a further step (see Postscript Note).
(c) East Midlands (Table II) (i) Outline of Operations.--A series of wells has been drilled in a search for homologues of the Millstone Grit reservoirs of the Eakring group of structures, and also to follow up oil shows encountered in coal exploration borings (Fig. 7). This work has produced four successes, the E g m a n t o n and Plungar oilfields described below, and the Langar and Bothamsall discoveries, which are now being followed up. Several of the holes were designed to trace the Eakring anticlinal trend, rerlethorpe No. 1, l o c a t e d down-pitch on the line of the north-western nose, did not find the dip reversal which general indications from colliery workings had suggested, but application of modern seismic reflection techniques to this
ON PETROLEUM EXPLORATION I N BRITAIN
1945-1957
17
area led to a test at Bothamsall, one mile north-east of Perlethorpe, and this has recently proved a commercial off accumulation in the Rough Rock 6 apparently of the same order of size as the E g m a n t o n field. Two wells were drilled at Hockerton on the south-western flank of the Duke's Wood field, where wedging of the beds offered a possibility of closure at depth, and one at Kirklington on the southern plunge, where a coal boring had encountered gas and where seismic work indicated a small subsidiary dome. None of these was successful, apparently through lack of closure in each case. Two wells were drilled at Farndon, near Newark, to intersect sands pinching out up-dip towards the crest of the Rolleston structure, but the structure proved too complex and too much invaded by igneous rocks in the Coal Measures and Millstone Grit to be productive. Igneous rocks were found in quantity also in borings on a seismic high at Screveton and at Harlequin (Radcliffe-on-Trent), east of Nottingham ; at Screveton sills and flows appear to have invaded or replaced both Coal Measures and the higher Millstone Grit sands, while at Harlequin a thick jointed sill in the basal Coal Measures flowed oil briefly but failed to give sustained production.
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FIO. 7 . - - E a s t M i d l a n d s b o r e h o l e localities, s h o w i n g v a r i a t i o n in t h e Millstone Grit sands.
I n North Leicestershire additional borings were drilled on the flanks of previously known structures at Bottesford (tested by three earlier wells which found moderate oil shows) and Plungar, the latter on the flank of a seismic refraction crest tested by the Barkestone well, which had failed through lack of sand. I t was correctly calculated t h a t sands would come in south-westwards (towards the thicker development at Long Clawson) and the small Plungar oilfield was discovered. Tests of seismic reflection crests at Granby and Sutton immediately to the north were unsuccessful, but an oil sand at the Rough Rock level has recently been located at Langar. The extent of this is not yet known. A boring on a seismic high at Sproxton (north-east of Melton Mowbray) found traces of oil in thin Millstone Grit resting on basement ; this is an area which will be further investigated. F a r t h e r north, oil-soaked but tight Millstone Grit sandstones at Farleys Wood (near Ollerton) were found to be tantalizingly rich but useless for production, and seismic reflection surveys were organized to find other structures with better sands in the same area. These resulted in definition of a W N W . - E S E . fold just south of Egmanton, which has since been drilled and developed as one of the larger fields of the East Midlands, with production from basal Coal Measures and Millstone Grit (see below). F a r t h e r east, a boring was drilled on a small seismic structure at Eagle Moor, starting in Lias in the e S u b s e q u e n t l y r e - i d e n t i f i e d as t h e C r a w s h a w S a n d s t o n e (base of l o w e r Coal Measures). l a t e r f o u n d to b e in a s a n d s t o n e b e l o w t h e A l t o n Coal.
2
The main production was
]8
FALCOI~ AND KEl~TT
broad Carboniferous synclinal area between the Trent and Lincoln. An oil show was found in the Carbordferous Limestone but proved non-productive. Two further holes were drilled on the :Nocton structure, the first for additional information on the non-commercial oil accumulation previously proved in the Carboniferous Limestone of :No. 3 well, and the second to investigate a show of oil in a basal Permian Sands pinch-out. Both were unsuccessful. A further seismic anticline was drilled at Ruskington on the edge of the Fens near Sleaford, down-flank from the :Nocton block at a locality where early :Namurian might possibly have been developed ; this proved a normal Mesozoic succession with thin Permian on Upper Coal Measures, and normal Middle Coal Measures with thin coals which rest directly on Carboniferous Limestone. Millstone Grit was absent, as on the higher block. Dry or tacky bitumen only was obtained, lack of oil being ascribed to non-development of suitable cap rocks.
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FzG. 8 . - - L i m i t s of the Widmerpool Lower Carboniferous gulf.
South of :Nottingham, seismic surveys indicated an anticline at Widmerpool, on which a test well was drilled. This passed through Keuper and thin Bunter into Millstone Grit, and then proved a long sequence of gulf facies of the Upper Visdan, in which drilling ceased (Fig. 9). Small gas shows only were encountered. Structural holes at Wysall, two miles to the west, found Keuper Marl resting directly on Lower Coal Measures (Bunter being absent) ; they were carried to the top of the Millstone Grit but did not define a drilling objective. Within the limits of the proved coalfield, borings have been drilled on anticlines at Trumfleet and Askern near Doncaster, at Ironville near Alfreton and on the Brimington anticline at Calow. The Trumfleet and Askern domes had been defined during the process of coalfield exploration (see, for example, contour maps in Edwards 1951), but although gas has been encountered in Lower Coal Measures and Millstone Grit it appears to be in moderate quantities only. The Ironville and Calow borings were further tests of major anticlines flanking the Pennine uplift which had been drilled in the 1918-22 drilling cam-
I
O~ PETROLEUM EXPLORATION IN BRITAIN 1945-1957
19
paign (Giffard 1923). The former was the third on the structure, located o n the Riddings dome which had been the site of a major oil seepage in the Coal Measures (Kent 1954) ; the Calow No. 1 test was situated two miles south of the original Brimington well, on a more southerly culmination which has now been accurately defined by the Geological Survey, partly from outcrop coal workings. Both these tests have yielded gas, the potentialities of which are still under consideration.
ILKESTON LITTLE HALLAM W.W.
RUDDINGTON COAL BORIN6 Alton co~,l Coal
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FIo. 9.--Stratigraphical columns in the Widmerpool gulf, South Nottinghamshire.
A structure contour map of the East Midland Coalfield and the area to the east is appended (P1. V). This is based on colliery information and on oil exploration. In order to show fold trends with maximum clarity, faults of less than 100 feet throw are omitted, and it becomes clear that there is an intersecting pattern of NNW.-SSE. and WNW.-ESE. folds. The N ~ W . - S S E . group is represented by a belt in the west of the exposed coalfield (Brimington, Heath, Hardstoft, Ironville, etc.), by the Eakring-Foston low farther east, and by the comparable Lincoln-Nocton uplift. The WNW.-ESE. group includes the folds at Kiveton Park, Manton, Egmanton, the Lindholm-Spital fold (off the present map), Mansfield and the complex belts near Nottingham ; all these are faulted, with the intensity of fracturing increasing south-
20
FALCON AND K E N T
wards. Between these intersecting trends are lozenge-shaped basins of remarkable structural simplicity. The relation between the two trends is not certain, although it is clear that both were produced within a single limited period. The map shows, however, that the fold pattern is not due to a single system of anticlines wandering haphazardly across country, but has a basic regularity which may reflect control by pre-Palaeozoic lines of weakness. They could, in this case, be contemporaneous. (ii) Stratigraphy.--The further borings have added detail to the broad picture described in 1945 but have not changed the essentials--a Carboniferous sequence of normal type and thickness extending from the Pennines as far east as Eakring, with marked thinning beyond. The more interesting features shown by the Carboniferous are described in the following paragraphs ; those of the later beds have been dealt with elsewhere (Swinnerton & Kent 1949, Edwards 1951, Kent 1953). The normal limestone block facies of the Lower Carboniferous was reached by borings north and east of Eakring, and as noted above the beds were dated as approximately D i at Eagle Moor and Ruskington. A test well at Widmerpool, south of Nottingham, proved an important development of the gulf facies, which may be an eastward lobe from the North Staffordshire gulf (Hudson & Cotton 1944, p. 259). Here the Millstone Grit ranges down to E~ and measures 1136 feet, overlying 1454 feet plus of mudstones, shales and limestones (base not reached) which are dated as P~ in the upper part by the occurrence of Girtyoceras (Fig. 9). Lower Vis~an beds have not yet been reached in the Widmerpool area, but all the other indications of a Carboniferous gulf, as usually defined, have been recognized--P beds are thick and in shMe facies, early Namurian (Ei-E~) is both present and well developed, later Namurian and Lower CoM Measures are expanded. The sedimentary history of the area can be traced from Carboniferous to Jurassic times, and it is intended in due course to make this the subject of a separate communication. A further discovery, so far as we know unprecedented in the British Carboniferous, was of a thick evaporite series lower down in the limestone at Hathern, in a boring drilled towards the south side of the Widmerpool trough five miles from the Charnwood outcrops. This was drilled to investigate an oil show in early Millstone Grit (Richardson 1931) ; it found beneath the grits 491 feet of normal limestone, dated as probably C a in the lower part, resting on an alternation of anhydrite, shale and limestone proved to an incomplete thickness of 391 feet. The anhydrite series showed an alternation of beds of pure white and grey anhydrites up to four feet thick with limestone and green and black shales. Some of the beds are contorted and there is much anhydritic veining, which is in some cases due to a replacement process. Some fine-grained limestones show a patchy replacement by anhydrite and dolomite. Hathern is only seven miles from Breedon Cloud, where Mitchell & Stubblefield (1941) recorded, in line with the Charnian axis, a condensed dolomitic limestone succession containing a thin conglomerate of C~Si age ; the horizon of the anhydrite may be approximately at the level of the stratigraphical break below the C~S1 beds there. The only boring so far made to the south of the Widmerpool trough is at Sproxton, six miles northeast of Melton Mowbray. This found the base of the Trias at 1733 feet, Coal Measures with a large proportion of igneous rock (partly contemporaneous) to 2298 feet, Millstone Grit with fairly good sands to 2543 feet, and then basement consisting of metamorphosed tufts and mudstones comparable with the Swithland Slates of Charnwood. The possibility of faulting cannot be entirely excluded, but overlap of Millstone Grit on to the older rocks of the Midland barrier would not be impossible here. In following the various changes of the Millstone Grit (Fig. 7) the incidence of sands has been a major concern, since several well-marked structures have failed to give production through lack of sands, and both Egmanton and Plungar have rapid sand variation as a complicating factor. Fortunately, the wellknown marine bands persist over the area, and the officers of the Geological Survey have been most helpful in supplying rapid determinations for dating. In general, sandstones tend to be very poorly developed east of a line running south from near Gainsborough, just east of Eakring, towards
ON PETROLEUM EXPLORATION IN BRITAIN
1945-1957
21
Nottingham and then curving south-westwards past Plungar. West of this line all the major grit groups are usually well developed, although the Rough Rock tends to be a variable unit even at outcrop, and the Chatsworth Grit is a true grit. To the east of the line the Rough Rock and " Longshaw "7 equivalents are discontinuous and thin, and the Chatsworth Grit, when present, is a medium or fine sandstone. Over the mid-Nottinghamshire part of the concealed coalfield the Kinderscout Grit is rarely of significant thickness and is only represented by very fine-grained sandstone or ganister, but it provides the main sandstone horizons farther south, at Plungar. T R U M F LE ET
HUDDERSFIELD 6ENERALISE0 's
CORRINGHAM NO.l
BELTON
NO
SECTION
No.I
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FIG. 10.----Millstone Grit cerrelation b e t w e e n t h e Huddersfield area a n d boreholes at Trumfleet, B e l t o n a n d Corringham.
The thinning of the group from the normal facies of the easterly Pennine outcrops (Fig. 10), or from the Widmerpool trough, tends to be firstly by attenuation of the sandstones, and at the next stage by attenuation of the interbedded shales. In the shales (at this level and in the Coal Measures above) the marine horizons are fortunately rather more persistent than the barren shales and fireclays, and there is a suggestion that the Millstone Grit as a whole is becoming more marine towards the south-east, a trend comparable to the south-westerly marine tendency in Lancashire (Kent 1948 ; Magraw & Ramsbottom 1956). An important element in the thinning is also the overlap of the lower beds, P, E and H zones being thin or absent on the block, where R 1 usually transgresses on to Vis6an limestone. This is clearly seen at Plungar (Fig. 23), where transgression presumably followed relative uplift and erosion. At Eakring, 7 While this paper was in preparation the Geological Survey announced that the " Longshaw Grit " in the type area was misidentified, and the name therefore lapses for an outcropping sandstone. Correlation of the parts in the borehole sections n o w needs review, b u t the n a m e " L o n g s h a w " i s temporarily retained for the s a n d s t o n e below t h e cancellatum-crencellx~tura marine bed in Nottinghamshire (Lees & Taitt 1946, p. 285).
22
FALCON
AND
KENT
in a region of comparable but less sudden overlap, the Carboniferous Limestone phase of deposition ended with an alternation of black shales with shelly limestone breccias which may well be of marginal type ; the first datable beds above are of the R 1 zone. The Productive Coal Measures beneath the Mesozoic unconformity on the periphery of the worked coalfield are being actively explored by the National Coal Board, but useful regional information is still being obtained from oil boring deeper into the basin than other operations yet go. In the north, the ~v.'.-'.."-.-~. " ~ W e s t BOTHAMSALfL.~:.~. :. :. :. :. : o . , ~
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::::::::::::::::::: ~:' :" :' :'~; :/Contemp. Ig n e o u s ~ ' ~ EGMAN TON
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ton
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FIG. 11.--Igneous rock distribution in the East Midlands Carboniferous rocks. Trumfleet (Thorpe in Balne) boring showed strong easterly attenuation as compared with the Barnsley area, intervals from the Barnsley (Top Hard) downwards being half to two-thirds of the measurement in the exposed coalfield. As in the case of the Millstone Grit in Nottinghamshire, the main thinning is due to attenuation of sandstones. Near Lincoln, the Eagle Moor boring encountered a Coal Measures sequence with few, thin coals (which seems to be the general condition in the buried syncline between Eakring and Nocton), but in the south the Plunger area shows coals in number and thickness comparable with those of the southern end of the working coalfield near Nottingham.
ON PETROLEUM EXPLORATION IN BRITAIN 1 9 4 5 - - 1 9 5 7
23
The upper part of the Coal Measures in the north becomes very much more arenaceous eastwards from Trumfleet to the Belton boring (Wilcockson 1950), and it has been suggested that some of the coarse sandstones and grits loosely grouped as ?Upper Coal Measures in Lincolnshire are in fact rather older. At Eagle Moor, however, where a series of buff, brown and yellow marls with quartz conglomerate and grit is ascribed to the Upper Coal Measures, comparison of the section with the Doddington coal boring (two miles north) suggests that this is an unconformable group which cuts out the measures around the Top Hard horizon southwards, and the similarly coloured beds described by Lees & Taitt at l~octon, Dnnston and Stixwould are also unconformably related to the Middle Coal Measures and earlier beds. At Ruskington, still farther south-east, 287 feet of mottled marls and sandstones with a 15-foot conglomerate with chert pebbles in the lower part are ascribed to the same series; there a greater thickness (397 feet) of grey (?Middle) Coal Measures is present beneath the unconformity. The electric logs show no indication of the cyclothems with marine beds near the base of the Coal Measures, and it is possible that the whole of the Lower Coal Measures are cut out with the Millstone Grit by Middle Coal i ~'kNAPTHORPE | I N~'G~
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extrusive rocks i n d i c a t e neighbourhood of coffLemporary Coal Me= . . . . . t.
F I o . 1 2 . - - L o c a t i o n m a p o f i g n e o u s r o c k s in K e l h a m Hills oilfield.
Measures overlap on to older rocks--in this case Carboniferous Limestone of approximately D 1 date-as was already suspected towards Stixwould (Lees & Taitt 1946, p. 291). (iii) Igneous Rocks in the Upper Carboniferous.--One of the ancillary results of oil drilling operations has been the definition of an important basic igneous province in the concealed Upper Carboniferous rocks eastwards of the East Midland Coalfield, with thicknesses of up to 600 feet of basaltic or doleritie rocks (Fig. 11). A preliminary account of the rocks in part of the area has been given by Edwards (1951). Much of the drilling has been carried out under conditions where speed was essential, coring necessarily restricted, and (under wartime conditions) with a minimum of staff, and only a limited amount of data was therefore obtained on contact phenomena at junctions with sedimentary rocks. Study of the relation between sedimentary marker beds has, however, provided a basis for distinguishing those igneous bodies which are displacive (and hence intrusive, probably post-Triassic) and those which are non-disp]acive (contemporaneous Lower Coal Measures and Millstone Grit extrusions). The conclusions reached from this study have been supported by several independent lines of evidence. The heaviest development is in South Nottinghamshire and North Leicestershire (Screveton, Sproxton, etc.), where it is associated with the major E.-W. fracture system which limits the southern Pennines and bounds the Widmerpool trough, but a belt trends generally northwards through Kelham
24
FALCON
AND
KENT
to Egmanton. Intrusive sills occur throughout this area, and contemporaneous extrusive rocks extend from Plungar as far north as Kelham, developed at two different levels of the Lower Coal Measures in the south and the north. Petrological identifications of the igneous rocks of the Caunton-Kelham area and at Widmerpool by Professor K. C. D u n h a m (Edwards 1951) are quoted below, and preliminary studies of the rocks N~9
N957
P
N~
N~
E~a R
Ne59
.-liJ
IA ~JN
M
i
I'
N98
! "" ~"-
.-. m
f
=
=
i
C
0
A
L
S! U
R
E
A
E
S
! ! ! i "'i
i
!
!
I
S
N A.
B~ FIG.
13.
A. Sections through contemporaneous igneous lenses, Kelham Hills oilfield, showing non-displs~ive relationships. B. Sections through intrusive igneous lenses, showing displacement of Coal Measures and Permian rocks. in the other areas have been made. A complete study of the material has still to be carried out, and the following description deals mainly with field relationships. C o n t e m p o r a n e o u s e x t r u s i v e r o c k s . - - T h e first recognition of contemporary flows was at Kelham Hills, where a belt of basic lavas occurs as a gently curving belt across the middle of the field 400 to 600 feet above the Millstone Grit, in the Lower Coal Measures (Figs. 12, 13A and B). This belt consists of one to three leaves of albitized olivine-basalt totalling about 60 feet, which are non-displacive, and have characteristic speckled (metamorphic) shale both beneath and in the interleaved sediments, but not in the overlying strata. Pyroclastic rocks occur at the same horizon in G4 boring a little farther to the
ON P E T R O L E U M E X P L O R A T I O N I N B R I T A I N
1945-1957
25
south-west. The same phase of extrusion is probably represented at Rolleston, five miles to the south, where an igneous sheet at about the same level in the Coal Measures close beneath the unconformable Permian is reddened by pre-Permian weathering, and can hence be ascribed to a relatively early date. The contemporaneous extrusives recognized farther south are at a lower level, replacing the early part of the Lower Coal Measures. At Screveton a thick igneous mass occurs from 2577 to 3044 feet, immediately above the Millstone Grit (the top of which may be missing) ; this was initially described as "alternations of light and dark grey altered basalt, probably lavas ", with ashy intercalations through the lower 150 feet. A group of coals immediately above was correlated with the Deep Hard-Deep Soft group, and spore analysis by R. W. Williams of the National Coal Board confirmed the absence of the lenisulcata Zone of the Lower Coal Measures. In a petrological examination L. M. Smith found the mass to be a series of highly altered flows of olivine-basalt, and noted that a thinner igneous leaf just below the top of the Millstone Grit (3059 to 3091 feet) was also of extrusive type. Thus almost the whole of that part of the succession normally occupied by the Lower Coal Measures and part of the Upper Millstone Grit is here represented by igneous extrusives. At Plungar the situation appears more complex, since extrusive and intrusive igneous rocks may be interleaved, and cannot easily be distinguished without continuous coring. 1~. G. W. Brunstrom, however, found a marker band (a speckled calcareous tuff) which maintains a constant distance of" 470 to 480 feet above the Millstone Grit despite variation of the igneous element in the interval from a normal 40 to 60 feet in the west to 200 to 280 feet in the east of the field, a relationship impossible to explain other than by a largely contemporary origin of the igneous rock. C. D. G. Black has described this igneous rock as so highly altered that the original constituent minerals are unrecognizable ; it is probably mainly micro-teschenite and micro-gabbro and (as at Screveton) built up from a series of flows. Farther south still, at Sproxton, north-east of Melton Mowbray, 330 feet of the 565 feet of beds ascribed to the Coal Measures is basic green igneous rock. At least one bed of tuff occurs, and a considerable proportion of the igneous rock may be extrusive. It was noted that a bed which occurred directly beneath the Bunter appeared to be weathered, and hence would be at least pre-Triassic. Contemporaneous igneous rocks probably occur at a number of localities in the Millstone Grit but information is mostly too scanty for diagnosis of their relationships, and they are (if present) of only minor importance. An ash bed was noted in the upper part of the Millstone Grit in North Nottingham, shire ; at Perlethorpe and West Drayton No. 1 this was thin (about five feet), at Farleys Wood No. 1 it measured 30 feet, including some agglomerates, in West Drayton No. 2 it had thickened to 75 feet and is presumably related to a local eruptive centre. At Bothamsall, close by, a rhyolitic tuff and agglomerate bed 178 feet thick occurs at a somewhat lower level, between the Chatsworth Grit and Kinderscout Grit horizons. Despite its thickness it has not been observed elsewhere. Palagonite tuff interbedded with mudstone was noted in the Pendleside Series (late P1 or P~) of the Widmerpool boring (5050 to 5160 feet) and tufts were identified also in lower P1. Previously, thin tuff bands had been noted at three levels in the P beds of the Ashby G1 boring (near Repton, South Derbyshire). Dr. G. H. Mitchell compared the latter with tufts in the limestone shales at Ashover farther north, and minor ash beds are probably a widespread feature in this series in the East Midlands. I n t r u s i v e r o c k s . - - I n t r u s i v e rocks are widespread at depth in East Nottinghamshire and southwards towards Melton Mowbray, but they die out completely at all horizons to east and west. They are in general of doleritic type, intruded as sills commonly of 30 to 100 feet in thickness. A number of these sills show contact features both above and below (for example at Kelham Hills, Farndon and Wysall), and the sills can frequently be distinguished from the extrusive rocks by their displacement of marker horizons. The preferred horizon for intrusion is just above the Millstone Grit, but they are also injected at higher levels in the Coal Measures where more strongly developed.
26
FALCON AND K E N T
In the north intrusive rocks are known at Egmanton, where a sill up to 61 feet thick is intruded into basal Coal Measures over half a square mile in the eastern part of the field ; at Cauuton, where the field spans the thinning edge of a 90-foot sill at the same level; in several isolated borings to the south and south-east of Eakring ; at Kelham Hills, where the sill follows an irregular N E . - S W . belt with a lobate southern m a r g i n ; and at Rolleston, where three sills total 250 f e e t . Both normal olivine-dolerite and the type described by Professor D u n h a m as analeite-olivine-dolerite occur in the basal Coal Measures of this area: their mutual relationships are not yet known. Farther south, sills occur at Screveton in Coal Measures above the thick extrusive mass (at 2308 to 2456 feet) and also immediately above the Carboniferous Limestone (3388 to 3457 feet). L. M. Smith identified the first of these as an alkaline dolerite and the second as a micro-teschenite. At Plungar multiple intrusion took place. From three to 11 igneous intercalations occur between the Kilburn Coal horizon and the basal Coal Measures sandstone, and several are sills, determined by C. D. G. Black as including micro-teschenites (mainly in the upper part), micro-gabbro and olivine micro-gabbro. Similar rocks have been found in the basal Coal Measures of South Nottinghamshire at Langar, Harlequin (Radcliffe-on-Trent), in a number of coal borings on the extreme south-eastern margin of the worked coalfield, at Widmerpool and at Long Clawson, but their intrusive relationship is mainly a m a t t e r of inference. The relative displacement of Coal Measures marker horizons can be demonstrated wherever there are several borings through sharply varying thicknesses of sill--at Egmanton, Caunton, Kelham Hills, Rolleston and Plungar. If the intrusion were a pre-Permian feature the arching which it causes would produce locally accentuated unconformity, but instead, in a number of cases, the Permo-Trias is displaced along with the Coal Measures. This is particularly clear in a section across the lobate margin of the Kelham Hills sill (Fig. 13A and B), but it is also shown by the local reversal of the regional easterly dip by the wedging action of the intrusion at Caunton and at Egmanton. (In the accompanying figure the top of the Millstone Grit is drawn as horizontal for clearer demonstration of this effect.) I t follows t h a t there is a strong probability of a post-Triassic date for the intrusion of the sills, as of the Swinnerton dyke of Staffordshire. A major intrusive phase of post-Permian date has lately been suggested for the northern Pennines (Bott & Masson-Smith 1957, p. 106). Among other matters, this provides a possible explanation of the occurrence o f " white trap " over the Kelham Hills oilfield (Edwards 1951, p. 79) but not down-flank, for if the igneous intrusion is as late as this it must post-date emplacement of the oil, and could well have reacted with p a r t of it to produce the characteristic abnormal development of carbonate-kaolin rock. H a r d bitumen specks in the oil sand beneath the intrusion may be a relic of the thermal metamorphism of the oil which took place at t h a t time.
(d) East Yorkshire (Table I I I ) (i) Fordon and Loclcton.--Two structures have been drilled in the southerly part of East Yorkshire, namely the surface Scarborough-Lockton anticline and a concealed structural high beneath the Chalk near Fordon indicated by geophysical work (Fig. 14). An a t t e m p t was made to assess the significance of the seismic structure at Fordon by drilling three shallow holes west of H u n m a n b y (:North Fordon G1, G2, G3). These and the subsequent deep test showed an expanded red chalk and marl development at the level of the " Belemnite Marl " in the Middle Chalk, a great thickening of the Red Chalk proper and of the Speeton Clay. Cores and samples showed this to be genuine stratigraphical thickening, not due to steepening of dip or to repetition. D a t a are tabulated below from west t o east : - -
1945-1957
ON P E T R O L E U M E X P L O R A T I O N I N B R I T A I N
27 SPEETON
Surface elevations Chalk base (below surface) Red Chalk (s.s.) thickness . Speeton Clay thickness
G3
G1
G2
No. 1
CLIFFS
537 OD
300 OD
245 OD
429 OD
--
285 52 610
160 75 695
523 91 446
-20-25 296
295 100 520-F
(All measurements in feet) The Speeton Clay micro-faunas from G 1 were examined by the Geological Survey, who reported t h a t cores from the middle p a r t (600 to 614 feet deep) correlated with the upper C~ level of the coast, and by Dr. J. W. Neale, who found a lower horizon (881 feet) to correspond with upper D/lower C. Dr. F. W. Anderson identified an Acroteuthis from a core just above the base at 917 to 923 feet. The thickening of the Speeton Clay is thus probably by expansion of the whole series. The top of the Kimmeridge is m a r k e d by a few inches of brown shale, with a change from the greenish grey of the Speeton Clay to dark grey or black shales below. A few feet beneath the junction in G3 boring an ammonite fauna was found by the late W. J. Arkell to contain Pectinatites and Keratinites of the pectinatusZone, suggesting t h a t
6~o or 6 4 0 0
~Oo ~
[ Gln(t
-/
ll~
_
jo;"1 /
le FIG. 14.--Fordon : seismic reflection contours on Permian limestone, and shallow borehole locations.
the westward expansion of the Speeton Clay is paralleled by the incoming of higher Jurassic beds beneath the Cretaceous unconformity inland from the coast. I n t e r p r e t a t i o n of the seismic work in the light of all the well information suggests t h a t the Chalk conceals a strongly step-faulted area, with some fractures reaching surface, comparable with and no doubt continuing the structures of the Howardian Hills (P1. I, fig. 2). Of the deep borings, Lockton No. 1 was drilled to test the Middle Jurassic sands and limestones, Fordon to test the Permian limestone reservoirs on behalf of the Gas Council. The sections are summarized in Fig. 16. The Lockton No. 1 boring proved a normal sequence down to the Lias, in which it terminated. Fordon No. I proved an expanded Kimmeridge Clay sequence b u t a t t e n t u a t e d beds from there down to the Bunter. Little coring could be carried out at Fordon and Dr. J. E. H e m i n g w a y gave much assistance in correlation at the time of drilling. The Corallian shows a single cycle of oolite on sandstone ; the Oxford Clay and Kellaways are thin ; the Cornbrash is apparently represented by 5 feet of recrystallized grey limestone, and the various marine members of the Estuarine Series are very thin (Scarborough limestone, 5 feet of sandy limestone with belemnites ; Millepore Bed, 57 feet of semi-oolitic limestone and sandstone ; Ellerbeck Bed, 4 feet of cementstone ; Dogger, a few inches of conglomerate). The J e t Rock of the early Upper Lias was entered directly beneath the Inferior Oolite and the Middle Lias Marlstone
28
FALCON
AND
KENT
Ironstone appears to be absent. Middle Lias pale silty shales and Lower Lias are lithologically normal but thin. The Keuper consists of 170 feet of red marl resting on 158 feet of sands and silty marls with a halitebearing bed in the lower part. This is a total of only 328 feet as compared with about 1000 feet at Eskdale and more than 700 feet near Market Weighton, but it is possible that at this level the boring crosses a fault. The Bunter measures 1037 feet and overlies 568 feet of Saliferous Marls (as near the Tees). The Permian section proved to be a southward extension of the potash basin of the Eskdale-Whitby area developed to full thickness, with three main evaporite groups (the uppermost rich in sylvine)
Exposed
Concealed -
~176176 o o
o
i Millstone Grit, o[ Lower Carboniferous
%,, o
-
Coal Measures
o~
- o,- 7 " / / / ~
~
; / /,,>'h,,,
7.'i i I i I i i i i i /
/ // 7 /~ / / ~ / . / / / "~co~b/ / . . / t "
- ;~_ /.--->, _ Eskdslell ,.- .: t J",,~Robir ,in Hoods Bay
o
/_
~.,,:/A,./ / / //5/G.
///A
C / / /Cl~yeFand Hills
.~
~.-~-
-~)
o
,.
/_
/-
--
--
_/--
--/-
(~. ~ l
--'~.
\
....
J~ o
0
0 0
Ok,.~ 0
x . . ~'--
0
: ~: ~oI 0
0 OMGO
o
o
o
~0
.
. 0
---__---~ ~ ~ 0 O ~ Fordon N g |
..
mu
**
o
o
0
~o~
i~176176 o
.
=--%
Strongly faulted bel~
~
OoOoOo o
......
o
o
L
o
0
0
o
o1,,
o - - _0
0 "~..~ <./_.~ ,A -<'/..//>Jk
~ /__~ __ t _ H. a. .y .t o n - N ~ .,.'::-
--
--
--
o,
t
- - ~ " " ~ "--.
.
~ C
M
,~ . . . . .
~--_-
~ o
$
10
I
!
I
20 I
Scale
3o I
40 I
50 MILES ,l
Fro. 15.--Hypothetical map of the sub-Permian floor in East Yorkshire. separated by the Carnallitic Marl and Upper Magnesian Limestone, resting on a very anhydritic development of the Lower Magnesian Limestone. From 7135 to 7559 feet (final depth) Fordon No. 1 penetrated Millstone Grit (to about 7245 feet) and "Yoredales", developed as pyritic siltstones, sandy shales and sandstones. Cravenoceratoides (E z age) was identified by the Geological Survey 50 feet below the Permian, and beds at 7175 to 7183 feet are considered to represent the Colsterdale Marine Beds of the West Yorkshire outcrop. (ii) Eskdale, Robin Hood's Bay and Redcar.--The first deep test in the centre of the Permian basin o f north-eastern Yorkshire was drilled from analogy with conditions in the potash basin of South Germany (Lees & Cox 1937); the discoveries made at that time have been followed by twelve more exploratory borings, of which ten were put down to define the thickness and value of the potash deposits by Imperial Chemical Industries Ltd. (Fleck 1950) and Messrs. Fisons Ltd., and two more sunk in continuation of the search for gas. One of the potash borings, made at Robin Hood's Bay by Fisons Ltd.,
1945-1957
ON PETROLEUM EXPLORATION I N BRITAIN
29
has also been deepened to explore for hydrocarbons, and two tests (one on behalf of Imperial Chemical Industries) have been made in the Kirkleatham area near the Tees (Fig. 17). The stratigraphy and mineralogy of the evaporite deposits have been described at length by Stewart (1954), Dunham (1948), Hollingworth & others (1948), and this aspect of the subject will not be included here. Surprisingly sharp changes in thickness have been discovered in the evaporites, and in consequence the positions of crests at depth in the two Permian limestone reservoirs are considerably displaced from the surface culminations. LOCATION
MAP
\
FORDON
CHALK
II !
No.1.
I--41 I
I
I
i'"(''("i RED CHALK SPEETON
? SCALE ?
?,,,,
614'
,'j'"-',
CLAY
LOCKTON No.1.
ESKDALE No.2.
1060'
/
KIMMERIDGE
CLAY
/oX CLA
....
~
/
J
234o"'71
LIAS
jKELLAWAYS
KEUPER
4,4,
I':.'-.:'"'I
/
80y
'u
,
M / I ~
:~ oso'
FEET
o2
]
/ ~ 3 1 S '
/
/I
I
500--
-;-.'/ 9 "," "~'I 67o /
/
I---b~891'-~
!::"'!
/, /
~I'-'.-~-.-'-i-I--~'*o
/:;.~.:.:':1 ~'77"r-" . . . . i 2865'~1".'.'"". U I
LOWER LIAS & RHAETIC
/
.=;_: :.~j. "" ":'." :'-~-,~.:1142'
CORALLIAN II!...! .I. . . . .I. .,.LL . . .IJ. 24os,~' ~ 1 " - , ' . OXFORD & KELLAWAYS ESTUARINE
o
Jrr'~r~-~ CORALLIAN ,
/
-':::'-::1
J: .',,, : %. ?,v / 9 ,:.-...: .. :l~oso,/ /
/
L
~
1
/
1000-_
( u I
++" '"
/
,
Du .,.c-r,.,, RHAETIC
-- ~ - 1 2 4 0
9 1,00'
"1_
~
1500.
KEUPER
2000 =
2190;
F r o . 1 6 . - - M e s o z o i c sections in E a s t Yorkshire.
The structural and stratigraphic knowledge gained by the potash exploration drilling suggested that the divergences between surface Jurassic structure and Permian sub-surface structure were great enough to warrant seismic investigation, in spite of the unfavourable topography. Seismic reflection work was consequently carried out over the area of the Eskdale anticline, with extension lines to the Robin Hood's Bay anticline ; the opportunity of some seismic ship trials also allowed some marine reflection work to be carried out in Robin Hood's Bay. This work confirmed the divergences and also depicted the PermianCarboniferous junction.
FALCON AND KENT
30
The major thickness changes in the Permian proved by drilling in this area (see Raymond 1953) occur in the evaporite group between the two Magnesian Limestones. It is not yet known how much of this change is due to relative upward movements during Permian deposition, or how much is regional due to the sinking of the Permian basin as a whole. Some stratigraphio anomalies in well records suggest that more faulting is present at depth than is known at surface, this being an additional hazard in seismic work. HAYTON
NO 1
FORDON
NO 1
ROBIN HOOD'S
BAY N ~ !
KIRKLEATHAIvl
r ,,, MARL
KEUPs
473'
] '
, 33"135'
597' KEUPER
WATERSTONES
L
/?
_
~
_
BUNTER
KEUPER
xf ? 3663'
:'::::: 884'
BUNTER
: : . . : :....,
1670 t
1148 w
ilii
BUNTER
i " : i "i"
9. : . ' . . ".
9 o,. Ao~9
.4700 ' ,. : ".'.... 2079~
SALIFEROUS MARLS
UPPER MARLS // , H, / / .2520 ~ U.MAGNESIAN LST. ,// MIDDLE MARLS~_ ' ' ' i,2409' LOWER MAGNESIAN LIMESTONE
%%§
~
" ~ ":-~ --~ --'='-r
_ U
/
"
~
^
::
X
COAL MEASURES
MILLSTONE GRIT?
+ A + A . ~: + l A+A+ 9 I
% ~L
I
\ L. EVAPORITES
+
/3822 ~ ".D.
+I
~
^
^
+
|
,
+ P + P §+ A I_ ~ MAONES,AN - 6 9 3 4
~ ~
L
J
~s2os
^^^
A
MAGNESlAN LIMESTONE
3380'
/
/
"~ "~
/
L/^
!^'
Iv ^ / ~ " / I I / / /I [/^/ 9
/ ~i ".:.' ;.' .. '.. .' . 131s4' / p J I . . . . . . . IEo~P,, / ? YOREDA,~ 1 " 4 - . I~lnthror~eros / . . . . . ~. . . . L lot (~ir/yoceras}
+
+^ ^I
l'l" + + AI l+ ^ + l + +^ ^
///19
/
/ " ' l . . MAGNESIAN //LIMESTONE / /
+1
/
+A ^ +^ / I I,,~ I'47~5'
/ ,_if' ,J
~
L.',..',.'.:
^ I I
I,I
,
"~Kirkleathorn
| MIDDLESBOROUGPI
I ^ 1A j__j___jj j '. :Q ?.~ I96'
~ ' ~ WHITBY
~ooln nooa's I}a~/
"
:..!'it
MILLSTONE GRIT I "M~ & YOREDALES l ? ' . ' : " ' : . '
,
2187
EVAPORITES +A ^+A A+ , LST; " , " , <: 2404 L.EVAPORITES ~ / ] ? ^ +. A "C! 2543w
~
~ 1 1 ^ 1 ^ I1 ^ I ^ I I
.
--"-------
~.'.-'_:
~ . M A G N E S I A N
+ + i+ •+ +"-+" +~. + ~+~. + + ---t..-- --
ppppp
~E_~
-500
+ P+
+
', ' / ^ I ^;" + "', 9^-i,38zo I
LOWER EVAPORITE GROUP
++%' + 1
§
+ + EVAPOR TES~ A+ + A A++^ + +
v---i-S877' ~
~'" "" " " " 1978'
UPPER_MIDDLE ~ X ' + A + ^ +
]
MARLS
SALIFEROUS MARLS
., 5268 U EVAPORITES 2 S .+S.:+"I CARNALLITE " .r 5 -t. J 5425' MARLS 9 ] 5501' _ M " EVAPORITES- + - + -+1 . . . . , ___..._-----U. MAGNESIAN ~. "~ "I-A.t-At /I ~oo~ LIMESTONE U. MAGNESIAN LI MESTON'E~
\\ X
.: -..:.
; : :" :.: " , - 9' " " 2680 --------SALIFEROUS
..::..:~
SANDS
N~ l
SAR,OROUG, Fordon
LEGEND "1000
Sa I t . . . . . . . . . . . . . . . . . .
Sylvine ......
Anhydrite
& Gypsum..
Dolomite ....
Polyhalite
.............
Limestone...
15(30
YORK |
0 i ,l
oHaytcn |,1
IO
20 MILES I
FIG. 17.--Permo-Triassic sections in East Yorkshire. Up to the present, gas in potentially commercial quantities has been found only in the Upper Magnesian Limestone in Eskdale No. 2 and in the Lower Magnesian Limestone in Eskdale 10, and in quantities somewhat below the commercial level in Kirkleatham 1 and Kirkleatham 2. C a r b o n i f e r o u s . - - T h e r e does not appear to be a regular structural rise southwards from the Durham Coalfield, for "Yoredales" were reached in old borings north of the Tees and were proved close to Redcar in Kirkleatham No. 2 boring, while probable early Millstone Grit was reached beneath the Permian a little farther south. The Cleveland Hills boring proved (containing shales of E2 age) Millstone
ON PETI%OLEUI~ E X P L O R A T I O N I N B R I T A I N
1945-1957
31
Grit overlying Lower Carboniferous "Yoredales" farther south-west (Fowler 1944) but later beds have been recently proved near the coast at Robin Hood's Bay (Fig. 15). In the northernmost of the Kirkleatham borings (No. 2) Dr. Stubblefield identified at 2900 to 2903 feet a fauna including the brachiopods Chonetes hardrensis (Phillips), Spirifer cf. calcaratus McCoy, S. bisulcatus oystermouthensis Vaughan and the ostracod Paraparchites cf. okeni (Mfinster). Lower down (2974 to 2977 feet) Productus (Dictyoclostus) muricatus Phillips was obtained. This compares with the fauna of the Middle or Upper Yoredale facies, although it is not closely diagnostic. Kirkleatham No. 1 well, one mile to the south, yielded a fauna likely to be somewhat younger ; the age was somewhat uncertain but a possible Anthracoceras (3351 feet) and latissimoid productids and other brachiopods suggested the E or P~ stages, to a limited extent comparable with faunas found in Cleveland Hills No. 1 (Fowler 1944). Twenty-five miles to the south-east of these borings, the deepening of Fisons No. 1 test at Robin Hood's Bay by Imperial Chemical Industries and BP Exploration Company proved Coal Measures beneath the Permianmmainly sandstone and siltstone, with a fauna of non-marine lamellibranchs and plants identified by Mr. M. A. Calver of the Geological Survey as indicating the junction of the similis-pulchra and modiolaris zones. Lamellibranchs identified included Naiadites (5216 feet), Anthraconaia cf. pulchra (Wright non Hind), Anthracosia intermediate between ovum Trueman & Weir and phrygiana (Wright) and Naiadites cf. productus (Brown) (5226 to 5232 feet). Seismic reflection data suggest that the axis of the Coal Measures syncline is likely to be somewhat to the south of Robin Hood's Bay, but a rise farther south is demonstrated by the recognition of basal Millstone Grit with Cravenoceratoides beneath the Permian at Fordon, as mentioned above. P e r m i a n . - - T h e r e is little to add to the descriptions of the Permian rocks near Whitby already published. Only one hole, at Robin Hood's Bay, has been taken through the Lower Limestone in the Whitby district, and this proved 461 feet of a dolomite-anhydrite rock, with these minerals partly intergrown, partly finely interbedded with strikingly " crinkled " bedding-planes (" enterolithic " structure), passing downwards near the base into calcite-mudstone, argillaceous limestone and shale. The lowest 20 feet were a silty mudstone with groups of small pebbles upon a red haematitic conglomerate. The Bunter in the various borings shows the fine- to medium-grained reddish sandstone facies characteristic of Yorkshire, with no well-marked subdivisions. Thicknesses increase from less than 800 feet at Redcar (Kirkleatham No. 2) to a maximum of 1157 feet at Eskdale (E5) ; the spread of records shows that, like the overlying Keuper, the axis of the depositional basin trended south-south-westwards from Eskdale towards York, where the thickness has been estimated at about 1400 feet. Keuper lithology varies mainly in the development of evaporite content. The junction with the Bunter appears quite sharp (with very slight representatives of the sandstone intercalations in the lower beds known farther south) and the lowest 100 feet in the Eskdale area and Robin Hood's Bay contains a large proportion of halite, with lesser quantities of anhydrite (Fleck 1950). The thinner Keuper of the Redcar-Guisborough area lacks this development, but halite in minor quantity was indicated at Fordon by a rise in the salinity of circulating fluid during drilling. The thickest halite is thus in the centre of the basin, with Fordon in a subordinate extension of the basin comparable to that of the Permian potash. At Eskdale No. 4, where this group was cored by Imperial Chemical Industries, the sequence showed 130 feet of closely banded red, brown, grey and mauve anhydritic or silty marls, overlying a 100-foot interval mainly of salt with anhydrite in the top few feet and a 15-foot red and grey marl parting near the base. This was separated from the Bunter by a further 25 feet of grey and red-brown anhydritic marl. This is a development corresponding in position and (except for absence of associated marly limestones) in lithology to the Muschelkalk of the western Netherlands. Gypsum beds near the top of the Keuper (the ~ewark Gypsum horizon) have been recognized at Redcar (Kirkleatham) but not elsewhere.
32
FALCON
AND
KENT
Overall the Keuper thickness reaches a maximum of 1000 to 1200 feet along a belt extending southsouth-westwards from Eskdale towards York, with attenuation to less than 700 feet near outcrop in the north-west and probably about 400 feet at Fordon in the east. Beyond this the axis of the trough swings southwards, maximum deposition south of the Humber being approximately along the line of the lower Trent (Swinnerton & Kent 1949, fig. 18). The Rhaetic sequence of the Eskdale area has been described in detail (Raymond 1955) ; in general it shows an upper group of greenish grey silty shales and mudstones (Cotham Beds) resting on normal Black Shales. Reddening of the Cotham Beds occurs locally as in Lincolnshire, and is particularly well marked at Fordon, although details there are uncertain (possibly through faulting). In general, thicknesses vary from about 35 feet near outcrop to a maximum of 50 feet in the centre of the basin. L o w e r L i a s . - - N o marked changes in the Lower Lias succession are seen between the North Yorkshire wells. The lithology in the Tees valley is very similar to that of Eskdale and Robin Hood's Bay, except that a well-marked silty band at Eskdale (oxynotumZone or a little higher) is poorly developed farther north. Thicknesses vary rather irregularly, from 870 to 912 feet at Moordale and Tocketts near Guisborough (one anomalous low measurement is probably faulted) to a maximum of 1027 to 1020 feet in Eskdale 3 and 11, and the formation thins both east and west (703 and 765 feet on the coast, 760 feet at the Cleveland Hills boring). This is a trend comparable with that of the Trias. Beds above the Lower Lias are well known from outcrop sections, and the deep borings beginning at horizons ranging as high as the Estuarine Series have not added critical information on them.
(e) West Yorkshire (Table III) Production of oil from the Lower Carboniferous at Duke's Wood (Eakring) led to renewed interest in this reservoir, which had produced oil for many years at Hardstoft (Derbyshire), and in this connexion A. H. Taitt directed attention to the easterly extension of the Ribblesdale group of folds. In three of these (Skipton, Burnsall and Harrogate) the Lower Carboniferous is exposed, but several others are eroded down to low Millstone Grit horizons only. It was considered that the edge of the Askrigg massif, bounded by the North Craven fault, swung east-north-eastwards towards Ripon, with the belt of midPennine folds and associated reef knolls on its southern side and the Coxwold-Gilling faults marking the continuation of the Craven fault-belt immediately to the north. The Aldfield and Sawley folds were selected for particular attention on the advice of Dr. R. G. S. Hudson, who carried out the field-work necessary for definition of the crests. Aldfield was contoured on the Cayton Gill horizon and had an indicated closure of 300 feet ; at Sawley mapping of the Brimham Grit, Cayton Gill Beds and Follifoot Grits suggested closure of about 100 feet. In addition, a seismic refraction survey near Boroughbridge defined a complex pattern of northeasterly trending folds on the same line ; one of these, at Ellenthorpe on the Swale-Ure confluence, was chosen for a test boring. Drilling proved that the tectonic expression provided by marked folding is not a reliable guide to recognition of the edge of the buried Askrigg block, for Aldfield drilled through an abbreviated blocktype early Millstone Grit succession, reaching massive limestone at 322 feet (PI. II). The limestone (penetrated for 105 feet) yielded a normal D 2 fauna. Sawley, only three miles to the south, started at approximately the same horizon but reached Lower Carboniferous almost a thousand feet deeper, at 1268 feet, and proved a normal gulf type of early Millstone Grit, with the Colsterdale Marine Beds at 425 to 435 feet (identified by Dr. J. E. Hemingway), the Red Scar Grits at 435 feet, the Grassington Grit at 937 feet and the Great Scar Limestone (in which drilling ceased) at 1268 feet.
ON
PETROLEUM
EXPLORATION
IN BRITAIN
1945-1957
33
The Ellenthorpe test proved to be not ideally situated, a thick (327 feet) Lower Permian limestone having vitiated interpretation of the seismic results, but it was drilled to 3198 feet through a gulf-type succession. The sub-Permian unconformity was passed at 1241 feet and the boring entered D~. zone (with Girvanella) ; Caninia juddi (Thomson) and Lithostro~ion loauciradiale (McCoy), suggestive of the D~ zone, were identified at 1388 feet and 1400 feet respectively. The boring then penetrated 2205 feet of alternating limestones, shales and sandstones of Yoredale facies, finally reaching massive limestone at 3465 feet. Dr. Stubblefield originally suggested that the latter might be of C~S~ date, from the evidence
FORMBY SEA LEVEL
N.o4
N~ 5 32' o.o.
N~
36' O.D.
Marls KEUPER
=
So.dst~'~
/
== 1
./
"JUpper~/
Waterstones --~3~, Mottled ::::::: Sandstone !iiiiiii Sandstones ::!:i:i: /BUNTER ....
Waterstones
Horls
Sandstones
KEUPER
lg'O.D.
-- sg"
130"
Naris
N? I
28" O.D.
KEUPER
~
26o'
.... ,:::. v.v.
,2so'
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S~ndston~es I
2.2
.:....
97.-'. .... ....
....
i.~:,8~5" Upper :':':': Pebble Bed/~s .ot.,d !:i:i:!: !!:i~' Sandstone :::::::: ':')~"2sl~~ blorls,;:'-:"2555' PERMIAN] ;':::::::: :"["LowerMillstone Gnt)l ~778" BUNTER I~::::::: ; ~ ~ BU.-'CARB" I 3 ~\,~\ 7~ Pebble Beds
::::-::
- -
Manchester Collyhurst PERHIAN
BUNTER
,:..:.
.....:
];UNTER
v,'.'. '.'.v. .... .... v.v. .... .... .... .... .... '.v.-. .... .... 9.-,..-.
.... '.'.v. 9...... ....... v::, '.v:. .... .... v::. ....... ..,..:. v.'.'~ .:.:-. .... .::.-. .:::. .... ....
9-
=,.,.=
32sd 3 5 4 0
.....: -'...
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U. CARB ~ 4 3 5 ~
Oott.om of /'/o/e
.-'.', v.v
.v:: .....:
:::22:2: :..
.:'2'2"2 X.2.
....
Monche PERMIAN~ Collyhurst
s
'2";-i :.2-2"2:
{(.-]
/4e3s'/ Collyhurst
:;ii:il
S~.ds*on, ?i.....i!i?
MillstoneGrit UPPER i CARBONIFEROUS !
5883
j= 7140
LOWER
CARBONIFEROUS m BOttom
FIG.
18.--Borehole
of
Ho/e
7680'
sections in the F o r m b y area.
of a~ assemblage including Girvanella ducii (Wethered), Koninckopora, Zaphrentis aft. delanouei Edwards & Haime and Syringopora reticulata Goldfuss. This ascription was, however, tentative, and is not now accepted by Dr. Hudson. Structurally it may be concluded that the edge of the Carboniferous block passes between Sawley and Aldfield, but from here it probably swings nearly north-eastwards parallel to the Ellenthorpe group of folds, which are on the gulf side. Whether this boundary is faulted (by fractures not recognized at surface) or whether the block sinks evenly into a downwarp beneath the Vale of York, as Dr. H. C. Versey 3
34
FALCON AND K E N T
suggested, cannot be determined from present evidence, but the suddenness of the change tends to favour the former. Versey's alternative suggestion of a trough between two rigid blocks (the easterly one being beneath the Market Weighton area) is supported by the gravity evidence (P. H. N. White 1949), and by seismic evidence of a structural syncline beneath the Permian (possibly a northward lobe of the coalfield). The significance of the Howardian Hills-Flamborough Head fault-belt in relation to sedimentation is still under consideration. (f) Lancashire (Table IV) The British Petroleum Company Ltd. has continued exploration of the Formby area, and has drilled also in the Upholland area of the exposed coalfield. Messrs. Steel Brothers have drilled two holes on the Croxteth inlier, Liverpool, operations described elsewhere (Magraw & Ramsbottom 1956, Pinfold 1958). (i) Forn~by Area. O p e r a t i o n s . - - D e s p i t e the negative results of earlier deep drilling at Formby (Kent 1948) the occurrence of oil in producible quantities in the Keuper has demanded continuation of a search for the primary reservoir, and three more deep test holes have been drilled (Fig. 18) with that object. In addition, sixteen " shallow" holes, ranging in depth from 65 feet to 1159 feet, have been drilled to investigate the Triassic rocks, and others were planned for 1958. These shallow holes aid the study of the Carboniferous structures by removing some of the unknown elements, and offer the prospect of fmding additional shallow oilfields. The results of this shallow drilling are reviewed later in this section. The first of the deep holes (Formby No. 4) was located on a gravity high west of Formby town. This had attracted attention as implying underground conditions contrasting with the great thickness of Permo-Triassic sandstone in Formby No. 1, and comparison was made b y one of us (N. L. F.) with the remnant of Permian on the floor of the Ribble valley near Clitheroe--a valley which is clearly an exhumed Permo-Triassic feature, with a homologue in the Formby area. A gravity analysis by L. H. Tarrant (unpublished) showed that a buried Carboniferous valley could explain the observed major anomalies. Seismic work (limited by surface obstructions) indicated a structural high, and the well when drilled encountered Lower Carboniferous (Pendleside Beds) directly beneath the Permian Manchester Marl, the 2345 feet of Collyhurst Sandstone in No. 1 being overlapped. The comparison with the Ribble valley was thus confirmed, and the valley east of Formby may in fact be its direct continuation (Fig. 19). Overlap of Manchester Marls on to a structural high suggested a possible seal of oil-bearing Millstone Grit at the unconformable junction, and as seismic evidence proved a steep northward dip in the Carboniferous rocks, No. 5 well was located on a seismic high on the outskirts of Ainsdale to search for such a stratigraphical trap. High Millstone Grit was encountered beneath the Permian, the fall from No. 4 being about 5000 feet in 389miles, but the Collyhurst Sandstone was present in a thin development and hence the Grit was not sealed. The Collyhurst itself, however, contained oil, no doubt migrated from below the unconformity, and a further test well (No. 6) was located immediately east of Freshfield to explore the wedging Collyhurst Sandstone at its up-dip edge, seismic refraction evidence being used to assist location. In the event, extreme velocity changes in the Bunter invalidated the interpretation of the evidence, and drilling ended abortively at 5294 feet in the top of the Collyhurst Sandstone, in a succession with the later Permo-Trias even thicker than in No. 1 well. A combination of stratigraphic overlaps on a pronounced Carboniferous topography, Carboniferous folds and faulting plus intra- and post-Triassic fault movement makes the Formby area a particularly difficult one for exploration. Between Ormskirk and the coast west of Formby seven important faults are now known from borehole and surface evidence, and others are suspected. Wherever their alignments are proved they run due 1~.-S. (Fig. 20). South of a line joining Ormskirk and the mouth of the Alt, five faults are mapped on the Geological Survey New Series Sheet 83, having alignments roughly NNW.-SSE., but the relative
ON PETROLEUM EXPLORATION IN BRITAIN
1945-1957
35
scarcity of borehole evidence makes the relationship between these and the N.-S. faults uncertain. Most of the faults near Formby cannot yet be identified with named faults farther south, but the Hillhouse fault has been shown to swing through 40 ~ at Hillhouse, and thence to run due north. The magnitude of some of the N.-S. faults is surprising. Thus, the Altcar borehole lies in a N.-S. graben less than a mile wide, bordered to the east by the Hillhouse fault with a throw of 600 to 700 feet and to the west by a fault (possibly the northward continuation of the Ince Blundell fault) throwing 800 feet. S u m m a r y of S t r a t i g r a p h y . - - T h e Lower Carboniferous of 1~o. 4 well was correlated with the Pendleside Limestone succession in Formby No. 1 ; the 1102 feet penetrated yielded Girtyoceras (P stage) at 3215 feet, Posidonia qnembranacea McCoy around 3700 feet, and sponge debris and sparse foraminifera similar to those of the Lower Bowland Shales at various depths. In part the beds were vertical, with alternations of shales with finely banded limestones and calcareous sandstones showing evidence of slumping during consolidation, and many small calcite-filled fault fractures. The beds were reddened
~~
W.9"S / Cost O D :]
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i ....
S.20"E.
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....
.........
, ....
i ....
W.
Z.
Crit~eroe .
.
verrnia n
~ "
Illlll,.,.i
Pendle Hill !
I ~"
|
C.M.
. . . . . . . . : :-- . ~ .- . . . . " f- ^n^s L C " :'. "-::'-'-:::::':!!f O.D.
A P TE.~I$
FIG. 1 9 . n C o m p a r a t i v e sections through the F o r m b y a n d Clitheroe areas.
to a lesser depth than was the Carboniferous of No. 1 well (700 as against 1100 feet), weathering not having reached so far down as in the original valley bottom. The Millstone Grit in No. 5 well was penetrated to a depth of 176 feet and showed empurpled shales with goniatites probably belonging to the G. cumbriense band (i.e. just below the Rough Rock), including Gastrioceras of. cumbriense Bisat and Anthracoceras, resting on 70 feet of reddened fine to medium sandstone in which drilling ceased. The Collyhurst Sandstone-Millstone Grit contact in Formby No. 5 was cored; the break was not marked by any angular unconformity or conglomerate band and was identified only after the discovery of the goniatites in a shale band. Variation of the thickness of the Permian Collyhurst Sandstone has already been mentioned ; the Manchester Marl above shows almost as much change, being 290 feet in No. 1,405 feet in No. 6, 223 feet in No. 4 and 53 feet in No. 5. The base is marked by a group of limestones or dolomites, which at No. 6 were fossilfferous with Bakewellia antiqua (Miinster), Pleurophorus costatus (Brown) and Pseudomonotis speluncaria (Schlotheim) identified by the Survey ; they also yielded to the late A. G. Davis a foraminiferal fauna of a richness unmatched in this country, including Pachyphlora sp. nov., Padangea cf. kingii (Jones), Hemigordius milioloides (Jones, Parker & Kirkby), Glomospira gordialis (Jones & Parker), and Ammodiscus roessleri (Schmidt) (provisional identifications). The upper limit of the Manchester Marl is not easy to fix in a transitional series, nevertheless the general evidence of marked regional attenuation towards the
36
FALCON
AND
KENT
north-west (independently of the form of the buried Carboniferous floor) seems reasonably strong. Not only are the limestones thicker in the fuller development, but bands of marly anhydrite also occur. The Bunter showed the effect of locally varying differential subsidence. No. 4 well on the structural high proved 1385 f e e t ; No. 6 (a mile and a half north-east) 3261 feet ; No. 1 (one mile south-east of No. 6) 2020 feet ; and No. 5, n o r t h w a r d of the others, 1648 feet. The Keuper Sandstone also shows strong variation, with 450 feet on the structural high, 561 feet at No. 5, b u t only 280 feet at No. 6, b e t w e e n there and the 970 feet of No. 1. Thus in the Manchester Marl and the Bunter, No. 6 was in a downwarp or graben, in the Keuper Sandstone it was on a block subsiding more slowly. These variations are best
SCARISBRICK~
O$~$ 4 , 3 - -
~Shallow Prod ucing~______ F i e l d about 5 0 ~ shallow boreholes "~=m~s a n d a r o u n d this a r e a ~ - ~ - v 0 ~
......... ........ ~176176176 ~176176 ....... ~ ..... ~176176176176176176176176176176176176176176176176176
,...,.....,..,
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ,,oc ":.:.:.:C.:.Z'.:.:.:.Z Z.Z Z :.; Z.Y::.:.:.:.Z.:.:.:'.Z: :~:~:~:~:~:.:~:~:~:~::~:~:~:~:~]~:~Z~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:.:~`:~:~ ".'#/.'.'.'.:'-.....'.'.',',',','.....'.'...':,,.......--'.'2..-..: - : : : ; [:::::: :::: :5:::: [:: :5:::[: ::::::::: k~'.'.'.'.':.';.'.'.*.'.'.':.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.;'.'.'.'.v
REFERENCE Faults
Shallow
Measured
_ _ _1.. Dips --~, Dip calculated f r o m B / H e l e v a t i o n s ~ , o f the Keuper Sandstone
Deep Boreholes Depth in feet below Sea Level to top o f K e u p e r Sandstone
FOR MAT IONS Keupsr Marl Keuper Sandstone Bunter Sandstone
BoPeholes
G4 0 mS 0
SURFACE E X P O S U R E S
,~, Keuper Bunter
Sandstone Sandstone
SCALE OF MILES 1 J
'
'
I
O
1
2
$
I
I
I
l
R. 0. W. 8RqNSTROM
FIo. 20.--Geological map of the Formby area, showing post-Triassic faults.
ON
PETROLEUM
EXPLORATION
IN
BRITAIN
37
1945-1957
explained by movement of some of the faults during Permo-Triassie times, but the controlling p a t t e r n is not yet apparent. The Keuper Waterstones (120 feet of greenish shales and sandstones at the Downholland oilfield) are not so clearly differentiated farther west or towards the south-east, and the greenness at the oilfield may be partly due to reduction by hydrocarbons or by the associated oilfield gases. (ii) Upholland.--Among the structures of West Lancashire the Upholland faulted inlier of Millstone Grit attracted attention as a large well-defined and accurately controlled feature, situated in an area in which, from the evidence of regional trends and the fold pattern, the Carboniferous might be expected to be in block facies or, alternatively, marginal to the P e n d l e - F o r m b y gulf. A gravity survey showed high values over the inlier, tending to support expectation of a Carboniferous structural block, and a seismic survey indicated a regional southerly rise of deep beds along the line of the inlier. A preliminary boring (Upholland G1) was sited on the upthrown side of the block to test the Upper UPHOLLAND N.Ol. ZTZ'I o.o.
5'66~ CRAWFORD
~. I
N. 66 ~ E. .~
.+"
"~Iz-I$ ~
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,,
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=I_ 5OO'"
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.ooo.-
o.,
isoo'
15oo'-:
+o
d
,4000'-
-3500' -4000"
4500'-:_ 5000~
d
9
ArleFM;ne(Coal)
AM
Coal Measures ~ Mills[one G r i t ~ FTG.
So.~tom o nole49951~
.
.-.: :"
9 9 .'""
2
'~'o6i/,+,~oe~ " 9 ;I
/
=,500. -5000' A.~r,,,+~.
21.--Structural section through Upholland No. l boring.
Millstone Grit beds, and the main hole was subsequently located near the southern end of the inlier, starting on the downthrown side to cross the main fault and encounter the Lower Carboniferous near the structural culmination. I n the event, the test drilled Middle Coal Measures to 290 feet, Lower Coal Measures to 962 feet (where the first major fault was crossed) and an expanded Millstone Grit in gulf facies ranging down to the E zones to 4995 feet, where drilling was abandoned (Fig. 21). Comparison with the standard sections in the area (some within two miles) shows t h a t from 600 to 700 feet of Lower Coal Measures are cut out by the first fault. The Upper Millstone Grit is developed much as in the Rossendale area and the upper part can be ascribed to the Rough Rock and Haslingden Flags, with the Middle Grit group below 1550 feet. At 1991 feet a further major fault was encountered, cutting out about 1700 feet of strata, and below this, fossiliferous mudstone (R1) with interbedded sandstones and shales can be correlated with the main Kinderscout and Parsonage sandstones of Rossendale, although appreciably thinner. Beneath are the Sabden Shales (H and Eg. stages) underlain by nearly 1300 feet of exceedingly hard silicified mudstones and fine sandstones, with E 1 fossils near the top. There was no evidence of age through the lower 800 feet ; on analogy with Formby, incoming of shale intercalations near the base indicated a possible approach to the Lower Carboniferous. A minimum figure of 5600 feet for the Millstone Grit thickness is thus obtained. Such a Millstone Grit development could hardly be envisaged over a structural block, and it seems
FALCON
38
AND
KENT
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ON PETROLEUM
EXPLORATION
IN
BRITAIN
1945-1957
39
likely that the margin of the Pendle gulf runs between Upholland and Croxteth, and possibly across the Rossendale area (Fig. 22). A considerable thickness of Lower Carboniferous rocks in a relatively un. attractive facies is thus to be expected beneath, and drilling depths to massive reservoir limestone would be relatively great. (g) The Midland Valley of Scotland (Table V) The basis of exploration in the Midland Valley of Scotland has been given in G. M. Lees's previous communications (Lees & Cox 1937, Lees & Taitt 1946). The Calciferous Sandstone Series has throughout been the principal objective, as containing good reservoir sandstones plus oil shales as possible source beds, and attention has been mainly given to those structures marginal to the basin where early migration conditions were favourable. In 1938 gas with a little oil had been found in the Cousland anticline, Midlothian, and three additional structures were drilled in 1944-46: Salsburgh (near Airdrie), Easter Pardovan and Blackness (near the Firth of Forth). Dr. W. Q. Kennedy gave valuable advice during these operations. Further exploration of Cousland has more recently been carried out for gas production, and an exhaustive study of the gas prospects of the region has been made under the direction of A. H. Taitt. Since resumption of operations is envisaged in the future the following account is limited to the specific objectives drilled since the last report. The Salsburgh structure is a broad, gentle, well-defined anticline, with closure of 200 feet in the coalfield east of Glasgow, which brings Millstone Grit up to 146 feet from surface. The boring therefore proved the whole sequence from the basal Coal Measures downwards, ending in probable Lower Old Red Sandstone lavas (P1. III). The Millstone Grit measured 306 feet, the Carboniferous Limestone Series 1613 feet and the Calciferous Sandstone Series 1925 feet, the basal part being overlapped against a southerly shoreline. These measurements are much thinner than in the basins to east and west, and confirm expectation of a transverse ridge (or swell) which controlled sedimentation. Sandstones were not well developed, but at 2739 to 2884 feet a sandy facies of the Upper Limestone Group (below the Houston Marls) yielded gas at the rate of 330,000 cubic feet a day. Apart from this show, hydrocarbons were represented only by slight traces of oil. Volcanic ash was reached at 3657 feet and red and purple tufts at 3990 feet. At 4041 feet the boring entered homogeneous white trachyte with feldspar phenocrysts. This was compared by Dr. W. Q. Kennedy with the acid lavas of the Lower Old Red Sandstone, the junction probably corresponding with lateritic beds at 3990 feet. The Easter Pardovan boring was located on the northern culmination of a faulted dome half a mile south-west of Philipstoun. It started in the Upper Oil Shale Group (Champfleurie-Dunnet horizon) of the Calciferous Sandstone Series and was taken into the Lower Oil Shale Group. The Dunnet Sandstone was proved at 292 to 402 feet and yielded gas at the rate of 13,000 cubic feet a day. Seven other horizons yielded a little gas with water, but on the whole reservoir conditions were poor. Structural control of the shallower horizons is good, and failure is to be ascribed mainly to lack of good sands at depth, with the possibility also that sharp thickness changes may displace the underground crest relatively to the surface. TheBlackness dome, on the southern shore of the Firth of Forth, is a symmetrical structure with closure exceeding 300 feet located near the northern margin of the main Calciferous Sandstone basinm a locality which should have been favourable both for reservoir conditions and for early migration. Drilling began in the Calciferous Sandstone Series 750 feet above the Burdiehouse Limestone, and a normal development of the Lower Oil Shale Group, unfortunately with few and indifferent sands, was drilled to 2085 feet. At this depth the well entered lavas (albitized basalt or rhyolite) which continued to the final depth of 2455 feet. These were considered unlikely to be the Arthur's Seat volcanic group but
40
FALCON AND KENT
were regarded as very early Carboniferous or possibly Devonian, and as deeper prospects were unpromising the well was abandoned. A small oil show was obtained by testing thin sands just above the lavas, and negligible quantities of gas were obtained at higher levels. Lack of success is due mainly to poor reservoir conditions, although, as at Easter Pardovan, divergence between surface and underground structure cannot be excluded. I I I . ESTABLISHED OILFIELDS (a) General At the time of the last review five oilfields had been discovered--four in Nottinghamshire and a very small one at Formby, Lancashire. Exploitation of each of these has continued and up to the end of 1957 had produced the following cumulative quantities : F o r m b y (1939) 9500 tons, Eakring (1939) 256,000 tons, Duke's Wood (1941) 473,000 tons, K e l h a m Hills (1941) 241,000 tons, and Caunton (1943) 32,000 tons. s The new fields at Plungar (North Leicestershire) and E g m a n t o n (near Tuxford, Nottinghamshire), both geophysical discoveries, have now come on production, with the following figures to date : Plungar (1953) 11,800 tons, E g m a n t o n (1955) 36,000 tons. I n the older felds there has been little new development (production from the thin Kinderscout Grit at E a k r i n g is a minor exception) and attention has been mainly concentrated on secondary recovery operations by peripheral repressuring of the sands--particularly of the R o u g h Rock, which is markedly lenticular and has poor natural water-drive characteristics. This has involved drilling a n u m b e r of new holes for water injection around the field margins at Eakring, Duke's Wood and K e l h a m Hills, b u t the additional structural and stratigraphical data obtained show no divergences from the interpretation of Lees & Taitt. Operation of the secondary recovery scheme has been described by Dickie & Adcock (1954), and the practical results have more recently been illustrated by W a r m a n & others (1956). Only the two recently developed fields are therefore described here. Of the additional discoveries of the last few months Bothamsall, on the Eakring nose, has an oil-sand development in excess of 85 feet and appears to have reserves of the same order as E g m a n t o n , although its areal extent is likely to be less. Corringham, near Gainsborough, m a y be somewhat smaller t h a n this.
(b) The Plungar Oilfield, Leicestershire The consensus of evidence up to 1952 suggested t h a t there was a higher probability of finding commercial oil accumulations in the zone of sharpest thinning of the Millstone Grit t h a n either to east or west. Plungar, situated in this zone in N o r t h Leicestershire between Barkestone No. 1 (with almost no sand) and Long Clawson No. 1 in the Widmerpool gulf (with thick sandy Millstone Grit), was believed to be on the western flank of a Carboniferous Limestone high defined by seismic refraction work and to offer the possibility of stratigraphic oil traps in lensing sands. This general expectation was fulfilled in 1953, although the structure as subsequently detailed independently by seismic reflection work and by drilling proved to be rather more complex, consisting of an irregular flattened subsidiary dome about one mile across with a steep southern flank on the edge of the Widmerpool gulf (Fig. 24). Three sandstone groups have been proved, one in the basal Coal Measures and two in the Millstone 8 The cumulative crude oil production figures to 31 December 1959 are as follows :-Formby . . . . . . . . . . . . . . . . . . . . 9,6{~8tons Bothamsall (1958) . . . . . . . . . . . . 8,066 tons Eakring . . . . . . . . . . . . . . . . . . 267,928 ,, Corringham (1958) . . . . . . . . . . . 2,485 ,, Duke's Wood . . . . . . . . . . . . 511,780 ,, Gainsborough (1958) . . . . . . . . . 1,211 ,, Kelham Hills . . . . . . . . . . . . . 259,151 ,, Kimmeridge (1958) . . . . . . . . . . 2,366 ,, Caunton . . . . . . . . . . . . . . . . . . 34,595 ,, Plungar . . . . . . . . . . . . . . . . . . . 18,650 ,, Egmanton . . . . . . . . . . . . . . . . 106,842 ,, [Note added 23 February 1960]
ON
PETROLEUM
EXPLORATION
IN
BRITAIN
41
1945--1957
Grit. Sand conditions in this marginal zone have, however, proved highly variable, and less than half of the wells drilled (21 by the end of 1957) have yielded commercial production, so that Plungar has remained one of the smallest fields of the United Kingdom. Its discovery and development are to be regarded as a stage in the exploration of a favourable belt adjoining the thick deposits of source-rock type in the Carboniferous gulf, a belt which may in the long run provide a number of fields.
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FIG. 23.---Millstone Grit succession at Plungar. Physical characteristics of the sands with specimens of the electric and gamma logs obtained at Plungar have been published by Warman & others (1956, p. 342). Plungar is situated on the Lower Lias, and the wells penetrate the earlier part of this formation, the Rhaetic, Keuper, Bunter and Carboniferous in downward sequence (the locality lies south of the limit of the Permian). The great development of igneous rocks in the Coal Measures has already been described ; the following paragraphs briefly outline the stratigraphy of the pre-Permian rocks. Carboniferous Limestone.--The top of the Carboniferous Limestone has been cored without finding diagnostic fossils, but a shelly horizon 464 feet below the top in No. 8 well yielded Gigantoproductus,
4~
FALCON
AND
KENT
Zygopleura cf. rugosa (de Koninck) and corals which are referred to D r This is the deepest penetration so far ; it encountered continuous massive "block facies " limestone with n o shale partings or igneous rock.
Millstone Grit.~Goniatite bands have been found in the Upper Carboniferous with sufficient frequency to give a fair idea of absolute dating. Identifications listed are by Dr. W. H, C. Ramsbottom of the Geological Survey. The first is the G. subcrenatum band (Pot Clay Marine Band) marking the base of the Coal Measures, which yielded the zonal goniatite in No. 8 and less distinctive faunas in other wells, in each case at the top of the middle group of sandstones. About 25 feet lower is a bed with G. cf. cancellatum Bisat, and 50 feet below this the R,. stage is indicated by Reticuloceras reticulatum mut. 7. Seventy feet lower is a group of shelly brachiopod shales with Productus carbonarius de Koninck and Punctospirifer cf. northi Muir-Wood, which may be a condensed deposit. Near the top it has yielded Reticuloceras j~
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paucicrenulatum Bisat & Hudson of R 1 age (No. 15 well) ; a little lower down goniatites identified as either Homoceras or Cravenoceratoides indicate H or E 2 age (No. 17 well). These beds (within the Lower Grit Group) may be transgressive, although the exact horizon of the possible stratigraphic break is still uncertain. The lower beds which wedge in south-westwards towards the gulf have not yet been dated, but from their lithology could be either P or E beds (Fig. 23). Sand Development.--The Plungar productive sands are conveniently :named, strictly locally and not implying correlation with any other locality, the Upper, Middle and Lower Grit groups. Of the three groups, the Upper Grits belong to the Lower Coal Measures, the Middle Grits represent Rough Rock to Chatsworth at outcrop (R~ and G), and the highest part of the Lower Grits is equivalent to the Kinderscout (R1). Both the Upper and Middle Grit sandstones proved to be exceedingly variable, and at the standard interval of 1000 feet between borings it was impossible to predict which bed would be of reservoir quality. The field has therefore been developed with production from six different sands, only one or two of which are yielding oil in any one well. The Lower Grits are individually more constant, but the lower part of the group (below the Rz stage) shows a remarkable expansion from 55 feet in the east of the field to 300 feet one mile away in the south-
ON P E T R O L E U M E X P L O R A T I O N I N B R I T A I N
1945-1957
43
west, an expansion on the edge of the Widmerpool gulf described above. This expansion takes place essentially by addition of beds between the main group of Lower Grits and the Carboniferous Limestone, beds including shale, muddy limestone and fine to coarse sandstone. Gamma-ray survey indicates that most of this series is marine, but up to the present it has not been dated. Coal Measures.--At :plungar 1400 to 1500 feet of Coal Measures survive beneath the unconformable Trias. The lower half of this thickness is occupied mainly by basic igneous rocks (partly contemporaneous and partly intrusive, as noted above) but includes coal seams of two or three feet in thickness at about the Kilburn horizon (identification based on a marker scheme by M. W. Strong ; see Appendix). The upper half is a normal Middle Coal Measures sequence with 10 to 12 coal seams, mostly of one or two feet but occasionally thicker. Reddening of the measures extends downwards about 150 feet in the south and west, but as much as 500 feet in the north (lqo. 5). A feature not yet finally settled is the age of a group o f " micro-conglomerates " beneath the Bunter. This group is 30 to 60 feet tMck and consists of one or two beds of fine conglomerate or breccia of Coal Measures material, usually immediately beneath the Bunter but sometimes separated from it or divided by 20 to 30 feet of shale. The micro-conglomerates appear to be unconformable to the stained Middle Coal Measures on which they rest and may represent either the missing Permian or Upper Coal Measures ; they are, however, lithologically different from both the breccias and conglomerates of the marginal :Permian and from the nearest known Upper Coal Measures. The basal Coal Measures sandstones which provide commercial production in one or two wells are presumably the split equivalent of the Crawshaw Sandstone of the outcrop, since they directly overlie the subcrenatum band. A persistent oil-bearing sand also occurs at the top of the igneous column (possibly at the Wingfield Flags level) but production has not been obtained from it. .
(c) The Egmanton Oilfield Shortly after discovery of the Eakring group of fields seismic refraction surveys defined a culmination north of Ollerton, at Farleys Wood, and drilling here found thick oil-soaked sandstones which were too impermeable for production. Attempts were made by reflection surveys to distinguish other structures in the adjoining areas, but it was not until 1954 that more modem equipment and methods led to the definition of a gentle WNW.-ESE. fold at Egmanton, near Tuxford. A location was chosen on the culmination and commercial oil production established in 1955. Nearly 50 wells have now been drilled under the geological supervision of H. R. Warman and K. H. Roberts, proving a field of size comparable to Eakring and Duke's Wood, with production from the basal Coal Measures and upper Millstone Grit. The Egmanton field as now defined measures three miles long by half a mile wide with an oil column of about 120 feet in the Millstone Grit. It has well-marked flanks to north and south (dipping at 3~ to 4 ~) but the plunge closure is so limited that it is reversed in different beds by stratigraphic thickness changes ; Coal Measures horizons have little or no closure to the west, while the Carboniferous Limestone continues to rise eastwards to beyond Sutton-on-Trent (Fig. 25). The only known fault of importance is a fracture along the southern flank, downthrowing north, which produces a minor subsidiary culmination. The field is situated on the Keuper outcrop (Fig. 26), and wells penetrate the normal mid-Nottinghamshire sequence of Bunter, :Permian, Coal Measures, Millstone Grit and Carboniferous Limestone. The development is closely similar to that of the Eakring group of folds five miles to the south-west, except that the Upper :Permian limestone is present here, and (unlike Eakring but as at Caunton and Kelham) an igneous sill occurs in the Lower Coal Measures in the eastern part of the field. Millstone Grit.--The top of the Millstone Grit has been taken at the base of a marine shale representing the Pot Clay Marine Band, subcrenatum horizon, although the fauna has not been recovered. (In contrast to Plungar, no identifiable marine faunas have been obtained in the Millstone Grit sequence, despite a
44
FALCON AND KENT
moderate amount of coring.) This is a more constant feature than the top of the Rough Rock, and is clearly recognizable from the gamma log (Warman & others 1956). The grits as a whole (with an unknown but probably small proportion of Lower Carboniferous) thin eastwards from 652 feet in No. 13 to 500 feet in No. 3, a distance of three miles. Correlation is lithological in the absence of datable faunas, but the sequence is so similar to Eakring t h a t broad identification is possible. The first grit group is the Rough Rock, which varies from a maximum of 90 feet (No. 1) to 20 to 30 feet (Nos. 3 and 5) and (as at Eakring) yields the greater part of the production of the field. The second grit group, correlated provisionally with the " Longshaw " of Eakring, varies from 20 to some 55 feet (No. 5) ; it has yielded commercial producCONTOURSON THE:.
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tion in four easterly wells. The lowest grit group, separated from this by 20 to 30 feet of shale, is the most consistent in thickness and grain-size. Generally it is coarse to medium in grain and measures 80 to 90 feet with two or three shale breaks ; it is correlated with the Chatsworth Grit of Eakring. I t has an oil content b u t has yielded water only on test. 9Beneath this level are 200 to 250 feet of dark shales, thinning eastwards, which may include a Lower Carboniferous element. I n general they are calcareous, but show a siliceous development in the area where the thick sill is present in the overlying Lower Coal Measures (in well No. 3). Igneous rock is also interleaved locally with the middle part of the lower Millstone Grit shales but its relationships have not been determined.
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Coal Measures.---The base of the Permian falls eastwards along the Egmanton structure more steeply than later Coal Measures horizons, and the thickness of Coal Measures consequently decreases from 1800 feet in the west to 1450 feet in the east. The highest marker horizon consistently recognized is a black impure limestone thinning eastwards from 20 to about three feet which is correlated with the Mansfield Marine Bed ; this is about 200 feet below the unconformity in the middle part of the field. The Clay Cross Marine Bed occurs 700 feet lower, as usual in a barren interval between the Top Hard and the Deep Hard-Deep Soft groups of coals ; the marine fauna has not been recovered but confirmation of identity is provided by the gamma-ray log. The chamositic horizon recognized by M. W. Strong as the Kilburn Marker, here without an associated coal seam (see Appendix), is 500 feet lower still, about 200 feet above the Millstone Grit. It was already known from exploratory diamond borings that the coals are poorly developed towards Tuxford, and the Egmanton borings (although not accurate as to thicknesses) confirm this tendency, which goes much further in the syncline between the Trent and Lincoln. From 20 to 25 seams of one foot or more are encountered, but nearly all appear to be below workable thickness. Of the main groups the Deep Hard-Deep Soft-Tupton group appears to be of most potential value. Both the basal Coal Measures sandstones and the Wingfield Flags equivalent are oil-bearing, but production has not been obtained from the latter owing to poor permeability. Acknowledgments.--The authors wish to thank the Chairman, Sir Neville Gass, and the Directors of the British Petroleum Company for permission to publish the information contained in this paper. It is based on the work of many members of the staff of the BP Exploration Company, but tribute must be paid to the co-operation and assistance received from various officers of H.M. Geological Survey, the East Midlands Division of the National Coal Board, a number of academic geologists who have acted as consultants, and the palaeontological staff of the British Museum (Natural History). In particular we would like to name the following :-H.M. Geological Survey : Dr. C. J. Stubblefield, Mr. W. N. Edwards, Dr. F. W. Anderson, Mr. R. V. Melville, and Dr. W. H. C. Ramsbottom. Academic : Professor F. H. Stewart, Dr. J. E. Hemingway, and the late W. J. Arkell. British Museum (Natural History) : Dr. L. R. Cox, Dr. Helen Muir-Wood, and the late L. F. Spath. The main burden of the compilation work and preparation of this paper has fallen on the junior author; valuable assistance has been provided by Miss P. B. Lapworth, Geological Librarian to the British Petroleum Company. IV. POSTSCRIPT NOTE (dated 5 January, 1959): MORE RECENT BORINGS IN SOUTHERN ENGLAND Since this paper was prepared, four additional borings of regional significance have been drilled : at Noke Hill, five miles north-north-east of Oxford ; at Shalford, two miles south-south-west of Guildford ; near Fordingbridge in Hampshire ; and at Radipole on the Weymouth anticline. These sections are summarized below, but it should be noted that positions of formational boundaries may be adjusted when full palaeontological and correlative information becomes available. Mr. A. P. Terris was Resident Geologist for all these boreholes. (a) Noke Hill, Oxfordshire Lat. 51 ~ 48' 40.8" ; long. 01 ~ 13' 06.6" ; elevation (ground) 314.5 feet O.D. The Noke Hill G1 boring was drilled on behalf of the Gas Council in an old quarry in the Great Oolite (White Limestones) on the Noke culmination of the Islip axis, five miles north-north-east of Oxford, to investigate the geology in the neighbourhood of the unconformity between Mesozoic and Palaeozoic
47
ON PETROLEUM EXPLORATION I N BRITAIN 1 9 4 5 - - 1 9 5 7
rocks near the junction of which gas was encountered in a boring at Calvert (Buckinghamshire) (Davies & Pringle 1913 ; Anon. 1911). No coring was carried out in the Mesozoic rocks, b u t Mr. J. M. E d m o n d s of Oxford greatly assisted with classification of the oolite limestones from cuttings. The section m a y be summarized as follows : - -
Depth Thickness of base in feet GREAT
OOLITE
SERIES
Oolitic limestones, silts and sandy limestones, with calcareous sandstone at the base . INFERIOR
125
125
17
142
220
362
18
380
433
813
OOLITE
Calcareous sandstones, carbonaceous and pyritic silts and sandy limestone . LOWER LIAS Blue clays, with ironstone nodules in upper part and shelly limestone beds below RHAETIC? Pale greenish grey silt and white calcareous pyritic sandstone DEVONIAN (OLD RED SANDSTONE),?with thin KEUPER above Grey-green silt, passing down by interdigitation into chocolate marl, on redbrown silty mudstone with wisps of interbedded sandstone. Lingula from 478 feet downwards. Bothriolepis at 574-580 feet and with Holoptychius from 658-660 feet. Penetrated to
The Lias section showed none of the pale, silty and s a n d y beds characteristic of t h e Middle Lias, and i t is consequently presumed t h a t Lower Lias only is present (as indeed the limited thickness suggests). The identification of the beds grouped as Rhaetie? is lithological ; t h e y are p r e s u m a b l y a marginal d e v e l o p m e n t of either this formation or (less probably) of basal Lias. The dating of the beds b e n e a t h is doubtful.
The grey-green silts are v e r y much like Tea Green Marl
and there m a y be some K e u p e r red marls present, b u t there is no lithological break between this and t h e mudstones with Devonian fossils (the fish were identified for us b y Mr. H. A. Toombs). Provisionally the whole m a y be grouped as U p p e r or Middle 01d R e d Sandstone, the greenish beds being regarded as c h e mically reduced during the marine Mesozoic transgression. The bedding was horizontal, or near horizontal, a n d the whole was in striking contrast to the lithology of the steeply dipping Lower 01d R e d Sandstone of F a r i n g d o n No. 1. I t compares closely with the description of t h a t at the Southall boring (Procter 1913). (b) Shalford, S u r r e y Lat. 51 ~ 12' 41" ; long. 00 ~ 35' 37.5" ; elevation 159.5 feet O.D. The Shalford test well was drilled two miles south-south-west of Guildford on the culmination of t h e Shalford (Peasmarsh) anticline, south of the sharp Hog's Back fold a n d t h r u s t near Guildford.
The
initial horizon was near the top of the Wealden (probably within 10 feet of the base of the Lower Greensand), and the section proved was as follows (normal lithologies are o m i t t e d ) : - -
Depth Th~kness of base in feet WEALDEN, 2208 feet Weald Clay . Hastings Beds . . PURBECK, C. 503 feet . PORTLAND and KIMMERIDGE, 1424 feet 9 Glauconitic sands and subordinate shales . Shales, mudstones, bituminous shales and thin limestones CORALLIAN, 205 feet Calcareous sandstones, mudstone and sandy oolitic limestones OXFORD CLAY, 219 feet GREAT OOLITE SEI~IES, 441 feet Cornbrash . . . . . . 9 ~ . . 9 Oolitic shelly limestones . Calcareous mudstones and silty argillaceous limestone
(Continued over)
.
1496 c. 712 c. 503
1496 c. 2208 2711
449 975
3160 4135
205 219
4340 4559
6 25 410
4565 4590 5000
48
FALCON AND
KENT
(Section continued)
I~E~XOR OOLITE, 229 feet Oolitic limestones, rubbly and muddy above, pisolitic in middle part, silty below . . . LIAs, 102 feet Grey calcareous mudstones and argillaceous limestone with ammonites RHAETIC, 54 feet Pale buff and grey, partly argillaceous and partly finely detrital sandy limestones with black shale in lower part CArBOnIFErOUS?, 245 feet Variegated red, yellow, greenish and purple mudstones with occasional thin sandstone bands Hard limestone breccia with quartz chert and jasper pebbles; red marl veins SILVRIA_N,87 feet proved Purple, green and grey mudstones with monograptids, Tentaculites and brachiopods
Depth Thickness of base in feet
229
5229
102
5331
54
5385
217 28
5602 5630
87
5717
The Wealden is remarkably well developed for a locality probably near its northern limit, but in this it compares with the section in the Geological Survey boring at Warlingham. The thick sandstone development beneath the Purbeck may well be entirely Portland Sands, b u t a sandier development of the late Kimmeridge comparable to t h a t of 0xfordshire is possible, and repetition by faulting is not excluded (although no sign of disturbance was seen in cores of the basal Purbeck or highest Kimmeridge
Clay). The Corallian was sandier t h a n in more central parts of the Wessex basin (contrasting with Ashdown and other places), but the Oxford Clay was normal. I n view of the occurrence of derived Oxford Clay fossils in the Lower Greensand of the Hog's Back it is interesting t h a t the upper part of the section to this level showed no major breaks, tending to confirm t h a t the erosion phase represented there is entirely post-Wealden. The Great Oolite Series was found to be in a very m u d d y facies, contrasting with the southern Weald, and it might be classified as mainly Fuller's Earth, with a thin Forest Marble development above, a repetition of the Dorset facies. Unfortunately only one core is available. In contrast to the Great Oolite, the Inferior Oolite was in the Cotswold facies. The very thin Lias section is likely to be defective, and lithology suggests t h a t Lower Lias only is present. A Rhaetic age for the lower beds was deduced from lithology, and this has since been largely confirmed by discovery of dark shales bearing pyritized shell fragments likely to be Pteria contorta (Portlock). No such beds are present at Ashdown. The beds grouped as Carboniferous were remarkably similar to the beds beneath the Lias at Henfield, cores of the breccia from the two holes being virtually indistinguishable. This further recurrence of similar red beds and breccia directly beneath the Lias again raises the question of whether they postdate the Variscan folding, and are thus late Carboniferous, Permian or Triassic. Below the breccia at 5630 feet the Silurian is weathered for 40 feet and shows steep dips. The fossiliferous grey mudstones in which the hole ended showed wavy and graded bedding in the silty and sandy bands. (c) l%rdingbridge, Hampshire Lat. 50 ~ 54' 17.7" ; long. 01 ~ 43' 59.6" ; elevation 229 feet O.D. The section of Fordingbridge No 1, drilled on a gravity and seismic high at Ogdens (Hasley Hill), near Fordingbridge, is still being worked out, b u t the following brief account may be given. Drilling began in the Tertiary beds of the Hampshire basin ; the Chalk was reached at 678 feet and the Upper Greensand and Gault penetrated from 1997 to 2251 feet. Beneath the Gault the well passed directly into Kimmeridge Clay, shown by a core 20 feet below the top to be Lower Kimmeridge (with
ON PETROLEUM
EXPLORATION
IN
BRITAIN
49
1945-1957
Aulacostephanus, etc.). 0 n l y 210 feet of Kimmeridge Clay remained beneath the Gault. The unconformity eliminates the Lower Greensand, Wealden, Purbeck, Portland and Upper Kimmeridge, measuring approximately 4000 feet in eastern Dorset (the nearest outcrops) and some 2700 feet at Portsdown on the other side of the same Tertiary basin. This represents a very considerable pre-Albian uplift. Beneath the Kimmeridge the boring proved a normal sequence of Corallian (about 170feet), Oxford Clay (about 430 feet), Cornbrash (35 feet) and Great Oolite Series (404 feet) 9 The last-named was mainly limestone, with only a minor development of argillaceous beds which could be ascribed to the Fuller's Earth, in marked contrast to recent borings nearer the Dorset coast (see the account of the t~adipole borings). Below, 118 feet of sandy and ferruginous limestones and ironstones are ascribed to the Inferior Oolite, and b e n e a t h this the well proved an Upper Lias development of Bridport Sands type, 250 feet thick. The remainder of the Lias was normal, except t h a t the Middle and Lower subdivisions totalled only about 450 feet and rested upon 60 feet of beds ascribed on fossil evidence to the Rhaetic. The well was completed at 4487 feet, 106 feet into the Keuper. (d) Radipole, Dorset Lat. 50 ~ 37': 53.4" ; long. 02 ~ 28' 56.8" ; elevation 48 feet O.D. Radipole No. 1 boring was the first to be drilled on the Weymouth anticline, and was sited on the basis of detailed structural mapping by M. R. House. The initial horizon was expected to be the base of the Forest Marble, but limestones continued to 242 feet. In view of the remarkable thickness of Fuller's E a r t h beneath, it seems possible t h a t they belong to the overlying formation, with abundant Rhynchonella fragments in the cuttings at 282 to 284 feet indicating the boueti Bed at the base of the Forest Marble. With this tentative qualification, the section is as follows : - -
Depth Thickness of base in feet FOREST MARBLE? Clayswith subordinate limestones to 163 feet, pyritic limestones and marl to 242 feet. Rhynchonella bed at base .
284
284
573
857
6
863
289 214
1152 1366
9 452
1375 1827
203
2030
FULLER~S E A R T H
220 feet of grey clay and pyritic marl, on 138 feet of grey silty limestones of " Fuller's Earth Rock " type, on 257 feet of calcareous mudstone, with rubbly impure limestones basally. INFERIOR OOLITE Shelly algal limestone UPPER LIAS Bridport Sands. Very fine grey quartz sand . . . . . . Down Cliff Clays. Silty mudstone on harder calcareous mudstone with nodules MIDDLE LLAS 9 Junction Bed. Glauconitic and micaeeous limestone . Sands. Fine glauconitic and micaceous sandstones and silty mudstones LowE~ LIAs Dark mudstones with silty bands and occasional nodules. Proved to
Cores showed the beds virtually horizontal, and no thickness correction is required for dip. Thicknesses of all formations were much greater than outcrop measurements or estimates. For the Forest Marble and Fuller's E a r t h this is partly due to the difficulty of piecing together faulted segments in the nearby outcrops, but the thickness of the Fuller's E a r t h far exceeds t h a t of any undisturbed section on record. The incomplete measurement of 450 feet at Chaldon Herring (corrected for dip) is perhaps the next largest so far known. Mr. G. A. Kellaway of the Geological Survey tells us that ammonite evidence suggests t h a t a lateral transition from Inferior Oolite limestone may be a factor augmenting the thickness. Earlier formations have undergone a marked easterly thickening, the Bridport Sands and Down Cliff Clays measuring much more than is recorded at outcrop (140 feet and 70 feet respectively), and the Middle Lias sands being nearly 80% thicker than near Bridport. 4
50
FALCON AND KENT N O T E ON T H E GEOLOGICAL S U R V E Y B O R E H O L E AT W A R L I N G H A M , S U R R E Y
T h e following details, supplied by Dr. C. J. Stubblefield, Assistant Director of the Geological Survey, will be useful for comparative purposes. This borehole was c o m m e n c e d in 1956 a n d completed in 1958 (Holmes 1958, p. 29). The base of the Chalk was reached at 395 feet a n d the base of the Weald Clay at 1624 feet overlying Hastings Beds a n d a full Jurassic succession. " The b o u n d a r y between t h e K i m m e r i d g e Clay a n d the clays at the top of t h e Corallian at 2987 ft is a fault ; at several levels in the Corallian below this fault natural gas a n d a little oil were found ; t h e gas yield was calculated at 35,000 cu. ft per day. Ferruginous beds occur b o t h in t h e U p p e r Lias a n d at the top of the Middle Lias. The base of the Jurassic was passed t h r o u g h at about 4500 ft a n d the borehole t h e n entered an i n t e r b e d d e d series of pale pinkish a n d grey crystalline limestones a n d red marls; marine fossils in the limestones indicated Lower Carboniferous age " (Pugh 1958, pp. 9-10). Rocks of this age continued to the final d e p t h of 5001 feet (Pugh 1959, p. 9).
V. APPENDIX.--LITHOLOGICAL A N D F A U N A L M A R K E R S
USEFUL FOR W E L L
IN THE U P P E R CARBONIFEROUS OF THE EAST M I D L A N D S SU~IMARIZED
FROM
UNPUBLISI~ED
REPORTS
BY
T. M. W .
CORRELATION
(PLATE IV) STRONG
The drilling of some 60 test wells outside the area of the productive fields of Eakring, Duke's Wood, Caunton and Kelham during the period 1942 to 1946 necessitated a study of the Middle Coal Measures and Millstone Grit sequences with a view to establishing reliable marker horizons, essential to the elucidation of the geological history of the area and sub-surface conditions in relation to oil formation, migration and accumulation. The Upper Carboniferous includes great thicknesses of measures in which similar cycles of sedimentation are repeated without major changes of conditions. In the lower 1500 feet of the Coal Measures, the paucity of marine markers and the impracticability of recognizing species among comminuted shell fragments in well cuttings forced attention on lithological sequences and peculiarities to augment such faunal data as could be observed. The results recorded below were obtained by binocular examination of cleaned well samples using a magnification of 50 diameters and strong illumination. Since these examinations were made extensive coring and electric logging have given a new precision to the stratigraphy of the Upper Carboniferous and may enable some corrections to be made to the correlations. The following notes refer mainly to the lower 500 feet or so of the Coal Measures, and portions of the Millstone Grit. LIST OF U S E F U L M A R K E R H O R I Z O N S D E S C R I B E D B E L O W (a) MIDDLE COAL MEASURES (i) Tile Mansfield-Two F o o t Marine Group (ii) The Clay Cross Marine B a n d (iii) The Lower W o o d Bed Sands (iv) False Kilburn (v) Kilburn Marker. (b) THE WINGFIELD FLAGS AND BASAL C o n MEASURES (LENISULCATAZONE) (i) The Wingfield Flags (ii) Green Shale a n d Thin Coal Group (iii) The Basal Black Silts, with fish a n d Lingula (iv) The Alton Marine Group (v) The Pot Clay Marine Group. (C) THE MILLSTONE GRIT (i) The R o u g h R o c k (ii) Pre-Rough R o c k (iii) Kinderscout (Hyalostelia Band).
(a) Middle Coal Measures (i) The Mansfield-Two Foot Marine Group.--Investigations of the Coal Measures lithology indicate the importance of recognizing black silts and black laminated shales, variably pyritic, ferruginous and calcareous. Many of the horizons represent widespread submergences and inundation by waters of varying
ON P E T R O L E U M E X P L O R A T I O N I N B R I T A I N
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51
salinity, with fish life and probably an associated micro-fauna, the conditions being sometimes indicated by chamositic material. These black silts contrast strongly with the paler grey and greenish beds which make up so much of the Coal Measures. If sampling is good they can be easily picked out and may prove more persistent t h a n some of the coals, which were laid down in swamps with changing margins and are sensitive to very small alterations of level. This group, some 200 feet thick, contains the Mansfield, Sutton, Haughton and Two Foot marine bands, which have been described by Edwards & Stubblefield (1948). I n the well cuttings, however, faunal remains are sometimes difficult to find and lithological guides are helpful. Marine or semi-marine bands are often associated with fine black silts, generally platy or splintery with fine disseminated specks of pyrites. Associated ironstones often exhibit micro-oolithic structure with spherical cavities from 0.25 to 1 mm. in diameter and filled with kaolinitic or dickitic matter. Frequently the Mansfield and the Two Foot are distinguished by hard black marlstone or "cank " developments which are recognizable. The Haughton and Sutton bands are fugitive and thin. These beds have been penetrated in the following wells : Mansfield No. 1, Perlethorpe No. 1, Farleys Wood No. 1, West Drayton No. 2, Sutton on Trent No. 2, Spital No. l, Norwood. (ii) The Clay Cross Marine Band.--This band, though widespread, is rather thin and variable in development. I n well cuttings useful local lithological developments include : Black shales with Lingula. Chalybitic, very calcareous siltstone, or silty limestone. Brown or grey micro-oolithic calcareous siltstone grading to limestone or ironstone, the ooliths being white kaolinitic or dickitic matter. Pale-green chamositic grains occasionally accessory. Similar to the above but with angu]ar white clay inclusions instead of round. The lithological developments are usually easier to find than the Lingula and among them the microoolithic siltstone and ironstone have been the most useful. The feature appears to be connected with brackish water or marine conditions and similar developments have been observed at several horizons higher up in the Coal Measures, particularly associated with such marine bands as the Mansfield and Two Foot etc. They are occasionally useful in tracking down such bands, which usually have black shale or ultra-fine silt developments. (iii) The Lower Wood Bed Sands.--About 200 feet below the Clay Cross in the Kelham, Eakring, Caunton and Normanton areas is the top of a sand group, up to 100 feet thick, with distinctive lithological features. I n this area the beds appear to overlie the Tupton Coal and may be an equivalent of the Tupton Rock. The sands are commonly of about 0.4 mm. diameter, sometimes fairly clean but with variable interstitial kaolinite. Chalybitic cementation is variable giving yellowish to deep-brown colours, and lower portions frequently show a tendency to micro-oolithic developments with kaolinitic material in sm~ll white round segregations. Sometimes a basal ironstone has a similar oolithic structure, and a green chamositic clay may be present both in the sandstone and in the ironstone. Coarse (0'5 mm.) mica flakes are occasionally present and also a basal ironstone, associated with much lignitic plant tissue giving a positive chloroform test. Local pyritic cementation near the base of the sand is not uncommon. Much of this lithology has been observed in higher sand groups, especially in those associated with the upper marine groups ranging from the Two Foot to the Top Marine Band. This suggests an association with brackish or semi-marine waters. The sands often contain small fragments of wood replaced by iron carbonate, the internal structure being well preserved. Large smooth spore eases (about 0"4 ram. diameter) are also found embedded in
52
FALCON
AND
KENT
the sands near the top and are easily recognized, though curiously indented by the pressure of the sand grains. Occurrences of these sands were found in the following wells, in addition to some of the Eakring, Caunton and Kelham Hills wells : Averham Park, Hockerton No. 2, Mansfield No. 1, Norwood No. 1, Normanton No. 1, Springwood :No. 1 and Sutton-on-Trent :No. 1. (iv) False Kilburn. About 300 feet or so below the Tupton Coal another useful band of black shale or silt, usually rather finer, typically contains chamosite and has been noted in many localities : e.g. Hockerton No. 2, Kirklington, Perlethorpe and Mansfield, as well as in Eakring, Caunton and Kelham Hills. This has been called the False Kflburn to distinguish it from the Kilburn (see below). (v) Kilburn Mar]cer.--Just below the Kflburn Coal, and usually separated from it by some 10 feet or so of pale fireclay and silty shMes, there is a bed of hardish black silt up to 20 feet thick usually distinguished by the presence of one or more bands of light- or dark-green chamosite grains (0.2-0.3 mm. diameter) or by dark-brown chalybitic grains in the lower portion. Fish-scales are commonly observed associated with the chamosite. This band has proved of use in general correlation and was found in the following boreholes : Averham Park No. 1, Eagle Moor No. 1, Farleys Wood No. 1, Farndon No. 1, Hockerton No. 2, Kirklington No. 1, Long Clawson No. 1, Mansfield No. 1, Maplebeck :No. 1, Normanton No. 3, :Norwood No. 1, Perlethorpe No. 1, Rolleston Nos. 1, 2, 3, 4, Spital No. 1, Springwood No. 1, Sutton-on-Trent No. 1, Sutton-on-Trent No. 2, Thorpe No. 1, Widmerpool No. 1, Winkburn No. 1 ; also in Eakring, Caunton and Kelham Hills. To the west and north, where the sequence thickens, additional beds of somewhat similar character are developed. For instance, at Mansfield No. 1 three beds of this type of silt are present, at 2280-2285 feet, 2308 feet and 2350-2360 feet, of which the bottom one overlies micaceous Wingfield Flags and is probably the equivalent of the beds elsewhere. The bed is useful where the Wingfield Flags are absent. Where several similar bands are developed, detailed lithological sequences would be necessary to ensure local correlation. Igneous intrusions often penetrate the Wingfield Flags and leave this bed still recognizable, though slightly altered, just above the contact. The action of the igneous material is apparently similar to that in the artificial " hydrafrac " process, and the preferred path is the base of a thick shale body above a sandstone, the sandstone being liable to assimilation.
(b) The Wingfield Flags and Basal Coal Measures (lenisulcata Zone) In the Eakring district this includes some 230 feet of strata divisible into the following groups, overlying the Rough Rock : - T h e Wingfield Flags Green Shale a n d T h i n Coal Group Basal B l a c k Silts, w i t h fish a n d Lingula Marine a n d Lingula groups (including A l t o n a n d ' P o t Clay lYlarine'groups)
c. c. c. c.
50 feet 80 ,, 50 ,, 50 ,,
(i) The Wingfield Flags.--These lenticular and variable sands underlie the Kilburn Marker and may exceed 50 feet in places. Shale breaks are usually present and may expand locally to occupy the whole interval, to the exclusion of sands. The top of the group is often recognizable through the inclusion of thin bands composed of brown, green and white mica concentrates, interbedded among highly micaceous or " f a k y " sands or flags. The bright brown and green micas are pseudo-uniaxial, while the white mica has a large optic axial angle. The diameters commonly reach 1 mm. No comparable mica concentrates have been observed by us in
ON PETROLEUM
EXPLORATION
IN
BRITAIN
1945-1957
53
the East Midland boreholes above this horizon. Below it, similar beds occur in the A l t o n - P o t Clay sequence, and possibly in the upper Rough Rock, but have not been observed below t h a t horizon. Conditions of deposition were rather quiet and the sediments in this region are mostly fine sands, usually less than 0.3 mm. diameter. I t may be mentioned t h a t the Wingfield Flags in places appear to contain black brackish-water silts, so t h a t it is possible t h a t at least some of their oil is indigenous, partly from such included sediments and partly from the overlying black silts. (ii) Green Shale and Thin Coal Group.--At Eakring this comprises some 80 feet of shales, with one or more thin coals with ironstones and fireclays. Dark-grey shale bands occur within predominantly palegreen shales and silts. The latter colour is extremely rare below this horizon. A fairly persistent coal with fireclay and sometimes ironstone often marks the base of the group. (iii) The Basal Black Silts, with Fish and Lingulae.--These beds, about 50 feet thick, occur over a wide area and form an important marker indicating the approach of the Alton beds. They are notably black and laminated and may contain disseminated and minute mica and pyrites. Occasional ferruginous staining gives a very dark-brown but distinctive colour. Several bands with fish-scales occur and there appear to be two thin coal and fireclay horizons with a thin shelly ironstone and black pyritic sandstone and ironstone near the base. This sandstone, or ganister, occasionally contains a few pebbles of 1 mm. or over and when stained black looks rather similar to the Black Grit t a n k which overlies the Alton Coal shortly below. With regard to the lateral passage of sandstone to ganister, many of the sandstones, especially in these basal groups, appear to have been very feldspathic and, when overlain by coals, were highly kaolinized, sometimes to such an extent t h a t the cuttings emerge as a white compressed kaolin putty, which has not been noted from other parts of the Coal Measures sequence. (iv) The Alton Marine Group : (a) The " B l a c k Grit ".--Below the basal coals of the Black Silt Group comes the Alton Marine Bed. This may be present as a shale with an Alton fauna passing down into a hard black or dark-brown, somewhat pebbly, sandy limestone or " eank ", carrying a marine fauna of goniatites, Lingula and Orbiculoidea. The cementation and colour are patchy. Zinc sulphide is often recorded at this horizon. This bed has been called the " Black Grit " and is a useful marker.
(b) The Alton Sand. I n many Eakring wells the Alton Marine Band overlies a chamositic sandstone with casts of Hyalostelia. This sandstone is variably altered by the overlying coal and may grade into a kaolinized or ganister-like rock. At other times it is a remarkably clean and porous oil-sand, up to 10 feet thick. Usually the sandstone contains bright-green chamosite grains and the casts of the central canals of Hyalostelia may be preserved as minute and short bright-green chamosite threads in cylindrical cavities in the sandstone. Beneath this at Eakring there are usually two coals and fireclays with a shelly ironstone roof. The rock is sometimes heavily cemented with pyrites and exhibits many forms depending o n its degree of alteration. When a highly kaolinized seat-earth overlies it, black sphaerosiderite is common. At other times a ganistery sandy fireclay is developed with a patchy, ankeritie cement, dark brown, translucent and crystalline. When the overlying sand contains mica, the kaolinization is accompanied by the development of soft white hydrated micas. All these developments are typical of, and apparently confned to, this group, but the presence of grits confirms the unstable conditions prevailing and it is not surprising t h a t local sequences vary rapidly over quite short distances. (c) The Alton Coal.--This Alton sandstone passes down into the Alton Coal with a variable shale cover and an underlying seat-earth which may be a fireclay or a sandy, gritty ganister, kaolinized and sometimes containing some brown, green and white mica.
54
FALCON
AND
KENT
(v) The Pot Clay Marine Group.--Underlying the Alton Coal are the marine black silts of the Pot Clay horizon carrying Gastrioceras 8ubcrenatum. This is the basal bed of the Coal Measures. The marine silts at times attain 10 feet at Eakring, but are not always found. They pass down into the Pot Clay Coal and fireclay which, though usually traceable and often thin, may reach about 10 feet in thickness. This fireclay, where well developed, has been known as the " Green Fireclay ", but is too patchy for more than local use.
(c) The Millstone Grit (i) The Rough Roclc.--The unstable conditions prevalent in the basal Coal Measures were even more disturbed during Millstone Grit times, and the variability of the Rough Rock has been noted in the literature. In most parts of Eakring the sands immediately underlying the Pot Clay Group are highly micaceous o r " faky ", and contain thin bands almost entirely composed of brown, green and white micas up to 1 ram. diameter. The top grits, which have pebbly streaks, are also peculiar in being remarkably clean and containing a noticeable quantity of euhedral quartz. These sands are usually not more than 25 feet thick and are underlain by a band of green fireclay with much sphaerosiderite. (ii) Pre-Rough Roclc.--The exact determination of the Rough Rock and post-Kinderscout Millstone Grit depends almost entirely on faunal evidence, particularly that of type goniatites in the associated shales, and lithological study has not proved of much help. The Rough Rock, Longshaw and Chatsworth are subject to very rapid changes in lithology and thickness and, without faunal evidence, only local correlations are possible. It has been noted, however, that below the Rough Rock of Eakring the dominant coarse mica is brown while the white and green micas are inconspicuous. Below the Chatsworth the Kinderscout and the underlying marine limestoneshale group are often distinguishable by a typical marine lithology and faunal content. (iii) Kinderscout Group (Hyalostelia Band).--Shortly above the H. striolatum horizon a sandstone occurs, often cherty and rich in spicular Hyalostelia remains, which is probably the equivalent of the Kinderscout Grit. Spicules have been observed in the following wells, in addition to some in the Eakring, Caunton and Kelham Hills fields: Averham Park, Farleys Wood No. 1, Barkestone No. 1, Bottesford No. 3, Long Clawson No. 1, Dunston 5To. 1 and Normanton No. 3.
Conclusions.--The main conclusions reached during these studies were as follows : - 1. In the Middle and Lower Coal Measures, black shales and silts either of marine or brackish-water origin are useful markers when used in relation to the main sequence. 2. Pseudo-oolithic ironstones are often associated with such beds. 3. The basal marine group of the Coal Measures, namely the Alton-Pot Clay Group, is traceable either wholly or in part over most of the East Midland area. Several distinctive lithological features, such as black silts and chamositic sands and coarse mica concentrates, can be used as guides limiting the search for faunal confirmation. 4. Between the Alton-Pot Clay Group and the Kinderscout only extremely local correlation is practicable owing to the disturbed conditions of sedimentation. 5. The limestone-shale group underlying the Kinderscout is generally distinguishable by its marine lithology and faunal content.
ON PETROLEUM EXPLORATION IN BRITAIN 1945--1957
55
V I . LIST OF REFERENCES
AGER, D . V . 1954. The genus Gibbirhynchia in the British Domerian. Proc. Geol. Assoc. 65, 25-51. 9 1956. The geographical distribution of brachiopods in the British Middle Lias. Q.J.G.S. 112, 157-88. ANDERSON, F . W . 1939. Wealden a n d Purbeck Ostracoda. Ann. Mag. Nat. Hist. (11) 3, 291-310. ANON. 1911. Coal boring a t Calvert. Iron & Coal Trades Rev. 83, 316-7. ARXELL, W . J . 1933. The Jurassic System in Great Britain. Oxford 9 . 1947A. The Geology of Oxford 9 Oxford. 9 1947B. The geology of the c o u n t r y around W e y m o u t h , Swanage, Corfe a n d Lulworth. Mem. Geol. Surv. BOTT, M. H. P., & D. MASSO~C-SMITH. 1957. The geological interpretation of a g r a v i t y survey of the Alston Block a n d t h e D u r h a m Coalfield. Q.J.G.S. 113, 93-117. DAvIEs, A. M., & J. PRrNGI~. 1913. On two deep borings at Calvert Station (North Buckinghamshire) a n d on the Palaeozoic floor n o r t h of the Thames. Q.J.G.S. {}9, 308-40 9 DICKIE, R. K., & C. M. ADCOCK. 1954. Oil production in the N o t t i n g h a m s h i r e oilfields. Journ. Inst. Pet. 40, 179-90. D~H_~M, K . C . 1948. A contribution to the petrology of the P e r m i a n evaporite deposits of Northeastern England. Proc. Yorlcs. Geol. Soc. 27, 217-27. ]~DM~I~DS, F . i . 1954. British Regional Geology. The Wealden District. 3rd edition. Geol. Surv. & Mus. EDWARDS, W. 1951 9 The concealed coalfield of Yorkshire a n d Nottinghamshire. 3rd edition. Mere. Geol. Surv. & C. J. STUBBLEFIELD. 1948. Marine bands a n d other faunal marker-horizons in relation to the sedimentary cycles of the Middle Coal Measures of Nottinghamshire a n d Derbyshire. Q.J.G.S. 103 [for 1947], 209-56. FALCON, N. L. 1955. [Results obtained from the borehole at Faringdon, Berkshire.] Proc. Geol. Soc. 1524, 93-5. & P. E. KENT. 1950. Chalk Rock of D o r s e t - - m o r e evidence of salt? Geol. Mag. 87, 302-3 9 & L. H. WARRANT. 1951. The gravitational a n d magnetic exploration of parts of the Mesozoic-covered areas of South-Central England. Q.J.G.S. 106 [for 1950], 141-70. FLECK, A. 1950. Deposits of potassium salts in N o r t h e a s t Yorkshire. Chemistry & Industry, Supplement, October 17, 1-15. FOWLER, A. 1944. A deep bore in t h e Cleveland Hills. Geol. Mag. 81, 193-205, 254-65. GIFFARD, H. P . W . 1923. The recent search for oil in Great Britain. Trans. Inst. Min. Eng. 65, 221-50. HOT.T,neGWORT~, S . E . 1942. The correlation of t h e g y p s u m - a n h y d r i t e deposits a n d the associated s t r a t a in the N o r t h of England. Proc. Geol. Assoc. 53, 141-51. , T. ROB~.RTSON, C. BURY & E. NAPIER. 1948. Evaporites : a symposium. Proc. Yorlcs. Geol. Soc. 27, 192-216. HOLMES, S. C . A . 1958. South-eastern District. Summ. Progr. Geol. Surv. for 1957, 29. HTYDSON, R, G. S., & G. COTTON. 1944. The Lower Carboniferous in a boring a t Alport, Derbyshire. Appendix I I : the U p p e r Vis~an a n d Lower N a m u r i a n of N o r t h Staffordshire. Proc. Yorlcs. Geol. Soe. 25, 254--329. KENT, P . E . 1947. A deep boring a t N o r t h Creake, Norfolk. Geol. Mag. 84, 2-18. --. 1948. A deep borehole at F o r m b y , Lancashire. Geol. Mag. 85, 253-64. ~. 1949, A structure-contour m a p of the surface of the buried pre-Permian rocks of E n g l a n d a n d Wales. Proc. Geol. Assoc. 60, 87-104. --. 1953 9 The Rhaetic beds of the N o r t h e a s t Midlands. Proc. Yorlcs. Geol. Soc. 29, 117-39. --. 1954. Oil occurrences in Coal Measures of England. Bull. Am. Assoc. Pet. Geol. 38, 1699-1713. KING, W. B . R . 1949. The geology of the eastern p a r t of the English Channel. Q.J.G.S. i04 [for 1948], 327-38. --. 1954. The geological history of the English Channel. Q.J.G.S. 110, 77-102. LEES, G . M . 1947 9 [Cores of red beds from the Willesden boring a n d boring log of a well at Formby.] Abs. Proc. Geol. Soc. London, 1436, 13-14. & P. T. Cox. 1937 9 The geological basis of the present search for oil in Gre~t Britain b y the D ' A r c y Exploration C o m p a n y Ltd. Q.J.G.S. 93, 156-94. & A. H . TAITT. 1946. The geological results of the search for oilfields in Great Britain. Q.J.G.S. 1Ol [for 1945], 255-317. MAGRAW, D., & W. H. C. RAMSBOTTOM. 1956. A deep borehole for oil a t Croxteth Park, near Liverpool. Liverpool & Manchester Geol. Journ. l, 512-35. MITCHELL, G . H . 1941. The geology of the Leicestershire a n d South Derbyshire Coalfield. [ A s h b y G 1 boring, pp. 3, 4.] Mere. Geol. Surv. Wartime Pamphlet, 22. & C. J. STVBBLEFIELD. 1941. The Carboniferous Limestone of Breedon Cloud, Leicestershire, a n d the associated inliers. Geol. Mag. 78, 201-19. PINFOLD, E. S. 1958. The search for oil in Lancashire. Liverpool & Manchester Geol. Journ. 2, 106-23. PROCTER, E. 1913. Notes on the discovery of fossiliferous Old R e d Sandstone rocks in a boring at Southall near Ealing. Q.J.G.S. 69, 78-84.
-
-
56
PETIt" '~.UM E X P L O R A T I O N
IN B R I T A I N
1945--1957
PUGR, W . J . 1958. Report of the Director. Suture. Progr. Geol. Surv. for 1957, 9-10. ~. 1959. Report of the Director. Suture. Progr. Geol. Surv. for 1958, 9. RAYMOND, L . R . 1953. Some geological results from the exploration for potash in North-East Yorkshire. Q.J.G.S. 108 [for 1952], 283-310. ~. 1955. The Rhaetic beds and Tea Green Marl of North Yorkshire. Proc. Yorks. Geol. Soc. 30, 5-23. REEVES, J . W . 1948. Surface problems in the search for oil in Sussex. Proc. Geol. Assoc. 59, 234-69. RICHARDSON, L. 1931. Wells and springs of Leicestershire. Mem. Geol. Surv. S~EWART, F . H . 1954. Permian evaporites and associated rocks in Texas and New Mexico compared to those of northern England. Proc. Yorks. Geol. Soc. 29, 185-235. STRONG, M . W . 1956. Marine iron bacteria as rock-forming organisms. Advancement of Science, 12 (49), 583-5. STVBBLEFIELD, C . J . 1947. [On cores collected from the D'Arcy Exploration Company's Willesden borehole.] Abs. Proc. Geol. Soc. 1437, 20. SWINNERTON, H. H., & P. E. KENT. 1949. The geology of Lincolnshire. Lincoln [Lincolnshire Natural History Brochure No. 1.] TAITT, A. H., & P. E. KENT. 1939. Note on an examination of the Poxwell anticline. Geol. Mag. 76, 173-81. & --. 1958. Deep boreholes at Portsdown (Hampshire) and Henfield (Sussex). Techn. Publ. B.P. Co. Ltd. London. WAR~L~N, H. R., K. It. ROBERTS, R. G. W. BR~NSTROM & C. M. ADCOCK. 1956. Report on oil and gas in the United Kingdom. X X Congr. Geol. Int., Mexico, 1956, Symposium sobre Yacimientos de Petroleo y Gas, 5 (Europa), 317-57. WHITE, H. J. OSBORNE. 1921. A short account of the geology of the Isle of Wight. Mere. Geol. Surv. WHITE, P. H . N . 1949. Gravity data obtained in Great Britain by the Anglo-American 0il Company Ltd. Q.J.G.S. 104 [for 1948], 339-64. WHI~rEN, E. H . T . 1957. A note on stereographic analysis of bedding planes with special reference to folding in the Isle of Wight. Journ. Geol. 65, 551-6. WILCOCKSON, W . H . 1950. Sections of strata of the Coal Measures of Yorkshire. 3rd edition. Midland Inst. Min. Eng. Wakefield. WILLS, L . J . 1956. Concealed Coalfields. London. WILson, G. V. 1926. The concealed coalfield of Yorkshire and Nottinghamshire. 2nd edition. Mem. Geol. Surv.
Note 9T h e s u b s t a n c e o f t h i s M e m o i r was c o m m u n i c a t e d t o a m e e t i n g o f t h e S o c i e t y o n 26 M a r c h 1958. T h e d i s c u s s i o n w h i c h f o l l o w e d t h e r e a d i n g will b e f o u n d in t h e S o c i e t y ' s Proceedings N o . 1560 (1958), p p . 87-8.
GEOL. SOO. LONDON, ~
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YORKSHIRE
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12 OO0
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.
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.
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.
.
.
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.
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.
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Phantom Horizon of Reflection Contour Mop used for making location . . . . .
Fia. 2.--INTERPRETATIVE SECTION THROUGH FORDON NO. 1 BORING
t2Doo
GEOL. Soc. LOnDOn, MEyI. 2, 1~. II
SAWLEY
NO1
ELLENTHORPE
N °1
Scale 0
500
t
~
~
I
I
I
1,000FEET I
I
I
I
R.T. Elevation 5 8 6 f t .
I
R.T. Elevation 60 ft.
Follifoot Grit(H) Pale fine micaceous sandstone 215t~t. / ~ Dark fossiliferous shale I I White felspathic g r i t Nat/ Hill - ~- ~--r-r--~-I Dark micaceous shales ?/ 210 ft. Grey muddy shelly limestone
B=dW%~
I
Colsterdale Marine Bed ? ft. / / Red Scar Grits
Dark calc. shale
tO
Coarse g r i t t y s a n d s t o n e s
180 ft.
ALDFIELD
Perrno- Triassic Rocks
Nidderdale Shales (E2)
N ol
/
Micaceous shales w i t h thin siltstones
322 ft.
A l t e r n a t i n g sandstones and shales Dark while speckled shales with thin calcareous sandstones
/
UPPER
CARBONIFEROUS
at Aldfield and Sawley (Interpretations on l e f t hand s i d e o f columns based on lithological characters, after Hudson)
LOWER
CARBONIFEROUS
J'rom surface to 1241 feet
.T. Elevation (525 f t . . Sandy calcareous shales with thfn sandstones / ?'""" Variabl~,felspathic sandstones Lindley i-~'~'~'i White fine to coarse grained sandstones I I Dark ghey s a n d y shales with thin s a n d s _ M.o,or, ~ Shales with thin siJtstones ~ Fine to medium calc. s a n d s t o n e mr~ts~-O I ' .... J / 1 ...... • 33 ft. shale I J Sand _, ,Y ..m~caceous . I~'.'.'.'l =~ekbl. . . . i" Lower Magnesian Limestone resting :~anoy limestone L: .-.oJ - - ] ~- • ~ . . . . . . . . . . . . ,.2-:;..., Shales w th thin grits unconformably on Lower Carboniferous '....... ~.oarse-pebb! s a n o s t o n e - ?~OWlanoz~naleE-.~-I-r--r4-Dark-micaceous s h a l e ~ ,:=,-~-~ . . . . . . . . . . . . . . . . ,' , I Dare I~t=w. Ortl~4~/Yra't=y-~la, LC~fifdr(na o¢~pt-ff~ta White c r i n o i ~ l l i m e s t o n e i , -fLight greymchocolate limestone with crinoids • ~-'--" oonuy ~n~les wl¢n T,nln ilmeyllna senay rIDS J~_Grey-chocolate limestones with J JBottom of hole 1295 feet ~ Sandy limestones I ' ' J-crinoids, corals, bryozoa and I / ~..'~r'.: Dark she e with LithostPotion sp. G~/ptop/eura sp. foraminifera. M o w c h / n i e below 3 4 0 ft. . . ;~ ' " FACIES B o t t o m of hole 4 2 9 feet GULF
~R
L.Brimham Grit(Re) T'/ft. Capelshaw Shales 65fto Libishaw Sandstone 37ft. Libishaw Shales 71ft. Cayton Gill Shell Bed 18ft. Cayton Gill Shales 32 ft. U.Follifoot Go'it{H) 22ft.
:~ Greymarlswithdarkcrinoidallimestones
BLOCK
FACIES
........
=(~
ULF ~e
:~ Dark Lst.end sandy Lst. with Koninckopor~ sp. •.......v Pale grey sandstone Dark carbonaceous marls with sandy bands Dark brown limestone :.-.v... Grey-white fine carbonaceous sandstone ~.-T____________Brown _~. sandy limestone Grey marls and black calc. shales •}i'i'~'~' White medium to coarse calc sandstones Interbedded s'sts, sandy I'sts. silts and marls ..... Grey silty marls 9.~.~ White fine non-ca~c.s'sts.with silty ~ ~.'-~. carbonaceous laminae
FACIES LOCATION MAP
REFERENCE
~C,
I
I Shale and mudstone Sandstone
J "
~J'~\
"
~=,dALDFIELD I] Ne, , _~.~r~BORO~C,N R • _ Ingertl~ USAWLEY o ~ Fern,ha
N° '~ l mpLY E
/
"~ ~/ELIENTHORPE ~ N°,
/
~,~
~~
X_~
%
~
Limestone
~'~
Siltstone
dark
Grey to marls and sandy marls with thin sandstones and sandy I'sts. ~ [.,.I
Coral ?
~ Crinoidal I:st.and some brown dolomite in sandy m a r l . . . . . S'sts.sandy rsts.and sandy marls• Crinoids ~Grey silts Calc.carb. s'sts, and sandy crinoidal i'sts. Kon/nckqoora Sp~ M/tche/~eania 1~-~4 Grey calcareous fine grained s'sts, and siltstones with I~YZ'I thin sandy and arg. r.~t. bands . ~ Grey silty calc. shaFes with arg. ~st.banes C a/careous silty shales with thin mic.s'sts.
andimpurecrinoidall'st.
Fireclay
Interbedded argillaceous t'sts and calcareous shales with occasional thin s'sts,
Chert Scale .,L,S~,,',
~
~
,O.,L,S
Silty shales with impure rst. partings Argillaceous Ist. .p._.~./..-JCalcareous and sandy shales with impure Est. and micaceous s'st.partlngs r~ Dark impure crinoidal I~st~with ~-J~ -~some darkshale• N//tche/dean/a
~
Grey crinoidal rsts with mudstone partings. Kon~nckopor~, Z~ph/-entis aff. delanoue/ ~ : ~ L B o t t o m of hole 3598 feet
BOREHOLE SECTIONS IN WEST YORKSHIRE
A.P. TERn/,,¢
GEOL. So(:;. LONDO:S', M]~M. 2, P L . I I I
SALSBURGH N°I
REFERENCE R.T Elevation 733ft,
C O A L MEASURES
FEET
~ A
A
200-
-
300-
o
Sandstone
LOCATION MAP
Y .Y 100- L•,..+.,';o'
;o
FALK/R
o
o F
F o
Limestone
1 1
T
Shale
• ,..., .°....l
MILL STONE GRIT
400-
,OA,
600-
Calmy Lst. H i r s ( Coal
LINL/TH
Lingula
500-
.:'X':'X' :::::::::::::
Silt
~
Fireclay
700-
Lyoncross Lst. 9001000-
Index Lst.
[-~-l Igneous
Foraminifera
O r c h a r d Lst. 8 0 0 )
0¢
~
::-;.;.;! .,.o.
Crinoids
C.-:--'>
0 i
"Black Metals"130°1400-
Shell bed with
Top Hosie Lst. 1 7 0 0 -
5
SCALE I0
I
I
15
20 MILE S
I
I
L/ngula, Serpvl/tes
%.jo°.%.,
:.:,:.-.:.:.
? K i l s y t h Coking Coal 1500J o h n s t o n e Shell Bed 1600-
EASTER PARDOVAN No1
m
BLACKNESS N°I
COUSLAND N°.I
1BOO-
R.T Elevation 565 ft. FEET
LIMESTONE
SERIES CALCIFEROUS SANDSTONE SERIE S
I~oo-
v
,L
2000-
Raesgill Ironstone Foul Hosie Lst
2100-
Hurlet Lst
2200-
23oo-
/
R T Elevation 8 5 ft.
FEET
R.T Elevation 260 ft. FEET 100 -
.....-°.
.
400-
2600-
,° .... ,°,,,,,,,,.
•
Houston Marls 2 7 0 0 - . 2800-
500/ 6 0/ 0 - .
-~---
,°°%°,'¢ 0°',',%" ,.,° ~.° °
2900Broxburn Marls 3000--? B r o x b u r n Shale 3100 -
J /
3200-__
19
/
3300Dunnet Shale 3 4 0 0 -
/ /
3500Barracks L s t • Ash 3600
/
." o V , ~
3800- V ' V V 3g00V V
4 000--
4200-
v
vvv
vv vvv
v
' Sandy shales Limestone with ostracods
400 500-
Sandy shales with thin sandstones its ea~.ivatent Ostracodsr-'^" - - ~ ~ -Dark banded limestone Shales with algal limestones Plant debris, fish scales
~00700 -
9001000-. 1100-
',r--
1000-
Dark calcareous shales with thin limestones
1200-
22002300-
o
.,,,.. o
¢
"o'#°°°,°. .... o
2400-
0
2500
V V % V?/,
26002700-
-.-.,.,.,...
Shales w t h Lingu/a, crinoids and plants Crinoidal limestone
1100-
Shales with thin limestones and ironstones Ostracod limestone Oily sandstones
Ostracod limestone
1600-
Shales with thin limestones
1700Black and grey shales
1800-
Posidonie#a,ostracod~ plants and
.~.'~.:.? fish scales 'JZZ:Z"
Shales, bituminous in places, with thin sandstones, and limestones O s t r a c o d s and molluscs
1g00-
18001g00-
v v
Sandy shales with thin ssts. Olivine basalt
2000-. 2 I00
. ,.,,,,
Shales with ironstone
2000-
2200 VV% V V
,,,..,,,....,
2 3 0 0 -i . . . . . .
-
VV~
White altered volcanics v v with calcite veins
V V VV%
vvv v v 2 4 0 0 - vv~
24002500-
AA
2 4 5 5 f t . Bottom of hole
26002700-
VV~
o .o. c
0
~
Dolerite ~ V -
Silts end tholeites
V V ~ V V
Tholeites
VV~ 3 0 0 0 - .'--V.'=~ " VV~ 3 1 0 0 - " " O "°
3ft.Coal Dark shales with Poxidon/e//a ostracods and plants
Card/opt er/a
Shales with sandy ribs and numerous traps
io ,'°'
M
.
y.'.°o*.'.°
2800-
28002900-
Dark shales with thin fine grained micaceous sandstones and ironstones
1000-
..,-,-.,,%*
1400-
1700-
2300-
_ 9OO-
C a r l o p s Lava
-
x A. l Thin limestone with ostracods
H
1600-
2100_• ,';,'*., .° ,°
800-
A A~ .%,.,.%%,
1500-
22 0 0 -
X A A
1300-
Sandstone with dolerite
,,....,.°.°°,
..'-r, ° "° ,., "o',,,,.
700-
Dunnet oil shale
1500-
Quartz-dolerite
2100-
Crinoidal limestone w i t h brachiopods
600-
VV
VV~ VV VV~
1400-
Dark shales and silts with thin fine grained sandstones and numerous thin white traps.
400
1200-
V V ~
Black fine gn sandstone 1 5 0 0 - ",.X.:-: with burnt shale bends Alternating sandy shales and free black sandstones 1600Dark fine g r sandstone with thin sandy shales 1700.,,o,.°.,,, Dark fine to mad grained o:°%,.,,,. 1800sandstone
l-O°O,O,,,,,,
A A ~
.
1300-
1100-
200 300
500-
.'2.'.'.'.
Taschenite
g00-
20004267 ft. Bottom of hole
........,..
VV%
.,°
v
300-
800-
: :.,.'.'.-
1900-
v
Y__
Boulder Clay
~o o~ Shales with ironstones 2 0 0 - ~ x Sandy shales
Limestone horizon Dar--~ s--~a~-limestone with oat racods
800-
1400-
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Dunnet Sandstone
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Champfleurie Dunnet
Dunnet Shale position 200Barracks Lst Ly_V Port Elgar Ash 300-
Netherfields Coal & L s t
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100-
Frazerdale Shale •
2 f t Coal 3 f t Coal N° | Limestone
100-
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2400 •
? L o w e r Old Red Sandstone f r o m 3 9 9 0 ft.
Ironstone
l.,...
11001200-
LOWER
~
3183 ft. Bottom of hole
BOREHOLE SECTIONS IN THE CARBONIFEROUS ROCKS OF SCOTLAND
2900-
%-.%-2°,,
Argillaceous limestone with ostracods and algae Shales and calc. shales with thin sandstones and limestones Ostracods, fish scales and plant Fine volcanic ash debris Sandy shales -2917 ft. Bottom of hole
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EXPLORATION WELLS IN SOUTHERN ENGIA_ND AND THE SOUTHERN MIDLANDS, 1945-57 D E P T H
IN
FEET
TO
CRET ACEOUS
Location
Well No.
Position
Rotary table elevn, in f t , above O.D.
Co-ordinates
U
1
ARRETON
500 40'
I s l e o f Wlght 3 m. 8. E. of NewPort
Eat.
Lon~
~o ~4' 55.Z.W.
125
Sussex I m. W. o~ Crowborough
Let. Long.
5 ~ 05' 00. l'N. 0v 08' ~8.5"E.
6~3
La&. L~
51° 02' 31.4,N. 0 ~ 09' 1 8 . 0 ' E .
585.4
Upper
M
Gault
OF TRIAS
JURASS IC
Chalk U G,sd.
TOP
G~OL Soc. LoxDo~, M~. 2, T~ns I
L G'sd. Weald
Middle
Rhaetic Keuper
Lower
PALAEOZGICITotal Depth
Hastings Sand
L
Completed in
Li~
Purbeck Portland Klmmerid~e Coralliam
Oxford Oolite Pullers' Inferior C l a y Kellaways C o r ~ b r a s ~ Series E a r t h Oolite
~.9'N.
210
2563
P~50
3757
3973
4423
565
1099
1170
2943
3400
3721
640
1180
1250
2910
3390
3650
4541
49~
4989
5"762
3801
3944
4034
4515
3693
8715
3873
3957
4378
4522
5161
Inferior Oollte
4538
Upper Llaa
5709
U. Carboniferous or New Red Sandsteme
4940
Devonlan, probably Lower
Cornbrash ASHDO~N
1
A,.~DO~
2
BRI ~HTLING
C~N
DO~
1
0"2
~ u s s e x
1 m. 8.W. o f C r o ~ o r o u ~
11 m. N.W. of H a s t i n g s
Long~
15.8.. 56.6 'E.
Dorse~
Lat. LOn~
500 20 37' 50.3"N. 14' 15.7"W.
~U~t~X
7 m. 8.W. of Wareham
501
365
370
1140
1310
1405
1512
474
1610
1911
2288
2314
P~50
2487
2543
2845
4665
3100
NRS or U. Cart. 5630
4790
3213
U.M. & L. L l a s r e p e a t e d by fault
Devonlan
1580
Kllerldge
1793
Clay
_
C~ALDON HERRING
CHALI~ HERRINO
1
0"3
Dorset 7 m. S.E. of Dorchester
Lat. Long.
500 59' 13.3'N. 2° 18' ~0.4"W.
286
129
551
Dorset 7 m. S.E. of Dorchester
Lat. Long.
500 59' 17.8,N. ~o 16' ~.4'W.
c.Z50
185
470
1350
?1320
1379
1440
1350
1468
1700
1885
L. PUllers, Earr~
P~44
FUllers, Earth
I
FARINODON (.q~el 1 I n g f o r d )
1
Ber~shlre 14 m. S.W. of Oxford
Lat. Long.
51 o 38, ~.lmN. I v 32' OI.9'W.
298
117
555
5651
735
=.
D evon 18~
745
810
885
955
1465
1525
2150
Old Red $smdstone or Do~tonlmn
3131
,--
HEATHFIELD
7
~ssex
11, m. S. 0~ Tunbrldge Wells
IAtt. Long.
500
oO 58' 13.4'N. 18' 3~.OeE.
527.5
348
788
c. 890
904
Klmmerldge Clay .....
PORTSDOM~
2
Hmp alxl re 5 m. N. of Ports~our~
Lat. Long.
500 51' 42.6'N. 1° 5' 29.1,W.
200
50
850
1090
1440
1550
1750
e. 1828
2595
28¢~
2871
Portland ..
WILLESDEN
1
London N.w. London
Lat. Long.
51 ° 8 2 ' ~.5",N. 0 v 15 t 24.7'W.
103
196
370
500
800
Devonl an 1010
840
1
All depths measured from rotary table elevation, (average height about i0' above 2round level. )
Includes
Cornbrash
~50
U. Devonian
k-I r~
0
-,4
ID ,.--I
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o ~,~ ~n~
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003
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EXPLORATION WELLS IN YORKSHIRE, 1945-57 DEPTH
Location
Well No.
Rotary table elevn. in ft. above O.D.
Co-ordinates
Position
ALDFIELD
Yorkshire 5 mls. E.N.E. o f Pateley Brid~e
Lat. 54 ° 6' 28.9" Long. I v 8"?' 55.6"
N. W.
625
ELLENTHORPE
Yorkshire i~ m~s. E. of Borou~hbridge
Lat. 54 ° 5' 50.2" Long. 1° 21' 9 . 5 "
N. W.
60
FORDON
Yorkshire 8 mls. S. o f Scarborou~h
Lat. 54° (X)' 57.8" N. Long. 0 ~ 22' 44.25" W.
429
HAYTON
Yorkshire 14 mls. E.S.E. Zork
of
IN F E E T
JURASSIC
L.Oolite
Lias
(measured
GEOL. SOC. LONDON, MEM. 2, TABLE I I I from R o t a r y
TRIAS
Rhaetic
Keuper
Table)
TO TOP OF
PERMIAN
Coal Measures
Bunter
Total DeF~h
CARBONIFEROUS Millst. Grit
Carb. LSt.
322
12AI Massive L'st 3476
535
2584
2777
3295
8835
7185
3663
4700
884
2079
3237
Completed
42@
Carboniferous Limestone
8598
Carboniferous Limestone
7559
Millstone G r i t
Lat. 53° 53' 24.0" Long. 0 v 44' 35.1"
N. W.
67
Lat. 54° 84' 59.5" Lon2. 1~ 5 ' 25.5"
N. W.
76
421
473
1148
? 1978
73154
8736
Carboniferous
Lat. 54° 38' 19.2" Long. 1~ 4' 58.9"
N. W.
33
170
220
88O
71648
728~7
3091
Carboniferous
Lat. 54~ 17' L~7.8" Long. 0u 36' 43.5"
N. W.
806
1499
Lower Lias
Lat. 54 22.0" Long. oO° 25' 32' 20.0"
N. W.
203
5378
Coal Measures
Lat. 54 ° 4' 49.4" Long. {o 87' 32.7"
N. W.
586
1295
Carboniferous Limestone
Millstone G r i t
3618
..........
KIRKLEATHAM (Redcar}
Yorkshire i~ mls. S.W. Redcar
KIRELEATHAM (Redcar)
Yorkshire 2& mls. S.S.W. Redcar
LOCKTON
Yorkshire 8 mls. E. of Scarborou$h
R O B I N H O O D ' S BAY (orl~inally F i s o n ' s No.l)
Yorkshire 5~ mls. E.S.E. WH itby
8AWLEY
Yorkshire 5 mls. E. o f P a t e l e y BridSe
of
of
of
484
1050
750
777
1670
268O
5196
1268
in
feet
EXPLORATION WELLS IN LANCASHIRE AND THE WEST MIDLANDS, 1 9 4 5 - 5 7
Location
Well No.
Rotary table elevn. in ft. above O.D.
Co-ordinates
Position
DEPTH
IN F E E T
JURASSIC L. O o l l t e
Llas
(measured
from R o t a r y
TRIAS Rhaetlc
Keuper
G E O L . SOC. L O N D O N ,
Table)
2, T A B L E
IV
TO TOP OF
PERMIAN
Total De th
CARBONIFEROUS Co al Measures
Bunter
MEM.
Grit
Carb. Lst.
Completed
in
feet
L
Sbropsbire, 2 miles N.W. of Edgmond village
Lancashire
~4BY
~3Y
FOI~BY
Lat.
5P~ 47~ 44.4" N.
Long.
38. i 'r W.
285
22O
380
Pre-Camb. 855
50O
Lat. 53 ° 33' 51.5" N. Long. 8 U i' 44.2" W. ~
19
100
1830
3250
5883
I ml. W. of For~by
Lat. 53° 33' 32.0" N. Long. 8 v 5' 0" W.
36
75
1170
2555
2'778
Lancashire 1 ml. W. of Ainsdale
Lat. 55 ° 3e' 13.45" N. Long. 3 v 3' 43.7" W.
130
1960
3608
4180
Lancashire 1 ml. N. of Formby
Lat. 53 ° 34' 21.05" N. Long. 3 v 3' 16.30" W.
89
1574
4835
Lancashire
28
887
-L. Carb.
Pre-Caabriau
7680
L. Carb. L. Bowland 8 h a l e s
388O
Carboniferous Limestone?
4356
Millstone Grit
5294
Permian
914
10@3
Carboniferous Limestone
71141
1832
Carboniferous Limestone
2013
2341
Carboniferous
4@95
Millstone G r i t
7244
Carb. L s t ? 3788
--,
Z~S~OD
~ ~ m ~ N
Flintshire, 3 miles S.E. of Mold
Lat. 53 Long. 3 °°
S h r o p s b i r e . 1 mile N.W. of Childs Ereall
Lat. 52 ° 49' 55" Long. 2 v 31' 07"
Sbropshire, 2~ mls. W. S.W. of Market Drayton
Lat. 5 ~o 52' ~9.75" N. Long. 2 - ~ ' 50.6" W.
Lancashire
Lat. 53° 31' 11.8" Long. 2 " 44' 51.0"
8' 52.6" N. 6' 04.5" W.
N. W.
382
15
229 ,
TBRI~IIT,T,
t
8
710
N. W.
Formby No. I was deepened to I t s present depth during the perlod 1945-57
Lower
1424
32
962
EXPLORATION WELLS IN SCOTLAND, 1945-57 .
.
.
Location
Well No.
Position
Co-ordinates
IN FEET
(measured
from r o t a r y
Millstone Grit
Carboniferous Limestone Series
5 mls. W of Queens ferry
mls. E.S.E.
(X)USIAND
of Dalkeith
3 mls. E. of
Dalkeith
Lat. 55° 59' Long. 3° 31'
Lat. Long.
55 ° 53' 3 ° O'
Lat. 55° 58' Long. 2° 59'
57.9" 2.6"
N W
122"
2. 5"
55.6" N 44.7" W
N
W
TO TOP OF
Dunnet
120
85
681
No.l L'st 55
89
No.2 L'st. I0 No. 1 L'et. 192
28O
551.8
Shale
5 mls. W.S.W.
SAT s~IRGH
of Queensferry
3% mls. E. of la
Airdrie
Lat. 55 ° 58' Long. 3 ° 31'
22.4" N 2.45" W
260
-
751-789
476-486
910-970
Lat. 55 ° 51' Lon~. 8 ° 53'
44.65" 27.78"
783
30
20
146
452
2065
OLD RED SANDSTONE
in feet
Completed
Calciferous Sandstone Series - Oil Shale Group
-
2,455
-
i, 995
-
1,918
_
3,183
Calciferous Sandstone Series - Oil Shale Group
4,2~7
Old Red 8andstone
Calciferous Sandstone Series - Oil Shale Group
Calciferous Sandstone Series - Oil Shale Group
,
53@-548
3388-34OO
-
Burdiehouse Limestone
.
E A S T ~ PAEDVAN
Total Depth
.......
Calciferous Sandstone Series Oil Shale G r o u p
Lr.L'st
BLACKNESS
table}
CARBONIFEROUS
Coal Measures
V
.
DEPTH Rotary table elevn. in ft. above O.D.
GEOL. SOC. LONDON, MEM. 2, T A B L E
3645-3657
3990
in