Journal of the Geological Sociely, London, Vol. 147, 1990, pp. 133-140, 6 figs. Printed in Northern Ireland

A buried granite batholith beneath the East Midland Shelf of the Southern North Sea Basin

JOHNA. DONATO' & JOAN B. MEGSON2 'Goal Petroleum plc, New Bond Street House, 1 New Bond Street, London W1Y 9PE, UK 2Maersk Olie Og Gas AS, 50 Esplanaden, DK-1263 Copenhagen K, Denmark

Abstract: Published BGS gravity data of the UK Southern North Sea Basin show the presence of a gravity low trending to the ESE across the northern half of Quadrant 47. Two simplified geological cross-sections have been constructed across this feature with sedimentary structure based upon well information and reflection seismic data. Gravity modelling of these sections demonstrates that the gravityanomaly is unlikely to beproduced by the presence of thick, low densitysediments. Consequently, the presenceof a large, buried granite batholithis postulated. The buoyant influenceof such a granite may have exerted considerable tectonic control during the developmentof the Southern North Sea Basin. In particular, its presence may help to explain the development of the East Midland Shelf, the associated complex fault movements along the FlamboroughHead and DowsingFault Zones, and the area1 distribution and thickness of the Rotliegendes sand.

Important zones of faulting occur along the Dowsing Fault In the offshore area, the sequence is not Zone and its onshore extension, the Flamborough Head clearly defined on reflection seismic data and consequently Fault Zone. These zones have been intermittently active the tectonic development during this period is not well throughout a long period of geological time,and clearly understood. The analogy with the onshore area to the west, represent an important lineament which separates the more where the sequence is in part exposed, suggests that stable block of the East Midland Shelf from the tectonically Carboniferous deposition commenced with an early, active areas of the Sole Pit Trough and the Cleveland Basin. fault-controlled,differential subsidence phase, driven by The acquisition of extensive seismicreflection data and crustal stretching. This was followed by a more gentle phase borehole information resulting from the exploration for gas of regional subsidence during which numerous interbedded in the SouthernNorth Sea Basin has revealed, in some coals were deposited. Towards the end of the Car- detail, the major and complex tectonic movements which boniferous, Variscan compression caused widespread uplift have occurred along this important lineament. The and an associatedunconformity eroded deeply intothe integration of these data with gravity field measurements are Carboniferous sequence. A period of subsidence followed, presented hereand have assisted in understanding the causedby faulting dueto tensional or trans-tensional tectonic evolution of this complicated area.In particular, stresses and at this time, the Rotliegendes desert the reason for the division of the sedimentary basin into the sandstone was deposited. This sandstone now forms the stable and less stable areas, either side of this fault zone major reservoir rock for gasin the Southern North Sea lineament, may now be understood in terms of the tectonic Basin sourced by the underlying Carboniferous coals. control of a buried, massive granite batholith located Widespread transgressionsflooded the subsidedbasin beneath the northern part of the East Midland Shelf. during the late Permian, resulting in the deposition of the Zechstein evaporite cycles.Whilst the early Permian subsidence and associated deposition was in response to Geological and structural review crustal stretching, these late Permian evaporites appear to Figure 1 shows a simplified version of the solid geology of have been deposited during a tectonically quiet period with the onshore and offshore area (Sub-Pleistocene Geology of little contemporaneous faulting.Similarly, the overlying the BritishIsles andthe AdjacentContinental Shelf, earlyTriassic sequence, whichconsists of desert lake 1 :2,500,000, BGS, 1979) with the location of the -20 mGal sediments (Bunter shale and sandstone), was deposited with Bouguer Anomaly gravity contours superimposed (BGS little evidence of significant faulting. A period of local Bouger Anomaly Maps 1:25O,OOO Series, Tyne-Tees, faulting and slight uplift of basin margins occurred during California, Humber-Trent andSpurn sheets). As may be the late early in association with the development of seen, rocks varying in age from Permo-Triassic to Tertiary a minor unconformity. This was followed by further gentle are exposed. To the north of the Flamborough Head and subsidence, during which time theRot, Muschelkalk and the Dowsing Fault Zones lie the thick sedimentary Keuper halites were deposited. successions within the Cleveland Basin and Sole Pit Trough. During the , a marked differentiation occurred To the south lies the more stable platform area of the East between the rapidlysubsiding Sole Pit Trough and Midland Shelf. The geological evolution of thearea is Cleveland Basin, and the slowlysubsiding East Midland complex and is described extensively in the literature (e.g. Shelf. Differing subsidence patterns were accommodated by Glennie & Boegner 1981; Glennie 1986; Kirby & Swallow significant, tensional and/or trans-tensional faulting particu- 1987; Kirby et al. 1987). Only a brief and simplified review is larly along the two major fault zones. The rapid subsidence attempted here. of the basinal areas, initiated during the Jurassic, continued 133

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/1/133/4890723/gsjgs.147.1.0133.pdf by guest on 24 September 2021 134 J. A.DONATO & J. B. MEGSON

('W 0'

Fig. 1. Simplified solid geology map of the onshore and offshore area under consideration. The-20 mGal contours along a pronounced gravity low trend and the locationsof areas of complex tectonic activity along the Flamborough Head Fault Zone and the Dowsing Fault Zone are shown. The Cleveland Basin and Sole Pit Trough are areasof thick sedimentation affectedby inversion l*E movements.

into the early , although a widespread unconfor- contour interval is 2 mGal and the area covered by the map mity was developed at the Jurassic/Cretaceous boundary. A is identical to that of Fig. l.. thick blanket of Chalk was deposited during theUpper Pronounced E-W and ESE-WNWgravity trendsare Cretaceousunder essentially tectonically quietconditions. apparent. The mostsignificant feature is a deep, negative This cover was subsequentlyremoved from the Sole Pit anomalyenclosing three minima, thedeepest reaching Troughand Cleveland Basin by amajor inversion phase approximately -30mGal. The western minimumhas been which reached a climax towards the end of the Cretaceous. interpreted by Bott et al. (1978) and Bott (1988)as being Onthe western flank of the Sole Pit Trough, however, produced by a buried granite body, the Market Weighton inversion movementshad commenced during the early Granite, although Aveschough (1986) favours an interpreta- Cretaceous(Glennie & Boegner 1981). Total uplift tionin terms of a thick Carboniferous basin. The estimates of 1.5 km (Marie 1975; Cope 1986) and 2 km interpretation of Bott et al. is preferred here. The locations (Kirby et al. 1987; Bulat & Stoker 1987) have been proposed of three profiles across the low trend are also shown in Fig. for the Sole Pit and Cleveland Basins respectively. These 2. Profile XY is the line of section across theMarket movements caused a widespread erosional unconformity Weighton Granite interpreted by Bott et al. (1978). Profiles resulting in the exposureof Jurassic and Triassic strata along AB and CD are the locations of two sections modelled here. the axes of the Sole Pit and Cleveland Basins. Little is To the north of this gravity low, higher values trend in known of the Tertiary section in this area since, as Fig. 1 E-W and ESE-WNW directions and overlie the axes of the shows, only limited outcrops are presently observed in the Cleveland and Sole Pit Inversions. As discussed earlier, north-eastern cornerof map. these inversion axes areareas where thick sequences of It may be possible to summarize, in simple terms, the deeply buried sediments have been uplifted significantly. tectonic development of thearea as consisting of three This processhas resulted in anomalouslyhigh density major fault-controlled phases of sediment deposition. These sediments close tothe surface with correspondingly high occurred during early Carboniferous, late Carboniferous to sonicvelocities (Marie 1975; Cope 1986; Bulat & Stoker early Permian, and Jurassic to early Cretaceous times. An 1987), and this may explain the presence of the coincident additional, more minor phase also occurred during the early gravity high trend (Donato & Tully 1981). On the northeast Triassic. Sediments depositedat other periods, however, end of Profile CDa narrow gravitylow reaches were more epeirogenic innature. There were also three approximately - 18 mGals. This coincides with the location significant phases of uplift which occurred during late of a salt diapir seen on reflection seismic data.The low Carboniferous, early Cretaceous and late Cretaceoustimes. density halite within the diapir possibly explains the presence of this gravity feature. The two profiles, AB and CD, are shown in Fig. 3. The Geophysical data and models simplified structure is based upon an interpretation of A Bougueranomaly gravity map of theonshore and onshoreand offshore seismicreflection data withseismic offshore area is shown in Fig. 2. It is a simplified version of events tied to exploration boreholes drilled nearby. Seismic parts of the Tyne-Tees, California, Humber-Trentand events which can be followed reliably on the reflection data Spurn sheets of the 1:25O,ooO Series of Bouguer anomaly in this areaare the Base Chalk, Base Cretaceous maps published by the British Geological Survey. The Unconformity (although these two events are occasionally

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/1/133/4890723/gsjgs.147.1.0133.pdf by guest on 24 September 2021 BURIEDGRANITEBENEATH SOUTHERN NORTH SEA 135

l0E

54' N

Fig. 2. Bouguer Anomaly gravity map covering the same area as Fig.1. The contour interval is2 mGal and the locations of three profiles (XY, AB and CD) discussed in the textare also shown. High gravity values overlie the Cleveland Basin and the Sole Pit Trough. Low values are observed over the East Midland Shelf.

coincidentowing tothe local absence of the Lower calculated curve from the observed curve andthen Cretaceous section), Base Jurassic, Top Lower Triassic, Top correctingthis result for a variation in the regional field. Zechstein and Base Zechstein. The pre-Permian sequence is This field hasbeen assumed to increase linearly tothe represented on the seismic data by discontinuous reflection northeast with an approximate gradient of 0.16 mGal km-' segments and no single event can be mapped reliably over such thatthe assumed regional background values atthe thearea. Consequently, isit not possible to deduce southern and northern ends of the profiles AB and CD are accurately the thickness of the Carboniferous section and approximately +l4 and +24 mGal respectively.Such a therefore the Carboniferous sequence has not beenincluded regional gradient may be related to a slight rise in Moho in the model sections. This uncertainty is discussed later. depthbeneath the SouthernNorth Sea Basin although In the central andsouthwestern portions of both profiles, significant crustal thinning is notpresent inthis area a thick sequence of Upper Cretaceous Chalk (Layer 1) is (Donato & Tully 1981). On both profiles, the residual curve present. This sequence, and some of the underlying Jurassic revealsasignificant low of amplitude between 15 and sequence (Layer 2), have been eroded on the northeastern 20 mGal. The magnitude of this residual value ismuch ends of the profiles as a result of the inversion movements greater than any possible error introduced by uncertainties along the Sole Pit Axis. The Triassic sequence (Layers 3 and in either the density values, orthe assumedregional 4) is tectonically disturbed across the Dowsing Fault Zone backgroundfield or by the approximation of the 2D but thickens onlyslightly tothe northeast. The Permian modelling. Consequently, it is considered that the residual sequence (Layer 5) varies considerably in thickness along anomaly represents a real and significant feature, probably profile CD and this is due to halokinesis. associatedwith pre-Permian geological structure not fully It is not easy to estimate the densities of the various resolved on the reflection seismic data. layersin orderto enable a calculation of the predicted The presence of either a thick Carboniferous basin or a gravityeffect of the two profiles. Density logs were buried granite batholith were considered as the cause of the examined from surrounding wells, but the limited coverage significant residual low. Attempts to model the gravity effect of the various log runs did not allow reliable values to be in terms of a thick Carboniferous basin indicated that the established for all intervals and some uncertainty in the basin required athickness in excess of 5 km andan assumed values remains. In order to attempt toallow for the implausible geometry. Additional strong evidence against anomalously high density values present to the northeast of this concept is supplied by pre-Permian reflection segments the Dowsing Fault Zone due to the inversion movements, seen on seismic data. An example of this is shown in Fig. 4. model density values were increased slightly to the right of This shows the pre-Permian section to be in an anticlinal the vertical, dashed lines shown in Fig. 3. In addition, the rather than basinal form below the centre of the residual Permian density of profile CD was decreased to the right of gravity anomaly low. In addition, the pre-Permian subcrop the dashed line to allow for the thick, low density, halite map of Fig. 5 reveals an eroded Carboniferous anticline section present in the salt diapir structure. offset only slightly to the north of the gravity low. Figure 3 shows thatthere is very pooragreement The preferred interpretation of the residual low, between the observed gravity values along both profiles and therefore, involves the presence of a buried granite those values calculated assuming the 2D structural models. batholith. Gravity anomaly values calculated from simple The residual profiles have been produced by subtracting the 2D batholith shaped bodies are shown in Fig. 3. These

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/1/133/4890723/gsjgs.147.1.0133.pdf by guest on 24 September 2021 A B C (a1 (b) (C) 0

1

2

3

I I I I I I 1 4

10 10 0-0 CflLCULflTED 8 0 - OBSERVED

-10 - 10

-28 -28

-30 -38

-40 -48

0 0

-10 - 18

-20 -20 1 0-0 CRLCULATED - RESIDURL -30 1-38 I 1 I I I I 1 I

0' 0' -l I

e '$ (-0.1) e l I l I l I l I I I 0 40 60 0 20 a40 60 e0 20 e0 4l (KM) (KM) Fig. 3. The two modelled profilesAB and CD. The layers shown in the simplified geological cross-section are:1, Upper Cretaceous Chalk; 2, Jurassic; 3, Upper Triassic; 4, Lower Triassic;5, Permian; 6, pre-Permian. (a), (b), (c) and (d) show the locationsof wells Winestead, 42/26-1, 47/18-1, and 48/65 respectively. These wells were usedto control the interpretationof the reflection seismic data upon which the simplified cross-sections were based. Layer densities (gm cc-') assumed for the gravity anomaly calculations were: 1-2.37, 2.42; 2-2.47, 2.52; 3-2.52, 2,57; 4-2.57, 2.62; 5-2.42,2.42 (for AB) and 2.32 (for CD); 6-2.72. The first and second values give the densities for each layer to the left and right of the vertical dashed line respectively.

136

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/1/133/4890723/gsjgs.147.1.0133.pdf by guest on 24 September 2021 BURIEDGRANITE BENEATH SOUTHERN NORTH SEA 137

A A'

NNW

0.0 v 'Sea Bed CHALK

/ /

JURASSIC 6 TRIASSIC U) 1.0 TOP ZECHSTEIN n 0 / S z c 2 2.0 PRE-PERMIAN REFLECTORS

3.0

Fig. 4. Line drawingof part of a NOPEC (UK) Ltd. reflection seismic section. The pre-Permian seismic reflection segments indicate that the Carboniferous section is in an anticlinal form beneath the axisof the low Bouguer anomaly values. The location of the seismic line (AA') is shown in Fig. 6.

models assume a density contrast between graniteand binations of density contrast value and depth to top and basement of 0.1 gm/cc and an assumed depth to the base of base of the block will provide equally adequate agreement the granite block of 10 km (Bott et al. 1978; Chroston et al. with the residual anomaly. An accurate assessment of the 1987; Evans & Allsop 1987; Rollin, undated).As can be detailed distribution, thickness and geometry of the granite seen in Fig. 3, such models provide an adequate match to mass has not been attempted and is probably not possible the residual gravity low and predict a depth to the topof the with the data currently available. granite of between 3 and 4 km. Clearly, various com- In summary, aninterpretation of the residual low in

54.N

Fig. 5. Pre-Permian subcrop map (after British Geological Survey, 1985). The area shown is the same as thatof Fig. 1 and 2 and the -20 mGal contour lines of Fig. 2 are superimposed. An eroded Carboniferous anticline occurs slightlyto the N of the axisof the gravity low. The locations of the Rough and Amethyst gas fields are also shown.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/1/133/4890723/gsjgs.147.1.0133.pdf by guest on 24 September 2021 138 J. A. DONATO & J. B. MEGSON

terms of a buried granitic batholith is consistent with the development drilling results have demonstratedthat gravity anomaly, the reflection seismic dataand the Namurian sediments subcrop locally beneath the Permianin pre-Permian subcrop evidence. the Amethyst area above the postulated granite, illustrating important detail of the pre-Permian subcrop geometry not apparent on the generalized map of Fig. 5. Discussion The Rotliegendes sandstones were deposited during The interpretation presented here suggests the presence of a early Permian times and were associated with the second large granite body with approximate dimensions of 140 km phase of extensional subsidence as discussed here.The in length and 40 km in width. By way of comparison, this distribution of this unit is now reasonably well understood, batholith is similar insize tothe onshore extent of the particularly in the offshore area, as it hasbeen the main Comubian batholith stretchingfrom Land’s Endto the exploration target for numerous years. Drilling has proved eastern margin of Dartmoor. As far as we are aware, the that the Rotliegendes section is markedly thinner over the proposed granite has not been penetrated in any wellsin postulated granite (Fig. 6), with a clear correspondence either theonshore or offshore area. This is due to the between Rotliegendes isopachs and the contours delineating significant depth to its upper surface,shown by modelling to the gravity low. As in the Carboniferous, granite buoyancy be at 3 to 4 km below sea level. Consequently, no samples mayhave influenced Rotliegendes facies and deposition of the postulated granite are available and in addition it is such that in local areas the Rotliegendes sand may be thin or not possible to determine its age from the geophysical data. absent. Fragments of granite and other igneous rocks are It is most probable, however, that it was emplaced during found within the Rotliegendes section in the Rough late Caledonian (early ) times (Allsop 1987). (Goodchild & Whitaker 1986)and Amethyst(e.g. well Bott et al. (1958) were first topropose the possible 47/13-2) areas. These may representthe reworking of a tectonic influence of large granite blocks. During tensional local intrusive body, although the gravity modelling predicts periods, normal faulting induced aroundthe granite mass the upper surface of the granite to be at considerable depth permits the low density block to maintain isostatic below the Base Permian unconformity. equilibrium. In this way, granites resist subsidence and form Jurassic to Lower Cretaceous times marked the third stable areas during periods of widespread subsidence period of extensive tensional or trans-tensional faulting associated with extensional faulting. In contrast, during described hereand it was during this period thatmajor periods of epeirogenicsubsidence, a lack of tensional activity occurred along the Flamborough Head and Dowsing stresses doesnot encourage the formation of any such FaultZones. These faults trend along thenorthern and compensating faults.Consequently, during such times the north-eastern margins of the granite block respectively (Fig. granite may exercise only minimal tectonic control. 1). Upper Jurassic and Lower Cretaceous sequences are thin Thereare now numerous examples of the tectonic or absent to the southof the faults, in contrast with the large influence of granites (e.g. Bott 1987; Bott et al. 1958; Bott et thicknesses observed tothe north in both the Cleveland al. 1978; Chroston et al. 1987; Dimitropoulos & Donato Basinand Sole Pit Trough. The batholith may have been 1981; Donato 1988; Donato et al. 1983; Donato & Tully responsible for the continued stability of the East Midland 1982; Scrutton et al. 1987)which broadly agree with the Shelf and also for the locations of the fault zones which were ideas brieflydiscussed above.It might beexpected, initiated earlier and subsequently reactivated during Jurassic therefore,that the presence of such an important granite and Lower Cretaceous times. Onthe Market Weighton block beneaththe Southern North Sea would exerta block, thin sequences of Lowerand Middle Jurassic significant tectonic effect. sediments were deposited with evidence of local uplift and As discussed earlier, there were three main periods of erosion (Kent 1955, 1978). Offshore, the Lower Cretaceous fault-controlled subsidence within the Southern North Sea Cromer Knoll Group is less than 250 ftthick over the Basin. These occurred during early Carboniferous,late postulated granite compared with a thickness of 500ft to Carboniferousto early Permian, and Jurassic to early 1OOOftin the Cleveland Basin and Sole Pit Trough. The Cretaceous times. Duringthese periods the proposed granite also appears to have exertedcontrol over Lower granite may have been an important feature in determining Cretaceous facies, as it marks the northern limit of the basal regional patterns of subsidence. Cretaceous Spilsby Sandstone (Glennie & Boegner 1981). Little detail is known of the development of the offshore Sediments depositedat times otherthan during these area during theCarboniferous. This is dueto insufficient three periods of extensional faulting appearto showno definition being available on reflection seismic data and also obvious relationship tothe underlying granite block. The to a lack of significant penetration of the sequence by the marginal and basinal facies of the Zechstein evaporite numerous wells drilled.Onshore, however, the pre-Coal cycles, forexample, appear to beuninfluenced by the Measure sequence thins over the Market Weighton Block granite in both theonshore (Kent 1978) and offshore (Kent 1978; Bott et al. 1978). This is indicative of a period (Taylor & Colter 1975) areas. In addition,the Triassic of stability of the block during early Carboniferous times BunterSand and Shale sequences showonly minor (Bott 1987), perhaps corresponding with the first period of thickeningacross the Dowsing FaultZone. The Upper fault-controlled subsidence discussed here. We predict that a Cretaceous Chalk seems to have been depositedover a wide fuller understanding of theCarboniferous development area with little major lateral variation, although the present offshore will reveal a similar influence of the granite block, day distribution is strongly controlled by thesubsequent with its effectbeing particularly evident during early inversion movements which occurred principally in the areas Carboniferous times. The proposed Carboniferoushigh may of thickest total deposition. have affected local patterns of sediment distribution, In addition, as Parnell (1988) notes,hydrothermal predominantly from the NE, by superimposing an E-W or circulation is commonly associated with granites, frequently WNW-ESE trend.Recent unpublished explorationand long after the period of intrusion. It may be expected that

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/1/133/4890723/gsjgs.147.1.0133.pdf by guest on 24 September 2021 BURIEDGRANITE BENEATH SOUTHERN NORTH SEA 139

Fig. 6. Rotliegendes sand thickness (contour interval50 feet) (after Taylor 1980). It can be seen that the Rotlie- gendes sand interval is less than50 feet thick in the area corresponding to the location of the low Bouguer anomaly values. The location of the seismic section (AA‘) of Fig. 4 is also shown.

local areas of anomalously high organic maturity,and -, ROBINSON,J. & KOHNSTAMM,M. A. 1978. Granite Beneath Market remobilization of Zechstein salts and carbonates could be Weighton, East Yorkshire. Journal of the Geological Society, London, produced by hydrothermal circulation. This could result in m, 535-543. BritishGeological Survey. 1 :ZrO,oOO Series,Bouguer Gravity map hydrocarbons being sourced locally from otherwise imma- (Provisional Edition) Tyne-Tees, California, Humber-Trent and Spurn ture sediments. The remobilization of Zechstein salts into sheets. British Geological Survey, Keyworth. theRotliegendes reservoir could provide additional seals -1979. 1:2,5OO,ooO,Sub-Pleistocene Geology of the British Isles and the and hence trapping mechanisms, as well as problems with AdjacentContinental Shelf. A. W. Woodland, Institute of Geological Sciences. reservoir quality prediction. -1985. 1 :l,ooO,ooO, Map : 1 Pre-Permian Geology of the United Kingdom In summary,it would appearthat the presence of an (South). British Geological Survey on behalf of Petroleum Engineering extensive granitebatholith and its associated tectonic Division of the Department of Energy, Keyworth. influence, especially during times of extensionalfaulting, BULAT,J. & STOKER,S. J. 1987. Uplift Determination from Interval Velocity Studies, UK, Southern North Sea. In: BROOKS,J. & GLENNIE,K. W. can be used to assist our understanding of the geological (eds) Petroleum Geology of North-West Europe. Graham & Trotman, development of this part of the Southern North Sea Basin. 293-305. CHROSTON,P. N., ALLSOP,J. M. & CORNWELL,J. D. 1987. NewSeismic We would like to thank NOPEC (UK) Ltd. for permission to show Refraction Evidence on the Origin of the Bouguer Anomaly Low near the line drawing of Fig.4. The drawingoffice of Carless Exploration Hunstanton, Norfolk. Proceedings of the Yorkshire Geological Society, 46, 311-319. Limited kindly assisted with the preparationof some of the figures. COPE, M. J. 1986. An interpretation of the Vitrinite Reflectance Data from One of us (JAD) would like to thank British Rail (Network South the Southern North Sea Basin. In: BROOKS,J., GOFF, J. C. & VAN East) for the provision, during many long occasions,of a warm and HOORN,B. (eds) Habitat of Palaeoroic Gas in N.W. Europe, Geological dryenvironment in which a significant part of thiswork was Society Special Publication, 23, 85-98. undertaken. DIMITROPOULOS,K. & DONATO,J. A. 1981. The Inner Moray Firth Central Ridge, a Geophysical Interpretation. Scottkh Journal of Geology, 17, 27-38. DONATO,J. A. 1988. A Buried Granite beneath the Southern NorthSea References (abstract). Geophysical Journal of the Royal Astronomical Society, 92, 547. ALLSOP, J. M. 1987. Patterns of Late Caledonian Intrusive Activity in Eastern -& TULLY,M. C. 1981. A Regional Interpretation of North Sea Gravity and Northern England from Geophysics, Radiometric Dating and Data. In: ILLING,L. V. & HOBSON,G. D. (eds) Petroleum Geology ofthe Basement Geology. Proceedings of the Yorkshire Geological Society, 46, Continental Shelf of N. W. Europe. Heyden, London, 65-75. 335-353. -& -1982. A Proposed Granite Batholith along the Western Flank of AVESCHOUGH,N.C. 1986. The Market Weighton Carboniferous Trough. the North SeaViking Graben. Geophysical Journal of theRoyal Yorkshire Geological Society Circular, 393, 3. Astronomical Society, 69, 187-195. m, M. H. P. 1987. SubsidenceMechanisms of Carboniferous Basinsin -, MARTINDALE,W. & TULLY,M. C. 1983. Buried Granites within the Northern England. In: MILLER,J., ADAMS,A. E. & WRIGHT, V.P. (eds) Mid-North Sea High. Journal of the Geological Society, London, 140, European Dinantian Environments, John Wiley & Sons Ltd., 21-32. 825-837.

~ 1988. The Market Weighton Gravity Anomaly-Granite or Graben? EVANS,C. J. & ALLSOP,J. M. 1987. Some Geophysical Aspects of the Deep Proceedings of the Yorkshire Geological Socie@, 47, 47-53. Geology of Eastern England. Proceedings of theYorkshire Geological -, DAY,A. A. & MASON-SMITH,D. 1958. The Geological Interpretation Society, 46,321-333. of Gravity and Magnetic Surveys in Devon and Cornwall. Philosophical GLENNIE,K. W. 1986. Development of N.W. Europe’s Southern Permian Tramactions of the Royal Society of London, 25M, 161-191. Gas Basin. In: BROOKS,J., GOFF,J. C. & VAN HOORN,B. (eds) Habitaf

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/1/133/4890723/gsjgs.147.1.0133.pdf by guest on 24 September 2021 140 DONATO J. A. & J: B. MEGSON

ofPalaeozoic Gas in N. W. Europe. GeologicalSociety Special WOODLAND,A. (ed.) Petroleum and the Continental Shelf of North West Publication, 23, 3-22. Europe. Institute of Petroleum, London, 205-210. -& BOEGNER,P. L. E. 1981. Sole Pit Inversion Tectonics. In: ILLING,L. PARNELL,J. 1988.Migration of Biogenic Hydrocarbons into Granites: a V. & HOBSON,G. D. (eds) Petroleum Geology of the Continental Shelfof Review of Hydrocarbons inBritish Plutons. Journal of Marine and N.W. Europe. Heyden, London, 110-120. Petroleum Geology, 5, 385-3%. GOODCHILD,M. W. & WHITAKER,J. H. McD. 1986. A Petrographic Study of ROLLIN,K. E. (undated). Interpretationofthe Main Features ofthe the Rotliegendes Sandstone Reservoir (Lower Permian) in the Rough Humber-Trent 1:25O,ooO Bouguer Gravity Anomaly Map. Institute of Gas Field. Clay Minerals, 21, 459-477. Geological Sciences, Applied Geophysin Unit, Report No. 74. KENT, P. E. 1955. The Market Weighton Structure. Proceedings of the SCRUTTON,R. A., ZERVOS,F. A., DAY, G.A., HILLIS,R. R. & CONDON,P. Yorkshire Geological Society, 30, 197-227. J. 1987. The Subsidence Behaviour of Granites (abstract). Geophysical - 1978.Subsidence and Uplift in East Yorkshire: A double Inversion. Journal of the Royal Astronomical Society, 09,488. Proceedings of the Yorkshire Geological Society, 42, 505-524. TAYLOR,J. C. M. 1980. Origin of the Werraanhydrit in the U.K. Southern KIRBY, G. A. & SWALLOW,P. W. 1987. Tectonism and Sedimentation in the North Sea-a Reapprasial. In: FUCHTBAUER,H. & PERY~,T. M. (eds) Hamborough Head Region of North-East England. Proceedings of the TheZechstein Basin, with Emphask on CarbonateSequences. Yorkshire Geological Society, 46, 301-309. Contributions to Sedmentology, Schweizerbart’scheVerlagsbuch- -, SMITH, K., SMITH,N. J. P. & SWALLOW,P. W.1987. Oil and Gas handlung, Stuttgart, 9, 91-113. Generation in Eastern England. In: BROOKS,J. & GLENNIE,K. W. (eds) TALOR,J. C. M. & COLTER,V. S. 1975. Zechstein of the English Sector of PetroleumGeology of North-West Europe, Graham & Trotman, the Southern North Sea. In: WOODLAND,A. (ed.) Petroleumand the 110-120. Continental Shelf of North West Europe. Institute of Petroleum, London, MARIE, J. P. P.1975. Rotliegendes Stratigraphy andDiagenesis. In: 249-263.

Received 25 February 1989; revised typescript accepted 31 May 1989.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/147/1/133/4890723/gsjgs.147.1.0133.pdf by guest on 24 September 2021