Cenozoic tectonics of Great Britain and geodynamic implications in western Europe

TECTONOPHYSICS ELSEVIER

Tectonophysics 252 (1995) 103- 136

Palaeostress analysis, a contribution to the understanding of basin tectonics and geodynamic evolution. Example of the Permian/Cenozoic tectonics of Great Britain and geodynamic implications in western Europe Christian Hibsch a3*,Jean-JacquesJarrige b, Edward Marc Cushing ‘, JacquesMercier a a URA-CNRS

(1369) Gophysique et CZodynumique interne, Biit 509, UniuersitC de Paris-&d, F-91 405 Orsuy, b ElfAquituine Production. Centre Scientijique et Technique Jean Feger. 64 000 Pnu, France ’ CEA /IPSN, 60-68 Au. du Ce%ral Leclerc, BP 6, F-92265 Fontenay nux Roses Cedex, Frunce

Frunce

Received 11 August 1994; accepted 21 March 1995

Abstract Microtectonic analysis in association with tectonic-sedimentological observations enables us not only to define palaeostress tensors but also to date each of them. Such a study, carried out in central and northeastern England and in southernmost Wales has permitted us to point out several tectonic stages during the Permian-Cenozoic period. (1) Inferred from syn-sedimentary faulting in the Late Permian series, the Permian/Early Triassic tectonic regime is characterised by a NNW-SSE-oriented extension. (2) During the Late Triassic to the early Late Jurassic, an E-W- to ENE-WSW-oriented extension was acting as suggested by syn-sedimentary normal faulting in Keuper, Lias and Middle Dogger sediments and post-sedimentary normal faulting in Oxfordian sediments. (3) The following tectonic event probably started during the Malm and was particularly active during the Early Cretaceous. It was characterised by a N-S- to NNE-SSW-oriented extension and was associated with an E-W- to WNW-ESE-oriented strike-slip tectonic regime (transtension). (4) A locally observed NW-SE-oriented transpressional strike-slip tectonic regime is thought to correspond to the ‘Laramide’ inversion phase of the Middle Paleocene. (5) The later tectonic event is characterised by a N-S-oriented transpressional strike-slip regime and affects a Paleocene tholeiitic dyke (‘Cleveland dyke’). It is supposed to be synchronous with the so-called Eocene ‘Pyrenean’ to the Early Miocene ‘Helvetic’ compressional stages. These paleostress tensors are compared with others defined in France, the Benelux countries and Germany and are also collated to the tectonic evolution of oil basins assessed from geophysical analyses. These comparisons raise discussions about the paleostress distribution within the geodynamic evolution of the West European shelf.

1. Introduction Since the end of the Variscan orogeny (late Westphalian), the English sedimentary basins (Fig. 1)

* Corresponding author. 0040.1951/95/$09.50 0 1995 Elsevier SSDI 0040-1951(95)00100-X

Science

B.V.

All rights

reserved

104

C. Hthsch

rr ul./T~ctonr)physi~.~

have undergone subsidence controlled by various stages of syn-sedimentary faulting (Whittaker, 1975; Dewey, 1982; Chadwick et al., 1989; Roberts, 1989). The analysis of their tectonic evolution is generally based on seismic data. Such studies allow a precise dating of tectonic events but can not define tectonic

STRUCTURAL SKETCH-MAP NORTH-WESTERN EUROPE -1

Location

v[ ,:

Paleozoic

Fig. 1, Structural Midland shelf; D.F. = Dowsing

252 (1995)

103-136

regimes. Kinematic reconstructions could only define qualitative and rough deduction of the directions of strains. Very few fault analyses aiming to define paleostress tensors have been conducted in Great Britain. The first purpose of this structural analysis was to

OF

of the area of study moles

sketch map of Great Britain and surrounding basins. Location MW = Market Weighton block; MM = Moreton-in-the-Marsh Fault; S.H.F. = South Hewett fault.

of the area of study. CB = Cleveland basin; EMS = East axis; M = Mendip axis; 0.S.p. = Outer Silver Pit fault;

C. Hibsch

et al./

Tectonophysics

define and date the tectonic regimes that have affected central Great Britain after the Variscan orogeny, in order to better understand the structural evolution of onshore and offshore surrounding basins, and secondly, to complete the paleostress framework of western Europe and collate these tectonic regimes with geodynamic reconstructions. Usually, chronology and dating of paleostress tensors are obtained from the relative chronology of superimposed striations on fault planes and with the retrotectonic method (Letouzey, 1986; Angelier, 1991, Angelier, 1994). From about 380 quarries and outcrops along the coasts of eastern England and southern Wales which have been analysed (see location of the study area in Fig. l), only 118 sites proved interesting for paleostress analysis and dating of paleotectonic regimes. Of the 118 sites, just a few relative chronological observations were done, some of which proved contradictory. The use of the retrotectonic method has not been totally significative for the outcome of the dating of the different paleostress tensors since some ages of the Permian/Cenozoic period were missing or were not represented with lithologies favourable to the recording of brittle tectonic features and since some deformations were more cautious than others, especially for extensional tectonics. The limitations of the retrotectonic method, particularly for such a long period with several superimposed paleostress regimes and a relative insufficiency of outcrops, have led us to look especially for evidences of syn-sedimentary fault activity in order to date the tectonic regimes. This approach was crucial to the outcome of this study. The tectonic regimes obtained are presented in Fig. 2, as well as a summary of the most significant localities for tectonic and tectonic-sedimentological observations. It must be emphasised that the aim of this preliminary paleostress analysis in Great Britain was to define general directions of paleostress axes for each tectonic stage in the perspective of wide regional applications, and not to study paleostress distributions and trajectories in detail, since the number of useful outcrops was insufficient. We rather suggest to obtain precise determinations of paleostress trajectories and paleostress deviations with the use of calcite twins analyses since this mineral is very common in great Britain and could afford to define paleostress tensors in regions where microtec-

252 (1995)

103-136

105

tonic analysis has proved helpless, such as in eastern central England.

2. Methods for paleostress tensor definitions 2.1. Fault kinematics analyses Mean deviatoric stress tensors have been computed, within a factor k, from the sets of striated faults measured in the field using the algorithm proposed by Carey (1976, Carey (1979). This computation assumes that sliding occurs in the direction of the shear stress as resolved on the fault plane. Separation of families of striations resulting from successive tectonic regimes are based on geological data demonstrating their relative chronology and their relations to regional or local tectonic deformation. Inversion results of the data for sites with few measured striations or with poor azimuthal variations are not strongly constrained. In this case, we have used a ‘test’ method to determine the best fitting stress tensor. For more detailed information concerning the method used, the reader may refer to Mercier et al. (1992). 2.2. Limitations of the retrotectonic method and contribution of the tectonic-sedimentological approach From the analysis of a set of striated faults, the basic principle to determine a paleostress tensor is to recognise geometric compatibility between slip vectors measured on fault planes. This assumes that the selected displacement indicators developed in the same paleostress environment. In a site characterised by the recording of several tectonic regimes, the element of sorting is preponderant. This sorting is a kind of subjective interpretation which could perturb the analytical phase of the study, which in turn could distort the conclusions. Chronologies of striations could help the sorting but are not always significant since they can be produced by local stress deviations or rotations of tectonic blocks, involving local chronologies which may have no relations to the regional stress situations (see Angelier, 1991). In this method, it is also assumed that the regional paleostress fields are quite homogeneous (Klein and

C. Hibsch

106

GEOLOGICAL

et ul./Tectomphysics

TECTONIC

252 (1995)

103-136

REGIMES

WESTERN

EUROPE

TECTONIC

PHASES

“HELVETIC” “OLIGOCENE” “PYRENEAN”

Sites 32,33,34,36,37 & 115 mesostructural

LARAMlAN

SUB-HERCYNIAN AUSTRIAN

LATE ::

CTMMERTAN

:;. MID CTMMERTAN Sites 6, 66

relative chronologies (NNE-SSW 8 ENE-WSW extensions)

ARLY

CIMMERIAN

LATE

VARTSCAN

Site 66 relative

chmnobgies (NNW-SSE and ENE-WSW extensions)

(Well and Tadcaster)

Fig. 2. Table of tectonic stages. A = paleostress tensor; B = other tectonic data. Numbers in parentheses 1989; 2 = Villemin, 1986; 3 = Letouzey, 1986; 4 = Bergerat, 1987; 5 = Vandycke, 1992; 6 = Coulon, 8 = Bevan and Hancock, 1986.

refer to authors: I = BEs et al., 1992; 7 = Benard et al.. 1985;

C. Hihsch

et al./

Tectomphysics

Barr, 1986; Letouzey, 1986). This basic hypothesis allows us to classify the paleostress tensors into families by type of tectonic regime and orientations of stress axes, each attributed to a separate regional tectonic event. But it is clear that stress deviations and permutations are frequent, especially during transcurrent deformation. Strike-slip, extensional and compressional stress fields can be coeval by place during the same regional tectonic event. The computed paleostress tensors then correspond to a spatial distribution and not to a temporal superposition. Analyses of focal mechanisms of earthquake aftershock sequences have also revealed stress instabilities under the same regional paleostress environment (Mercier and Carey-Gailhardis, 1989). All of these natural perturbations of the paleostress fields could contribute to define tectonic regimes without regional significance and have been considered during the analytical phase. Another limitation in the use of the retrotectonic method consists in the unequal distribution of the tectonic fracturing. For example, in the area of study, it is noteworthy that only the strike-slip compression of Middle Cenozoic age released a sufficient amount of energy to affect the basins with a penetrative faulting when extensional deformation was very localised. Monophased sites were frequently encountered with extensional deformation where only compressional deformation was superimposed. The relative spatio-temporal independence of these sites has made the work easier, even in sediments as old as the Permian, because of the limitation of the contamination among the different extensional kinematics. In many cases, it has been possible to compute paleostress tensors nearly without any sorting. In the particular case of Late Cretaceous Chalk deposits, such sorting could have been applied to separate different kinematics of normal faulting but this might have led to define artificial events while most of these faults result from compaction processes and correspond to an uniaxial stress tensor (discussed below). Although the local monophasing of the tectonic sites has proven very helpful, it also resulted in a significant lack of relative chronologies which has weakened the efficiency of the method. In order to compensate for these deficiencies, special attention was given to syn-sedimentary tec-

252 (1995)

103-136

107

tonic evidences. This means that microtectonic analyses were conducted in conjunction with sedimentological observations. For more detailed data about the microtectonic sites and tectonic-sedimentological observations, the reader may refer to Hibsch (1992) and Hibsch et al. (1993). The contribution of this approach is clearly evident for the Permian/ Early Triassic and late Oxfordian/Aptian extensional tectonic regimes which are both close to N-S and which might have not been differentiated with the retrotectonic method. Precise dating of the deformation can be obtained. This could make it possible sometimes to evidence local perturbations of the regional paleostress field such as deviations and permutations of stress tensor axes as well as strongly curved paleostress trajectories, since the computed paleostress tensors can be compared in time. This approach also permits us to work in folded areas while a precise dating of a fault activity might allow a rotation back to the horizontal of the fault planes if the folding is proven to be due to a more recent event. The accuracy of dating, thus, could define whether a paleostress field was homogeneous or not. This might be also useful in order to evaluate rotations of crustal blocks and these results might then be compared to paleomagnetic data.

3. Geological and tectonic background studied

of the area

The area studied consists of wide platforms of Permian to Late Cretaceous sediments. This western extremity of the Anglo-Dutch basin area is located between the London-Brabant high to the south and the Pennine Highs to the north (Fig. 1). From the various main stages in its geological evolution the following events could be noted. A strong angular unconformity can be observed between the Lower and Upper ‘Coal Measures’ of the Carboniferous (British Regional Geology, 1969). This event is related to the inversion of Carboniferous basins in the English Variscan foreland (Ziegler and Van Hoom, 1989). The front of the Variscan fold belt (Fig. 1) crosses into South Wales where measurements of tension gashes in the Carboniferous sediments have pointed out two superimposed transpressional stages of the Late Paleozoic (at the Og-

108

C. Hihsch

et ul./

Tectonophy.sic.s

more-by-Sea and Barry Island sites, British National grid respectively X: 286.1/Y: 175.4 and X: 3 11.2/Y: 166.4). A first N-S-oriented strike-slip tectonics pre-dated a more clearly expressed E-Woriented stage. This latter kinematics has not been observed in the Keuper and Lias series of this region and, according to the chronology, rather suggests a Paleozoic age for these two stages of deformation. Carboniferous E-W compression has been proposed for central England, along the Malvem trend (Wills, 1956 quoted in Whittaker, 1975). A succession of two compressional stages from a N-S to an E-W direction was also described for Stephano-Autunian times (Ziegler, 1990a). After the post-Carboniferous peneplanation, the sedimentation in central and northern England basins began during the Permian and lasted almost uninterrupted until the Late Cretaceous. It is noteworthy that major extension ended prior to the Albian which corresponded to the onset of the Chalk sedimentation. One of these main extensional structures onshore, the ‘Market Weighton block’ and the associated Pickering Graben (Fig. l), are fossilised by the Chalk with a clear unconformity (Kent, 1980). Cenozoic sediments only crop out in southern England and have rarely been encountered in the area of study. However, an igneous intrusion (the ‘Cleveland dyke’) of Late Paleocene age (58.4 + 1.1 Ma British Regional Geology, 1980) is located to the

Table 1 Parameters

of the stress tensors

Site

ND

Lat. N (“)

Long.

1-4 40 41 42 44 61(t) 66 67

8 I5 19 8 33 4 14 IO

54.727 53.876 53.862 53.853 53.804 53.3 52.911 52.964

1.526 1.319 1.314 1.301 I.289 1.252 1.971 1.981

computed W (“)

for the Permian/Early 01

252 (1995)

103-136

north, in the mid-Yorkshire region (site 10; Great Ayton). It belongs to a large tholeiitic dyke swarm which crosses a large part of Scotland, the north of England and northern Ireland (Vann, 1978; Ziegler, 1982, Ziegler, 1990a; Dewey and Windley, 1988). Following this volcanic event, the Cleveland basin was uplifted during the Cenozoic inversion phases (Kent, 1980). The geological setting is quite different in South Wales, where Mesozoic basins are superimposed on the Variscan fold belt (Fig. 1). Post-Variscan tectonics were influenced by old Variscan thrusts which have been reactivated, firstly as normal faults during Permian to Early Cretaceous times, and secondly as (transcurrent) reverse faults during the Late Cretaceous to Cenozoic inversion tectonics (Stoneley, 1982; Chadwick, 1986; Lake and Kamer, 1987; Brooks et al., 1988; Day et al., 1989).

4. Permian to Cenozoic tectonic paleostress of central Great Britain 4.1. Stage I: Permian/ Early Triassic NNW-SSEoriented extension (Fig. 2) This tectonic regime has been only pointed out in Permian and Early Triassic beds (Fig. 3 and Table 1). It is characterised by syn-sedimentary tectonic

Triassic

o2

NNW-SSE a3

Azim.

Dip.

Azim.

Dip.

Azim.

Dip.

142” 202” 297” 189” 041” 078” 041” 321”

83” 80” 64” 87” 80” 65” 86” 71”

037” 058” 075” 094” 257” 261” 246” 106”

02 08” 20” 00” 08 25’ 04” I I”

307” 327” 171” 004” 166” 171° 156” 197”

07 06” 16 03” 06 01” 02” 08”

extension R

MMA(?

SD(“)

D

Ref

0.75 0.68 0.71 0.92 0.89 0.52 0.91 0.82

4.6 6.8 9.9 6.7 9.0 4.2 7.0 3.7

5.5 9.1 12.0 8.1 12.4 4.8 8.7 4.4

P(l)

Old-cor3 Tadcasn8 Tadcasd3 Tadcass3 Millhil Anston4 Freehay Teanford:!

P(1) P ‘(I) P(l) Ft, P-T(I) P-T(I)

(1) Mean test computed stress tensor; ND: number of data used for computation; o I, @ 2 and u 3 give the principal stress directions and the R stress ratios (o 2 - o 3/a 2 ~ cr 1 of the optimum models; MMA: misfit angle; SD: standard deviation; D: age of the series affected by the faulting (P = Permian, T = Trias, L = Lias, D = Dogger, M = Maim, J = undifferentiated Jurassic, C = Late Cretaceous, Pa = Paleocene), numbers in parenthesis mean a relative dating of the faulting, in comparison with at least another kinematics observed in the same site, (* J: means syn-sedimentary faultin g; references are the name of the computed files

C. Hibsch

et al./Tectonophysics

features such as underwater truncations, syn-sedimentary horst and graben structures (Fig. 3, site 41, Tadcaster Darrington quarry) and sedimentary dykes (Fig. 3, site 22, Well Quarry) (Hibsch et al., 1993). This extensional event also seems to have controlled Permian to Early Triassic continental sands and conglomeratic deposits on the northern side of the

252 (1995)

103-136

109

Malvem trend (Fig. 3, sites 66 and 67) (personal communication Tarmac Roadstone geologist’s staff). During the study at site 66, numerous E-W- to ENE-WSW-striking normal faults were observed. They have been displaced by NNW-SSE-striking normal faults with more than 10 m downthrows. In the vicinity of one of these latter faults, a smaller

5t

5

4‘

5

a

5:

2‘

Fig. 3. Permian/Early

Triassic

NNW-SSE

extension.

(A) Stereonet

of the statistical

direction

of the a3 axis (95%

confidence

angle.)

C. Hihsch

110

et al./

Tectonophysm

ENE-WSW-striking normal fault has registered two episodes of faulting (cross-checked striations) indicating a NNW-SSE extension prior to a ENE-WSW extension. The latter kinematics could be related to the subsequent Keuper to early Oxfordian extension. In the North Tadcaster Steetley quarry (Fig. 3, site 40) this extension seems to be associated with a N60”E-oriented strike-slip regime (transtension). 4.2. Stage 2: Triassic/ early Ox$ordian E-W ENE- WSW-oriented extension (Fig. 2)

Site

of the stress ND

9 12 18 55

22 5 14

56(t) 63 66-67

8 17 12

69(t) 74 84 118

5

9 12

5

Same symbols

Lat.

tensors

N (“)

54.555 54.410 54.246 53.620 53.607 53.268

52.971 52.823 52.706 52.262 51.412 as for Table

Long.

0.822 0.534 0.377 1.243 0.6 1.214 1.971 0.715 1.412 1.384 3.341 1.

computed W (“)

for the Keuper

to

al

to early

Oxfordian

a2

E-W

a3

01”

0.88

10.4

04" 07" 11” II”

0.81 0.63 0.76 0.94

5.5 5.6 8.1 1.4

7.4 10.0 1.7

0.54 0.85

9.1 9.7

10.2 12.1

D’ P(l) L(1) HI) P-T1(2)

0.55 0.80 0.76 0.87

3.5 11.5 8.2

4.5 12.7 11.9 4.8

T’ L(l) L(l)

Azim.

Dip.

Azim.

194” 216"

8P 86"

356"

03" 02

087"

329”

059”

083"

83" 70"

351"

00”

149”

17"

79”

139” 3" 021" 134" 332" 182" 319"

01°

00”

86" 87"

269”

89”

164” 315 065"

88" 86" 85"

04" 02" 01” 02" 02"

01”

092” 229"

extension

MtiA

Dip.

261" 243" 230" 246" 111” 044” 062"

to ENE-WSW R

Azim.

045" 151" 261"

103-136

field study confirm the persistence of the ENEWSW-oriented extension during this period. Synsedimentary normal faulting was attributed to the Peak fault (Sellwood and Jenkyns, 1975) striking N160”E on the Ravenscar coastline (Fig. 4, site 12). This fault affected Upper Lias sedimentation. On the Ravenscar coastal flat we observed some normal faults displaying a hydro-plastic style of deformation, indicating an ENE-WSW-oriented extension before the lithification of the upper Lias and lower Dogger sediments. The fault planes of this early soft-sediment faulting were subsequently cut by brittle extensional fractures of tens of centimetres in size, displaying an E-W strike which is compatible with the following late Oxfordian-Aptian extensional event. Dogger units. Along the coast of Yorkshire, Dogger sediments are affected by several NNW-SSEstriking normal faults. One of these faults in the Cayton Bay area (the ‘Red fault’) clearly controlled Bajocian sedimentation (middle Dogger ‘Estuarine’ beds) with evidences of tectonic activity contemporaneous of the sedimentation such as syn-sedimentary block tilting and underwater truncation associated with soft-sediment tectonic faulting (Fig. 4, site 18 and Fig. 5) (Hibsch et al., 1993). The analysis of this faulting gives a N81”E orientation of extension (Fig. 5C). Two synchronous directions of brittle extensional fractures observed in the underlying lower Bajocian sediments (‘Millepore beds’) also

This extensional event has been registered in Permian to early Oxfordian sediments. Syn-sedimentary faults in Late Triassic, late Lias and middle Dogger formations demonstrate that an E-W- to ENEWSW-oriented extension was active in central and northern England during most of the first half of the Mesozoic (Figs. 2 and 4 and Table 2). Triassic units. Syn-sedimentary tectonic activity is evidenced with several data, such as sealed faults, fan-shaped stratification along the faults, beds pinching out and thickness variations of the beds which were observed in the Keuper sandstones and marls of the Coalville colliery (Fig. 4, site 63) (Hibsch et al., 1993). Kinematics analysis of the NNW-SSE-striking faults in the Keuper marls, provided a N62”E direction of extension (Table 2). Lias units. Thickness variations described in the Lias series (British Regional Geology, 1980) and our

Table 2 Parameters

252 (1995)

(“)-~ SD (“)

D

Ref

Dip.

03"

01” 00” 03" 04"

3.9

Il.9

7.9

L(l) L-D

*(I)

Staithe I Ravens4 Cayton 1 Smeaton4 Scuntho I Crewel16 Freehay Saltby I Coalvil I southam Rhoose4

C. Hibsch

et al./Tectmwphy.sics

to ENE-WSW

extension.

252 (1995)

103-136

T 3 53’-

/ 300 -

Fig. 4. Keuper angle).

to Early

Oxfordian

E-W

indicate an ENE-WSW extension. The NNW-SSE fractures display a purely extensional component while the E-W to WNW-ESE ones show a relative right-lateral strike-slip component. After this synsedimentary deformation phase, normal faulting along the ‘Red fault’ continued at least during the early Oxfordian.

(A) Stereonet

of the statistical

direction

of the (r3 axis (95%

confidence

4.3. Stage 3: Late Oxfordian/Aptian (?) N-S- to NNE-SSW-oriented extension and associated E-Wto WNW-ESE-oriented strike-slip regime (Fig. 2) This extension is recorded in Malm limestones (‘Malton oolith’, Yorkshire and Oxfordian ‘Corallian’ levels around Oxford), Dogger limestones, Lias

C. Hihsch

er al./

Tecronophy.sic.s

252 (1995)

103-136

Ycm Nab beds

Fig. 5. Syn-sedimentary faulting at Cayton Bay site in Dogger ‘Estuarine beds’. (A) Late Bajocian situation (at the end of the ‘Gristhorpe beds’ deposition): I = eastward tilting and deltaic-shaped deposits; 2 = truncation of the top of the tilted block; 3 = syn-sedimentary faulting. (B) Details of soft-sediment tectonic faulting of the ‘Red fault’: I = hydro-plastic striations (with coal debris incrustations over the slickensides). (C) Computed stress tensor stereodiagram of the ‘Red fault’ tectonic activity during the Dogger and the early Oxfordian, including early hydro-plastic striations.

sediments of central England and South Wales and Permian ‘Magnesian limestones’ (Fig. 6 and Table 3). Faults have not been observed in Lower Cretaceous (Berriasian to Aptian) deposits, these being principally sands and clays in which brittle deformation is poorly registered. The Early Cretaceous age of this extensional event is supported by seismic and well data of a graben located on the northern side of the ‘Market Weighton block’, bounded by the EW-striking Foxhole/Bempton and Langtoft normal faults (part of the Pickering Graben system: Kirby

and Swallow, 1987). In this graben, sedimentation of the Lower Cretaceous ‘Speeton clay’ was strongly controlled by these faults. This extensional regime is clearly expressed on the northern side of this tectonic structure where Jurassic and Permian sediments crop out (Fig. 6). No other extensional regime has been encountered in the Malm of this region. Published data and some field evidences suggest that this extension started during late Oxfordian times: the Oxfordian Malton oolith sedimentation was controlled by the E-W-striking Howardian Hill faults (part of

C. Hibsch

et al./

Tectomphysics

the Pickering Graben system: Wright, 1976, quoted in British Regional Geology, 1980; Kent, 1980) and syn-sedimentary deformation was observed at the top of a Nl lO”E-striking normal fault in the central Hovingham quarry (Fig. 6, site 27). Kirby and Swallow (1987) also noticed a thickening of the ‘Kim-

Fig. 6. Late Oxfordian/Aptian direction of the (T 3 axis (95%

NNE-SSW extension confidence angle).

and associated

252 (1995)

103-136

113

meridge clay’ in the Foxhole-Langtoft Graben. In central England (Peterborough region), E-W-striking sedimentary (Neptunian) dykes have been observed in the Oxfordian ‘Oxford clay’ (Martill and Hudson, 1989). Around Oxford, the reefal Oxfordian ‘Corallian’ formation was deposited on the top of

WNW-ESE

strike-slip

tectonics.

(A)

Stereonet

of the statistical

114

C. Hihsch

Table 3 Parameters Site

s(t) 12(r) 2627 31 53(t) 56(t) 59(t) 63(t) 64 65 77 84 85 108 IlSa IISb(t) 116 II7 118

of the stress tensors ND

II 3 16 8 5 8 5 6 13 14 5 7 7 6 3 5 12 8

Same symbols

Lat. N f?

54.555 54.410 54.164 54.156 53.685 53.607 53.443 53.268 53.243 53.174 52.646 52.262 52.227 5 1.808 51.441 51.441 5 1.397 5 1.389 51.412 as for Table

computed

Long.

0.822 0.534 1.004 I.590 I.248 0.6 I.194 1.214 0.499 0.42 1 0.549 1.384 1.445 I.223 3.605 3.605 3.192 3.277 3.341

W (“1

et ul./

Tec.tonoplty.ysics

for the middle

Oxfordian/Aptian(?)

D I

u2

252 (1995)

103-136

NNE-SSW u3

Azim.

Dip.

Azim.

Dip.

Azim.

Dip.

115” 302” 314” 028” 229” 254” 344” 049” 293” 327” 055” 237” 119” 082” 354” 249” 066” 017” 307”

69” 85” 81” 89” 89” 89” 83” 83” 74” 81” 77” 79” 83” 59” 75” 89 37” 80” 82

309” 068” 093” 275” 094” 119” I 18” 274” 108” 112” 289” 083” 293” 269” 088” 114” 287” 268” 07-I”

20 03” 07” 00 01” 01” 05” 05” 16” 07” 07” 09” 07” 31” 01” 01” 45” 03” 05”

217” 159” 183” 185” 004” 029” 209” 184” 199” 203” 198” 353” 023” 177” 179” 024” 174” 178” 168”

04” 04” 06 01” 01” 01” 05” 05” 01” 05” 10” 05” 01” 03” 15” 01” 22” IO” 06

extension R

MMA(“J

SD(“)

D

Ref

0.60 0.60 0.60 0.92 0.85 0.50 0.64 0.60 0.79 0.72 0.22 0.85 0.62 0.59 0.63 0.40 0.77 0.37 0.78

7.6 3.3 10.6 3.6 4.0 9.7 7.1 6.4 9.8 2.5 5.5 5.0 7.5 4.2 I .2 0.6 4.7 6.4 5.1

9.3 3.4 12.4 4.8 5.3 12.4 12.1 8.8 13.8 3.4 6.9 5.7 10.5 5.4 1.4 I .o 5.4 1.5 5.9

L(2) LD(2) M(I) P(l) P(l) L(2) D(l)

Staithe6 Ravens2 Hovinghl Suttong:! Dating3 Scuntho2 Maltby Crewel7 Lincoln1 Dunston 1 Stmford3 Southam Harbury I Islip Dunravn4 Dunravn5 Sully I Barry2 Rhoose3

P(2) D(1) J D(2) L(2) L Mf I) L(1) L(l) T T(1) L(2)

I.

E-W-striking tilted blocks, while the lower compartments were infilled by argillaceous deposits (Wet, 1987). All these data suggest that the N-S- to NNESSW-oriented extension began during the Late Jurassic. The end of this extensional tectonics occurred before the Albian onset of Chalk sedimentation (Kirby and Swallow, 1987). The great amount of normal faults in the Chalk are thought to have been caused mainly by compaction processes (Hibsch et al., 1993). Most of the sites related to the late OxfordianAptian event indicate an extensional tectonic regime (1 vertical) with a mean a3 axis trending NO@20”E (stereonet A in Fig. 6, and Table 3). However, at sites 64 (Lincoln) and 77 (Stamford), both in Middle Jurassic limestones, strike-slip faulting resulted from N-S-striking a3 and an E-W-striking (T 1 stress axis. At the Stamford site, oblique strike-slip faulting is clearly associated with normal faulting. We suggest that both the N-S- to NNE-SSW-oriented extension and E-W to WNW-ESE strike-slip regimes were coeval during the Late Jurassic/Early Cretaceous period.

4.4. Stage 4: Paleocene ‘Laramide’ f?) strike-slip tectonic regime (NW-SE-oriented CTI; NE-SWoriented ~3) (Fig. 2) Several tectonic features, such as NW-SE-oriented horizontal styloliths and NW-SE-striking tension gashes, and relative chronologies, suggest the occurrence of a NW-SE-oriented strike-slip tectonics prior to a N-S-oriented strike-slip tectonics. For this deformation phase, only few paleostress tensors could be determined (Fig. 7 and Table 4). These tectonic sites are almost always situated along regional inherited structural trends, such as the E-Wstriking Pickering Graben zone or the N-S striking Malvern trend (Fig. 7). While the second transpressional event is linked to the Eocene ‘Pyrenean’ event, this one could be related to compressional events of Late Cretaceous and/or Paleocene age, as evident in basins of the northwestern European shelf (Ziegler, 1982). No decisive answer could be given to this question since we have observed neither deformation affecting the Cenozoic sediments nor syn-sedimentary compressional deformation affecting the Late Cretaceous Chalk. Only regional data

C. Hibsch

Fig. 7. Paleocene/Early

et ul./

Eocene

Tectomphysics

‘Laramide’C?)

allow us to propose a Paleocene age for this compression. Such data will be discussed later. 4.5. Stage 5: post-Paleocene (‘Pyrenean’ and/or ‘Helvetic’) strike-slip tectonic regime (N-S-oriented al, E-W-oriented (~3) (Fig. 2) Brittle deformations resulting from a N-S-oriented transpression have affected Permian to Late

252 (1995)

NW-SE

103-136

transpressional

strike-slip

tectonics.

Cretaceous sediments (Fig. 8 and Table 4) and also the ‘Cleveland dyke’ of Late Paleocene age at Great Ayton (Fig. 8, site 10). The maximum (u 1) and minimum (U 3) principal stress directions computed from fault kinematics data are generally both horizontal (Table 4). In the northem area (Ain Fig. 8) they statistically trend N170”E and N80”E and, in the southern area (B in Fig. 8)

116

C. Hihsch

Table 4 Parameters compression Site 2-3 4 s-7 IO 14 19(t) 21 22 23-24 25 29 26-27 28 30 31 32 33 34a 34b 35 37 38 35x1) 40 41 42 45 47 49 48-50 51 53 54 55 57 58 59 60 61 63 64 78 88 92-93 94-95 98 99-100 loo(t)

of the stress tensors computed for and Middle Paleocene/Early Eocene ND 8 7 7 19 13 8 I5 12 IO 16 6 33 41 21 23 8 33 22 20 47 39 I7 16 5 I9 15 9 27 29 I5 IO 42 6 21 38 23 I8 II IO 8 19 25 II 6 7 I I 10 I5 3

Lat. N (“) 54.7 13 54.696 54.683 54.492 54.27 1 54.247 54.221 54.2 16 54.200 54.169 54. I63 54.095 54.162 54.163 54. I56 54.151 54.126 54.125 54.125 54.1 IS 54.083 54.082 54.043 53.942 53.876 53.862 53.853 53.789 53.782 53.771 53.779 53.741 53.685 53.673 53.620 53.591 53.492 53.443 53.347 53.3 53.268 53.243 52.560 52.820 5 I.986 5 1.970 5 I .957 5 I .923 5 I .923

Long. 1.521 1.540 I s49 1.149 0.866 0.749 0.304 I.613 0.443 0.584 0.672 0.882 0.990 0.246 1.590 0.482 0.1 I6 0.1 I4 0.114 0.819 0.479 0.48 I 0.396 0.742 I.319 I.314 1.301 0.53 I 0.609 0.479 1.324 0.548 1.248 0.513 I .243 0.375 0.316 I.194 -0.012 1.252 1.214 0.499 0.617 1.431 1.807 I .884 I .85 I I.815 1.815

W (“)

et crl./T~ctonophy.sic.s

the Middle ‘Laramide’

al Azim.

Dip.

347” 166” 001” 349” 154” 015” 010 186” 359” 355” 195” 354” 002” 182” 346” 001” 143” 326” 357” 177” 007” 014” 199” 164” 144” 355” 172” 350” 339” 172” 009” 158” 352” 350” 348” 345” 333” 154” 353” 328” 179” 356” 004” 202” 188” 192” 194” II9 009”

06 08” 03” 06 05” 05” 03” 07 07” 19” 26” II” 02” 02” 15” 57” 01” 00” OS” 03” 08” 00” 00 01” 07” 02” 06” 03” 08” 02” 02” 05” 01” 02” 01” 04” 02” 08” 03” 06” 04” 02” 06 03” 02” 00” 03” 03 05

u2 Azim. 222” 073” 112” 102” 282 165” 226” 001” 199” 220” 103” 127” 143” 069” 156” 092” 048” 233” 098” 298” 170 283” 259” 289” 097” 275” 177” 207” 054” 152” 204” 089” 095” 080” 248” 225” 064” 295” 127” I89 009” 088” 286 348” 228” 240”

252 (1995)

IOS- I36

‘Pyrenean’ Eocene/Early Miocene NW-SE strike-slip compression Dip. 80” 21° 81” 75” 82O 84” 86” 83” 82O 64” 03” 74” 87” 84” 74” 00 83” 85” 67” 85” 82” 73” 88” 80” 82” 80” 66 87 78” 86” 87” 81” 88” 80 87” 79” 83 26” 85” 46” 82” 88” 84” 87” 77” 86 86” 80” 83”

CT3 Azim. 276 271” 258” 063” 285” IO0 096” 089 091” 262” 272” 273” 255” 182” 233” 056” 265” 087” 277” 104” 109 074” 053” 265” 080” 080” 070” 262 279” 067” 082” 258” 254” 242” 049 083” 232” 088” 266” 094” 112” 278” 102” 104” 028 099

(and/or

‘Helvetic’)

R

MMA(“)

SD(3

0.94 0.98 0.76 0.91 0.29 0.90 0.84 0.93 0.96 0.94 0.75 0.98 0.63 0.8 I 0.32 0.98 0.77 0.83 0.99 0.52 0.96 0.85 0.86 0.35 0.5 I 0.68 0.53 0.52 0.78 0.65 0.63 0.80 0.44 0.63 0.91 0.70 0.84 0.94 0.48 0.99 0.84 0.58 0.66 0.74 0.9 I 0.73 0.95 0.85 0.60

2.9 3.2 4.8 8.2 10.2 3.6 4.6 8.5 4.0 8.9 1.9 8.1 7.9 8.3 8.1 6.7 9.1 8.6 7.7 7.5 8.1 6.6 6.6 2.8 7.4 9.0 6.2 7.5 4.6 12.2 4.7 7.2 2.2 8.2 7.1 I I .3 7.6 7.0 7.2 4.9 8.6 4.5 8.1 I .8 2.3 4.0 7.7 3.6 2.9

3.7 4.7 6. I 1 I.6 12.8 4.3 6.0 10.7 5.2 10.7 2.9 10.5 Il.0 10.4 10.3 8.5 II.3 10.5 9.6 9.6 9.6 8.0 8.2 3.1 10.1 11.4 8.1 IO.0 5.7 15.3 6.8 8.8 3.1 9.5 9.5 14.2 9.0 8.7 8.6 6.6 10.9 5.9 10.4 2.2 2.7 5.0 9.6 4.8 3.0

N-S D

strike-slip Ref

Dip. 08” 68” 08” 14” 06 03” 02 01” 03” 17” 64” I2 02 05” 03” 33” 07” 05” 23” 05” 02 I7 02” 10” 05” 10” 23” 00 08” 04” 02” 07” 01” 10” 03” IO” 07” 63” 04” 43” 07” 02” 01” 01” I 2” 04” 02” IO” 05”

>2) P L-Pa M M M P C C C M(2) M C

P(2) C C C C M c C C ;2)

P(2) PC.9 C C C P :2) C P(2) C 22) C P(2) D(3) J(2) D L D D D D(l) D(2)

Cox-hel Comforl Thri-mi I Gtaytonl Loandho8 Thorton Filey I Well 1 Fli-sta Sherburl KnaptonS Hovingc I Hovinge I Speeton2 Suttong I Foxhole2 Flamb6 Selwih-3 Selwik-2 Belvue I Lngtofn I Lngtofs2 Ruston Warren I Tadcasn3 TadcasdS Tadcass4 Ltwghtn I Sthcavel Willerbl Hillam 1 Welton I Darring 1 Ferriby I Smeaton 1 Crox ton I Caistor I Maltby Louth I Anston3 Crewel12 Lincoln3 Harrigw I Alkrton I Bourton2 Ctsdean2 Tmplgtn I Chlkhil2 Chlkhil3

C. Hibsch Table Site 105 106 108 109 110 Ill 112a 112b 115a 115b 117 118

et ul./

Tectonophysics

252 (1995)

103-136

117

4 (continued) ND 8 8 20 14 12 8 7 12 12 6 4 12

Same symbols

Lat. N (“) 5 1.874 51.854 51.808 5 1.793 5 1.790 5 1.784 51.752 51.752 51.441 51.441 51.389 51.412 as for Table

Long. 1.388 1.308 1.223 1.562 1.569 1.598 2.000 2.000 3.605 3.605 3.277 3.341

W (“)

(~1 Azim.

Dip.

a2 Azim.

Dip.

u3 Azim.

Dip.

359” 189” 242” 003” 004” 168” 297” 198” 359” 009” 002 198”

00 13” 01” 00” 03” 01” 03” 06” 01” 16” 08” 01”

089” 343” 334” 144” 199” 070” 055” 358” 099” 274” 147” 303”

07” 75” 73” 90” 87” 85” 84” 83” 85” 19” 81” 85”

267” 098” 152” 273” 094” 258” 206” 108” 269” 1” 271” 105”

83” 06” 17” 00” 01” 05” 05” 02” 05” 65” 05” 0.5”

R

MMA(“)

SD(“)

D

Ref

0.78 0.48 0.95 0.61 0.83 0.95 0.41 0.61 0.51 0.42 0.76 0.64

3.5 2.8 9.3 1.9 5.9 4.3 6.4 5.8 2.1 2.1 1.5 2.5

4.5 3.5 12.4 2.4 7.0 5.5 7.3 6.8 2.6 2.4 1.7 3.2

M M

Wooton 1 Shiptonl Islip Burford 1 Worshaml Shilton 1 Dgngwth2 Dgngwth 1 Dunravn2 Dunravn3

M(2) D D D D(1) D(2)

L(2) L(2) X2) L(3)

6Wl Rhoose 1

1.

they trend NlO”E and NlOO”E. As such, they indicate a strike-slip tectonic regime. Some local deviations of the (T1 direction are observed in the vicinity of major faults (Fig. 8, sites 33, 34, 36, 37, 38, 40 and 108 and Table 4). Evidences of transpressional inversions of normal inherited faults were observed in the field (Fig. 8, sites 32, 36, 37, 41, 108 and 115 and Table 4). In the Foxhole and Langtoft areas (Fig. 8, sites 32 and 36, 37), locally, Late Cretaceous series are affected by major ENE-WSW- to E-Wstriking flexures showing beds with dips reaching 70”. These flexures are located above inherited EW-striking normal faults, of several kilometres in length (Kirby and Swallow, 1987). They are also observed in the Late Cretaceous Chalk at Flamborough and Selwicks Bay along the coast (Fig. 8, sites 33 and 34). Similar major transpressional deformation of Mesozoic sediments has been observed in South Wales (Fig. 8, site 115) and in southern England (Arkell, 1947; Whittaker, 1972b). This tectonic regime, which clearly affects a Paleocene dyke, could be related to the N-S ‘Pyrenean’ compression, which started during the Eocene in western Europe and/or to the ‘Helvetic’ phase which continued until Early Miocene times. This will be discussed below. 4.6. Discussion about the origin of normal faulting in Late Cretaceous Chalk deposits The idea of doing microtectonic analysis of normal faulting in the Chalk has proven quite controver-

sial. From our point of view, various data suggest that this faulting was mainly a result of compaction processes (Hibsch et al., 1993). Whatever the strike azimuth of the normal fault, it displays dip-slip faulting. During the field study, nowhere does any chronology of striations allowed us to separate different episodes of normal faulting. Everywhere the tectonic features of the N-S-oriented compression post-date this phase of normal faulting. Sedimentary features, such as early siliceous concretions along the fault planes, and deformation evidences, such as smooth dip-slip grooves and striations, conic vertical ‘indenters’ of several decimetres in size and intraChalk listric fault morphologies, are indicative of superficial and generally syn-diagenetic faulting. This faulting corresponds to a radial extensional stress tensor (a2 = cr 3). This radial tensor is clearly depicted by these vertical conic indenters, encompassed with dip-slip early soft-sediment striations. This normal faulting is well expressed in the Chalk of the East Anglia region (central-eastern England), although it is absent in the underlying Jurassic sediments. It is noteworthy that the N-S-oriented transpression is not registered in this region, even in the Chalk, but it is clearly expressed around major inherited tectonic structures of Great Britain (Cleveland basin, ‘Market Weighton block’, Worcester basin and Variscan fold belt front in South Wales; see location in Fig. 11. This indicates that East Anglia has behaved as a stable domain (triangular zone from Peterborough to Norwich and west of London), corresponding to a stable block in the Variscan foreland

C. Hihsch

et al. / Tectonophysics

Fig. 8. Post-Paleocene N-S transpressional strike-slip tectonics (‘Pyrenean’ directions of the CT I and a3 axes (95% confidence angle) in the northern

(Chadwick et al., 1989) where no significant subsiding Mesozoic structure for oil and gas exploration has been identified. Therefore, without underlying crustal extensional tectonic structures, it seems difficult to explain and argue for an extensional tectonic

252 (1995)

103-136

and/or ’‘Helvetic’ and in the southern

stages). (A, B) Stereonets region, respectively.

of the statistical

event which only affected the Late Cretaceous sediments. The lack of significant Late Cretaceous or Cenozoic extension in these regions supports our interpretation of these deformations as compaction features.

C. Hibsch

5. Regional structural rope tectonics

et al./Tecronophysics

evolution and western Eu-

A relative chronology was established for at least five tectonic episodes characterised by different stress regimes (Fig. 2). Using the retrotectonic method and the observation of syn-sedimentary faulting, most of these paleostress regimes could be dated with sufficient accuracy during the analysis. When field data have proven insufficient, we have referred to regional data to improve the age and duration of the different tectonic stages. Upon comparing the tectonic regimes to the structural evolution of Great Britain and surrounding basins (see below), these results could be compared to tectonic regimes defined for France, the Benelux countries and for Germany. According to the scale of these comparisons, average directions of the paleostress axes were attributed to each tectonic stage, using a statistical 95% confidence angle determination presented with stereonets on Figs. 3, 4, 6 and 8. Next, we will discuss how these results of paleostress analysis can be integrated in the western Europe geodynamic scheme. The stress trajectories presented on the following figures must be considered as rough extrapolations based on average paleostress results. Local stress deviations are not considered at this scale of reconstitution. 5.1. Permian/Early Triassic (NNW-SSE-oriented extension - stage I) (Figs. 2 and 9) 5.1. I. Southern UK structural evolution Sole Pit basin. The location of Sole Pit main tectonic structures is shown in Fig. 1. During this period, the NW-SE-striking Downsing fault could have acted principally as a transfer fault, because it runs nearly parallel to the NNW-SSE direction of extension. This could explain the weak differential subsidence along this fault during the deposition of the Zechstein evaporites. By contrast, the main normal faulting occurred along E-W-striking faults, nearly orthogonal to the direction of extension, such as the E-W-striking Outer Silver Pit fault (northern limit of the Sole Pit basin, probable eastward prolongation of the ‘Market Weighton’ faulted block)

252 (1995)

103-136

119

(Glennie and Boegner, 198 1). However, no differential subsidence during the Zechstein period is observed onshore on the northern side of the E-Wstriking ‘Market Weighton’ block (Kent, 1980). Southern basins. The behaviour of the Wessex, Channel, Bristol Channel, Celtic Sea and Western Approaches basins differed from that of northern basins due to their location above inherited Variscan thrusts (Chadwick, 1986; Brooks et al., 1988; Day et al., 1989). During the Permian - Early Triassic rifting event, the WNW-ESE- to WSW-ENE-striking inherited thrusts were reactivated as low-angle normal faults (Ziegler, 1987a, Ziegler, 1987b, Ziegler, 1989; Van Hoom, 1987b; Chapman, 1989; Petrie et al., 1989). This deformation provided the accumulation of thick Permian to Triassic sediments and local magmatic activity in the Wessex basin (Crediton trough) (Whittaker, 1975; Stoneley, 1982; Chadwick, 1986; Lake and Karner, 1987) and in the Western Approaches basin (Ziegler, 1982; Day et al., 1989). This deformation agrees with the NNWSSE-oriented extension we have defined in central and northern England and which was also proposed by Chapman (1989) for the Western Approaches basin. In such a tectonic regime, the NW-SE- to NNW-SSE-striking old inherited right-lateral Variscan faults could have been reactivated as leftlateral transfer faults (Lake and Karner, 1987; Ziegler, 1987a; Van Hoom, 1987b). 5.1.2. Western Europe tectonics Similar tectonic regimes are described in France, such as N-S- to NNE-SSW-oriented extension around the Rhine Graben during Permian to Early Triassic times (Villemin, 1986) and a contemporaneous N-S- to NW-SE-oriented extension for the French Massif Central (Blss et al., 1989) (Figs. 2 and 9). This first clear post-Variscan rifting pulse announces the break-up of the Pangea and seems to correspond to a roughly homogeneous paleostress field in western Europe. A slight rotation of the (r3 direction is possible from west to east [respectively NNW-SSE-striking (this study and Bl& et al., 1989) and NNE-SSW-striking (Villemin, 1986)]. The clockwise rotation of the w3 direction could continue to the east and be compatible with the WNWESE to NW-SE orientation of the Polish trough. This fan-shaped configuration of the ~3 might have

120

C. Ilihsch

ef (II./

Tecronophy.sic.s

been influenced by the inherited curved morphology of the late Hercynian tectonic belt. This tectonic stage takes part in the onset of a

PERMIAN

252 (19951

103-136

multi-directional rift system where both the ArcticNorth Atlantic and western Tethys zones have influenced the tectonic evolution of western Europe (Zie-

I EARLY TRIASSIC

EXTENSION

STRlKESLlPTECTONIC

Fig. 9. Sketch map of western Europe B.B. = Bay of Biscay; B.C. = Bristol Sea; G.G.F. = Great Glen fault; L.S. trough; S.P. = Sole Pit; V.G. = Vikin Wessex; War. = Worcester. Numbers

REGIMES

1 EXTENSION

/straur tmjsctaies

for the Permian/Early Triassic deformation stage. (A) Paleostress results. (B) Other tectonic results. Channel; C.E.G. = Central European Graben; C.G. = Central Graben; Ch. = Channel; C.S. = Celtic = Lower Saxony; M.C. = ‘Massif Central’; M.F. = Moray Fhth; P.R. = Paris Basin; R.T. = Rockal g Graben; W.N. = west Netherlands; V.F. = Variscan Front; W.A. = Western Approaches; Wes. = refer to authors: I = in this paper; 2 = Villemin (1986); 3 = Blks et al. (1989); 4 = Chapman (1989).

C. Hihsch

et al./Tectomphysics

gler, 1990a). The orientation of the paleostress axes as well as the southern position of the subsiding basins suggest an influence of the western Tethys rift system, rather than an influence of the NorwegianGreenland rift system. 5.2. Late Triassic/ early Late Jurassic (ENE-WSWto E-W-oriented extension - stage 2) (Figs. 2 and IO) 5.2.1. Southern UK structural evolution In Great Britain, three main directions of Triassic to Middle Jurassic subsidence axes are evidenced: the NW-SE- to NNW-SSE-striking structures such as the Peak fault and the Moreton-in-the-Marsh axis (M.M. in Fig. 1) (British Regional Geology, 1980), the N-S-striking trends such as the Worcester basin and Malvem trend (Fig. 1) (Whittaker, 1972a, Whittaker, 1975) and the E-W direction, illustrated by both flanks of the ‘Market Weighton block’ (‘Cleveland trough’ on its northern side and ‘Scunthorpe iron-stones belt’ to the south; in British Regional Geology, 1980) and also the E-W-striking Mendip axis (M in Fig. 1) and Wessex basin in southern England. These different paleotectonic directions show at a regional scale the multi-directional rift system framework of western Europe (Ziegler, 1990a). In an ENE-WSW-oriented extension context, NW-SE- to N-S-striking faults might have acted principally as normal faults, while the inherited E-W structures might have been active as transcurrent fault zones (Ziegler, 1982) with a right-lateral strike-slip component (Kirby and Swallow, 1987). Such a normal-dextral movement has been observed in the Dogger at Cayton Bay (Fig. 4, site 18). Sole Pit basin. A tectonic pulse is indicated by the differential subsidence of the Sole Pit basin during the Keuper (Glennie and Boegner, 1981). It coincided with the change in the paleostress regime that we have described for onshore England. Subsidence of the Sole Pit basin persisted during the Lias (Glennie and Boegner, 1981; Van Hoom, 1987a) but decreased during the Middle Jurassic, with the onset of the ‘middle Cimmerian’ thermal uplift of the central North Sea (Ziegler, 1982). During this period, the ENl-WSWto E-W-oriented extension defined onshore could have involved a normal (de-

252 (1995)

103-136

121

xtral?) faulting along the NW-SE-striking Downsing and South Hewett faults. Southern basins. These WNW-ESE- to ENEWSW-striking basins also subsided during the Late Triassic to early Late Jurassic period. Fault-controlled sedimentation is evident in the Bristol Channel until the Lias (Kammerling, 1979), intermittently in the Wessex basin (Wilson et al., 1958; Whittaker, 1975; Stoneley, 1982; Chadwick, 1986; Lake and Kamer, 1987; Jenkyns and Senior, 1991) and in the Celtic Sea during the Triassic (Roberts, 1989). Differential subsidence of the Celtic Sea basin appears to have decreased at the end of the Triassic (Petrie et al., 1989). During the same period N-S- to NWSE-striking new directions appeared in the tectonic framework of these regions. For the Triassic period, N-S-striking directions have been evidenced in the Wessex basin from sedimentological variations related to the presence of paleofault scarps (AudleyCharles, 1970 quoted in Lake and Kamer, 1987). Similar N-S-striking syn-sedimentary structures have been evidenced, such as the Bath axis (Wilson et al., 1958) and the Mangerton and Hooke faults (Jenkyns and Senior, 199 1) for the Lias and Dogger period. In the Western Approaches basin, normal syn-sedimentary faulting was also observed along NW-SE- to NNW-SSE-striking faults (Day et al., 1989). Day et al. (1989) and Chapman (1989) attribute the onset of an ENE-WSW-oriented extension to the Middle Triassic. Although facies thickness variations are clearly related to E-W-striking fault zones, this does not necessarily prove that the extension direction was N-S, as in these basins the late Variscan and Permian structural inheritance was strong and might have influenced the direction of extension. The exact extensional directions might be defined after trying a microtectonic analysis of the numerous syn-sedimentary faults observed in southern England by Jenkyns and Senior (1991).

5.2.2. Western Europe tectonics The Rhine Graben region was subjected to an E-W-directed extension during Early to early Late Jurassic times (Villemin, 1986). A similar tectonic regime was defined in the French ‘Massif Central’ (Bles et al., 1989) from the Lias to late Middle Jurassic and in the Lower Saxony basin (Betz et al.,

C. Hihsch

122

W#TcRN

et al./

BUROPlQIODYWIWtc

LATE TRIASSIC OXFORDIAN

Tectonophysics

252 (1995)

Q

/03-136

;

I EARLY EXTENSION

Fig. 10. Sketch map of western Europe for the Keuper to early Oxfordian deformation stage. (A) Paleostress results. (B) Other tectonic results. B.S. = Bay of Biscay; B.C. = Bristol Channel; C.E.C. = Central European Graben; C.G. = Central Graben; Ch. = Channel; C.S. = Celtic Sea; G.G.F. = Great Glen fault; L.S. = Lower Saxony; M.C. = ‘Massif Central’; M.F. = Moray Firth; P.S. = Paris Basin; R.T. = Rockal trough; S.P. = Sole Pit; V.G. = Viking Graben; W.N. = west Netherlands; V.F. = Variscan Front; W.A. = Western Approaches; Wes. = Wessex; Wm. = Worcester. Numbers refer to authors: I = in this paper; 2 = Villemin (I 986); 3 = Bles et al. (I 989); 4 = Chapman (1989); 5 = Day et al. (1989); 6 = Betz et al. (1987). The dotted zone could correspond to paleostress deviations or stress axes permutations.

C. Hibsch

et al./Tectotwphysics

1987) from Triassic to Dogger times (Fig. 10). These data suggest a wide distribution of the E-W to ENE-WSW extensional paleostress field in western Europe although multi-directional rift systems were active at the same time (Ziegler, 1988). In England, the change of paleostress regime seems to have occurred during the middle of the Triassic. Regionally, it is considered that this wide stage of extension affected western Europe since the beginning of the Triassic (Ziegler, 199Oa), but it is unsure whether to the Early Triassic correspond the beginning of a new stage or the culmination of the previous rifting event characterised by a different paleostress regime. The Triassic extension corresponds to the onset of sinistral movements between Europe and Africa as a consequence of crustal extension in the central Atlantic. Elsewhere in Europe, Permo-Carboniferous fracture system troughs were reactivated and new NW-SE- to N-S-striking basins clearly appeared in the central North Sea (Sole Pit, Viking and Central Grabens) (Ziegler, 1982, Ziegler, 1988, Ziegler, 1990a; Ziegler and Van Hoom, 1989). This new setting of basins points out the change between the old NNW-SSE-oriented extension to the subsequent ENE-WSW- to E-W-oriented extension. The Middle Triassic period also corresponds to the junction of the Norwegian-Greenland and western Tethys rift systems in the north and north-central Atlantic regions (Ziegler, 1988, Ziegler, 199Oa). After this junction, the Arctic-North Atlantic rift system continued its southward propagation and clearly took a major influence in the geodynamic evolution of northwestem Europe as evident in the paleostress distribution (Fig. 10). As mentioned above, the E-W-striking basins superimposed on the old Variscan fold belt (Wessex, Channel, Bristol Channel, Celtic Sea and Western Approaches basins) were still clearly subsiding during this period. This fact raises a question as to whether a N-S-oriented extension was active during the Late Triassic to early Late Jurassic on the southern side of the old Variscan front or whether these basins were affected by an oblique extension. The presence of an E-W to ENE-WSW extensional paleostress field of Early to Middle Jurassic age in France (Villemin, 1986; Bl&s et al., 1989) suggests that the regional paleostress field did not change radically upon crossing this major inherited structure. Anyway, without paleostress data coming from

252 (1995)

103-136

123

southern England at least three hypotheses could be proposed (Fig. 10): (1) These basins have been affected by an oblique E-W- to ENE-WSW-oriented extension. The main inherited WSW-ENE- to WNW-ESE-striking normal faults were reactivated as transcurrent normal faults. (2) The strong structural inheritance has produced a local deviation of the (r3 axis; therefore, the trend could have taken a NE-SW or NNE-SSW direction. (3) This structural inheritance could have involved a local stress permutation between a2 and ~3. The cr 3 axis showing then a N-S- to NNWSSE-oriented direction. 5.3. Late Oxfordian/Aptian(?) (N-S- to NNES&W-oriented extension and associated E-W- to WNW-ESE-oriented strike-slip regime - stage 3) (Figs. 2 and 11) 5.3.1. Southern UK structural evolution Sole Pit basin. Opposite motions of transcurrent faulting have been described along NW-SE-striking faults of the Sole Pit basin. Interpretations of the western Netherlands, Broad Fourteens and southern Sole Pit basins (Fig. 11) suggest that right-lateral displacement occurred along NW-SE-striking faults during this period (Van Wijhe, 1987; Van Hoom, 1987a) but a left-lateral motion is also described in the Sole Pit basin and related to a strike-slip tectonic regime (N-S tension and E-W compression; Fig. 11; Glennie and Boegner, 1981). This last result is in accordance with the paleostress tensor defined in central Great Britain. Normal faulting may have occurred mainly along E-W-striking fault zones as described onshore in the Pickering fault zone (Kirby and Swallow, 1987). During the same period, local compressional uplifts occurred in the northeastern part of the Sole Pit basin, along the Outer Silver Pit fault zone and in the west and central Netherlands basins (Glennie and Boegner, 1981; Ziegler, 199Oa). These inversions may be due to major left-lateral displacements along the NW-SE-striking Downsing fault and to the reactivation of Permo-Carboniferous fracture systems in the Netherlands. This sinistral displacement could have involved extensional defor-

C. Hihsch

124

BSTMRN

-IKESLIP

lUROPE

ef al./

Tcctonophysic.s

252 (1995)

103-136

QEODYNAMIC~

TECFIC

REGIMES

EXTENSION

Fig. I 1. Sketch map of western Europe for the late Oxfordian to Aptian deformation stage. (A) Paleostress results. (B) Other tectonic results. B.B. = Bay of Biscay; B.C. = Bristol Channel; C.E.G. = Central European Graben; C.G. = Central Graben; Ch. = Channel; C.S. = Celtic Sea; G.G.F. = Great Glen fault; 13. = Lower Saxony; M.C. = ‘Massif Central’; M.F. = Moray Firth; P.B. = Paris Basin; R.T. = Rockal trough; S.P. = Sole Pit; V.G. = Viking Graben; W.N. = west Netherlands; V.F. = Variscan Front; WA. = Western Approaches; Wes. = Wessex; War. = Worcester. Numbers refer to authors: I = in this paper; 2 = Blks et al. (1989); 3 = Glennie and Boegner (1981); 4 = Vejbaek and Andersen (1987); 5 = Betz et al. (1987); 6 = Benard et al. (I 985); 7 = Hibsch et al. (1992). The dotted zone could correspond to paleostress deviations or stress axes permutations.

C. Hihsch

et al./

Tectonophysics

mation at the northwestern end of the Downsing fault (Pickering fault zone) and local compressional deformation at its northeastern end (Outer Silver Pit fault zone>. Sourhern basins. A clear renewal of the differential subsidence has been described in the Wessex, Channel, Bristol Channel, Celtic Sea and Western Approaches basins from the Late Jurassic to the late Early Cretaceous. As for the Permian/Early Triassic extensional period, which corresponded to a quite similar paleostate of stress, volcanic activity occurred in the Western Approaches and Wessex basins during the early Aptian (Ziegler, 1987a, Ziegler, 1987b). This extension was associated with transcurrent faulting involving synchronous uplifted and subsided zones in the Wessex and Channel basins (Arkell, 1947; Wilson et al., 1958; Lake and Karner, 19871, the Bristol Channel basin (Kammerling, 1979; Ziegler, 1987a; Roberts, 1989), the Celtic Sea basin (Van Hoom, 1987b; Ziegler, 1987a) and the Western Approaches basin (Ziegler, 1987a, Ziegler, 1987b, Ziegler, 1989; Chapman, 1989). As encountered in central England, a similar E-W-oriented strike-slip tectonic regime was described in southern England (Benard et al., 1985). Normal faulting along WNWESE- to E-W-striking faults and normal dextral motions along ENE-WSW-striking faults described in the southern Celtic Sea basin (Van Hoom, 1987b) are also in agreement with the N-S- to NNE-SSWoriented extension observed in central and northern England. Following the middle Aptian, the differential subsidence aborted and the E-W fault trends might subsequently have displayed a late Albian to early Cenomanian left-lateral transcurrent faulting (Drummond, 1970; Lake and Kamer, 1987). A NS-oriented transpressional strike-slip tectonic regime of early Cenomanian age has been described in the Boulonnais (northwestern France) (Vandycke, 1992) and might correspond to the continuing of the strike-slip faulting described in southern England. 5.3.2. Western Europe tectonics From the Late Jurassic through the end of Early Cretaceous times, the extensional direction was trending N-S to NNE-SSW in central France (BRs et al., 1989). During the same period, a NE-SW-oriented extension was acting in the Lower Saxony basin (Betz et al., 1987) and Danish Central Graben

252 (1995)

103-136

125

(Vejbaek and Andersen, 1987). This extension was associated with transtensional and transpressional deformation (NW-SE-striking horizontal (T 1 axis) (Fig. 11). If these data seem to indicate a relative homogeneity of the Late Jurassic/late Early Cretaceous paleostress field in western Europe, in reality this period could be related to a wide transtensional strike-slip regime that has involved local extensional, transcurrent and maybe even compressional paleostates of stress. The analysis of syn-sedimentary faulting in the Early Cretaceous of the southeastern French basin points out the succession of a Neocomian E-W-oriented extension, followed by a late Early Cretaceous to early Late Cretaceous NNESSW to NE-SW strike-slip tectonic regime (Hibsch et al., 1992) (Fig. 11). The Late Jurassic/Early Cretaceous paleostress distribution in the West European shelf has proven to be quite complicated. Late Jurassic-Early Cretaceous times correspond to a period of regional stress reorganisation in response to crustal separation in the Tethys rift system and continued crustal extension across the ArcticNorth Atlantic rift system (Ziegler, 1988, Ziegler, 199Oa). The N-S to NNE-SSW extension defined during the field study strongly affected E-W structural trends during the Malm and the Early Cretaceous. This new rifting pulse seems to have acted earlier in the southern area (basal Callovian and intraOxfordian unconformities in the Western Approaches basin; Ziegler, 1987a, Ziegler, 1987b). This northward evolution of the extensional tectonics is directly linked to the development of the wrench rifting of the Bay of Biscay (Ziegler, 1982; Lake and Kamer, 1987) (Fig. 11). During the same period, the northern N-S- to NNE-SSW-striking basins of the Norwegian-Greenland sea have also recorded a strong tectonic subsidence linked to a rifting pulse in the Arctic-North Atlantic domain (Ziegler and Van Hoom, 1989) (Fig. 111, when the North Sea rift was affected by oblique extension (Ziegler, 1988, Ziegler, 199Oa). In northern Scotland, normal syn-sedimentary faulting has occurred during Kimmeridgian times along NE-SW-striking faults, on the western border of the Moray Firth basin (Bailey and Weir, 1931; Pickering, 1984). These data seem to indicate a more E-W-oriented extension in the northern regions. Two synchronous rifting zones were clearly active in

126

C. Hihxh

et al./

Tectomphysic.~

western Europe: the E-W- to WNW-ESE-striking Bay of Biscay and the N-S- to NE-SW-striking Arctic-North Atlantic zone. Two different extensional regimes might have been coeval. Major inherited structures such as the Great Glen fault might have acted as a transcurrent transition zone or the transition has been accommodated by numerous oblique wrench faults such as described in the Irish Sea and the Rhenish-Bohemian Massif (Ziegler, 1990a). The NNE-SSW-oriented extension could have then occurred south of a zigzag line joining England to Germany (Fig. 11). During the middle Aptian, the onset of sea-floor spreading in the Bay of Biscay was coeval with the end of the tectonic subsidence of nearly all the West European shelf basins (Ziegler, 1982) and announced the onset of thermal relaxation and Late Cretaceous Chalk sedimentation (Ziegler, 1982, Ziegler, 1987~). The transcurrent faulting still continued locally during late Early Cretaceous and early Late Cretaceous times (Arkell, 1947; Drummond, 1970; Lake and Karner, 1987, Ziegler, 1990a). Strain concentrated in the Rockall trough (Ziegler, 1990a). This stopping of differential subsidence in England and the occurrence of local compressional (transpressional) inversions were related to the onset of the middle Aptian ‘Austrian’ compressional phase (Ziegler, 1982) (Fig. 2). In fact, the ‘Austrian’ deformation might instead be a result of transcurrent displacements in the Austrian region, which occurred at a large scale in western Europe and which are evidenced by the displacements and rotations of the Iberian and Apulian blocks. The evolution of the paleostate of stress in southeastern France (Hibsch et al., 1992) reflects this geodynamic evolution. The compressional deformation encountered on the West European shelf could be linked to local states of stress due to strike-slip tectonics rather than the distant influence of this early Alpine compressional phase. 5.4. Late Cretaceous tectonics: ‘sub-Hercynian’ compressional phase or extension? The Late Turonian-Senonian ‘sub-Hercynian’ compressional event is weakly expressed in southern England but much more strongly to the east (southem Sole Pit, western Netherlands, Broad Fourteens,

252 (1995)

103-136

Lower Saxony and Danish Central Graben basins) (Betz et al., 1987; Van Hoom, 1987a; Van Wijhe, 1987; Ziegler, 1987~). The Danish Central Graben was affected by contemporaneous NNE-SSW- to NE-SW-oriented transpressional deformation (Vejbaek and Andersen, 1987; Cartwright, 1989). Glennie and Boegner (1981) proposed the occurrence of an E-W-oriented compression of Late Cretaceous age in the southern Sole Pit basin. The Maastrichtian E-W-oriented compression described in the Maastricht basin (Vandycke, 1992) has not yet been observed in England. Our field study was not able to substantiate these compressional stages. The distribution of ‘sub-Hercynian’ deformation in the Netherlands, Germany, the Bohemian Massif and in Poland suggests their association with collisional events in the Alpine domain (Ziegler, 1982, Ziegler, 1987c, Ziegler, 1990b). Although Senonian compressional deformation was evidenced in the Pyrenees (Ziegler, 1990 a), no clear Late Cretaceous inversions have been observed in southern Great Britain basins. It suggests that paleostresses were not projected far away into the foreland. Apart from this compressional stage, it has been suggested that there may have been extensional tectonic regimes during the Late Cretaceous. Microtectonic analyses conducted in the Chalk of regions such as the Kent (southern England), the Boulonnais (northern France) and the Mons and Maastricht basins (Belgium) (Vandycke, 1992) suggest that at least four extensional regimes occurred (two Late Cretaceous and two undated). If we try to compare this normal faulting registered in the Chalk with the regional geology of Great Britain, we notice that all the Mesozoic extensional basins were inactive since the end of the Early Cretaceous (Ziegler, 1982). Evidences of Oligocene extensional tectonics were described in the Chalk of the eastern Paris basin (Coulon and Frizon de Lamotte, 1988a, Coulon and Frizon de Lamotte, 1988b; Coulon, 1992) and some recent normal faulting is described from the Niederrhein Graben (cf. Vandycke, 1992), but there is no clear evidence from reflection seismic data for Late Cretaceous or even Cenozoic extensional events in and around central Great Britain, except some Oligocene transtensional deformation in and around Ireland (Ziegler, 1988) that will be discussed later. From our field studies we conclude that the great

C. Hihsch

et al./Tecronophysics

majority of normal faults we observed in the Chalk are related to heterogeneous compaction processes. 5.5. Middle Paleocene/ Early Eocene (NW-SE-oriented transpressional strike-slip regime - stage 4) (Figs. 2 and 12) 5.5.1. Southern UK structural evolution As the ‘sub-Hercynian’ compressional stage has weakly affected Great Britain, the NW-SE-oriented transpression measured in the field has been linked instead to the ‘Laramide’ transpressional event which affected southern England and its offshore basins more strongly. The NW-SE-oriented transpression was measured onshore along the E-W-striking Pickering fault zone (northern side of the ‘Market Weighton’ block, Fig. 7, sites 33 and 34a) and in the Worcester basin (Fig. 7, sites 99, 100 and 112). No positive inversion was observed along the NW-SEstriking Downsing fault zone of the Sole Pit basin (Ziegler, 1987c, Ziegler, 1990b; Van Hoom, 1987a). This is probably due to the direction of this fracture, which is nearly parallel to the NW-SE strike of the horizontal u 1 axis of this regime and to the shielding effect of ‘Laramide’ deformation that affected the western and central Netherlands and Broad Fourteens basins (Ziegler, 199Oa). The age of the NW-SE-oriented transpression observed in central and northern England has not been proven by field data. It pre-dated the N-S-oriented transpression attributed to the ‘Pyrenean’ event and has been related to the ‘Laramide’ event of Middle Paleocene to Early Eocene age. Several NW-SE-striking open fractures filled by Paleogene sediments which occur in the Chalk of the Wessex basin (Lake and Karner, 1987) may be regarded as having developed during the ‘Laramide’ tectonic pulse. The setting of an Early Eocene granite and the subsidence of basins of Eocene/Oligocene age have been related to an early Cenozoic left-lateral movement along the NNW-SSE-striking SticklepathLustleigh fault zone (Holloway and Chadwick, 1986). This motion is in accordance with the NW-SE direction of the strike-slip tectonic regime we have defined for the ‘Laramide’ event, but it is assumed that this compression ceased until the Middle Eocene. This problem will be discussed below.

252 (1995)

103-136

121

Evidences of ‘Laramide’ tectonic inversions have been observed in the Celtic Sea, Western Approaches and Channel basins (Ziegler, 1982, Ziegler, 1987a, Ziegler, 1987b). 5.5.2. Western Europe tectonics In the French ‘Massif Central’, successive (a, b, c in Fig. 12) NE-SW-, NW-SE-, then N-S-oriented compressional directions of Late Cretaceous(?)Cenozoic age have been described (Bles et al., 1989). Several authors have postulated that the Middle Paleocene ‘Laramide’ event was characterised by a NWSE-oriented compression (Vann, 1978; Lake and Kamer, 1987; England, 19881, but others preferred a N-S trend (Ziegler, 1982). This compression is expressed in the Alps and is synchronous with the development of the Thulean hot spot centred in Iceland (Ziegler, 1982, Ziegler, 1990a). Volcanism affected an area over a 1000~km radius around this island. This event was associated with the setting of NW-SE-striking tholeiitic dyke swarms in northern Great Britain (Vann, 1978; England, 1988). The orientation of the dyke swarm suggests that the NW-SE-oriented transpression measured in Great Britain is coeval with this magmatic event. A spatial evolution could be proposed from a compressional regime in the Alps to a transpressional then transtensional strike-slip tectonic regime in Great Britain. This evolution corresponded probably to permutations of paleostress axes (Fig. 12). During this period, basin inversions were strongly expressed in the Broad Fourteens, western Netherlands, Lower Saxony, and Paris basins (Ziegler, 1982; Betz et al., 1987; Van Hoom, 1987a; Van Wijhe, 1987) but less strongly registered in the more westerly basins (Celtic Sea, Channel, Bristol Channel and Western Approaches basins) (Ziegler, 1982, Ziegler, 1987a, Ziegler, 1987b, Ziegler, 1987~; Van Hoom, 1987b; Roberts, 1989). This distribution still suggests that this inversion was directly related to the front of the Alpine compressional deformation, rather than to the Pyrenees. This could explain why, in Great Britain, this weak compressional event was only locally registered along zones of weakness such as inherited tectonic trends. This compression is thought to have impeded the evolution of the North AtlanticNorwegian-Greenland sea rift system (Ziegler, 1988).

C. Hihsch

128

-IKE-SLIP

et al./

TECmtC

Tectonophysic.s

REGIMES

252 119951 103-136

EXTENSION

Fig. 12. Sketch map of western Europe for the Paleocene to Early Eocene ‘Laramide’ deformation stage. (A) Paleostress results. (B) Other tectonic results. B.B. = Bay of Biscay; B.C. = Bristol Channel; C.E.G. = Central European Graben; C.G. = Central Graben; Ch. = Channel; C.S. = Celtic Sea; G.G.F. = Great Glen fault; L.S. = Lower Saxony; M.C. = ‘Massif Central’; M.F. = Moray Firth; P.B. = Paris Basin; R.T. = Rockal trough; S.P. = Sole Pit; V.G. = Viking Graben; W.N. = west Netherlands; V.F. = Variscan Front; W.A. = Western Approaches; Wes. = Wessex; Wm. = Worcester. Numbers refer to authors: I = in this paper; 2 = Vann (1978), England (1988); 3 = Lake and Kamer (1987); 4 = Blks et al. (1989). The dotted zone could correspond to paleostress axes permutations.

C. Hibsch

et al./Tectonophysics

5.6. Middle Eocene/Early Miocene (N-S-oriented transpressional strike-slip regime - stage 5) (Figs. 2 and 13) 5.6.1. Southern UK structural evolution The observed structures resulting from a N-S-oriented transpressional strike-slip regime which affect the Late Paleocene ‘Cleveland dyke’ (Fig. 8, site 10) clearly demonstrate a post-Paleocene age for this tectonic regime. Sole Pit basin. In the Sole Pit basin, a clear inversion started during the Late Eocene (Ziegler, 1987~) and continued during the Oligocene (Van Hoom, 1987a), but does not seem to have been active during the Early Miocene. During this stage, the NW-SE Downsing fault displayed important transpressional deformation (Glennie and Boegner, 198 1; Van Hoom, 1987a) that could be related to a dextral-reverse movement controlled by the N-S-oriented transpressional stress field defined onshore. This event also caused reverse-sinistral deformation along E-W-striking fault zones at the northern side of the ‘Market Weighton’ block (Fig. 8, sites 30, 32, 36 and 37) and the Outer Silver Pit fault (Glennie and Boegner, 1981; Van Hoom, 1987a). Southern basins. In the Wessex basin, the main transpressional stage is dated as Late Oligocene to Early Miocene times, although local inversions of Eocene age have been described in southern England (Ziegler, 1982, Ziegler, 1990b). The major E-Wstriking inherited normal faults could then have been reactivated as reverse faults with a relative strike-slip movement that is difficult to assess (dextral according to Lake and Kamer, 1987, sinistral to Plint, 1982). The ENE-WSW-striking fault zone of the southern Celtic Sea basin was related to a transtensional Oligocene/Miocene left-lateral deformation (Van Hoom, 1987b). The NW-SE-striking faults were affected by a right-lateral displacement clearly observed along the Sticklepath-Lustleigh fault, with shear fractures expressed in the Eocene to Oligocene sediments (Holloway and Chadwick, 1986) and local thrusting of Devonian rocks upon the Cenozoic sediments of the Bovey basin (Bristow and Hughes, 1971). Holloway and Chadwick (1986) have proposed that the previous left-lateral movement on the Sticklepath-Lustleigh fault, pre-dating its rightlateral reactivation, was acting until Oligocene times.

252 (1995)

103-136

129

If we admit the onset of the N-S-oriented transpression during the Middle Eocene as observed in France, this fault motion appears incompatible. Interpretations made by Kammerling (1979) and Ziegler (1982, , 1987a) more to the north (west of Wales) where they have shown that ‘en echelon’ grabens were formed during the Oligocene along NW-SE-striking right-lateral strike-slip faults are more in accordance with the paleostress field change we propose. These transcurrent movements are thought to be also linked with tectonic activity along the Iceland transform fault during the reorganisation of the sea-floor spreading axes in the Norwegian-Greenland Sea (Ziegler, 1988). Indications about the evolution of the Cenozoic transpressional regimes might also be obtained from tectonic-magmatic data coming from the Thulean volcanic province of Middle Paleocene to Early Eocene age (northern Great Britain). This volcanic activity has been related to the interplay between a hot spot in Iceland (Fig. 12) and a ‘Laramide’ NWSE direction of compression with a NE-SW direction of tension (Vann, 1978; England, 1988; Ziegler, 199Oa). Several volcanic complexes were set during the Thulean event. In western Scotland, these last volcanic centres display a regional N-S-striking alignment and also a N-S strike of the magmatic chambers (Vann, 1978). Some N-S-striking dykes localised around these centres were firstly interpreted as local deviations of the ‘Laramide’ stress direction, involved in these volcanic complexes (Vann, 1978). More recently, these N-S-striking dykes were explained as extensional overstep structures linked to dextral movements registered along the NW-SEstriking faults, with an E-W-striking (~3 axis (England, 1988) (Fig. 13). This Eocene change in the paleostress directions proposed by England (1988) is in accordance with the evolution of the transpressional tectonic regimes we have observed in England. The change from a ‘Laramide’ NW-SE-oriented transpression to a ‘Pyrenean’ (and/or ‘Helvetic’) N-S-oriented transpression could then have occurred during Early to Middle Eocene times. 5.6.2. Western Europe tectonics This tectonic regime could be related to the NS-oriented ‘Pyrenean’ compression which started in western Europe during the Senonian, but only clearly

130

C. Hihsch

et cd./

Tectonophy.sics

252 (1995)

103-136

STRKESLIP TECTONIC REQIMES 1 EXTENSION /seam err

Fig. 13. Sketch map of western Europe for the Middle Eocene to Late Eocene ‘Pyrenean’ deformation stage. (A) Paleostress results. (B) Other tectonic results. B.B. = Bay of Biscay; B.C.= Bristol Channel; C.E.G. = Central European Graben; C.G. = Central Graben; Ch. = Channel; C.S. = Celtic Sea; G.G.F. = Great Glen fault; L.S. = Lower Saxony; M.C. = ‘Massif Central’; MI. = Moray Firth; P.R. = Paris Basin; R.T. = Rockal trough; S.P. = Sole Pit; V.G. = Viking Graben; W.N. = west Netherlands; V.F. = Variscan Front; W.A. = Western Approaches; Wes. = Wessex; War. = Worcester. Numbers refer to authors: I = in this paper; 2 = Villemin ( 1986). Bergerat and Geyssant (1980), Bergerat (1987); 3 = Letouzey (1986); 4 = Blbs et al. (1989); 5 = England (1988).

C. Hibsch

et ul./Tectonophysics

affected the European foreland since the Eocene (Arthaud and Choukroune, 1972; Bergerat and Geyssant, 1980; Arthaud and SCguret, 1981; Ziegler, 1982; Villemin, 1986; Letouzey, 1986; Bergerat, 1987; Bles et al., 1989) and/or to the ‘Helvetic’ phase which continued until Early Miocene times (Ziegler, 1982) (Fig. 13). In central Europe, these phases have been partly interrupted by the Oligocene extension (Bergerat and Geyssant, 1980; Villemin, 1986; Letouzey, 1986; Bergerat, 1987) (Fig. 14), but the Middle Eocene to Early Miocene period corresponds to the main positive tectonic inversion stage in and around the southern British Isles. The Eocene evolution of the paleostress regimes in Great Britain might have also been influenced by the reorganisation of sea-floor spreading axes in the NorwegianGreenland Sea (Ziegler, 1990a). The change of paleostress we dated as Early Eocene age is coeval with the onset of crustal separation in this region. It can be suggested that the N-S-oriented ‘Pyrenean’ compressional stresses were almost parallel to the direction of this rift system and did not interfere with its evolution as did the previous NW-SE-oriented aH max. of the ‘Laramide’ event (see above). During the Oligocene, the Rhane-Rhine Graben system was active in France and Germany, and was associated with an E-W-oriented extension. A NESW-oriented compression has been observed in southeastern France and northern Germany (Roux, 1974; Letouzey, 1986; Le Pichon et al., 1988; Ritz, 1992) and has been attributed to the Late Oligocene/Miocene (Fig. 14). Data coming from England and surrounding basins show intermittent compressional inversions until the Early Miocene (Celtic Sea, Western Approaches, Wessex, Channel, Bristol Channel, Rockall trough and Sole Pit basins; Ziegler, 1982, Ziegler, 1987a, Ziegler, 1987c, Ziegler, 1990b; Van Hoom, 1987b; Petrie et al., 1989; Roberts, 1989). It is noteworthy that in the western Netherlands, Broad Fourteens and Lower Saxony basins, the N-S-oriented transpression has been active only until the Late Eocene, before the onset of the Oligocene extension (Betz et al., 1987; Ziegler, 1987c, Ziegler, 1990b; Van Wijhe, 1987). Presumably, the N-S-oriented transpression continued during the Oligocene and Early Miocene more to the west of the central European graben system in relation with ‘Pyrenean’ deformations clearly ob-

252 (199.5)

103-136

131

served in Spain (Ziegler, 1990a). The spatial paleostress evolution from west to east could have corresponded to a permutation between (T 1 and (+2 stress axes. The (~3 stress axis strike remained E-W in both the extensional and strike-slip tectonic regimes. The transition zone is presented in the middle of the Paris basin in Fig. 14 since Oligocene extension was described in the Chalk in the east of this basin (Coulon and Frizon de Lamotte, 1988a, Coulon and Frizon de Lamotte, 1988b; Coulon, 1992). This zone could be displaced more to the west if we also consider the results of Vandycke (1992) obtained in the Chalk of Belgium, the Kent and Boulonnais regions. As mentioned above, observations made in central and northern Great Britain suggested that this sediment was affected by a very penetrative normal faulting resulting from compaction processes. The significative non-tectonic normal faulting due to the diagenesis of this sediment does not allow to clearly separate tectonic and compaction faulting and could have contributed to artificially extend westerly the Oligocene extensional zone (see Fig. 14). The onset of the western European graben system might be due to a relative divergence between (1) a northward movement of the Iberian block (counterclockwise rotation), associated with the N-S-oriented transpression registered in Great Britain and surrounding basins, and (2) a northeastward displacement of the Apulo-Penninic block (Fig. 14). This divergence could be related to different plate motions (western vs. central Europe) (Tapponnier, 1977; Le Pichon et al., 1988). The Oligocene extension was coeval with major compressional deformation in Spain (Ziegler, 1988). During the Miocene, this rift system developed until reaching sea-floor spreading in the AlgCro-ProvenGal basin. 5.7. Late Miocene to Present (W-SE-oriented pression)

com-

The following NW-SE Alpine compression was active since the Late Miocene. This last Alpine event is weakly expressed west of the Rhine-Rhane Graben system (Bevan and Hancock, 1986; Letouzey, 1986) and corresponds to the present-day ‘in situ’ stress direction of aH max (Klein and Barr, 1986) (Fig. 2). This event has not been characterised by faulting analyses in central and northern Great Britain.

C. Hihsch

132

STRIKE-SLIP

-IKE-SLIP

et ai./

Tectonophysica

COMPRESSION

TECTONIC

252 (1995)

103-136

&

REGIMES

EXTENSION

Fig. 14. Sketch map of western Europe for the Oligocene (to Early Miocene) deformation stage. (A) Paleostress results. (B) Other tectonic results. B.B. = Bay of Biscay; B.C. = Bristol Channel; C.E.G. = Central European Graben; C.G. = Central Graben; Ch. = Channel; C.S. = Celtic Sea; G.G.F. = Great Glen fault; L.S. = Lower Saxony; M.C. = ‘Massif Central’; M.F. = Moray Firth; P.B. = Paris Basin; R.T. = Rockal trough; S.P. = Sole Pit; V.G. = Viking Graben; W.N. = west Netherlands; V.F. = Vat&an Front; W.A. = Western Approaches; Wes.= Wessex; War.= Worcester. Numbers refer to authors: I = in this paper; 2 = Villemin (1986). Bergerat and Geyssant (l980), Bergerat (1987); 3 = Letouzey (1986); 4 = Blks et al. (1989); 5 = Roux (1974), Coulon (1992). The dotted zone could correspond to paleostress deviations and stress axes permutations.

C. Hihsch

et al./Tectonophysics

6. Conclusions Our field work has pointed out the obvious link between paleostress fields and basin settings, in and around Great Britain, both controlled by the geodynamic evolution of the western European shelf. Five successive tectonic regimes associated with paleostress tensors were obtained from microtectonic analysis. 6.1. Stage 1: Late Permian/Early SSE-oriented extension

Triassic NNW-

This first clear post-Variscan rifting pulse seems to be quite homogeneous throughout western Europe. The basins were located especially over inherited Variscan compressional structures which were affected by a subsidence. This extension is linked to the influence of the western Tethys rift system. 6.2. Stage 2: Late Triassic/early Late Jurassic ENE-WSW to E-W-oriented extension The change of tectonic regime clearly corresponded to the appearance of new structural trends in the central North Sea such as the Sole Pit, the Viking and Central grabens. Subsidence was active both in newly formed N-S- to NW-SE-striking basins and in the old inherited E-W-striking basins of southern Great Britain. The presence of a similar paleostate of stress in France suggests a relative homogeneity of the Late Triassic/early Late Jurassic paleostress field in western Europe. The E-W-striking basins of southern Great Britain could have been affected by an oblique extension accommodated with strikeslip-normal faulting. The strong structural inheritance in this region might have also produced local paleostress deviations and/or paleostress axis permutations between (T2 and u 3. This early phase of the Pangea break-up is characterised by a multi-directional rift system with dimensions exceeding 2000 X 3000 km (Ziegler, 1988). 6.3. Stage 3: Late O$ordian/Aptian (?) N-S to NNE-SSW-oriented extension and associated E-Wto WNW-ESE-oriented strike-slip regime This event corresponds to a clear pulse of tectonic subsidence in E-W-striking basins. The paleostress

252 (1995)

103-136

133

field seems quite perturbed in western Europe during this period. Major stress reorganisation took place as a consequence of Mid-Jurassic crustal separation in Central Atlantic and Tethys rift systems. We notice spatial evolution from a roughly E-W-oriented extension in the Arctic-North Atlantic zone, to a NNE-SSW-oriented extension and associated WNW-ESE-oriented strike-slip tectonic regime in Great Britain, central and northern France to an E-W-oriented extension, then a NNE-SSW- to NESW-oriented strike-slip regime in southeastern France. The NNE-SSW-oriented extension could have occurred south of a zigzag line joining England to Germany. This limit probably displayed transcurrent deformation due to the interplay between two main rifting zones (Arctic-North Atlantic zone and Bay of Biscay area). The Late Jurassic/Early Cretaceous period to the south of this limit corresponds to a strike-slip tectonic regime influenced by the wrench rifting in the Bay of Biscay and by the displacements and rotations of the Iberian and Apulian blocks. It remains unknown if this spatial evolution was associated with paleostress rotations or with paleostress axes permutations. The Middle Aptian corresponded to the onset of sea-floor spreading in the Bay of Biscay and was coeval with the end of differential subsidence in nearly all the western European shelf basins, but the transcurrent faulting continued at least during late Early Cretaceous and early Late Cretaceous times and strain concentrated in the Rockall trough. 6.4. Stage 4: Middle Paleocene/Early Eocene ‘Laramide’ NW-SE-oriented strike-slip transpression This transpression was not strongly registered in Great Britain but this paleostress field has controlled the volcanic setting of the Thulean Province (northem Great Britain) due to an interplay between the distant influence of this alpine compression and a hot spot centred in Iceland. Relatively weak Laramide tectonic inversions have been observed in the Celtic Sea, Western Approaches and Channel basins. This transpressional stage impeded the evolution of the North Atlantic-Norwegian sea rift system, since its direction was nearly perpendicular to the ‘Laramide’ (TH max.

134

C. Hi&h

et cd./

Tectonophysics

6.5. Stage 5: Middle Eocene/Early Miocene N-Soriented transpressional strike-slip regime This tectonic regime clearly demonstrated a postPaleocene age. This event is strongly expressed in Great Britain and could be related to the main positive inversions observed in the country and in surrounding basins. The N-S trend of this kinematics make it possible to correlate this tectonic regime with the ‘Pyrenean’ event clearly dated in France. An E-W-oriented extension appeared in central Europe during the Oligocene, but this N-S-oriented transpressional strike-slip tectonic regime seems to have lasted until Early Miocene times in the western regions. The onset of the western European graben system might be due to a relative divergence between (1) a northward movement of the Iberian block, associated with the N-S-oriented transpression registered in Great Britain and surrounding basins until the Early Miocene, and (2) a northeastward displacement of the Apulo-Penninic block. This divergence could be related to different plate motions (western vs. central Europe). Transtensional deformation observed to the west of Great Britain (Ziegler, 199Oa) could be interpreted as a lower transmission into the foreland of the horizontal compressional stresses, due to the shielding effect of the subduction zone in the Bay of Biscay, when these stresses were more transmitted into the foreland at the front of the transcurrent collisional frontier in the Pyrenees, and involved basin inversions in central and southern Great Britain. It can be also discussed whether the Early Eocene reorganisation of sea-floor spreading axes in the Norwegian-Greenland Sea was the motive of this transtensional faulting or if the reorganisation of the crustal separation was influenced by the change in direction of the compressional stresses in western Europe.

Acknowledgements

We would like to thank Elf Aquitaine Production, which has provided financial support. This study has also involved visiting numerous quarries with the very helpful contribution of quarry managers and the geological staff of several companies. We also express great thanks to A. Whittaker and S. Holloway

252 (1995)

103-136

of the British Geological Survey for the very fruitful discussions we had at Keyworth and for the very kind help they have provided.

References Angelier, J., 1991. Analyse chronologique matricielle et succession regionale des e%nements tectoniques. C.R. Acad. Sci. Paris, Strie II, 3 12: 1633- 1638. Angelier, J., 1994. Palaeostress analysis of small-scale brittle structures. In: P. Hancock (Editor), Continental Deformation. Pergamon Press, London, pp. 53- 100. Arkell, W.J., 1947. The geology of the country around Weymouth, Swanage, Corfe and Lulworth. Mem. Geol. Surv. G.B., explanation of sheets 341, 342 and 343, HMSO, London, 386 PP. Arthaud, F. and Choukroune, P., 1972. Methode d’analyse de la tectonique cassante a I’aide des microstructures dans les zones peu deformees. Exemple de la plate-forme Nord-Aquitaine. Rev. Inst. Fr. Pet., XXVII, 5: 715-732. Arthaud, F. and Seguret, M., 1981. Les structures pyreneennes du Languedoc et du Golfe du Lion (Sud de la France). Bull. Sot. Geol. Fr., XXIII, I: 51-63. Bailey, E.B. and Weir, J., 193 1. Submarine faulting in Kimmeridgian times: East Sutherland. Trans. R. Sot. Edinburgh, 57: 4299468. Benard, F., De Charpal, O., Mascle, A. and Tremolieres, P., 1985. Mise en evidence d’une phase de serrage E-W au C&act inferieur en Europe de I’ouest. C.R. Acad. Sci. Paris, 300(15): 765-768. Bergerat, F., 1987. PalCo-champs de contrainte tertiaires dans la plate-forme europkenne au front de I’orogene alpin. Bull. Sot. Gtol. Fr., (8), III, 3: 61 I-620. Bergerat, F. and Geyssant, J., 1980. La fracturation tertiaire de 1’Europe de I’Ouest: r&bat de la collision Afrique-Europe. C.R. Acad. Sci. Paris, D, 290: 1521-1524. Betz, D., Fuhrer, F., Greiner, G. and Plein, E., 1987. Evolution of the Lower Saxony Basin. Tectonophysics, 137: 127- 170. Bevan, T.G. and Hancock, P.L., 1986. A late Cenozoic regional mesofracture system in southern England and northern France. J. Geol. Sot. London, 143(2): 355-2. Bles, J.L., Bonijoly, D., Castaing, C. and Gros, Y., 1989. Succesive post-Variscan stress fields in the French Massif Central and its borders (Western European plate): comparison with geodynamic data. Tectonophysics, 169: 79- I 1 I Bristow, C.M. and Hughes, D.E., 1971. A Tertiary thrust fault on the southern margin of the Bovey Basin. Geol. Mag., 108: 61-68. British Regional Geology, 1969. Central England. British Geological Survey, No. IO, 141 pp. British Regional Geology, 1980. Eastern England (from the Tees to the Wash). British Geological Survey, No. 9, 150 pp. Brooks, M., Trayner, P.M. and Trimble, T.J., 1988. Mesozoic reactivation of Variscan thrusting in the Bristol Channel area, U.K. J. Geol. Sot. London, 145(3): 439-444.

C. Hibsch

et al./Tectonophysics

Carey, E., 1976. Analyse numerique d’un modtle mecanique tltmentaire applique a l’etude d’une population de failles: calcul d’un tenseur moyen des contraintes a partir des stries de glissement. These 3Cme cycle Univ. Orsay, Paris Sud. Carey. E., 1979. Recherche de directions principales de contraintes assocides au jeu dune population de failles. Rev. Geol. Dyn. GCogr. Phys., 21: 57-66 Cartwright, J.A.. 1989. The kinematics of inversion in the Danish Central Graben. In: M.A. Cooper and G.D. Williams (Editors), Inversion Tectonics. Geol. Sot. London, Spec. Publ., 44: 153-175. Chadwick, R.A., 1986. Extension tectonics in the Wessex Basin, southern England. J. Geol. Sot. London, 143(3): 465-488. Chadwick, R.A., Livermore, R.A. and Penn, I.E., 1989. Contiuental extension in southern Britain and surrounding areas and its relationship to the opening of the North Atlantic ocean. Am. Assoc. Pet. Geol. Mem., 46: 41 l-424. Chapman, T.J., 1989. The Permian to Cretaceous structural evolution of the Western Approaches Basin (Melville sub-basin), U.K. In: M.A. Cooper and G.D. Williams (Editors), Inversion Tectonics. Geol. Sot. London, Spec. Publ., 44: 177-200. Coulon, M., 1992. La distension oligoctne darts le nord-est du bassin de Paris (perturbation des directions d’extension et distribution des stylolites. Bull. Sot. G601. Fr.. 5, 163: 531540. Coulon, M. and Frizon de Lamottc, D., 1988a. Les extensions cenozoiques dans 1’Est du Bassin de Paris: mise en evidence et interpretation. C.R. Acad. Sci. Paris, S&ie II, 307: 1113- 1119. Coulon, M. and Frizon de Lamotte, D., 1988b. Les craies Cclatees du secteur d’Omey (Mame, France): le resultat d’une brkhification par fracturation hydraulique en contexte extensif. Bull. Sot. GCol. Fr., 8, IV, 1: 177-185. Day, G.A., Edwards, J.W.F. and Hillis, R.R., 1989. Influences of Variscan structures of southwest Britain on subsequent phases of extension. Am. Assoc. Pet. Geol. Mem., 46: 425-432. Dewey, J.F., 1982. Plate tectonics and evolution of the British Isles. J. Geol. Sot. London, 139(4): 400-412. Dewey, J.F. and Windley, B.F., 1988. Paleocene-Oligocene tectonics of North West Europe. In: AC. Morton and L.M. Parson (Editors), Early Tertiary Volcanism and the Opening of the North East Atlantic. Geol. Sot. London, Spec. Publ., 39: 25-31.

Drummond, P.V.O., 1970. The mid-Dorset Swell. Evidence of Albiat-cenomanian movements in Wessex. Proc. Geol. Assoc., 81: 679-714. England, R.W., 1988. The Early Tertiary stress regime in NW Britain : evidence from the patterns of volcanic activity. In: A.C. Morton and L.M. Parson (Editors), Early Tertiary volcanism and the opening of the North East Atlantic. Geol. Sot. London, Spec. Publ., 39: 381-389. Glennie, K.W. and Bocgner, P.L.E., 1981. Sole Pit inversion tectonics. In: Petroleum Geology of the Continental Shelf of North-West Europe. Institute of Petroleum, London, pp. 1 lo120. Hibsch, C., 1992. Apports de l’approche tectonosedimentaire pour l’analyse et la datation des paleocontraintes tectoniques. Ap-

252 (1995)

103-136

135

plications en domaine tabulaire (tectonique permo-ctnozoique en Grande Bretagne) et en domaine plisse (tectonique &tact% de l’arc de Castellane, S.E. France). Implications gtodynamiques. These, Univ. Paris XI, 246 pp., 1 amiexe. Hibsch, C., Kandel, D., Montenat, C. and Ott D’estevou, P., 1992. Evtnements tectoniques cretaces darts la partie mtridionale du bassin subalpin (massif Ventoux-Lure et partie orientale de l’arc de Castellane, SE France). Implications gtodynamiques. Bull. Sot. Gtol. Fr., 163(2): 147-158. Hibsch, C., Cushing, M., Cabrera, J., Mercier. J., Prasil, P. and Jarrige, J.J., 1993. Paleo-stress evolution in Great Britain from Permian to Cenozoic: a microtectonic approach to the geodynamic evolution of the southern U.K. basins. Bull. Cent. Rech. Explor. Prod. Elf Aquitaine, 17(2): 303-330. Holloway, S. and Chadwick, R.A., 1986. The SticklepathLustleigh fault zone : Tertiary sinistral reactivation of a Variscan dextral strike-slip fault. J. Geol. Sot. London, 143: 447-452. Jenkyns, H.C. and Senior, J.R., 1991. Geological evidence for irmaJurassic faulting in the Wessex Basin and its margins. J. Geol. Sot. London, 148: 245-260. Kammerling P., 1979. The geology and hydrocarbon habitat of the Bristol Channel basin. J. Pet. Geol., 2: 75-93. Kent, P.E., 1980. Subsidence and uplift in East Yorkshire and Lincolshire: a double inversion. Proc. Yorks. Geol. Sot., 42(28): 505-524. Kirby, G.A. and Swallow, P.W., 1987. Tectonism and sedimentation in the FLamborough Head region of North-East England. Proc. Yorks. Geol. Sot., 46(4): 301-309. Klein, R.J. and Barr, M.V., 1986. Regional state of stress in Western Europe. Proc. Int. Symp. Rock Stress and Rock Stress Measurements, Stockholm, pp. 33-44. Lake, S.D. and Karner, G.D., 1987. The structure and evolution of the Wessex Basin, southern England: an example of inversion tectonics. Tectonophysics, 137: 347-378. Le Pichon, X., Bergerat, F. and Roulet, M.J., 1988. Plate kinematics and tectonics leading to the Alpine belt formation; a new analysis. Geol. Sot. Am., Spec. Pap., 218: 111-131. Letouzey, J., 1986. Cenozoic paleo-stress pattern in the Alpine Foreland and structural interpretation in a platform basin. Tectonophysics, 132: 215-23 1. Martill, D.M. and Hudson, J.D., 1989. Injection elastic dykes in the Lower Oxford Clay (Jurassic) of central England: relationship to compaction and concretion formation. Sedimentology, 36: 1127-l 133. Mercier, J.L. and Carey-Gailhardis, E., 1989. Regional state of stress and characteristic fault kinematics instabilities shown by aftershock sequences: the aftershock sequences of the 1978 Thessaloniki (Greece) and 1980 Campauia-Lucana (Italia) earthquakes as examples. Earth Planet. Sci. Lett., 92: 247-264. Mercier, J.L., Carey-Gailhardis, E. and Sebrier, M., 1992. Paleostress determinations from fault kinematics: application to the neotectonics of the Himalayas-Tibet and the Central Andes. In: R.B. Whitmarsh, M.H.P. Bott, J.D. Fairhead and N.J. Kusznir (Editors), Tectonic Stress in the Lithosphere. Philos. Trans. R. Sot. London, A, 337: 41-52.

136

C. Hihsch

et ul./T~‘~.t~n~~phy.si~s

Petrie, S.H., Brown, J.R., Granger, P.J. and Lovell, J.P.B., 1989. Mesozoic history of the Celtic Sea Basins. Am. Assoc. Pet. Geol. Mem., 46: 433-444. Sellwood, B.W. and Jenkyns, H.C., 1975. Basins and swells and the evolution of an epeiric sea (Pliensbachiat-Bajocian of Great Britain). J. Geol. Sot. London, 131: 373-388. Pickering, K.T., 1984. The Upper Jurassic ‘Boulder Beds’ and related deposits: a fault-controlled submarine slope, NE Scotland. J. Geol. Sot. London, 141: 357-374. Plint, A.G., 1982. Eocene sedimentation and tectonics in the Hampshire Basin. J. Geol. Sot. London, 13x3): 249-254. Ritz, J.F., 1992. Tectonique recente et sismotectonique des Alpes du Sud: analyse en termes de contraintes. Quatemaire, 3(3-41: 111-124. Roberts, D.G., 1989. Basin inversion in and around the British Isles. In: M.A. Cooper and G.D. Williams (Editors), Inversion Tectonics. Geol. Sot. London, Spec. Pub]., 44: 131- 150. Roux, M., 1974. La sedimentation tertiaire et les etapes dc la tectonique provenGale et alpine au Sud et au Sud Ouest de I’arc de Castellane. Le bassin d’Eoulx-Brenon et ses dependances (Feuilles de Castellane et de Moustiers-Sainte-Marie). Bull. B.R.G.M., SCrie 2, Section I, 2: 83-99. Stoneley, R., 1982. The structural development of the Wessex Basin. J. Geol. Sot. London, 139(41: 5455554. Tapponnier, P., 1977. Evolution tectonique du systeme alpin en Mtditerrarke: poinsonnement et tcrasement rigide-plastique. Bull. Sot. Gtol. Fr., 7, XIX, 3: 437-460. Van Hoom, B., 1987a. Structural evolution, timing and tectonic style of the Sole Pit inversion. Tectonophysics, 137: 239-284. Van Hoom, B., 1987b. The South Celtic Sea/Bristol Channel Basin: origin, deformation and inversion history. Tectonophysics, 137: 309-334. Van Wijhe, D.H., 1987. Structural evolution of inverted basins in the Dutch offshore. Tectonophysics, 137: 17 I-2 19. Vandycke, S., 1992. Tectonique cassante et paleo-contraintes dans les formations c&a&es du Nerd-Ouest europeen. Implications geodynamiques. Mem. Sci. Terre, Univ. P. et M. Curie, Paris, 92.02, 178 p. Vann, I.R., 1978. The siting of Tertiary vulcanicity. In: D.R. Bowes and B.E. Leake (Editors), Crustal Evolution in Northwestern Britain and Adjacent Regions. Geol. J., Spec. Iss., IO: 393-414.

252 (1995)

103-136

Vejbaek, O.V. and Andersen, C., 1987. Cretaceous-Early Tertiary inversion tectonism in the Danish Central Trough. Tectonophysics, 137: 221-238. Villemin, T., 1986. La chronologie des evenements tectoniques dans le Nord-Est de la France et le Sud-Ouest de I’Allemagne du Permien a I’Actuel. C.R. Acad. Sci. Paris, 303, Serie II, 18: 1685-1690. Wet, C.B. de, 1987. Deposition and diagenesis in an extensional basin: the Corallian Formation (Jurassic) near Oxford, England. In: J.D. Marshall (Editor), Diagenesis of Sedimentary Sequences. Geol. Sot. London, Spec. Publ., 36: 339-353. Whittaker, A., 1972a. Intra-Liassic structures in the Sevem Basin area. Institute of Geological Sciences, London, 5 pp. Whittaker, A., 1972b. The Watchet Fault - a post-Liassic tran scurrent reverse fault. Bull. Geol. Surv. G.B., 41: 75-80. Whittaker, A., 1975. A postulated post-Hercynian rift valley system in southern Britain. Geol. Mag., I l2(2): 137-149. Wilson, V., Welch, F.B.A., Robbie, J.A. and Green, G.W., 1958. Geology of the country around Bridport and Yeovil. Mem. Geol. Surv. G.B., explanation of sheets 3 I2 and 327, HMSO, London, 239 pp. Ziegler, P.A., 1982. Gt. >logical Atlas of Western and Central Europe. Elsevier, Amsterdam, 130 pp. Ziegler P.A., 1987a. Celtic Sea-Western Approaches area: an overview. Tectonophysics, 137: 285-289. Ziegler, P.A., 1987b. Evolution of the Western Approaches Trough. Tectonophysics, 137: 341-346. Ziegler, P.A., 1987~. Late Cretaceous and Cenozoic intra-plate compressional deformations in the Alpine foreland ~ a geodynamic model. Tectonophysics, 137: 389-420. Ziegler, P.A., 1988. Evolution of Arctic-North Atlantic and Westem Tethys. Am. Assoc. Pet. Geol. Mem., 43, 198 pp. Ziegler, P.A., 1989. Evolution of the North Atlantic an overview. Am. Assoc. Pet. Geol. Mem., 46: I I I-129. Ziegler, P.A., 1990a. Geological Atlas of Western and Central Europe, 2nd ed. Shell International Petroleum Mij. B.V., distributed by Geol. Sot. Publ., House, Bath, 239 pp. Ziegler, P.A., 1990b. Collision related intra-plate compression deformations in Western and Central Europe. J. Geodyn., I I: 357-388. Ziegler, P.A. and Van Hoom, B., 1989. Evolution of North Sea rift system. Am. Assoc. Pet. Geol. Mem., 46: 471-499.