Subsurface structure of the Netherlands results of recent onshore and offshore mapping

Transcription

1 etherlands Journal of eosciences eologie en ijnbouw ubsurface structure of the etherlands results of recent onshore and offshore mapping.j.t. Duin, J.C. Doornenbal,... ijkers *, J.W. Verbeek & Th.. Wong T uilt nvironment and eosciences eological urvey of the etherlands,.. ox 80015, 3508 T Utrecht, the etherlands. * Corresponding author. mail: [email protected] anuscript received: eptember 2006; accepted ovember 2006 bstract This paper presents depth maps for eight key horizons and seven thickness maps covering the onshore and offshore areas for the ate ermian to recent sedimentary section of the etherlands. These maps, prepared in the context of a T regional mapping project, are supported by nine regional structural cross sections and a table summarizing the timing of tectonic activity from Carboniferous to recent. These new regional maps enable the delineation of various structural elements but also reveal the development of these elements through time with improved detail. ince the latest Carboniferous the tectonic setting of the etherlands changed repeatedly. During successive tectonic phases several pre-existing structural elements were reactivated and new elements appeared. The various identified regional structural elements are grouped into six tectonically active periods: ate Carboniferous, ermian, Triassic, ate Jurassic, ate Cretaceous and Cenozoic. This study demonstrates that many structural elements and fault systems were repeatedly reactivated and that a clear distinction exists between long-lived elements, such as the oer Valley raben, and short-lived structural elements, such as the Terschelling asin. Keywords: geological maps, structural elements, ermian, Triassic, Jurassic, Cretaceous, Cenozoic, etherlands Introduction This paper presents the results of a regional geological mapping project of the Dutch onshore and offshore subsurface at a scale of 1 : 2,500,000 that was carried out by T at the request of the inistry of conomical ffairs with the following objectives: to promote exploration efforts in the etherlands; to obtain a regional framework for a detailed geological mapping program ; to enhance research for the use of the subsurface for C 2 storage and geothermal energy production. The onshore part of the maps presented, was recently published in the eological tlas of the ubsurface of the etherlands onshore (T-IT, 2004), while the offshore part is being published for the first time. In this paper we present these new integrated maps and cross sections and briefly discuss the main regional structural elements. Depth and thickness maps have been created for the Zechstein roup (ate ermian), the ower and Upper ermanic Trias groups, the ltena roup (arly and iddle Jurassic), the chieland-cruff-iedersachsen groups (ate Jurassic), the ijnland roup (arly Cretaceous), the Chalk roup (ate Cretaceous), the ower and iddle orth ea groups (aleogene) and the Upper orth ea roup (eogene) (ig. 1). These maps provide an overview of the geological development of the deep subsurface of the etherlands since the Carboniferous. In this paper the presented maps are discussed in two paragraphs for each lithostratigraphic group by describing (a) depth, thickness and basin development and (b) structural development (faults, erosion and salt movements). igure 1 shows the geological time scale of radstein et al. (2004) together with the mapped lithostratigraphic intervals that are discussed in this paper. or detailed information on the lithostratigraphy of the mapped intervals and a discussion on regional structural elements readers are referred to earlier publications by T-IT (2004) and Van drichem oogaert 245

2 Time (a) ra CZIC eriod poch ge eogene aleogene leistocene-olocene liocene iocene ligocene ocene aleocene euverian runssumian essinian Tortonian erravallian anghian urdigalian quitanian Chattian upelian riabonian artonian utetian Ypresian Thanetian Danian aastrichtian ithostratigraphy according to Van drichem oogaert & Kouwe ( ) Upper orth ea roup U iddle orth ea roup ower orth ea roup Tectonic phase avian yrenean aramide rogeny 100 Cretaceous ate Cretaceous Campanian antonian Coniacian Turonian Cenomanian lbian Chalk roup CK ubhercynian ustrian I arly Cretaceous ptian ijnland roup K ZIC Jurassic ate iddle alm Dogger arremian auterivian Valanginian yazanian ortlandian Kimmeridgian xfordian Callovian athonian ajocian alenian Toarcian chieland roup ltena roup T chieland, cruff and iedersachsen groups,, K ate Kimmerian id-kimmerian arly ias liensbachian inemurian ettangian haetian Triassic ermian arly ate ate Keuper orian Carnian uschelkalk adinian nisian untsandstein lenekian Induan Changhsingian opingian Wuchiapingian Capitanian uadalupian Wordian oadian Kungurian rtinskian Cisuralian akmarian ower otliegend roup V Upper ermanic Trias roup ower ermanic Trias roup Zechstein roup Z Upper otliegend roup arly Kimmerian ardegsen aalian ZIC Carboniferous arly ate ilesian Dinantian sselian tephanian Westphalian amurian Visean imburg roup DC Carboniferous imestone roup C sturian udetian VIC Tournaisian 359 ig. 1. eological time scale (after radstein et al, 2004) and lithostratigraphic column (after Van drichem oogaert & Kouwe, ) showing main tectonic deformation phases. 246

3 & Kouwe ( ). arlier structural geological models and studies of basin evolution in the etherlands have been published by eybroek (1974), Van Wijhe (1987), ijkers & Duin (1994), acero-aena & Drake (1996), ijkers & eluk (1996), Dirkzwager (2002), Wórum (2004), Van alen et al. (2005) and De Jager (in press). ll depth maps, thickness maps and figures that are presented in this paper can be downloaded from urther improvement of the structural reconstruction is necessary to explain geological distribution of aquifers, reservoirs and hydrocarbon systems. In particular the reconstruction and timing of salt tectonics in the etherlands can be improved strongly. egional maps are also required for analysis of paleo-stress fields and timing of salt movement and contribute to an improved understanding of fault patterns, reservoir configuration and burial evolution on a local scale. Data base and map reliability The data used for the construction of the maps were acquired from various oil companies during their exploration and production activities since the beginning of the 20th century. or this project, only publicly released seismic and borehole data have been used (ig. 2). The stratigraphic information of 1756 boreholes has been incorporated in the interpretation of the seismic data. The interpreted seismic data were converted from time to depth using the seismic velocity model of Van Dalfsen et al. (this volume). In contrast to the onshore area, the offshore part shows a lower density of used seismic lines. In the onshore area much more seismic data were available than in the offshore region resulting in a higher reliability of the map data in the onshore area. ffshore areas in which 3D seismic data have been interpreted are the Cleaver ank igh (C), meland lock () and Terschelling asin (T) (igs 2 and 4d). In these areas the maps show more detail and are more reliable than the areas with a low coverage of 2D seismic data. In the southern part of the offshore region the thickness map of the Zechstein roup is largely based on well data. In this area, the depth map of the Zechstein roup was constructed by adding the Zechstein thickness to the Triassic depth map. or the period , a detailed geological mapping project is programmed during which more recently released (3D) seismic and well data will be accessed, which will result in the improvement and higher reliability of the depth and thickness maps. tructural elements ine regional geological cross sections were constructed to illustrate the main structural elements of the etherlands (ig. 3). In this paper the term structural element is given to regional structures with a uniform deformation history in terms of subsidence, faulting, uplift and erosion during a specific time interval. The structural element maps have been reconstructed from the depth and thickness maps presented in this paper. In order to map these regional structural elements systematically, the following structural types are used: basin, high, platform and fault (-zone). The boundaries of structural elements, including basins, are delineated by subcrops, (major) faults or salt structures. In this study a high is defined as an area with significant erosion down into Carboniferous or ermian strata (otliegend and/or Zechstein). platform is characterized by ate Jurassic erosion into the Triassic and the absence of ower and Upper Jurassic strata. The term graben is used for subsided structural elements that are clearly delineated by major linear faulting. xceptions on this systematical methodology in nomenclature of structural elements are the ms ow (), auwerszee Trough (T), etherlands well () and Zandvoort idge (Z). These names are not changed because of their common use in literature. The regional structural elements have been reconstructed for six tectono-stratigraphic periods, namely ate Carboniferous - arly ermian (Variscan phases), iddle and ate ermian, Triassic (arly Kimmerian phase), ate Jurassic (ate Kimmerian phase), ate Cretaceous (ubhercynian phase) and Cenozoic (aramide, yrenean and avian phases) (igs 4a - 4f). Improved delineation of basin structures is obtained by using the subcrops of the ower and Upper Jurassic strata. Table 1a indicates the active geological period for each structural element with regional significance that is recognized in these new maps. ajor fault zones that are indicated in the deformation scheme in Table 1a are recognized both in the maps and the cross sections. In Table 1b the geological description and the used abbreviations of these main structural elements are given. It is strongly recommended not to mingle names of structural elements that have been active during different geological periods. or instance, the larger part of the id orth ea igh () is a Variscan structure, while the lbow pit igh (), at more or less the same location, is of ate Jurassic origin (igs 4a and d). The structural grain has been strongly influenced by fault systems in the basement that came into existence during the Variscan orogeny (ate Carboniferous - ermian phases). It is obvious from the structural element maps that the ate Jurassic - arly Cretaceous extensional tectonics dominates the structural configuration of the Dutch subsurface, involving Kimmerian reactivation of pre-existing ermo-carboniferous faults. ate Jurassic and arly Cretaceous subsidence of basins and uplift of flanking platforms, combined with effects of salt movement, reflect the development of a complex structural setting. The geological setting during the ate Jurassic was characterized by erosion of elevated platforms together with the accumulation of sediment in the local basins along the edges of the uplifted blocks. It is emphasized that ate Jurassic depositional areas are relatively small as compared to 247

4 3D surveys eismic lines Well location eological cross section ' cale 1 : rojection UT31 llipsoid D50 D ' C' D' ' C I ' ' D ' I' ig. 2. ap showing the locations of seismic lines and wells used, and geological cross sections given in ig

5 0 Cleaver ank igh -' lbow pit igh tep raben -' ' Dutch Central raben Tectonic inversion axis ' 1 ' 2 C' 3 D' Depth (km) 4 5 C I ' ' ' 6 D 7 ' 8 Cleaver ank igh Dutch Central raben chill rund igh ' I' 6 7 -' Tectonic inversion axis -' Depth (km) Upper orth ea roup ower and iddle orth ea groups Chalk roup ijnland roup chieland, cruff and iedersachsen groups ltena roup ower and Upper ermanic Trias groups Zechstein roup ower and Upper otliegend groups imburg roup C Winterton latform road ourteens asin Central ffshore latform Terschelling asin meland Terschelling asin lock Tectonic inversion axis -' -' chill rund igh C' Depth (km) ig. 3a. W- geological cross sections -', -' and C-C'. 249

6 D D' oord-olland latform Texel- IJsselmeer Indefatigable igh ault Zone Vlieland asin riesland latform antum ault Zone auwerszee Trough roningen igh Upper orth ea roup ower and iddle orth ea groups Chalk roup ijnland roup chieland, cruff and iedersachsen groups ltena roup ower and Upper ermanic Trias groups Zechstein roup ower and Upper otliegend groups imburg roup Carboniferous imestone roup Devonian ilurian rdovician Depth (km) riesland latform rabant assif Zeeland latform Winterton latform road ourteens asin I-I' otterdam ault Zone Tectonic inversion axis -' -' 6 0 ' rabant assif Zeeland latform West etherlands asin Central etherlands asin riesland latform ower axony asin ouwzee Trough Voorne Trough Tectonic inversion id-etherlands I-I' axis ault Zone Tectonic inversion axis aalte oundary ault Texel- IJsselmeer igh -' -' Depth (km) Depth (km) Zandvoort idge rabant assif Zeeland latform oer Valley raben aasbommel igh eel Venlo lock lock ijen ault Tectonic eel oundary Tegelen inversion I-I' axis ault ault -' Central etherlands asin ower axony asin Tectonic inversion axis ronau ault Zone ' 4 5 ig. 3b. W- geological cross sections D-D', -' and -'. 250

7 lbow pit igh tep raben Dutch Central raben chill rund igh Terschelling asin meland lock auwerszee Trough ower axony asin ' -' Tectonic inversion axis -' ifgronden ault Zone Tectonic inversion axis C-C' D-D' -' olsloot ault Zone Tectonic inversion axis Depth (km) Cleaver ank igh Central ffshore latform Central etherlands asin ' -' -' Texel-IJsselmeer igh oord-olland latform C-C' D-D' -' Tectonic inversion axis -' ermany Depth (km) I West etherlands asin Zeeland latform I' D-D' -' -' elgium Upper orth ea roup ower and iddle orth ea groups Chalk roup ijnland roup chieland, cruff and iedersachsen groups ltena roup ower and Upper ermanic Trias groups Zechstein roup ower and Upper otliegend groups imburg roup Depth (km) road ourteens asin Winterton latform otterdam ault Zone 5 ig. 3c. W- geological cross sections -', -' and I-I'. ermany 251

8 D D Depocentre Z (C) Z () TIJ C V Z C Z a. Variscan structural elements b. ate ermian structural elements 6 7 egend ajor fault D DC ig. 4a Dinantien amurian and older Westphalian / Westphalian /C Westphalian C Westphalian D - tephanian ig. 4b outhern ermian asin Depocentre, thickness otliegend >300 m ermian basin fringe on-deposition outhern limit halokinesis (Zechstein salt) ig. 4c Thickness of Triassic deposits in m > W V km cale 1 : rojection UT31 llipsoid D50 Triassic deposits absent by erosion or non-deposition c. Triassic structural elements (arly Kimmerian phase) ig. 4 tructural element maps (1 : ) summarizing main structural features active during the six tectono-stratigraphic periods (4a - 4f). The structural elements are mainly based on the present-day thickness maps in igs or explanation of the abbreviations of the structural elements and the faults see Table

9 T D DC Z C T C V Z V T TIJ W C D W DZ Z C Z W D IDZ DC T C W V Z V d. ate Jurassic - arly Cretaceous structural elements (ate Kimmerian phases) e. ate Cretaceous-arly Tertiary structural elements and basins (ubhercynian and aramide phases) egend ajor fault ig. 4d asin: ower Jurassic present asin: Upper Jurassic present D Depocentre latform: Jurassic deposits absent alf graben: ower Jurassic absent, Triassic partly eroded igh: Triassic absent, otliegend and/or Zechstein absent ig. 4e Thickness Chalk >1000 m Z ZZ T Z Z ig. 4f Thickness Chalk <1000 m ubhercynian/aramide inverted basins Tectonic axis Depth base orth ea upergroup <250 m Depth base orth ea upergroup m K VT V T V km cale 1 : rojection UT31 llipsoid D50 Depth base orth ea upergroup m Depth base orth ea upergroup m Depth base orth ea upergroup >1000 m f. Cenozoic structural elements (yrenean and avian phases) 253

10 Table 1a. Deformation scheme of regional structural elements in the subsurface of the etherlands onshore and offshore. The scheme indicates for each structural element individually the minimum age and the periods that tectonic activity occurred can be assigned. Included with 'tectonic activity' are basin subsidence, (reverse) faulting and uplift. xcluded from this table is doming and piercing from halokinetic activity..g. the Cleaver ank igh has been tectonically active during Variscan phases. During the ermian, Triassic and arly and iddle Jurassic no significant tectonic activity occurred. During the ate Kimmerian phase (ate Jurassic) until the aramide phase, resp. uplift inversion and erosion occurred on the Cleaver ank igh. Depth maps presented in this paper otliegend roup ig. 5 Zechstein roup ower and Upper ermanic Trias groups ig. 6 ig. 7 ltena roup rogeny Tectonic phase and unconformity ge of tectonic phase egional stress field Variscan orogeny lpine orogeny aalian - ardegsen arly Kimmerian y y y compression extension extension extension Tectonic expression Time wrench faulting subsidence subsidence subsidence ate Carboniferous ermian arly Triassic ate Triassic asins, platforms and highs meland lock rabant assif road ourteens asin Campine asin Central etherlands asin Central ffshore latform Cleaver ank igh Dalfsen igh Dutch Central raben lbow pit igh ms ow riesland latform roningen igh Kijkduin igh auwerszee Trough ower axony asin aasbommel igh id orth ea igh etherlands igh etherlands well oord-olland latform orth ea asin eel lock henish assif oer Valley raben chill rund igh outhern ermian asin tep raben Terschelling asin Texel-IJsselmeer igh Venlo lock Vlieland asin Vlieland igh Voorne Trough West etherlands asin Winterton igh Winterton latform Zandvoort idge Zeeland latform Zuiderzee ow Zuid-imburg lock aults and fault zones eldbiss ault ronau ault Zone antum ault Zone Indefatigable ault Zone id-etherlands ault Zone eel oundary ault aalte oundary ault ifgronden ault Zone ijen ault otterdam ault Zone Tegelen ault bbreviation C C C C D DC K T V T T TIJ V V V VT W W W Z Z ZZ Z Z Z IDZ Z Z DZ T 254

11 tructural elements of Carboniferous (or older) tectonic age tructural elements of ermian tectonic age tructural elements of Triassic tectonic age tructural elements of Jurassic tectonic age (incl. ate Cretacous inversion) tructural elements of Cenozoic tectonic age (incl. arly Tertiary inversion) Upper Jurassic groups ijnland roup Chalk roup ower & iddle orth ea groups Upper orth ea roup ig. 8 ig. 9 ig. 10 ig. 11 ig. 12 lpine orogeny id Kimmerian ate Kimmerian ubherc./aramide yrenean avian y y y y y eotectonics extension extension compression compression extension extension regional (thermal) uplift local rifting and uplift strong inversion inversion subsidence subsidence alenian - ajocien Tithonian - erriasian Campanian - aleocene ate ocene - arly ligoc. iocene uaternary verprinted by Voorne Trough verprinted by orth ea asin verprinted by ower axony asin verprinted by riesland latform 255

12 Table 1b. eological description and abbreviations of regional structural elements. eological descriptions of structural elements asins, platforms and highs meland lock rabant assif road ourteens asin Campine asin Central etherlands asin Central ffshore latform Cleaver ank igh Dalfsen igh Dutch Central raben lbow pit igh ms ow riesland latform roningen igh Kijkduin igh auwerszee Trough ower axony asin aasbommel igh id orth ea igh etherlands igh etherlands well oord-olland latform orth ea asin eel lock henish assif oer Valley raben chill rund igh outhern ermian asin tep raben Terschelling asin Texel-IJsselmeer igh Venlo lock Vlieland asin Vlieland igh Voorne Trough West etherlands asin Winterton igh Winterton latform Zandvoort idge Zeeland latform Zuiderzee ow Zuid-imburg lock aults and fault zones eldbiss ault ronau ault Zone antum ault Zone Indefatigable ault Zone id-etherlands ault Zone eel oundary ault aalte oundary ault ifgronden ault Zone ijen ault otterdam ault Zone Tegelen ault bbreviation table area between chill rund igh, Terschelling asin and riesland latform ower aleozoic structural element of folded Caledonian rocks, unconformably overlain by Cretaceous rocks; locally overlain by Upper aleozoic rock Depositional basin during the Triassic that was strongly activated during the Jurassic C asin flanking the northern border of the rabant assif, indicated by thick sequence of Westphalian C/D and tephanian C ermian and Jurassic basin trending WW- C Jurassic erosional area between Vlieland asin, Terschelling asin, Dutch Central raben, Cleaver ank igh and oord-olland latform C rea uplifted and eroded during ate Jurassic and arly Cretaceous D igh structure between riesland latform and Central etherlands asin DC Triassic and Jurassic depositional area, delineated as subcrop of ower Jurassic; southern extension of northerly Viking raben W- structure with Kimmerian erosion down to Carboniferous and Devonian; high area during ermian - trending basinal structure along the Dutch-erman border, active in Westphalian C and Triassic table platform area with significant Jurassic erosion, situated between Texel-IJsselmeer igh, ower axony asin and Central etherlands asin table structural high between auwerszee Trough and ms ow delineated by normal faults and by re-ermian subcrop map K igh area in the centre of the W due to inversion in ate ocene, W- trend T ault block between the riesland latform and the roningen igh, flanked by the antum ault Zone in the west Jurassic basin defined by occurrence of Upper Jurassic and ower Cretaceous deposits Jurassic erosional area where ower Cretaceous unconformably overlies Triassic, ermian and Carboniferous tructural high during ate Carboniferous and ermian age rosional area in northern etherlands during ate Carboniferous and arly ermian rosional area in northern etherlands during the Triassic, delineated by absence of Volpriehausen ember Jurassic erosional area where ower Cretaceous unconformably overlies Triassic, ermian or Carboniferous resent-day orth ea asin table fault block, northeast of the oer Valley raben igh structure, etherlands at erman border. ocks deformed during the Variscan and uplifted during Jurassic and Cenozoic V raben system in southwest etherlands located between rabant assif and eel lock table platform area southerly of the ynkøbing yn igh, flanking the Dutch Central raben ermian depositional area located between rabant assif and ynkøbing yn igh T Intermediate fault block between lbow pit igh, Cleaver ank igh and Dutch Central raben; Upper Jurassic locally present T Upper Jurassic basin in the etherlands offshore, delineated between the Dutch Central raben and the riesland latform; ower Jurassic is absent TIJ Tilted and uplifted structure between Central etherlands asin and riesland latform, where Carboniferous was eroded during the Jurassic V table fault block, northeast of the eel lock and oer Valley raben V ate Jurassic and arly Cretaceous basin in the etherlands offshore area V latform area between Terschelling and Vlieland asin VT arly Tertiary subsidence area, between West etherlands asin and Zeeland latform W Depositional area during Triassic and Jurassic, between rabant assif and etherlands well W table structural unit between rabant assif and road ourteens asin, Triassic completely eroded W latform area surrounding the Winterton igh, Triassic partly eroded Z ault block between Central etherlands asin and West etherlands asin defined by severe faulting Z Jurassic erosional area between the rabant assif and the West etherlands asin ZZ arly Tertiary basin in the central onshore area Z table fault block at northern flank of the rabant assif that was strongly uplifted during Variscan pulses Z Z IDZ Z Z DZ T outhern fault of the oer Valley raben trending W- eparating Central etherlands asin and ower axony asin eparating the meland lock from the Vlieland igh and the riesland latform, active since Carboniferous eparating road ourteens asin and the Winterton latform eparating the Central etherlands asin and the West etherlands asin and flanks the Zandvoort idge orthern border of oer Valley raben, active since Carboniferous and rabant trending W- eparating the Texel-IJsselmeer igh and Central etherlands asin eparating the Terschelling asin and the chill rund igh outhwestern limit of the northwestern part of the oer Valley raben ault zone in the axis of the inversion zone of the West etherlands asin eparating the eel lock and the Central etherlands asin the ermian, Triassic and Cretaceous basins. trong halokinetic movements took place in the northern offshore and the northeastern onshore area. The thickness variation of Zechstein salt can be easily observed in the geological profiles and the thickness map of the Zechstein (ig. 5b). alt structures are revealed by thicknesses of Zechstein larger than 1300 m (ig. 5b). alt pillows, walls and diapirs have been active since the ate Triassic. oth intensity and (re-)activation of salt movement varies locally very strongly. re-zechstein Carboniferous In the etherlands, arly Carboniferous (Tournaisian and Visean) sediments are only known from a few wells. In the southern part of the Dutch onshore and offshore these sediments consist of black limestones whereas in the northern offshore arly Carboniferous rocks are of clastic origin. Upper Carboniferous deposits (amurian, Westphalian and tephanian) are widely distributed in the subsurface of the etherlands (Van drichem oogaert & Kouwe, ). The total thickness and distribution of the Carboniferous strata is not known in detail due to their deep burial. In large parts of the etherlands the Carboniferous subcrop is well-documented as it is the source rock of many gas fields and a target of gas exploration (ijnlieff, 2005). The depth of the top of the Carboniferous can be greater than 6000 m and the Carboniferous deposits locally reach thicknesses of more than 4000 m (T-IT, 2004). ence, in many locations these deposits are thicker than the total thickness of the cumulative ermian to Cenozoic deposits. The 256

13 Carboniferous deposits are overlain by iddle and ate ermian sediments of the Upper otliegend and Zechstein groups (ig. 3). The Carboniferous is unconformably overlain by the arly Cretaceous ijnland roup on structural high elements, such as the Texel-IJsselmeer (TIJ) (ig. 3c), and Winterton highs (W) or by the Chalk roup in the southern parts of the etherlands. Carboniferous strata are absent in the southernmost part of the onshore and offshore and locally on the lbow pit igh, where Devonian strata directly are overlain by the ate Cretaceous Chalk roup. The Variscan structural elements map (ig. 4a) shows the Campine asin (C), oer Valley raben (V), ms ow () and the Cleaver ank igh (C) that developed in response to ermo-carboniferous wrench tectonics (ijnlieff, 2005). Westphalian D strata are present in these synclinal structures which resulted from Variscan tectonics (chroot & De aan, 2003). ost large fault zones that have come into existence during the ermo-carboniferous have been reactivated repeatedly later, such as the antum ault Zone (Z), ronau ault Zone (Z), aalte oundary ault () and eel oundary ault (). ccording to chroot & De aan (2003) the Carboniferous fault system of the Cleaver ank igh shows W- and -W orientations. The orientation of Variscan faults in W-urope is generally developed in a W- to WW- direction (check-wenderoth & amarche, 2004; chroot & De aan, 2003; Ziegler et al., 2004). ower and Upper otliegend (arly and iddle ermian) fter the transpressional tectonics of the Variscan orogeny, ower and Upper otliegend sediments were deposited under continental conditions during the arly and iddle ermian in the outhern ermian asin () (ig. 4b). The outhern ermian asin is defined by the occurrence of otliegend and Zechstein deposits, south of the id orth ea igh () and the ingkøbing yn igh. The thickness of the otliegend section reaches a maximum value of more than 900 m in the -block in the northeastern offshore area (ig. 4b; eluk, 2005). ubsidence of the central parts of the outhern ermian asin took place during the iddle and ate ermian, in conjunction with the pre-cursor of the road ourteens asin () and the Central etherlands asin (C). The outhern ermian asin has developed in a WW- direction north of the rabant assif (). The local absence of the otliegend deposits within the outhern ermian asin, such as on the Texel-IJsselmeer igh (TIJ) and on the Winterton igh (W), is the result of Jurassic erosion. owever, it was also shown by ijkers & eluk (1993) that the Texel-IJsselmeer igh was a high structure during the ermian, which is indicated by the thickness development and sedimentary facies changes of the Upper otliegend and Zechstein groups around the high. Zechstein roup (ate ermian) Depth, thickness and basin development The outlines of the Zechstein basin coincide largely with the occurrence of deposits of the Upper otliegend roup (ig. 3b). The southernmost occurrence of Zechstein sediments defines the southern margin of the outhern ermian asin. The present-day depth of the base of the Zechstein roup ranges from almost 700 m in the southeastern part of the etherlands to more than 5000 m in the Dutch Central raben, the road ourteens asin and the West etherlands asin (ig. 5a). asins that have subsided further during the arly and ate Kimmerian phases, such as the Dutch Central raben (DC), Terschelling asin (T), road ourteens asin (), ms ow () and oer Valley raben (V), are clearly outlined in the depth map of the base of the Zechstein roup (ig. 5a). The thickness of the Zechstein roup increases strongly to the north up to more than 900 m on ate Jurassic platforms (ig. 5b). tructural development t the aasbommel (), Winterton (W), Texel-IJsselmeer (TIJ), Dalfsen (D) and lbow pit highs () the Zechstein is absent due to id- and ate Kimmerian erosion (igs 5a and 5b). The absence of Zechstein deposits on the Texel-IJsselmeer igh is the result of strong id- and ate Kimmerian uplift and erosion (ijkers & eluk, 1994). In the southern part of the etherlands only thin Zechstein deposits are present due to shallow basin development. The Dutch Central raben and the Terschelling asin show pronounced occurrences of salt diapirs and walls. The northeastern onshore and northern offshore areas are characterized by the widespread occurrence of salt structures with local thicknesses of more than 1300 m (ig. 5b). The area of mobilized Zechstein salt is clearly visible by the lateral thickness variations. In the areas that have been tectonically active, such as the Terschelling asin and the Dutch Central raben, the original Zechstein depositional thickness is obscured by halokinesis (ig. 5b). n platforms like the Cleaver ank igh and the meland lock, where post-zechstein tectonics have been relatively quiet, the Zechstein is thicker than 900 m, which indicates the minimum depositional thickness of the Zechstein sequence for the offshore,, K, and -blocks. The absence of Zechstein deposits on Kimmerian highs in the northern salt province is the result of strong Kimmerian uplift and erosion. In the Dutch Central raben (DC), Terschelling asin (T) and the western part of the chill rund igh () the Zechstein salt is locally absent due to salt movement (ig. 5b). The thin Zechstein sections in these halokinetic areas consist of residual carbonates and anhydrites. 257

14 ower and Upper ermanic Trias groups Depth, thickness and basin development The present-day depth of the base of the ower ermanic Trias roup ranges from approximately 500 m in eastern etherlands to over 5000 m in the Dutch Central raben (ig. 6a). s the result of Jurassic subsidence, thick Triassic deposits have only been preserved in the Dutch Central raben, Terschelling, road ourteens, Central etherlands, ower axony basins and oer Valley raben (igs 6a and 6b). In the other areas the Triassic deposits were eroded during the ate Jurassic. The total thickness of Triassic deposits amounts to more than 1800 m in the Dutch Central raben (ig. 6b). During the Triassic the Dutch Central raben, oer Valley raben and the road ourteens asin have subsided relatively faster than the surrounding highs which resulted in greater thicknesses in these basins (ig. 6b; eluk, 2005). The etherlands well is the area in the northern part of the etherlands that is strictly defined by the subcrop of the Volpriehausen andstone ember in the ower ermanic Trias roup (eluk, et al., 2005). The etherlands well was a relative high during the arly Triassic and was paralleled by the ardegsen event in the arly Triassic (eluk, 2005; ig. 4c). tructural development rosion of Triassic deposits occurred on structural highs such as the lbow pit (), Cleaver ank (C), Texel-IJsselmeer (TIJ), Dalfsen (D), Winterton (W) and aasbommel highs () and riesland latform (), sometimes removing the entire Triassic succession (igs 6a and 6b). The greater part of the erosion of Triassic deposits occurred in response to ate Jurassic uplift. oreover, salt walls and erosion obscure such faulting. The borders of the Dutch Central raben and the Terschelling asin appear to be preferential sites for the development of thrust (inversion) faults together with salt walls and diapirs. The faults in the Triassic maps in igs 6a and 6b are the cumulative result of Jurassic rifting and ate Cretaceous inversion tectonics. Triassic extensional tectonics in the etherlands was paralleled by rifting in the rctic- orth tlantic domain (Ziegler, 1988). ltena roup (arly and iddle Jurassic) Depth, thickness and basin development The depth of the base of the ltena roup ranges from less than 1000 m in the eastern etherlands to more than 5000 m in the Dutch Central raben and the road ourteens asin (ig. 7a). In the easternmost part of the Central etherlands asin, strata of the ltena roup outcrop. The Central etherlands asin has developed in a WW- direction and the Dutch Central raben in a - direction (ig. 4d). The road ourteens asin, oer Valley raben and West etherlands asin have developed in W- to W- directions (ig. 4d). The antum ault Zone, as the southern boundary of the Terschelling asin, is considered to be the feature link between the ower axony asin and the southern parts of the Dutch Central raben. In addition, the Vlieland asin (V) has been activated in response to a ate Jurassic dextral strike-slip faulting (erngreen et al., 1991). tructural development Due to ate Cretaceous basin inversion and uplift, ower Jurassic deposits have been partly eroded in the Central etherlands asin, especially on higher fault blocks (igs 7a and 7b; ig. 3). The Central etherlands asin and the oer Valley raben have been strongly inverted during the ubhercynian/aramide phase removing most of its Jurassic (and Cretaceous) infill (igs 7a, 9a and 10a). ocal uplift and subsequent erosion during iddle Jurassic to arly Cretaceous tectonic phases have almost completely removed ltena deposits on the structural highs and platform areas (ig. 7a). In the transition zone between the West etherlands asin and the oer Valley raben, subtle but distinct structural W- and WW- fault directions can be observed on the depth and thickness maps of the ltena roup (igs 7a and 7b). chieland, cruff and iedersachsen groups (ate Jurassic) Depth, thickness and basin development Upper Jurassic deposits are only found in depocentres of the Dutch Central raben (DC), oer Valley raben (V), Vlieland (V), Terschelling (T), road ourteens (), West etherlands (W) and Central etherlands basins (C) (igs 8a and 8b). The geographical extension of ate Jurassic deposits is very similar to those of the arly Jurassic deposits (ig. 7a). The depth of the Upper Jurassic sediments ranges from almost 100 m in the eastern etherlands to over 3000 m in the Dutch Central raben, Terschelling asin, Vlieland asin and road ourteens asin (ig. 8a). The thickness of the Upper Jurassic deposits is strongly influenced by inversion and erosion during the ate Cretaceous. thickness of over 1000 m is only present in the most active ate Jurassic structures, such as the Dutch Central raben and the road ourteens asin (ig. 8b). These basins were deformed by strong local rift tectonics of the ate Kimmerian phases. Complex ate Jurassic tectonics obscure the earlier geological deformation history because ate Kimmerian tectonics initiated both basin subsidence and uplift of platforms and highs. Upper Jurassic deposition started in the Dutch Central raben during the xfordian in continental and lacustrine facies. These depositional environments of the 258

15 Kimmeridgian in the Dutch Central raben expanded towards the south into the road ourteens and the West etherlands basins during the ortlandian (Van drichem oogaert & Kouwe, ; erngreen & Wong, 1989). tructural development n the ate Jurassic structural highs the deposits of the Triassic, Zechstein and otliegend are completely eroded (ig 4d). ate Jurassic platforms are delineated by complete erosion of ltena and/or Upper Jurassic deposits. ate Jurassic basins in the southern offshore and onshore of the etherlands are controlled by W- trending fault systems, with WW- and W- trending faults playing a subsidiary role (ig. 8a). eriods of enhanced salt flow correspond with tectonic phases (emmelts, 1996). ate Jurassic faulting together with sea level fluctuations resulted in a large variety of facies systems ranging from open marine to continental deposits (erngreen & Wong, 1989; Van drichem oogaert & Kouwe, ). The Zuidwal volcanic complex in the Vlieland asin was active during the ate Jurassic, dividing this basin into a continental and a marine part (igs 8a and 8b). Volcanic activity in the Vlieland asin was coupled to transpressional wrench tectonics during the xfordian (erngreen et al., 1991). ate Jurassic rifting and wrench tectonics in the etherlands was paralleled by a major extensional event in the central and northern orth ea as well by the rctic-orth tlantic rifting phase (Ziegler, 1988, 1990), locally referred to as ate Kimmerian rifting phase. ijnland roup (arly Cretaceous) Depth, thickness and basin development The present-day depth of the ijnland roup ranges from the outcrops in the eastern part of the etherlands to more than 3000 m in the West etherlands asin, the Central ffshore latform (C), the chill rund igh () and the northern offshore (ig. 9a). The thickness map of the ijnland roup shows the ower Cretaceous depocentres in the road ourteens and the West etherlands basins. The Vlieland, Terschelling and ower axony basins formed minor depocentres (ig. 9b). The present-day depth and occurrence of deposits of the ijnland roup is strongly influenced by ate Cretaceous inversion (ig. 9a). rosion of ijnland deposits occurred in the oer Valley raben, Central etherlands asin and Dutch Central raben (ig. 9a). The present-day depth of the ijnland roup of more than 3000 m in the - and -blocks is partly due to the large basin subsidence of the orth ea asin during the Cenozoic (ig. 9a). tructural development s a result of ate Cretaceous inversion, the ijnland roup is locally absent or reduced in thickness in the areas of strongest inversion, especially in the West etherlands asin (ig. 9a). rom the depth maps it can be concluded that inversion has also occurred in the oer Valley raben, Central etherlands asin and road ourteens asin (igs 9a and 9b). The thickness map of the ijnland roup also reveals intense salt tectonics on the Central ffshore latform and in the Terschelling asin and the southern part of the Dutch Central raben, where the ijnland roup is locally thin or absent. Chalk roup (ate Cretaceous) Depth and thickness The Chalk roup comprises sediments of Cenomanian to Danian age (Van drichem oogaert & Kouwe, ). The base of the Chalk roup outcrops in the eastern and southern parts of the etherlands (igs 10a and 10b). The depth increases towards the north to more than 2800 m in the northern offshore blocks. The base of the Chalk roup is uplifted to 1500 m in the inverted Dutch Central raben (ig. 10a). ore than 1800 m of sediments of the Chalk roup have been preserved on the Jurassic platforms, whereas ate Cretaceous inversion has partly and completely removed the sediments across the axial parts of the West etherlands (W), road ourteens (), Central etherlands (C), Vlieland (V) and ower axony basins () and Dutch Central raben (DC) (igs 4e and 10b). Thin deposits of Danian age, that are stratigraphically the top of the Chalk roup, have been deposited in the inverted basins after the ubhercynian phase. These occurrences are absent on the presented maps (igs 10a and 10b) due to their small thickness. tructural development The axes of maximum inversion are deduced from the regional distribution and thickness of the Upper Cretaceous (ig. 4e). The tectonic inversion phases seem to have been active simultaneous in most basins. Inversion of these basins appears to have been synchronous during the ubhercynian (antonian- Campanian), aramide (aleocene) and yrenean (ocene) phases of intraplate compression that is attributed to collisional coupling of the lpine orogenic wedge with its northern foreland (eybroek, 1974; Ziegler, 1990; De Jager, 2003; eybroek, 1974; Ziegler, 1990; Van der olen, 2004). The strongest inversion occurred in the Central etherlands asin where the aalte oundary ault has a reversed offset of more than 2000 m (ig. 3b: -'). 259

16 D Depth in metres below (sea level datum) < >5000 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 5a. Depth map of the base of the Zechstein roup (ate ermian)

17 D Thickness in metres >1300 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 5b. Thickness map of the Zechstein roup (ate ermian)

18 D Depth in metres below (sea level datum) < >5000 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 6a. Depth map of the base of the ower ermanic Trias roup

19 D Thickness in metres >1800 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 6b. Thickness map of the combined ower and Upper ermanic Trias groups

20 D Depth in metres below (sea level datum) < >5000 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 7a. Depth map of the base of the ltena roup (arly and iddle Jurassic)

21 D Thickness in metres >1800 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 7b. Thickness map of the ltena roup (arly and iddle Jurassic)

22 D Depth in metres below (sea level datum) < >3000 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 8a. Depth map of the base of the chieland, cruff and iedersachsen groups (ate Jurassic)

23 D Thickness in metres >1800 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 8b. Thickness map of the chieland, cruff and iedersachsen groups (ate Jurassic)

24 D Depth in metres below (sea level datum) < >3000 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 9a. Depth map of the base of the ijnland roup (arly Cretaceous)

25 D Thickness in metres >900 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 9b. Thickness map of the ijnland roup (arly Cretaceous)

26 D Depth in metres below (sea level datum) < >2750 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 10a. Depth map of the base of the Chalk roup (ate Cretaceous). 6 7

27 D Thickness in metres >1800 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 10b. Thickness map of the Chalk roup (ate Cretaceous)

28 D Depth in metres below (sea level datum) < >2250 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 11a. Depth map of the base of the ower and iddle orth ea groups (aleogene)

29 D Thickness in metres >900 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 11b. Thickness map of the ower and iddle orth ea groups (aleogene)

30 D Depth in metres below (sea level datum) < >1125 ot present due to erosion or non-deposition ault cale 1 : rojection UT31 llipsoid D ig. 12. Depth (and isopach) map of the Upper orth ea roup (eogene)

31 orth ea upergroup (Cenozoic) Depth, thickness and basin development The base of the orth ea upergroup outcrops in the eastern and southern parts of the etherlands and is located at depths of more than 2000 m in the Dutch part of the Cenozoic orth ea asin () (ig. 11a). The outlines of this basin roughly coincide with the present-day orth ea (Van drichem oogaert & Kouwe, ). The depth map of the base of the orth ea upergroup shows the strong Cenozoic subsidence in the oer Valley raben and the offshore part of the orth ea asin, while the Voorne Trough (VT), located on the W-flank of the inverted part of the West ederlands asin (the Kijkduin igh), underwent only moderate subsidence (ig. 11a). Whilst differential subsidence of the Voorne Trough ceased at the beginning of the iocene, the oer Valley raben continued to subside (igs 12 and 11b; De Jager, 2003; Kuhlmann, 2004). n the other hand, subsidence of the Central etherlands asin, road ourteens asin and orth ea asin accelerated during the eogene (ig. 12). This has also been observed by ichon et al. (2003), who conclude that the ate ocene inversion was restricted to the southern orth ea. tructural development Uplift of the West etherlands asin resulted in depositional thinning and in erosion of the Upper Cretaceous Chalk and aleogene clastics, as well as in local truncation of older sediments (De Jager, 2003). trong halokinesis was active during the aleogene in the Dutch Central raben, Cleaver ank igh, Central ffshore latform, meland lock, antum ault Zone and ower axony asin (ig. 11b). In the northern parts of the Dutch offshore subsidence has continued strongly and eogene deposits reach a thickness of 1400 m. Cenozoic regional thermal subsidence of the orth ea asin was from the iddle ocene paralleled by the evolution of the hine rift system that propagated during the ligocene northwards (Ziegler, 1988). This is evidenced by the subsidence of the oer Valley raben and activation of the antum, id- etherlands and the eel oundary ault (igs 12 and 11b). urther growth of salt diapirs during the Cenozoic continued in the northern offshore area, as can be seen on the thickness maps of the ower and iddle, and Upper orth ea groups (igs 12 and 11b). cknowledgements The presentation of the maps given in this paper is the result of the work of many colleagues at T uilt nvironment and eosciences, especially within the regional mapping team. We thank ora Witmans and Carla lmers for their assistance in collecting, interpreting and processing the data into integrated maps and figures. The authors thank the reviewers ark eluk and eter Ziegler for their technical comments to improve this manuscript. eferences De Jager, J., Inverted basins in the etherlands, similarities and differences. etherlands Journal of eosciences / eologie en ijnbouw 82: De Jager, J., in press. eological Development. In: Wong, Th., atjes, D..J. & De Jager, J. (eds): eology of the etherlands. oyal etherlands cademy of rts and ciences. Dirkzwager. J.., Tectonic modeling of vertical motion and its near surface expression in the etherlands, hd thesis, VU-msterdam: 156 pp. eluk,.c., tratigraphy and tectonics of ermo-triassic basins in the etherlands and surrounding areas. hd thesis, University of Utrecht: 171 pp. radstein,.., gg, J.. & mith,.. (eds), geologic time scale Cambridge University ress: 589 pp. erngreen,..w. & Wong, Th.., evision of the ate Jurassic stratigraphy of the Dutch Central raben. eologie en ijnbouw 68: erngreen,..w., mit,. & Wong, Th.., tratigraphy and tectonics of the Vlieland asin, The etherlands. In:.. pencer (ed.): eneration, accumulation and production of urope s hydrocarbons. pecial publications no. 1, xford University ress (xford): eybroek,., xplanation to tectonic maps of the etherlands. eologie en ijnbouw 53: Kuhlmann,., igh resolution stratigraphy and paleoenvironmental changes in the southern orth ea during the eogene: n integrated study of ate Cenozoic marine deposits from the northern part of the Dutch offshore area hd Thesis, University Utrecht: 205 pp. ichon,., Van alen.t., erle,. & agnier,., The Cenozoic evolution of the oer Valley oft ystem. Tectonophysics 367: ijnlieff,., Top re-ermian distribution map and some thematic regional geologic maps of the etherlands ( acero-aena,. & Drake,.J., tructural style and reservoir development in the West-etherlands oil province. In: ondeel,.., atjes, D..J. & ieuwenhuizen, W.. (eds): eology of gas and oil under the etherlands. Kluwer (Dordrecht): emmelts,., alt tectonics in the southern orth ea, the etherlands. In: ondeel,.., atjes, D..J. & ieuwenhuijs, W.. (eds): eology of gas and oil under the etherlands. Kluwer (Dordrecht): ijkers,... & Duin,.J.Th.,1994. Crustal observations beneath the southern orth ea and their tectonic and geological implications, Tectonophysics 240:

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