Æ G. Bresser Multiphase salt tectonic evolution in NW Germany: seismic interpretation … ·...

\ORIGINAL PAPER

M. Mohr Æ P. A. Kukla Æ J. L. Urai Æ G. Bresser

Multiphase salt tectonic evolution in NW Germany: seismic interpretationand retro-deformation

Received: 20 October 2004 / Accepted: 7 April 2005 / Published online: 11 November 2005� Springer-Verlag 2005

Abstract The Central European Basin is a classic area ofsalt tectonics, characterized by heterogeneous structuralevolution and complex salt movement history. Westudied an area on its SW margin, based on prestackdepth-migrated 2D and 3D seismic data. We use seismicinterpretation and retro-deformation to obtain a betterunderstanding of salt tectonics, structural control, andsedimentary response in this region. The first phase ofsalt tectonic evolution started with two main events ofNW–SE extension and rafting in the Triassic before theUpper Bunter and before the Upper Muschelkalk.Rafting was accompanied by first salt diapirism and anincreased sedimentary thickness adjacent to the saltstructure. After salt supply ceased updip to the saltstructure, a mini-basin grew in the intra-raft area. Thissedimentary differential loading caused salt movementand growth of a pillow structure basinward. The secondphase of salt movement was initiated by the formationof a NNW–SSE striking basement graben in the MiddleKeuper that triggered reactive diapirism, the break-through of the pillow’s roof and salt extrusion. Thefollowing downbuilding process was characterized bysedimentary wedges with basal unconformities, onlapstructures and salt extrusions that ceased in the Jurassic.The third and latest phase of salt tectonic evolution was

activated in the Late Cretaceous to Lower Tertiary bycompressional tectonics indicated by salt rise and a smallhorizontal shortening of the diapir. The interpreted salttectonic processes and the resulting geometries can nowbe better tied in with the regional heterogeneousframework of the basin.

Keywords Salt tectonics Æ NW Germany ÆRetro-deformation Æ Seismic interpretation ÆStructural evolution

Introduction

Salt tectonics play a major role in many sedimentarybasins. One classic area of salt tectonics is the NWGerman basin. Here, the mobile Permian Zechstein saltformed a large number of salt walls, diapirs and pillows(Trusheim 1960; Jaritz 1973; Lokhorst 1999; Baldschuhnet al. 2001) (Fig. 1) during long periods of salt tectonicactivity (Kockel 1998; Jaritz 1973): major changes insedimentation patterns and structural regimes are com-mon (Kockel 2002, 2003). It is perhaps surprising then,that the most recent studies in salt tectonics which aresummarised in a number of review papers (Jackson andTalbot 1994; Jackson 1995; Stewart and Clark 1999)were undertaken outside this area.

In Germany, the debate on the reasons for saltmovement started at the beginning of the last centurywith buoyancy (Arrhenius and Lachmann 1912) or tec-tonics (Stille 1910, 1925) as the driving forces. Thebuoyancy-driven halokinetic model of Trusheim (1957,1960) who postulated an autonomous, isostatic rise ofsalt and piercement of the overburden due to Rayleigh-Taylor instabilities defined the way of thinking of salttectonics in the North German Basin for the next fortyyears.

Evolutionary stages of the Trusheim model are thepillow stage with the primary peripheral sink, the diapirstage with the secondary peripheral sink and the post-diapiric stage with the tertiary peripheral sink. Because

Unfortunately, the entire article was originally published OnlineFirst with errors. The publishers wish to apologize for this mistake.The correct article is shown here.

The online version of the original article can be found at http://dx.doi.org/10.007/s00531-005-0498-8c

M. Mohr (&) Æ P. A. Kukla Æ J. L. UraiGeologisches Institut, RWTH Aachen, Wullnerstr. 2,52056 Aachen, GermanyE-mail: [email protected].: +49-241-8095732Fax: +49-241-8092151

G. BresserGaz de France Produktion Exploration Deutschland GmbH,Waldstr. 39, Lingen (Ems), Germany

Int J Earth Sci (Geol Rundsch) (2005) 94: 917–940DOI 10.1007/s00531-005-0039-5

a viscous overburden is a necessary requirement inTrusheim’s model, and the sedimentary cover’s defor-mation is dominantly frictional, this model is nowwidely regarded as not relevant in salt tectonics(Vendeville and Jackson 1992a; Weijermars et al. 1993).Supplemented by the theory of prograding gravityinstabilities forming successive generations of diapirsand salt dome families (Sannemann 1968) the concept ofgravity inversion was later modified by assuming apossible tectonic reason for the initiation of salt move-ment (Meinhold and Reinhardt 1967; Ruhberg 1976;Jaritz 1973, 1987, 1992; Zirngast 1996). Brink et al.(1992) proposed a strong connection between diapirismand strike-slip faulting, including rim-syncline rotation.Ge et al. (1997) interpreted diapiric families andperipheral sinks in North Germany as the result ofprograding sedimentary wedges and lateral migration ofsalt. Descriptions of raft tectonics during Keuper times(Best 1996; Thieme and Rockenbauch 2001), and recent

studies by Kossow et al. (2000) and Scheck et al. (2003)in the eastern part of the North German basin, proposemore influence due to decoupling by salt, and structur-ally-triggered salt movement. Also Baldschuhn et al.(2001) argue for important structural control duringseveral tectonic phases (Kockel 1998), but many detailsof the process are still unclear.

Therefore the aim of our study is the better under-standing of the interaction between sedimentation andsalt tectonics in the NW German Basin from thePermian to Recent, considering changing tectonicframeworks through time. Our approach is a combina-tion of seismic interpretation including structural andsedimentary analysis and balanced retro-deformation.This iterative process of seismic interpretation andstructural reconstruction minimizes uncertainties ofinterpretation. We focus on a study area located at theSW margin of the Southern Permian Basin and thewestern flank of the Triassic Ems Low.

Fig. 1 Location of the central part of the Southern Permian Basinand the distribution of salt diapirs and pillows (after Lokhorst1999). The basin margin is marked by the facies changes of the

Zechstein 2 carbonates from slope (grey) to basin (light grey). Ourstudy area in NW Germany is located inside the rectangle

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The data used for the present study consist of pre-stack depth-migrated 2D and 3D seismic data from a30·30 km area, including deep boreholes and a highnumber of non-depth-migrated seismic sections.

Geological framework

In NW Germany, the evolution of the Southern PermianBasin (Ziegler 1990) (Fig. 1) began with post-Variscanvolcanism and latest Carboniferous strike-slip faulting(van Wees et al. 2000). Late Rotliegend to Early Triassicthermal subsidence (Kossow et al. 2000) was accompa-nied by rifting (Gast 1988; Geluk 1999). On the WNW-ESE striking basin margin in NW Germany, sedimen-tation began in the Upper Rotliegend with a suite ofarid-semiarid sediments arranged around the centralPlaya lake (Fig. 2). Subsequent deposition of Zechsteinevaporites produced an approximate thickness of at least

800 m (Jaritz 1973), but estimates are uncertain due tolateral migration or dissolution loss.

The ensuing sedimentation in the Buntsandstein(Bunter) took place under fluvial, aeolian and lacustrineconditions. After a short period of tectonic quiescenceduring Lower Bunter times, rifting of the basin startedagain at the beginning of the Middle Bunter. This re-sulted for example in a syn-rift increase of sedimentarythickness in the Ems Trough (Rohling 1991). The ero-sional event in the uppermost Middle Bunter completedthis rifting sequence. First movement of salt is describedin this interval based on rim-syncline analysis (Jaritz1973). Extremely thin-skinned extension on the marginof the subsiding troughs caused rafting of the MiddleBunter blocks (Best 1996; Thieme and Rockenbauch2001; Kockel 2002). During Upper Bunter and Mu-schelkalk times, rifting continued and accumulated up to1,000 m sediments in local depocentres, such as theWestdorf Graben on the northwestern margin of the

Fig. 2 Time chart of the stratigraphic units (Menning and GermanStratigraphic Commission 2002), an outline of the differentlithologies of the study area and the interpreted seismic horizons

with the used stratigraphic abbreviations. Additionally, theregional tectonic events are compiled from different authors. Seethe different time scales on both sides of the figure

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Ems Trough (Gaertner and Rohling 1993). Depositionalconditions in Upper Bunter and Muschelkalk times wereshallow marine to evaporitic. Intra-formational saltlayers are observed in both sequences with locally highlyvariable thickness distribution (Geluk et al. 2000). Eu-static changes let to a regression which brought aboutthe clastic-evaporitic sedimentation of the Keuper (Zie-gler 1990). Thick halite sequences formed in local basindepocentres like the Ems or Gluckstadt Graben duringMiddle Keuper times (Beutler 1998). An ‘Early Cim-merian‘ extensional event (starting at �232 Ma) is seenin context of the North Sea rifting (Ziegler 1990); strongdilatation was coeval with the beginning of main saltdiapirism, subsequent rim-syncline development and apossible re-sedimentation of Zechstein salt (Frisch andKockel 1999; Jaritz 1973). Since the Lower Jurassic, theLower Saxony Basin in the south underwent riftingalong a WNW-ESE axes with a peak in the UpperJurassic (Baldschuhn et al. 2001), whereas the SouthernNorth Sea area was uplifted and eroded during the ‘LateCimmerian’ tectonic phase. In this region sedimentationended at the latest in the Upper Jurassic (Ziegler 1990).

Deposition in the Cretaceous reflected several phasesof transgressive sequences and tectonic pulses culmi-nating in Late Cretaceous to early Cenozoic inversionphases (Baldschuhn et al. 1991; de Jager 2003). Sedi-

mentation in the Cenozoic of NW Germany was mainlycontrolled by subsidence and eustatic sea-level changes.

Methods

The data set (Fig. 3) includes a high-quality 10·13 kmprestack depth-migrated 3D seismic cube. In addition anetwork of 28 depth-migrated seismic 2D sections with atotal length of approximately 430 km was used. Further,we used a high number of non depth-migrated sectionsfor qualitative interpretation. Eleven hydrocarbonexploration wells, all reaching the Rotliegend, serve forstratigraphic calibration of the seismic data.

In general, the seismic data images the sub-saltbasement very well. Nevertheless, typical difficulties ofseismic interpretation such as uncertainties in sub-saltimaging at the flanks of a diapir, are also apparent in theinvestigated area. In this study, 16 seismic reflectors anda consistent fault network were interpreted in the depth-migrated 2D sections and the 3D seismic cube (Fig. 3).The interpretation was gridded to 3D horizons inter-polating for areas without data coverage.

We analysed fault pattern and regional dip for several3D horizons using depth- and non-depth-migrated seis-mic information. The sub-salt Rotliegend Formation

Fig. 3 Simplified map of thestudy area demonstrating thelocation of the salt structures(grey), the 3D seismic cube(light grey) and the presentedseismic lines and interpretations

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and its structural configuration is, as exploration target,the best-analysed geological horizon in the area. Thepattern of sub-salt Rotliegend faults were comparedwith the structures in the overburden and the regionalgeological framework.

We also used data from the regional geo-history fordating of structural events, sedimentary thickness dis-tribution and preference of salt tectonic models. Themost likely model of salt movement is presented andtested against alternative models.

Several authors (e.g. Rowan 1993; Hossack 1995;Buchanan et al. 1996; Schafer et al. 1998) have demon-strated that palinspastic restoration in salt regimes is anuseful tool to reconstruct the structural and sedimentaryevolution through time. Superposed effects of youngerstrata and structures are removed sequentially tounderstand the individual structural components andsalt tectonic mechanisms. In addition, different possiblesubsurface geometries from the seismic interpretationcan be tested and uncertainties constrained.

In salt structure restoration, the overburden evolu-tion is seen as a direct result of salt flow. Salt itself canonly be passively restored. In addition, salt area mayvary due to dissolution or out-of-section migration andthe algorithms developed for retro-deformation of brit-tle rocks cannot reproduce the kinematics of the salt(Rowan 1993).

In a full restoration the effects of sedimentation,compaction, isostasy, thermal subsidence, and thedynamics of faulting and salt movement should be in-cluded. Our structural restoration contains sedimenta-tion, the kinematics of faulting and salt movement as themain factors. Variations in isostasy and thermal subsi-dence are negligible for the balanced section with alength of �30 km. Compaction influences the verticalthickness of sedimentary sequences through time, but isonly relevant when lateral variations in thickness orfacies are present, and affects mainly the uppermostsequences. Sensitivity analyses have shown that dis-regarding decompaction did not influence the results forthe mechanisms and processes of structural and salttectonic evolution interpreted from section restoration.Because our primary focus lies on the mechanisms andprocesses, rather than the rates and masses we did notdecompact the sections at this stage of the analysis.

An essential assumption in 2D structural balancing isplane strain, and that the section should be orientatedparallel to the tectonic transport (Woodward et al.1989). Our E-W orientated section is sub-perpendicularto the NE-SW structures of Lower Triassic, the NNW-SSE extended structures of Upper Triassic and the N-Sdirection of the Cenozoic structures. The decoupling bysalt necessitates the treatment of the salt layer, the sub-salt and supra-salt sequence as three autonomous tec-tonic systems during the restoration process (Schaferet al. 1998). In addition the positioning of the regionalelevation or target horizon to which a template line isrestored is of importance. Regional elevation representsthe pre-deformational relief, which is deduced from a

point without deformation or a line that defines areabalance above and below as a consequence of saltmovement and sedimentary response (Hossack 1995).

The usual restoration algorithms [as used in thesoftware package 2DMove (Midland Valley 2002)] insalt regimes are oblique shear and flexural slip. Obliqueshear preserves area, but line-length is not constant,which causes a significant length loss when restoringsteeply-dipping layers. Most workers prefer obliqueshear for downbuilding and extension while flexural slipis preferred for structural shortening and active saltdiapirism. Fault displacement may be removed by Fault-Parallel Flow, Inclined Shear or using the Move andRotate tools.

Because seismic interpretation has often non-uniqueresults, an iterative process of structural balancing fol-lowed by an update of the interpretation should be used.The final model is consistent with all known constraintsand is therefore more likely than others, but not neces-sarily unique (Woodward et al. 1989). Further con-straints e.g. by mechanical modelling, can improve thismodel.

2D and 3D seismic interpretation

Interpretation of seismic sections

The southernmost W-E running 2D seismic transect(Fig. 4) shows Top Rotliegend rising 780 m from east towest towards the Groningen High. This change inbasement topography is concentrated at two majornormal faults in the western part of the section. Faultingof upper Rotliegend age occurs along easterly dippingfaults, indicating structural activity in this area in theLower Permian. The section line crosses a sub-salt gra-ben directly beneath the western salt structure.

The Lower and Middle Bunter sequences in thissection show a sedimentary thickness of �650 m. Nor-mal faults running through these sequences have aneasterly dip in the west and a westerly dip in the centralpart. In the western part of the profile, three gaps of500–750 m are interpreted, where this sedimentary se-quences are absent (Fig. 4). The seismic reflectors of theLower and Middle Bunter at the western and easternedges of this structures run uniform and parallel. Sig-nificant syn-depositional interaction to the adjacent saltarea, such as converging reflectors or onlap-structures,was not observed. We interpret two disconnected Lowerand Middle Bunter blocks in the centre of this structurewith reasonable confidence in spite of the low seismicresolution in this area.

The Upper Bunter thickness varies between 500 m inthe west and 100 m in the centre of the profile. Threedisconnected blocks are interpreted, located directlyabove Zechstein salt. A former connection of theseblocks is indicated by good correlation of the seismicreflectors across their broken edges. The disconnectedUpper Bunter blocks are covered and surrounded by

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displaced Zechstein salt. The Lower and Middle Mu-schelkalk show a large thickness increase from east towest, from 250 m to 650 m, and are missing in the

western part of the section. The lower boundary of theUpper Muschelkalk Formation is formed by anunconformity in the central part of the profile. The

Fig. 4 Depth-migrated W-Eseismic section (2D data locatedin Fig. 3) and geologicalinterpretation. The top of thissection represent the surfaceline at sea level. The blackarrows mark the unconformitiesmentioned in the text for eachsection respectively. For usedstratigraphic abbreviations, seeFig. 2. The section shows thewestward rise of basement, thedisconnected Lower/MiddleBunter, three salt structures(Fig. 3) and the largedepocentre of the LowerKeuper and lowermost MiddleKeuper. The unconformity atthe base of the LowerCretaceous cuts the eastward-dipping layers of the Triassic.This section is used forsequential restoration, seeFigs. 12 and 13

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formation entirely covers the western salt structure.Three normal faults cutting this sequence are spatiallyassociated with sedimentation of a local depocentre inthe Lower Keuper and lowermost Middle Keuper(Grabfeld-Formation, KM1) with a maximum thicknessof 1,000 m. Their seismic reflectors converge eastward todiapir A. The sequences are absent adjacent to the dia-pir, where the Stuttgart-Formation (Middle Keuper 2,KM2) rests unconformable on Upper Muschelkalk. Inthe central part of the section, the interpreted MiddleKeuper to Lower Jurassic rim-syncline belongs to thesalt diapir A described in detail later in this chapter. Thebase Cretaceous unconformity truncates the Triassicsequences down to Muschelkalk in the west and down tothe Jurassic in the east (Fig. 4). Cretaceous to Quater-nary sequences dip slightly to the west with an increasingthickness and westward dipping normal faults.

The salt structure in the western part of the profileshows large variations in thickness of Zechstein saltbelow Upper and Lower/Middle Muschelkalk se-quences. The sub-vertical diapiric part of this saltstructure truncates the sequences at least up to theMiddle Keuper.

Two W-E and one N-S transects from the 3D cubeare presented in Figs. 5, 6, 7. The high quality of sub-saltseismic resolution in Fig. 5 allows us to identify anumber of antithetic normal faults in the RotliegendFormation with a graben in the centre of the section. Athin residue of Zechstein salt is present in the gaps be-tween the tilted sub-salt basement blocks and the BunterFormation. In this section, which is just south of thediapir A, the Lower Bunter up to the Middle Keuper istruncated by a pair of conjugate normal faults in thecentre of the profile. Fault movement started in UpperBunter times as indicated by a marked increase in sedi-mentary thickness across the fault. Furthermore, weobserve normal faults in the Lower/Middle Bunter in thewestern part of the profile. Directly above, blocks ofUpper Bunter and Lower/Middle Muschelkalk are ar-ranged in domino-like fashion between the layered saltof Upper Bunter and Middle Muschelkalk. Furthersignificant structures are the general decrease of thick-ness of the Lower and Middle Muschelkalk sequences tothe centre of the section, an unconformity at the base ofUpper Muschelkalk and irregular reflectors below thebase of the Stuttgart-Formation (Middle Keuper 2,KM2), where the Lower Keuper and the Grabfeld-Formation (Middle Keuper 1, KM1) is absent. Themaximum depocentre of the Lower Keuper to lower-most Middle Keuper sequences are located in the west ofthe section directly above an area without Lower andMiddle Bunter. Sedimentation of the Stuttgart-Forma-tion (Middle Keuper 2, KM2) started above an uncon-formity and the Grabfeld-Formation (Middle Keuper 3,KM3) formed characteristic peripheral sinks and turtleback structures. The sedimentary thickness maximum ofthese sequences moves from the eastern turtlebackstructure (Stuttgart and lower Grabfeld-Formation,KM2/3) to the central peripheral sink (Arnstadt-For-

mation, KM4). Another important unconformity isobserved at the base of the Arnstadt-Formation in theeastern part of the profile. In this eastern peripheral sinkof another salt structure just outside the working areathe Jurassic reaches a thickness of about 350 m. Localthickness increase of the Lower Cretaceous above themajor unconformity is consistent with a subcrop of in-ter-layered salt sequences of the Middle Keuper.

The northerly section (Fig. 6) through the salt diapirA also shows the absence of Lower/Middle Bunter in thewestern part and faulting in the central part. In thissection the pair of conjugate normal faults, describedabove, are positioned off the centre of the diapir. Thepredominantly parallel and flat lying reflectors of theUpper Bunter to lowermost Middle Keuper (KM1) inthe east of the profile are truncated by the prominentunconformity at the base of the Stuttgart-Formation(KM2). Thickness variations and geometry of theoverlying Middle Keuper sequences has been tradition-ally interpreted as a secondary rim-syncline. The typicalturtleback structure in the eastern part of the sectionconsists of sedimentary wedges with thick salt interlayersof Middle Keuper age. At the salt-sediment interface weinterpreted local unconformities, onlapping and salt jagsindicating lateral spreading of the salt. Diapir A shows anarrow geometry at the bottom and widens upwards.The peripheral sink represents an asymmetric evolutionparticularly during sedimentation of the upper Weser-Formation (upper part of KM3) and Arnstadt-Forma-tion (KM4). Prominent seismic reflectors at the roof ofthe salt diapir are caused by the strong acousticimpedance contrast between the material of the caprock,the overlying sediments and the underlying salt. Thisreflector is elevated about 500 m in comparison to theregional datum given by the base Cretaceous uncon-formity. Relating to this, thickness of the Cretaceousand Cenozoic sedimentary strata above the diapir arereduced and faulted. A Cretaceous graben structure atthe crest of the ‘turtle back’ is present directly abovesubcropping salt of the Middle Keuper.

The N-S section in Fig. 7 cuts the structural patternat low angle and thus represents a longitudinal section.Southward dipping normal faults in the sub-salt base-ment show a maximum offset of 250 m. The Lower/Middle Bunter is faulted, truncated and partially erodedin the central part of the profile. In the northern part ofthe seismic line, these sequences are absent and theUpper Bunter lies directly above Zechstein salt. Blocksof Lower/Middle Muschelkalk and Upper Bunter aredomino faulted, tilted and displaced on a unit inter-preted as Rot salt (Upper Bunter). These faulted blocksin the south and the flat lying sequences of Lower/Middle Muschelkalk in the north are truncated by anunconformity at the base Upper Muschelkalk. UpperMuschelkalk sequences are thickened in the centralparts, where they rest upon Zechstein salt. The overlyingLower Keuper (KU) and lowermost Middle Keuper(KM1) Formation has its maximum depocentre in thenorthern part of the profile, where Lower/Middle Bunter

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sequences are absent or incomplete. In addition, thesesequences show syn-sedimentary normal faulting andsouthward converging seismic reflectors.

The SW-NE section (Fig. 8) shows salt diapir Bpositioned above a structural basement high. The strongrelief of the Top Rotliegend in the profile reaches about800 m between the central high and the northeast. TheLower/Middle Bunter Formations have a thickness ofabout 450 m in the northeast, an increased thickness ofabout 650 m in the southwest and a triangular block inbetween. These sequences are absent below the saltdiapir B. In the far northeast, the Upper Bunter thick-ness reaches 400 m. The same formation has a thicknessof 150 m southwest adjacent and about 300 m at the

southwestern flank of the salt diapir where the sequencesare faulted and converge. The Lower/Middle Muschel-kalk sequences have two depocentres: one in thenortheast and one above the Lower/Middle Bunter gapin the southwest. In the latter depocentre, we interpretedabout 300 m inter-layered salt of Middle Muschelkalkage. Above this area, the intra-Muschelkalk unconfor-mity separates a northeast-migrating zone of maximumthickness of the Upper Muschelkalk to lowermostMiddle Keuper (KM1) sequences. In the northeasternpart of the section, these sequences are thinning towardsthe diapir. Their depocentre at the northeastern end ofthe profile has a thickness of at least 1,000 m. Above theunconformity, at the base of the Stuttgart-Formation

Fig. 5 Depth-migrated W-Eseismic section (3D data locatedin Fig. 3) and geologicalinterpretation. The top of thissection represent the surfaceline at sea level. For usedstratigraphic abbreviations seeFig. 2. The section showsantithetic basement faults, agraben in the centre of theoverburden and an erosionalsurface above. Note thesecondary rim-syncline of thenortherly adjacent diapir A inthe central part

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(KM2), the Middle Keuper to Jurassic sequences show acharacteristic secondary rim-syncline geometry relatedto diapir B. The asymmetric configuration of the LateTriassic rim syncline is similar to that of salt diapir A inthe south. The thickest sedimentary wedges in the east ofthe diapir are represented by sequences of the Weser-Formation (KM3). They contain a high amount of inter-layered salt. Typical for the salt-sediment interfaceforming the geometry of the diapir are salt jags, sedi-mentary onlapping and unconformities at the base ofeach sedimentary wedge. The diapir has a caprock, andits roof is about 400 m higher than the base Cretaceousas the regional datum. The overlying Cretaceous andTertiary layers wrap around the top of the structure and

show reduced thickness as well as normal faulting in thecrestal region. No peripheral sink can be observed inthese sequences.

A NNW-SSE to NW-SE transect (Fig. 9) runs in itsnorthern part parallel to the strike of the diapirs A and Bas well as to the main structural pattern in the sub-saltbasement. Therefore the Top Rotliegend shows onlyminor relief in the north in contrast to the southern partof the section, where the seismic line crosses a smallbasement graben. In the southern part, the seismic line isvery similar to the section in Fig. 5, south of diapir A.The Lower and Middle Bunter is interpreted with atruncated side in the NNW, a steep sided block in theSSE and a triangular block in between. The Upper

Fig. 6 Depth-migrated W-Eseismic section (3D data locatedin Fig. 3) and geologicalinterpretation. The top of thissection represent the surfaceline at sea level. For usedstratigraphic abbreviations seeFig. 2. The section shows thejagged geometry of diapir Aand the asymmetricsedimentary record

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Bunter shows significant lateral changes in thickness,with discrete changes across faults directly above theZechstein salt in the central part of the section. Theoverlying Lower/Middle Muschelkalk is absent in theSSE part. The intra-formational salt in the MiddleMuschelkalk reaches about 300 m thickness. In the

NNW its overlying sequences are block-faulted and haverotated counter-clockwise. As compared to the UpperBunter to Middle Muschelkalk sequences, the maximumdepocentres of the Upper Muschelkalk to lowermostMiddle Keuper (KM1) are located further to the southand lie directly above the triangular block of Lower and

Fig. 7 Depth-migrated N-Sseismic section (3D data locatedin Fig. 3) and geologicalinterpretation. The top of thissection represent the surfaceline at sea level. For usedstratigraphic abbreviations seeFig. 2. The section shows theabsence of the Lower/MiddleBunter in the north. Faultedand tilted blocks of UpperBunter and Lower/MiddleMuschelkalk are truncated byan unconformity at the base ofUpper Muschelkalk

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Middle Bunter. Two syn-depositional normal faults of agraben structure frame the 800 m thick depocentre.Another remarkable feature is an anticlinal flexure in thecentre of the profile affecting the Keuper stratigraphybelow the Cretaceous unconformity.

Interpretation of seismic horizons

The 3D model of the study area is based on 2D and 3Dseismic data (cf. Fig. 3). For gridding of the horizons, weused a data density of 100·100 m and interpolated be-tween the seismic sections. The colour maps reveal the3D relief of the horizons, overlain by the mapped faultstructures, thereby reflecting the complex structural andsalt tectonic evolution of the area.

The top Rotliegend 3D horizon (Fig. 10a), inter-preted as the sub-salt basement, shows a N-S trendinghigh in the west and a low in the east respectively. Thetwo local basement highs in the central area are locateddirectly below the salt diapirs A and B. The exact depthposition of the northern structure is confirmed by two

boreholes. The most prominent set of faults in the sub-salt basement strikes NNW-SSE to N-S. In the west, thissystem consists primarily of easterly dipping normalfaults. In the east, the faults are primarily westerly dip-ping antithetic faults. Consequently, an asymmetric half-graben is formed. Subordinate fault sets are striking NE-SW and WNW-ESE. An exact chronology and dating offault activity is not possible due to the decoupling effectof the salt layer and possible later reactivation of thefault sets under changing stress regimes during multipletectonic events.

The base Muschelkalk 3D horizon (Fig. 10b) liesextremely deep in an area 1 to 10 km wide and at least25 km long, that trends NNE-SSW to NE-SW. In thisarea, Lower and Middle Bunter sequences are absent oronly small separated blocks are underlying the Mu-schelkalk layers. The Upper Bunter to Lower Keupersequences have their thickest depocentres in this area.Seismic interpretation in the 3D cube allowed us to de-tect a fine network of normal faults located at themargin of the depocentre, where small blocks of hun-dreds of meters length and width moved downward on

Fig. 8 Depth-migrated SW-NEseismic section (2D data locatedin Fig. 3) and geologicalinterpretation. The top of thissection represent the surfaceline at sea level. For usedstratigraphic abbreviations seeFig. 2. The section shows thediapir B placed above abasement high. The intra-raftareas are filled by two differentsedimentary depocentres ofUpper Bunter to MiddleMuschelkalk and UpperMuschelkalk to Middle Keuper.Similar to the south (Fig. 6), thesecondary rim-syncline has anasymmetric geometry

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the underlying Upper Bunter salt. The relatively highposition of the 3D horizon in the northeast shows anoval, NNE-SSW elongated shape that corresponds to anarea with thickest present-day salt (approximately800 m) in the study area.

The base Lower Keuper 3D horizon (Fig. 10c) isabsent in the southern central part of the investigatedarea where Muschelkalk is partially present. This areahas a NNE orientated long axis, at an angle to the laterdiapir, which runs NNW-SSE. The depocentre of theLower Keuper sequences has the same configuration asthe underlying formation but shows a shift of about1 km to the ESE.

The depth structure of the base of the uppermosthalite layer of the Weser-Formation (KM3) (Fig. 10d) isdominated by the NNW–SSE structural orientation notobservable in the underlying Lower and Middle Triassicsequences. The two central salt structures A and B andtheir peripheral sinks are tracing this direction, which isknown from the fault pattern of the sub-salt basement.The relatively high position of this horizon in thenortheast corresponds to an area with thickest present-day salt of about 800 m in the study area. In the eastern

part the horizon subcrops against the base Cretaceousunconformity and is eroded over a large area.

The base Cretaceous horizon (Fig. 10e) is a majorunconformity and all horizons above have an averageregional dip to the west and southwest, in contrast to theolder sequences. A small graben structure in the south-east is positioned directly above the crest of the MiddleKeuper ‘turtle back’, where inter-layered salt of MiddleKeuper age subcropped. The salt structures are clearlyreflected by a prominent positive relief. Peripheral sedi-mentary sinks are minor or absent. Diapir-parallelconjugate faults directly above the roof of the centraland southern diapir and normal faulting above thenorthern diapir are observed.

Interpretation of salt tectonic evolution

We present our preferred model of salt tectonic evolu-tion, resulting from a series of iterations where seismicinterpretations and reconstructions were adopted whenconflicts with geological data or requirements of bal-ancing were found. Figures 12 and 13 show the seismic

Fig. 9 Depth-migrated NNW-SSE seismic section (2D datalocated in Fig. 3) andgeological interpretation. Thetop of this section represent thesurface line at sea level. Forused stratigraphic abbreviationssee Fig. 2. The section showsthe Lower Triassic extensionand the two depocentres abovethe intra-raft area. To the SSE,a reduced Upper Bunter toMiddle Keuper sequence islocated below the sediments ofthe secondary rim-syncline ofdiapir A

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section of Fig. 4 restored to 16 time slices. The geolog-ical and salt tectonic evolution are presented in threephases beginning with the oldest. Distinct phases ofbasin evolution are described in forward direction.

First phase of salt movement: Zechstein to MiddleKeuper

Preferred interpretation and modelling concept

Our interpretation is based on the general idea that de-coupled basement extension at the basin margin was thetrigger for initial salt movement (Jackson and Vendeville1994; Vendeville and Jackson 1992a). Detached faultingof the cover sequences and continued extension initiatedsalt diapirism and rafting of the sedimentary blocks. Saltflows towards the extensional structures in the supra-salt, in particular above the basement fault and towardsthe distal zone of detached extension, (Koyi et al. 1993).Between these structures, differential sedimentary load-ing created an increased sedimentary thickness until asalt weld is formed and lateral salt flow stops. As aconsequence, the diapir falls and a mini-basin grows inthe intra-raft area (Vendeville and Jackson 1992a, b).Salt migrates laterally along dip and forms a pillow-likesalt structure basinward adjacent.

In the investigated area, we interpret a major spatialgap between the blocks of Lower and Middle Bunter,and thus a significantly shorter section than the overly-ing sediments (Figs. 4, 9). Seismic reflectors at the edgesof the Lower/Middle Bunter blocks are truncated byfaulting and several faulted blocks lie isolated in thecentre of the gap. The starting phase of this rafting eventat the end of Middle Bunter is illustrated in Fig. 11,where a listric fault and the collapse of a roll overanticline in the hanging wall is indicated by antitheticnormal faults. In Fig. 11 Upper Bunter layers coverundisturbed the fault blocks suggesting a pre-UpperBunter age of the first extensional faulting event.

In the sub-salt basement of the working area nocorresponding normal faults running parallel to therafting structure are detected. This argument for thin-skinned extension is also supported by the regionalsubsidence trend to the east (Rohling 1991). In additionto rafting at the northwestern margin of the Ems Troughdescribed here, other coeval rafting events are knownfrom marginal positions of the basin (Kockel 2002).

Outside the working area an early Triassic NE-SWdirected basement step at the western basin margin(Baldschuhn et al. 1991) is documented. Basementfaulting caused salt diapirism directly above (Baldschuhnet al. 1991), detached supra-salt faulting and increasedMiddle Bunter to Middle Muschelkalk layer thickness atthe hangingwall—both visible in our data (Fig. 4). Twoextensional phases are documented by the rafted blocksof Lower/Middle Bunter and Upper Bunter. We proposethat salt reached the surface in both events, but wascovered subsequently by younger sediments.

Fig. 10 The colour maps present fault pattern and relief of sub-and supra-salt horizons (red high, blue low). Gridded 2D and 3Dseismic interpretations are used as data base

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The sedimentary thickness distribution shows asoutheastward migration of the Upper Muschelkalk tolowermost Middle Keuper (KM1) depocentres ontoZechstein salt and normal regional thickness above theformer depocentres in the west (Fig. 4, 10c). Thereforewe suggest that the primary salt-source layer in thenorthwest was exhausted, resulting in the fall of thediapir and the development of a mini-basin with in-creased sedimentary thickness in the intra-raft area. Inthe northern continuation of this zone, the WestdorfGraben, an extreme increase in thickness of UpperBunter to Lower Keuper sediments is described (Ga-ertner and Rohling 1993), that corresponds with a zoneof absent Lower/Middle Bunter sequences (Rohling1991).

West of the intra-raft area we observed erosion, re-duced thickness of Upper Bunter to lowermost MiddleKeuper (KM1) sequences and a crestal collapse struc-ture. Additionally domino-like faulted and tilted blocksof Upper Bunter to Lower/Middle Muschelkalk weredisplaced towards the intra-raft indicating a local dip tothe northwest. We interpret these as the result of thegrowth of a pillow-like salt structure caused by differ-ential loading and lateral basinward salt flow. Theinterpretation of a primary salt pillow at the southeast-ern flank of the intra-raft is further supported by theresults of Best et al. (1993) and Baldschuhn et al. (1991).

Distinct tectonic phases from retro-deformation

Top Zechstein (Fig. 12a) is modelled with �0.3� east-ward dip and Top Rotliegend starts without faults andwith minor relief dipping �0.6� to the east. We assumean original thickness of the Zechstein salt between 820 mand 940 m increasing to the east based on our modellingresults. The assumed amount of salt thickness was re-stored step by step using sedimentary thickness inducedby salt withdrawal as a function of total subsidenceminus regional subsidence. Regional subsidence wasseen as unaffected by local salt diapirism.

The total amount of salt area in our section is notconstant for the different time slices because salt loss isqualitatively observable especially since the beginning ofdeposition of the Stuttgart-Formation (KM2) (Figs. 12and 13). We interpret this as the consequence of thedissolution processes during a phase where the centraldiapir was close to the surface. Out of section move-ments of salt into the perpendicular growing diapir canbe another reason for the changing salt area.

The Lower and Middle Bunter sequences (Fig. 12b)are interpreted to initially completely cover the salt withan eastward thickness increase from 540 m to 760 mcorresponding to the regional dip. The (missing) lightpink area of Lower/Middle Bunter at the eastern enddemonstrates the difference of section length to sequencelength and thus a regional extension between TopMiddle Bunter times and present. Before Upper Buntertimes (Fig. 12c) the first extensional event brought�950 m (�3%) extension in the supra-salt by faultingand rafting, whereas the sub-salt stayed unfaulted.(Differential extension at section scale caused by struc-tural decoupling must be balanced in the complete intra-continental basin (Letouzey et al. 1995). Basementfaulting elsewhere at the basin margin and shortening inthe basin centre can compensate this thin-skinnedextension.) The early stage of extension and rafting ini-tiated reactive salt diapirism, followed by active pierce-ment of thinned overburden and possible salt extrusion(Fig. 12c).

The configuration at the Base Upper Bunter(Fig. 12c) is modelled as either the result of 180� blockrotation of the embedded Bunter block or as the effect oferosion at the eastern edge of the salt structure and 45�counter clockwise rotation of the Bunter block. Bothwere caused by the upward flow of salt.

Sediments of the Upper Bunter covered this early saltdiapir (Fig. 12d) and show a laterally variable thicknessdistribution with increased sedimentary thickness to thewest and a decreased thickness adjacent to the intra-raftdue to differential loading and lateral basinward salt

Fig. 11 Lower part of a depth-migrated W-E seismic section(2D data located in Fig. 3) andgeological interpretation. Forused stratigraphic abbreviationssee Fig. 2. The section showsthe Lower/Middle Buntersequence characterised by alistric fault in the west and acollapsed roll-over anticline.This is interpreted as a startingconfiguration for rafting

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flow. A slight thickness increase to the eastern part ofthe section is interpreted as the result of regional dip tothe east. The Lower/Middle Muschelkalk (Fig. 12e)shows a slight westward migration of its depocentre incomparison to the underlying sequence. The primary

salt source at this stage is nearly exhausted in the wes-tern part of the section.

We interpreted another extensional event before thebeginning of Upper Muschelkalk times (Fig. 12f) thatalso triggered rafting and diapirism. Extension calcu-

Fig. 12 Sequential retro-deformation of the interpreted W-E seismic section (2D data) of Fig. 4 from the base of the uppermost halitelayer of the Weser-Formation (Middle Keuper) (h) to the Top Zechstein (a). See Fig. 13 for the second part of the restoration

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lated from the balancing for this phase was �1650 m(�5.4%). Salt rise was accompanied by drag folding anderosion at the flanks of the Middle Muschelkalk diapir.

An unconformity truncated this sequence before thebeginning of Upper Muschelkalk sedimentation thatcovered the former diapir.

Fig. 13 Sequential retro-deformation of the interpreted W-E seismic section (2D data) of Fig. 4 from the base of the uppermost halitelayer of the Weser-Formation (Middle Keuper) (h) to the present day geometry (o). See Fig. 12 for the first part of the restoration

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Reconstruction to the Top Grabfeld-Formation(KM1) (Fig. 12g) shows major mini-basin growth of�1,100 m above the intra-raft area and eastward adja-cent �300 m erosion down to the Top Middle Buntersequences. Salt flow from the west then stopped initiat-ing the fall of the diapir due to the eastward regional dip.Differential loading, sedimentary prograding and lateralsalt flow resulted in the formation of the Lower Keuperdepocentre, the pillow-like salt structure and the pri-mary rim-syncline in the eastern end of the section.Erosion and faulting at the crestal zone of the saltanticline weakened its roof and provided the possibilityof the collapse of the structure.

Alternative models

An alternative explanation for the Zechstein to MiddleKeuper phase of salt movement and the absence ofLower/Middle Bunter in this area is structurally con-trolled erosion. The development of ‘horst and graben’structures at the end of Middle Bunter produced pri-marily a high position under erosion which evolved to agraben structure before Upper Bunter times (Bald-schuhn et al. 1991). Both should be caused by verticallycoupled basement faulting. However in the sub-saltbasement with the Top Rotliegend horizon as one of thebest interpreted seismic layers no fault system was de-tected which runs parallel to the supra-salt structure(Fig. 10a). The thick salt layer of about 800 m in com-parison to about 450 m of sedimentary overburdenshould mechanically result in a strong decoupling ofsub- and supra-salt instead of vertical coupling of thefaulting, as shown by the analogue modelling of With-jack and Callaway (2000). It seems furthermoreimprobable that during one short tectonic phase ofpresumably less than one million year at least 450 m ofLower/Middle Bunter should have eroded from the topof a structural high that evolved subsequently into agraben.

The early growth of a pillow-like salt structure asanother concept could explain erosion and collapse ofLower/Middle Bunter sediments without extension(Koyi et al. 1993; Coward and Stewart 1995). The iso-lated blocks in between the Lower/Middle Bunter gapcould therefore be the remains of the former cover-sediments (c.f. Hudec and Jackson 2002). But peripheralsinks with changing sedimentary thickness at the flanksof such a hypothetical salt pillow have not been ob-served, and faulted edges of the Bunter blocks showingless erosion do not support this concept.

Static downbuilding, where sediments sink into thesalt layer from the beginning of Bunter times, could beanother possible model. But characteristic features ofsyn-depositional interaction to the adjacent salt area likeconverging reflectors, onlap-structures, salt jags andunconformities at the base of distinctive sedimentaryunits are missing. In contrast, parallel seismic reflectorsare sharply truncated at the edges of the blocks andextensional faults of pre-Upper Bunter age are inter-

preted (Fig. 11). In addition, it is difficult to explain inthis model why Bunter blocks occur inside the down-building diapir.

Second phase of salt movement: Middle Keuper toLower Cretaceous


The second phase of salt movement is interpreted tohave started as the consequence of sub-salt extensionthat triggered normal faulting in the overburden as de-scribed in the concept of reactive diapirism (Vendevilleand Jackson 1992a; Jackson and Vendeville 1994;Stewart and Clark 1999). Previous erosion and faultingon top of a pillow-like salt structure can weaken a par-ticular location to localize supra-salt extension (Cowardand Stewart 1995). Reactive diapirism followed by ashort phase of active diapirism passes into passive dia-pirism (Vendeville and Jackson 1992a), also known asdownbuilding (Barton 1933; Jackson and Talbot 1991;Vendeville and Jackson 1991, 1992a; Buchanan et al.1996). This special type of differential loading involvesdeposition while salt remains close to the surface. Sedi-ments sink into the salt layer, while salt migrates into thegrowing diapir. Passive diapirism ceases only when saltmigration cannot keep up with sedimentation because ofincreasing sedimentation rate or when the evacuation ofsalt forms a salt weld (Rowan et al. 2003). Typical fea-tures are near-diapir onlapping, salt re-sedimentation,increased thickness, unconformities and salt jags at theedge of the down-built sedimentary wedges (Giles andLawton 2002); Rowan et al. 2003).

These concepts are the base for our retro-deforma-tion of salt movement from Middle Keuper to LowerCretaceous times in the working area. Above the majorunconformity at the base of the Stuttgart-Formation(KM2), the depocentres migrated to the flanks of thepresent diapirs. Since then, the sedimentary thicknessdistribution is directed along a NNW-SSE axes parallelto diapir A and B (Fig. 10). The underlying older supra-salt sequences in contrast show erosional surfaces at theflanks of these diapirs and a NNE-SSW to NE-SW di-rected thickness distribution and faulting oblique tolatter structures (Fig. 10). A striking change in structuralpatterns is therefore inferred for the end of the Grabfeld-Formation (KM1). Major faulting in the sub-salt base-ment, seen as the reason for this evolution, formed agraben structure that corresponds to these NNW-SSEstructural direction of the supra-salt. This ‘Early Cim-merian’ extensional phase was caused by intensifiedNorth Sea rifting that brought about major extensionand faulting in the onshore Ems region or in theGluckstadt Graben (Ziegler 1990; Frisch and Kockel1999). Strong dilation was associated with the beginningof major salt diapirism, subsequent rim-syncline devel-opment and extrusion of Zechstein salt in this and many

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other parts of the North German Basin (Frisch andKockel 1999; Baldschuhn et al. 2001; Jaritz 1973).

Seismic indications for the downbuilding phase areMiddle to Upper Keuper sedimentary wedges with basalunconformities and onlap structures as well as salt jagsof the laterally extruded diapirs. The proposed wedgescorrespond to well-known sedimentary cycles and se-quences of the Keuper (Wolburg 1969; Aigner andBachmann 1992). Jurassic sequences onlapping diapir Aand B and covering diapir C indicate slower salt riseprobably caused by exhaustion of the salt source layer.The base Cretaceous unconformity truncated theJurassic at the flanks of the daipirs and the Muschelkalksequences in the west. This is in good agreement with theresults for uplift, tilting and erosion of this area (Kettelet al. 1984) in context of the Upper Jurassic domingevent in the Southern North Sea (Ziegler 1990).


At the end of the Grabfeld-Formation (Fig. 12g, h) thebasement underwent extension by normal faulting andformation of an asymmetric graben structure with themajor faults in the west. The amount of basementextension inferred from balancing was �260 m (0.9%).Basement extension triggered normal faulting andextension in the overburden with an elongation of�1120 m (3.7%). Supra-salt extension is focussed in twozones. One position in the west was a preferential sitebecause it was adjacent to a major basement fault. Itshows low salt thickness and was located above theprevious rafting area. The other zone of focussedextension was already weakened by previous faultingand erosion above the central salt structure. Salt piercedthe overlying sequences as reaction to extension andextruded to the surface, starting a downbuilding processwith peripheral sedimentary sinks as secondary rim-synclines. The following three reconstructions to thebase of the uppermost halite of the Weser-Formation, tothe Top Weser-Formation and to the Top Keuper times(Fig. 13h, i, j) show the central diapir with ongoingdownbuilding and salt at the surface. The migration ofthe local Middle Keuper subsidence-maxima towardsthe diapir indicates the successive collapse of the formersalt pillow. An almost constant sedimentary thickness ofthe sequences west of the diapir suggests less saltmovement on this side. We suggest that outside thegraben structure only a thin section of Middle andUpper Keuper (�120 m) is preserved in the west andnone in the east, in contrast to the area in between (up to1,600 m). The western salt structure could not evolve asa downbuilding diapir because of the exhausted saltsource and is therefore modelled to be already coveredby the Arnstadt-Formation (Fig. 13j). At the easternend of the profile a pillow-like salt structure evolvedabove a westward dipping basement fault since thedeposition of the Weser-Formation (Figs. 13h, i). Nor-mal faulting after sedimentation of the Weser-Forma-

tion resulted in reactive diapirism and subsequentdownbuilding at the easternmost salt structure(Fig. 13j). Ongoing basement extension through theMiddle Keuper ceased before the beginning of the Up-per Keuper.

For restoration to the Top Jurassic time slice(Fig. 13k) the eroded Muschelkalk to Keuper sequencesand a thickness of 550–700 m of Jurassic deposits hasbeen assumed (Kettel et al. 1984). The sub-salt basementis modelled with 1.1� regional dip. The termination ofdownbuilding is proposed for the Middle to UpperJurassic, when salt was completely removed from be-neath the sedimentary pile, salt rise ceased and the diapirwas covered by sediment.

Before the beginning of sedimentation in the LowerCretaceous, more precisely the base Upper Hauterivian(�128 Ma), the last tectonic pulse of the ‘Late Cimme-rian’ phase took place. We modelled this by regionaluplift and tilting (Fig. 13l). Tectonic uplift of 1,170 m inthe west and 650 m in the east produces an �2.1� east-ward-dipping sub-salt basement, which is in goodagreement with the results of Kettel et al. (1984). Thisenabled erosion of most Jurassic sequences, parts of theKeuper and Muschelkalk and the uppermost �160 m ofthe salt diapirs roof.

We interpreted two disconnected Bunter blocks in theCentral salt structure (generated by supra-salt extensionand embedded by Zechstein salt, Fig. 13h–k). Kinematicand geometrical modelling provide no constraints toreconstruct whether these blocks sink into the salt oreven ascend with the rising salt. Using simple mechani-cal considerations based on Stoke’s law, one can esti-mate the velocity of a sinking Bunter block in salt. Forexample, we calculate the velocity for the westerly blockusing 250 m for the radius and 2,500 kg/m3 for thedensity of the Bunter. We used 2,160 kg/m3 as anaverage value for the density of salt. The criticalparameter in the calculation is the salt viscocity whichmay vary between 1017 Pa s for fine grained salt at rel-atively high temperatures and 1020 Pa s for coarsergrained salt at relatively low temperatures (Van Kekenet al. 1993). This results in a steady-state velocity of15 m/Ma to 15·103 m/Ma. The salt’s upward velocity inthe opposite direction is estimated between 1.2·103 m/Ma and 1.0·102 m/Ma for the different time steps. Thesesimple calculations indicate that the Bunter blocks mayor may not sink. For a more accurate constraint, moreprecise data on halite rheology are required.

Alternative models

Erosion of the overlying sediments of a former saltstructure (Coward and Stewart 1995) without extensionis an alternative model for this phase of salt movement.Upper Bunter to lowermost Middle Keuper sequencesshow erosional surfaces at the flanks of the later saltdiapir indicating a reduced thickness and weakening ofthe sedimentary roof. If the overlying sediments were

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thinned enough, salt could be enabled to breakthroughactively by buoyancy effects (Schultz-Ela et al. 1993) andthus starting a downbuilding evolution. We deny theinfluence of erosion as the main trigger mechanism be-cause extension is well documented regionally (Ziegler1990; Frisch and Kockel 1999) and locally, coeval withthe beginning of salt movement in the Middle Keuper.Sedimentary thickness distribution since the depositionof the Stuttgart-Formation (KM2) and orientation ofthe diapirs are directed parallel to this structural pattern.In addition, the erosional features did not effect theLower/Middle Bunter which would be expected, if ero-sion acted as an exclusive trigger mechanism. But it ispossible that erosion played a minor role besidesextension.

Another alternative for the Middle Keuper to LowerCretaceous phase of diapiric growth is the ongoingdownbuilding without extension as the continuation of afirst phase of salt movement. However since the end ofthe deposition of the Grabfeld-Formation (KM1), saltstructures and sedimentary depocentres show completelydifferent three-dimensional orientations (Fig. 10b–d)and the major change from erosion to maximum sedi-mentation at the flanks of diapir A (Figs. 4, 6) is notconsistent with continued downbuilding. Therefore weprefer the oblique collapse of a covered pillow-like saltstructure triggered by extension.

Third phase of salt movement: Lower Cretaceous torecent


The process of this latest phase of salt movement isinterpreted as episodic horizontal shortening of saltstructures (cf. Vendeville and Nilsen 1995; Vendeville2002). Regional compression rejuvenates diapiricgrowth by squeezing the salt structure which is weakerthan the higher-strength sediments laterally adjacent.Deformation is concentrated in the salt structure and inthe sedimentary sequences above. The latter should beaffected by regional shortening and additionally bydiapiric rise. In this model, structural decoupling is

required between sub- and supra-salt, but no additionalsalt source is needed to rejuvenate diapiric growth(Vendeville and Nilsen 1995).

Arguments from seismic data supporting this kind ofmodel in the investigated NW German basin are thepositive relief of the salt structures in relation to theregional datum indicating Cretaceous to Cenozoic up-lift. Peripheral sinks are weakly developed, so that thevolume of rising salt can not be balanced by the volumeof sediment in the peripheral sinks. Sedimentary se-quences above the salt structures show erosionalunconformity surfaces, toplaps and reduced thickness indistinctive layers (Fig. 14). Pairs of conjugate faultsobserved on top of the diapirs can be interpreted as theresult of oblique compression (Fig. 10). Reverse faults,minor folding and arching of layers as well as the for-mation of crestal grabens are interpreted. Argumentsfrom the regional evolution are different phases ofCretaceous to Cenozoic compressional tectonics under aN-S to NE-SW stress field that are well known frominversion of German and Dutch basins (Kockel 2003, deJager 2003). By the iterative process of re-deformationto Base Tertiary and Base Campanian, we first usedvertical shear as the restoration algorithm for a staticpure vertical movement of salt and sediment. In thiscase, vertical shear affects the layers producing anunsatisfying geometry of the diapir and the adjacentsediments. The use of a flexural slip to model a smallamount of shortening reasonably reproduces the previ-ous configuration.


The Lower Cretaceous sedimentary sequence has a slightthickness increase to the West and a reduced dip of thesub-salt basement visible in the restoration to the baseCampanian (Fig. 13m). This trend is observablethroughout the whole Cretaceous (Fig. 13m, n). Sub-surface salt dissolution above areas of subcroping salt ofthe Middle Muschelkalk or Middle Keuper causedwestward dipping normal faults and a local thicknessincrease of the Cretaceous units. Differentiated sedi-mentary thicknesses at the top of the diapirs (Fig. 13m)are also interpreted as a subrosion effect.

Fig. 14 Geologicalinterpretation of the uppermostpart of a depth-migratedseismic section (2D data locatedin Fig. 3). For usedstratigraphic abbreviations seeFig. 2. The top of this sectionrepresents the surface line.Compressional structures areobserved in the Cretaceous andTertiary sequences above diapirC

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Layer thicknesses of the uppermost Cretaceous andPaleogene (Fig. 13n, o) are clearly thinned at the roof ofthe central diapir, accompanied by only minor thicknessincrease at the flanks. This unbalanced diapiric rise of�400 m above the regional datum is modelled as a thin-skinned shortening event (Figs. 13m, n) due to UpperCretaceous and Tertiary compression. Strain is concen-trated in the weak and incompressible salt of thesqueezed and uplifted diapir. Calculated shorteningfrom modelling is around 0.3% (�100 m). We identifiedtwo phases of shortening in the uppermost Cretaceousand in the Paleogene that were finished before thebeginning of Neogene (Fig. 13n, o).

The present-day interpretation (Fig. 13o) as thesource for restoration presents a �1.5� eastward dippingsub-salt basement and a uniform Neogene layer thick-ness. The youngest interpreted time interval shows noindications for salt movement.

Alternative model

An alternative model for this phase of salt structureevolution is active salt diapirism with an attempt ofactive piercement through the overlying sediments(Schultz-Ela et al. 1993). The driving mechanism wouldbe buoyancy without the need of external tectonics. Forsuch salt rise, a relatively thin overburden in relation tothe diapir’s height and width is required. During theCretaceous, continuous salt rise had to decelerate andstop by increased overburden thickness in the Tertiary.In contrast, we interpreted episodic diapiric growth witha minimum of one pulse in the Tertiary. This mechanismalso implies an undepleted salt source layer and syn-sedimentary response to salt flow into the diapir. Ourmodelling results (Fig. 13) and seismic data (Fig. 4, 10e)suggest that no sufficient sedimentary response in termsof peripheral sink development is observable duringCretaceous to recent so that most of the primary salt wasexhausted prior to Cretaceous transgression. Thisargument does not exclude active salt diapirism totally;particularly, it could play a minor role in the lowermostCretaceous sequences. Although the final investigationsare not completed in detail, we propose shortening as thecontrolling factor for Cretaceous to Cenozoic diapiricevolution.

Implications for the evolution of the Central EuropeanBasin system

The results of this study of multiphase salt tectonicevolution from a selected area in NW Germany bearimplications for the entire Central European Basin sys-tem.

Our model suggests that the initial salt movement inthe study area was controlled by extension of the riftingEms sub-basin at the end of the Triassic Middle Buntersequence. Basement faulting at the northwestern marginof the Ems Trough caused decoupled supra-salt faulting

and gravity-gliding along basin dip. Rafting and initialdiapirism were accompanied by differential sedimenta-tion. We suggest a broader distribution of these mech-anisms in other marginal positions, for example at theedge of the Eichsfeld-Altmark Swell, see Fig. 15, wherethe Lower and Middle Bunter sequences are also locallyabsent. Because rifting in the NW German Basin startedalready in early Middle Bunter times (Kockel 2002) thiscould be the time of basinwide initial salt diapirism andrafting.

We observed locally increased sedimentary thicknesssince the Upper Bunter due to differential loading andlateral salt flow. After the salt source was exhaustedupdip of the diapir, salt supply ceased and the fall of thediapir began, accompanied by Lower Keuper to lower-most Middle Keuper mini-basin evolution. Lateral salt-flow produced a pillow-like salt structure at the basin-ward shoulder of the intra-raft area. We also proposethis evolution for the Northern continuation of thestudy area, the Westdorf Graben (Gaertner and Rohling1993). Other rafting events described from the basinwith an assumed Keuper age (Best 1996; Thieme andRockenbauch 2001) could be reconsidered using thisconcept and timing.

Our retro-deformation shows that high extension ofthe supra-salt during the thin-skinned extensional phaseexceeds the value of extension due to basement faulting,and therefore must be balanced by shortening in thebasin centre—associated with reverse faulting andbuckle folding. We suggest that this buckle folding is onemechanism for salt pillow evolution in Bunter andMuschelkalk times, especially if no basement faults aredetected below the salt structure. Figure 15 indicates theLower Triassic basin configuration presenting theLower/Middle Bunter thickness variation below a lev-elling unconformity (Rohling 1991). Expected positionsof these salt pillows are in the centre of the Ems Low.

We described the mechanism where sub-salt faultingcaused extension in the overburden and triggered reac-tive diapirism at the end of the deposition of theGrabfeld-Formation. As overburden faulting is pre-dominantly delocalised due to the decoupling of the saltlayer (Withjack and Callaway 2000), it can be focussedat weakness zones and, therefore, would prefer fracturedcrestal zones of salt pillows if existent. As intensifiedNorth Sea rifting in the Middle Keuper brought aboutmajor extension and faulting in the Ems region and theGluckstadt Graben (Ziegler 1990; Frisch and Kockel1999), this concept of reactive diapirism is proposed forthe breakthrough of mostly Triassic Gluckstadt Grabenand Ems region salt diapirs as well as for Jurassic toLower Cretaceous diapirism due to WNW-ESE strikingbasin evolution.

Following reactive diapirism and diapiric break-through, we observed downbuilding, the passive growthof a diapir near the surface. Usually downbuildingdominates the evolution of most salt diapirs as a self-organised process, without the need of external forces,even if compression and extension play a modifying role

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(Rowan et al. 2003). Typical features are near-diapironlapping, salt re-sedimentation, increased thickness,unconformities and salt jags at the edge of the down-built sedimentary wedges. The peripheral sinks of thediapirs usually preserve these characteristics, but belowsalt-overhangs they are difficult to detect in seismic data.We expect that most of the diapirs in the NW Germanbasin have a long-term downbuilding history subsequentto diapiric breakthrough, which resulted in a complexsalt-sediment interface and diapir geometry. The saltjags we interpreted from seismic data are sedimentaryfeatures of an extrusive diapir evolving from low accu-mulation rates in relation to the salt rise rates. Thisfeature should not be confused with the phenomenon ofwedge-shaped intrusions of Zechstein salt into Mesozoicsalt layers caused by compressional tectonics (Kockel1998), which is well known from parts of the basin whichsuffered strong inversion tectonics (Baldschuhn et al.2001).

Our results are consistent with a small influence ofUpper Cretaceous to Paleogene compressional tectonicson salt movement in the study area. The diapirs wereshortened and uplifted while the overlying sedimentswere faulted and folded. Reactivation of salt movementis possible due to thin-skinned compression (Vendevilleand Nilsen 1995). Decoupled compression responsiblefor Late Cretaceous pillow growth in the NE Germanbasin (Kossow and Krawczyk 2002; Scheck et al. 2003)leads to the squeezing of diapirs with narrowing of theirnecks, up-doming roofs and typical mushroom geome-tries in areas hardly affected by basin inversion. As abasinwide feature, late salt movement produced a posi-tive relief of the base Upper Cretaceous or base Tertiaryabove salt structures in relation to the regional datum.This should be reconsidered in the context of compres-sional tectonics and should be quantified by balancing inorder to get a better understanding of strain distributionin the basin.

Discussion

Our data set, predominantly consisting of reflectionseismic data, allows non-unique interpretations in somecases. Although near-diapir data can show artefacts ofprocessing or non-traceable reflectors, the depth-mi-grated seismic data, including a 3D block and repro-cessed 2D lines, is of high quality and provides themaximum resolution available today.

The restoration technique used has specific restric-tions which should be kept in mind when interpretingthe results. For example salt kinematics are not con-trolled by the mechanics of salt flow (Urai et al. 1986,1987; Carter et al. 1993; Spiers and Carter 1998).Therefore, it is possible to have different interpretationswhich can all be balanced, but restoration does enable toexclude impossible interpretations. The model presentedin this paper is consistent with all known regional andseismic constraints and fits to the current concepts in salttectonics and is therefore preferred.

We interpret regional tectonic movements as thetriggering and controlling factor for all three phases ofsalt movement. Strong changes of seismic patterns atdistinctive times coincide with timing and patterns ofregional tectonic events. The first extensional phase withfaulting and rafting of pre-Upper Bunter and pre-UpperMuschelkalk age is in agreement with the rifting of theEms sub-basin (Kockel 2002; Geluk and Rohling 1997).Subsequent salt tectonic evolution until Middle Keuperis interpreted as the consequence of extension andgravity-gliding. The second phase of extension and salttectonics is marked by a structural pattern oblique to theprevious one, a major unconformity and an entirelydifferent sedimentary thickness distribution. The ob-served extensional event fits well with models of theformation of the Ems-Graben (Frisch and Kockel 1999)due to incipient North Sea rifting (Ziegler 1990).

Fig. 15 North German Basinsubcrop map of the stratabeneath the uppermost MiddleBunter indicating the basinconfiguration before thelevelling erosional event (H-unconformity) (after Geluk andRohling 1997). The study area(inside the rectangle) is locatedat the margin of the Ems Low,marked by raft tectonics(ellipse). We suggest that therafting implicates pillow growthin the centre of the Ems Low;see text for explanation

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Downbuilding events subsequent to reactive diapirismproduced geometries of diapirs and peripheral sinksparallel to the structural pattern.

Middle Jurassic to Lower Cretaceous uplift and tilt-ing, as a consequence of regional thermal doming andstrike-slip movements (Ziegler 1990) is only indicated inthe data by a major erosional unconformity. Structuresindicating local faulting or salt movements are not pre-served. This is interesting, because an active, transpres-sive stress regime can be expected to have reactivated thegrowth of the covered salt structures (Letouzey andSherkati 2004; Vendeville and Nilsen 1995).

The last phase of structurally-controlled salt move-ment is indicated by the Cretaceous and Tertiary salt riseand faulting above the diapirs. This phase correlates wellwith the regional phases of inversion in the German andDutch basins (Kockel 2003; de Jager 2003).

Our balanced reconstruction preserving length andthickness of layers shows thin-skinned extension at dis-tinctive times due to regional dip and decoupling by thesalt layer. There is no need for near-field faulting be-neath the salt structures to initiate tectonically drivensalt movement. For the early phase of salt movement, wereject downbuilding and rather find evidence for raftingand lateral salt flow as the important mechanism.

In comparison, the Late Devonian to TertiaryDniepr-Donets Basin as another intra-continental basinshows similarities in both basin and salt tectonic evo-lution to the study area in NW Germany. Stovba andStephenson 2002 have pointed out that in the Dniepr-Donets Basin, salt movement was similarily episodicaland tectonically triggered by phases of extension andcompression. Basement faulting and structural decou-pling by the salt layer on the one hand and sedimenta-tion rate and salt supply on the other hand had a stronginfluence on the configuration of salt structures andsedimentary cover sequences (Stovba and Stephenson2002). In contrast to the NW German basin with a post-rift Permian salt accumulation (van Wees et al. 2000)and first salt movement during Middle Bunter due torenewed rifting, both salt deposition and initial saltmovement in the Dniepr-Donets Basin occurred duringsyn-rift (Stovba and Stephenson 2002).

Conclusions

– Our analysis demonstrates a complex, multiphase salttectonic evolution in changing regional stress fields.Each phase was initiated by regional tectonics andwould not have evolved into the next phase withoutthis tectonic driver. An autonomous evolution in thesense of Trusheim’s halokinetic model (1957, 1960) isnot supported by our data.

– A first phase of salt movement was initiated by riftingof the Ems Basin at the end of Middle Bunter thatproduced NE-SW faulting and rafting in the over-burden.

– Decoupled extension was accompanied by first saltdiapirism, lateral salt flow and differential sedimen-tation with increased sedimentary thickness. After thesalt source was exhausted updip to the intra-raft, saltsupply ceased, the diapir fell and a mini-basin grew.This differential loading caused lateral salt flow andthe growth of a NE-SW directed pillow-like saltstructure basinward-adjacent.

– Two extensional phases before Upper Bunter andbefore Upper Muschelkalk times can be differentiatedby their sedimentary and structural response. Wecalculate thin-skinned extension of �8.4%. We sug-gest, that this thin-skinned extension was associatedwith compressional structures and pillow growth inthe centre of the Ems Low.

– The second phase of salt movement was caused by theformation of a NNW-SSE striking basement graben(Ems-Graben) before the deposition of the Stuttgart-Formation oblique to the older structures. Sub-saltfaulting triggered supra-salt extension focussed inweakness zones and was accompanied by reactivediapirism, breakthrough and extrusions of salt.

– Subsequent downbuilding formed sedimentary wed-ges, salt extrusions, unconformities and onlap-struc-tures. This structurally autonomous downbuildingprocess was terminated in the Jurassic when the saltwas totally depleted and the diapir was buried bysediment.

– No salt tectonic activity is recorded in the supra-saltas reaction to Middle Jurassic to Lower Cretaceoustectonics because regional uplift and tilting causedhigh amounts of erosion and salt dissolution at thediapir’s roof.

– Upper Cretaceous to Lower Tertiary compressionaltectonics reactivated vertical salt movement leading toa small amount of diapir shortening.

Acknowledgements We thank GDF Produktion Exploration Deu-tschland, EMPG and EWE Aktiengesellschaft for providing ahigh-quality data set and the Deutsche Forschungsgemeinschaftand the SPP 1135 (Dynamik sedimentarer Systeme unter wech-selnden Spannungsregimen am Beispiel des zentraleuropaischenBeckensystems) for financial support (KU 1476/1–1). MidlandValley Exploration Ltd. is thanked for their software support.M.R. Hudec (Austin) and Ch. Krawczyk (Potsdam) are thankedfor their comments and remarks which greatly helped to improvethis paper. This is publication no. GEOTECH-124 of the pro-gramme GEOTECHNOLOGIEN of BMBF and DFG.

References

Aigner T, Bachmann GH (1992) Sequence-stratigraphic frameworkof the German Triassic. Sediment Geol 80:115–135 DOI:10.1016/0037-0738(92)90035-P

Arrhenius S, Lachmann R (1912) Die physikalisch-chemischenBedingungen der Bildung von Salzlagerstatten und ihre An-wendung auf geologische Probleme. Geol Rund 3:139–157

Baldschuhn R, Best G, Kockel F (1991) Inversion tectonics in theNorth-west German basin. In: Spencer AM (ed) Generation,accumulation, and production of Europe’s hydrocarbons. SpecPubl Eur Assoc Petroleum Geosci 1:149–159

938

Baldschuhn R, Binot F, Fleig S, Kockel F (2001) GeotektonischerAtlas von NW-Deutschland und des deutschen Nordsee-Sek-tors. – Strukturen, Strukturentwicklung, Palaogeographie. GeolJb A 153:1–40

Barton DC (1933) Mechanics of formation of salt domes withspecial reference to Gulf coast salt domes of Texas and Loui-siana. AAPG Bull 17:1025–1083

Best G, Rohling HG, Bruckner-Rohling S (1993) SynsedimentareTektonik und Salzkissenbildung wahrend der Trias in Nord-deutschland. In: Hagdorn H, Seilacher A (eds) Muschelkalk.Schontaler Symposium 1991. Goldschneck Verlag, Stuttgart, p37

Best G (1996) Floßtektonik in Norddeutschland: Erste Ergebnissereflexionsseismischer Untersuchungen an der Salzstruktur‘‘Oberes Allertal’’. Z dt geol Ges 147:455–464

Beutler G (1998) Keuper. Hallesches Jahrbuch fur Geowissens-chaften B6:45–58

Brink HJ, Duerschner H, Trappe H (1992) Some aspects of the lateand post-Variscan development of the northwestern GermanBasin. Tectonophysics 207:65–95. DOI: 10.1016/0040–1951(92)90472-I

Buchanan PG, Bishop DJ, Hood DN (1996) Development of salt-related structures in the central North Sea; results from sectionbalancing. Geol Soc Spec Publ 100:111–128

Carter NL, Horseman ST, Russell JE, Handin J (1993) Rheologyof rocksalt. J Struct Geol 15:1257–1271. DOI: 10.1016/0191-8141(93)90168-A

Coward M, Stewart S (1995) Salt-influenced structures in theMesozoic-Tertiary cover of the southern North Sea, U.K. In:Jackson MPA, Roberts DG, Snelson S (eds) Salt tectonics; aglobal perspective. AAPG Memoir 65:229–250

De Jager J (2003) Inverted basins in the Netherlands, similaritiesand differences. Geol Mijnbouw-N J G 82:355–366

Frisch U, Kockel F (1999) Early Cimmerian movements inNorthwest Germany. Zbl Geol Palaont I:571–600

Gaertner H, Rohling HG (1993) Zur lithostratigraphischen Gli-ederung und Palaogeographie des Mittleren Muschelkalks imNordwestdeutschen Becken. In: Hagdorn H, Seilacher A (eds)Muschelkalk. Schontaler Symposium 1991. Goldschneck Ver-lag, Stuttgart, pp 85–103

Gast RE (1988) Rifting im Rotliegenden Niedersachsens. DieGeowissenschaften 6:115–122

Ge H, Jackson MPA, Vendeville BC (1997) Kinematics anddynamics of salt tectonics driven by progradation. AAPG Bull81:398–423

Geluk MC, Roehling HG (1997) High-resolution sequence stra-tigraphy of the Lower Triassic ’Buntsandstein’ in the Nether-lands and northwestern Germany. Geol Mijnbouw 76:227–246DOI: 10.1023/A:1003062521373

Geluk MC (1999) Late Permian (Zechstein) rifting in the Nether-lands: models and implications for petroleum geology. PetrolGeosci 5:189–199

Geluk MC, Brueckner-Roehling S, Roehling HG (2000) Saltoccurrence in the Netherlands and Germany: new insights in theformation of salt basins. In: Geertmann M (ed) 8th world saltsymposium, vol 1, pp 125–130

Giles KA, Lawton TF (2002) Halokinetic sequence stratigraphyadjacent to the El Papalote diapir, northeastern Mexico. AAPGBull 86:823–840

Hossack J (1995) Geometric rules of section balancing for saltstructures. In: Jackson MPA, Roberts DG, Snelson S (eds) Salttectonics; a global perspective. AAPG Memoir 65:29–40

Hudec MR, Jackson MPA (2002) Structural segmentation, inver-sion, and salt tectonics on a passive margin; evolution of theinner Kwanza Basin, Angola. GSA Bull 114:1222–1244

Jackson MPA (1995) Retrospective Salt Tectonics. In: JacksonMPA, Roberts DG, Snelson S (eds) Salt tectonics; a globalperspective. AAPG Memoir 65:1–28

Jackson MPA, Talbot CJ (1991) A glossary of salt tectonics.University of Texas at Austin, Bureau of Economic GeologyGeological Circular 91-4, pp 1–44

Jackson MPA, Talbot CJ (1994) Advances in salt tectonics. In:Hancock PL (eds) Continental deformation. Pergamon Press/International Union of Geological Sciences, Oxford, pp 159–179

Jackson MPA, Vendeville BC (1994) Regional extension as ageologic trigger for diapirism. Geol Soc Am Bull 106:57–73.DOI:10.1130/0016-7606(1994)106<0057:REAAGT>2.3.CO;2

Jaritz W (1973) Zur Entstehung der Salzstrukturen Nord-westdeutschlands. Geol Jb A 10:1–77

Jaritz W (1987) The origin and development of salt structures inNorthwest Germany. In: Lerche I, O’Brien JJ (eds) Dynamicalgeology of salt and related structures. Academic, Orlando, pp479–493

Jaritz W (1992) Fortschritte und offene Fragen zur Entstehung derSalzstrukturen NW-Deutschlands. Veroff Nieders Akad Geo-wiss 8:16–24

Kettel D, Devay L, Block M, Schroder L, Porth H, Cordes R,Dorn M, Stancu-Kristoff G (1984) Untersuchungen zur Erd-gaslagerstaettenbildung in der Nordfortsetzung der unterper-mischen Emssenke. Forschungsbericht, BMFT 84–259, pp 1–90

Kockel F (1998) Salt problems in NW-Germany and the GermanNorth Sea Sector. J Seismic Explor 7:219–235

Kockel F (2002) Rifting processes in NW-Germany and the Ger-man North Sea Sector. Geol Mijnbouw-N J G 81:149–158

Kockel F (2003) Inversion structures in Central Europe—expres-sions, reasons, an open discussion. Geol Mijnbouw-N J G82:367–382

Kossow D, Krawczyk CM (2002) Structure and quantification ofprocesses controlling the evolution of the inverted NE-GermanBasin. Mar Petrol Geol 19:601–618. DOI: 10.1016/S0264-8172(02)00032-6

Kossow D, Krawczyk C, McCann T, Strecker M, Negendank JFW(2000) Style and evolution of salt pillows and related structuresin the northern part of the Northeast German Basin. Int J EarthSci 89:652–664. DOI: 10.1007/s005310000116

Koyi H, Jenyon MK, Petersen K (1993) The effect of basementfaulting on diapirism. J Petrol Geol 16:285–311

Letouzey J, Colletta B, Vially R, Chermette JC (1995) Evolution ofsalt-related structures in compressional settings. In: JacksonMPA, Roberts DG, Snelson S (eds) Salt tectonics; a globalperspective. AAPG Memoir 65:41–60

Letouzey J Sherkati S (2004) Salt movement, tectonic events, andstructural style in the central Zagros fold and thrust belt (Iran).In: Post PJ (ed) 24th annual GCSSEPM research conference2004, pp 90–118

Lokhorst A (ed) (1999) NW European gas atlas CD-Rom. Bund-esanstalt fur Geowissenschaften und Rohstoffe, Hannover

Meinhold R, Reinhardt HG (1967) Halokinese im Nordostdeuts-chen Tiefland. Ber dt Ges geol Wiss, A, Geol Palaont 12:329–353

Menning M, German Stratigraphic Commission (2002) A geologictime scale 2002. German Stratigraphic Commission Strati-graphic Table of Germany 2002

Midland Valley (2002) 2DMove3.1. Midland Valley ExplorationLtd. Glasgow

Rohling HG (1991) A lithostratigraphic subdivision of the LowerTriassic in the North-west German Lowlands and the GermanSector of the North Sea, based on gamma ray and sonic logs.Geol Jb A 119:3–24

Rowan MG (1993) A systematic technique for the sequential res-toration of salt structures. Tectonophysics 228:331–348.DOI:10.1016/0040-1951(93)90347-M

Rowan MG, Lawton TF, Giles KA, Ratliff RA (2003) Near-saltdeformation in La Popa basin, Mexico, and the northern Gulfof Mexico: a general model for passive diapirism. AAPG Bull87:733–756

Ruhberg N (1976) Probleme der Zechsteinsalzbewegung. Z AngewGeol 22:413–420

Sannemann D (1968) Salt-stock families in northwestern Germany.AAPG Memoir 8:261–270

939

Schafer F, Griffiths PA, Osborn R (1998) Balancing salt structuresin 3D. DGMK-Mintrop-Seminar 18:69–107

Scheck M, Bayer U., Lewerenz B (2003) Salt movements in theNortheast German Basin and its relation to major post-Perm-ian tectonic phases; results from 3D structural modelling,backstripping and reflection seismic data. Tectonophysics361:277–299. DOI: 10.1016/S0040-1951(02)00650-9

Schultz-Ela DD, Jackson MPA, Vendeville B (1993) Mechanics ofactive salt diapirism. Tectonophysics 228:275–312. DOI:10.1016/0040-1951(93)90345-K

Spiers CJ, Carter NL (1998) Microphysics of rocksalt flow innature. In: Aubertin M, Hardy HR Jr (eds) The mechanicalbehaviour of salt. Proceedings of the 4th conference, vol 22, pp115–128

Stewart SA, Clark JA (1999) Impact of salt on the structure of thecentral North Sea hydrocarbon fairways. In: Fleet AJ, BoldySAR (eds) Petroleum geology of Northwest Europe. Proceed-ings of the 5th conference, vol 5, pp 179–200

Stille H (1910) Faltung des Deutschen Bodens und des Salzgebir-ges. Kali Zeitschrift 5:17

Stille H (1925) The upthrust of the salt masses of Germany. AAPGBull 9:417–441

Stovba SM, Stephenson RA (2002) Style and timing of salt tec-tonics in the Dniepr–Doucts Basin (Ukraine) implications fortriggering and driving mechanisms of salt movement in sedi-mentary basins. Mar Petrol Geol 19:1169–1189. DOI:10.1016ISO264-8172(03)00023-0

Thieme B, Rockenbauch K (2001) Floßtektonik in der Trias derDeutschen Sudlichen Nordsee. Erdol Erdgas Kohle 117:568–573

Trusheim F (1957) Uber Halokinese und ihre Bedeutung fur diestrukturelle Entwicklung Norddeutschlands. Z dt geol Ges109:111–151

Trusheim F (1960) Mechanism of salt migration in northern Ger-many. AAPG Bull 44:1519–1540

Urai JL, Spiers CJ, Zwart HJ, Lister GS (1986) Weakening of rocksalt by water during long-term creep. Nature 324:554–557

Urai JL, Spiers CJ, Peach C, Franssen RCMW, Liezenberg JL(1987) Deformation mechanisms operating in naturally de-formed halite rocks as deduced from microstructural investi-gations. Geol Mijnbouw 66:165–176

Van Keken PE, Spiers CJ, Van den Berg AP, Muyzert EJ (1993)The effective viscosity of rocksalt: implementation of steady

state creep laws in numerical models of salt diapirism. Tec-tonophysics 225: 457–476. DOI:10.1016/0040-1951(93)90310-G

Van Wees JD, Stephenson RA, Ziegler PA, Bayer U, McCann T,Dadlez R, Gaupp R, Narkiewicz M, Bitzer F, Scheck M (2000)On the origin of the Southern Permian Basin, Central Europe.Mar Petrol Geol 17:43–59. DOI: 10.1016/S0264-8172(99)00052-5

Vendeville BC (2002) A new interpretation of Trusheim’s classicmodel of salt-diapir growth. Trans Gulf Coast Assoc Geol Soc52:943–952

Vendeville BC, Jackson MPA (1991) Deposition, extension, andthe shape of downbuilding salt diapirs. AAPG Bull 75:687–688

Vendeville BC, Jackson MPA (1992a) The rise of diapirs duringthin-skinned extension. Mar Petrol Geol 9:331–353. DOI:10.1016/0264-8172(92)90047-I

Vendeville BC, Jackson MPA (1992b) The fall of diapirs duringthin-skinned extension. Mar Petrol Geol 9:354–371. DOI:10.1016/0264-8172(92)90048-J

Vendeville BC, Nilsen KT (1995) Episodic growth of salt diapirsdriven by horizontal shortening. Society of economic paleon-tologists and mineralogists, Gulf Coast section, 16th annualresearch conference program and extended abstracts, pp 285–295

Weijermars R, Jackson MPA, Vendeville B (1993) Rheological andtectonic modeling of salt provinces. Tectonophysics 217:143–174. DOI: 10.1016/0040-1951(93)90208-2

Withjack MO, Callaway S (2000) Active normal faulting beneath asalt layer: an experimental study of deformation patterns in thecover sequence. AAPG Bull 84:627–651

Wolburg J (1969) Die epirogenetischen Phasen der Muschelkalk-und Keuper-Entwicklung Nordwest-Deutschlands, mit einemRuckblick auf den Buntsandstein. Geotektonische Forschungen32:1–64

Woodward NB, Boyer S, Suppe J (1989) Balanced geological cross-sections: an essential technique in geological research andexploration. American Geophysical Union: Short Course inGeology 6, Washington, pp 1–132

Ziegler PA (1990) Geological atlas of Western and Central Europe(2). Bath: Shell International Petroleum Mij, BV dist by GeolSoc Publ House, pp 239

Zirngast M (1996) The development of the Gorleben salt dome(Northwest Germany) based on quantitative analysis ofperipheral sinks. Geol Soc Spec Publ 100:203–226

940

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