3d seismic study of complex intra-salt deformation: an ... · we used the seismic interpretation...

Geological Society, London, Special Publications

doi: 10.1144/SP363.23p489-501.

2012, v.363;Geological Society, London, Special Publications F. Strozyk, H. Van Gent, J. L. Urai and P. A. Kukla western Dutch offshoreexample from the Upper Permian Zechstein 3 stringer, 3D seismic study of complex intra-salt deformation: An

serviceEmail alerting

new articles cite this article to receive free e-mail alerts whenhereclick

requestPermission

part of this article to seek permission to re-use all orhereclick

SubscribeCollection London, Special Publications or the Lyell

to subscribe to Geological Society,hereclick

Notes

© The Geological Society of London 2013

at RWTH Aachen on February 19, 2013http://sp.lyellcollection.org/Downloaded from

http://www.lyellcollection.org/cgi/alerts

http://www.geolsoc.org.uk/en/Publications/Permissions

http://sp.lyellcollection.org//site/subscriptions/

http://sp.lyellcollection.org/

3D seismic study of complex intra-salt deformation: An example fromthe Upper Permian Zechstein 3 stringer, western Dutch offshore

F. STROZYK1,2*, H. VAN GENT2, J. L. URAI2 & P. A. KUKLA1

1Structural Geology, Tectonics and Geomechanics, RWTH Aachen University,

Lochnerstraße 4-20, Haus A, D-52056 Aachen, Germany2Geological Institute, RWTH Aachen University, Wullnerstraße 2, D-52056 Aachen, Germany

*Corresponding author (e-mail: [email protected])

Abstract: Most of the information on subsurface evaporitic structures comes from 3D seismic data.However, this data only provide limited information about the internal structure of the evaporites,which is known from salt mines and salt diapir outcrops. Brittle intra-salt layers (carbonate, anhy-drite, clay) of at least 10 m thickness form good reflectors in evaporites, but the structure and dynam-ics of such ‘stringers’ in the salt movement are poorly understood. In this study, we investigate theintra-salt Zechstein 3 (Z3) stringer from 3D seismic data in an area offshore the Netherlands.Observations show complex deformation including boudinage, folding and stacking. Reflectionsfrom thin and steep stringer parts are strongly reduced, and we present different structural modelsand tests of these. We compare our observations to structural models from salt mines and analogue/numerical models of intra-salt deformation. A smoothed representation of the upper surface of thestringer fragments follows the shape of Top Salt, but smaller-scale stringer geometries stronglydiffer from this and imply boudinage. The imaged disharmonic patterns of constrictional folds pro-vide evidence for the complexity of the intra-salt, in agreement with observations in salt mines.This may be explained by interaction of the layered salt rheology, complex three-dimensional saltflow, different phases and styles of basement tectonics and movement of the overburden.

The Southern Permian Basin in NW Europe is aclassic area of salt tectonics (Ziegler 1990; Taylor1998; Mohr et al. 2005; De Jager 2007; Geluket al. 2007; Hubscher et al. 2007; Littke et al.2008). Its evolution regarding salt tectonics stronglydiffers from what can be observed in passive-marginsettings (e.g. Nigeria, Gulf of Mexico; Hubscheret al. 2007; Littke et al. 2008). The Dutch offshorepart of the basin, where the study area is located(Fig. 1a), contains at least the lower four of the eva-poritic cycles of the Late Permian Zechstein Groupwith a total thickness of 400–1000 m in c. 1.5–3 km depth (Z1–Z4, locally maybe Z5; Fig. 1b).The thick and dominant Z3 cycle contains a rela-tively brittle layer of anhydrite, carbonate andclay, which is fully encased in massive halite (‘strin-ger’). Whereas the Z1, Z2 and Z4 are also localreflectors, Z1 and Z2 are mechanically coupledto the underburden and the Z4 (+Z5) to the over-burden. However, the Z3 stringer reflectors aremechanically decoupled from the sub- and supra-salt sediments (van Gent et al. 2011; Fig. 1b).According to Taylor (1998) salt movement ismainly accommodated by flow of Z2 salt, whereasthe Z3 and Z4 salts are more or less ‘passively’ dis-placed. Halokinesis strongly influenced the geome-try of the Z3 stringer (Geluk 1995; Burliga 1996;Behlau & Mingerzahn 2001; Bornemann et al.

2008; van Gent et al. 2011). The Z3 stringer in theDutch offshore further shows a large variety oflocally restricted and strongly varying deformationfeatures, such as boudinage and folding associatedwith compression or shearing and extension orshearing, respectively (in the sense of Zulauf &Zulauf 2005; Zulauf et al. 2009). These featureshave been associated with the formation of saltdomes, walls and pillows (Geluk 2000b; Geluket al. 2007; van Gent et al. 2011) as well as exten-sional Z2 and Z3 salt thinning and supra-salt sedi-ment basin growth (compare to data in e.g. Mohret al. 2005). Similar structures have been observedin salt mines (e.g. Fulda 1928; DeBoer 1971;Richter-Bernburg 1972; Schleder & Urai 2005;Schleder 2006; Alsop et al. 2007; see alsoFig. 2d). Field data is given by salt diapirs outcrop-ping, for example, in the Iranian Dasht-e-Kavir(Jackson et al. 1990) and Zagros Mountains (Kent1979) in Oman (Reuning et al. 2009; Schoenherret al. 2009) and in the Spanish Pyrenees (Wagneret al. 1971), which may represent analogues forburied salt structures (Geluk 2000b).

Nevertheless, the structure of the intra-salt is stillpoorly understood in comparison to the externalshape of salt structures. Field observations showcomplex folding and rupturing of an initiallymore or less continuous stringer, while modern

From: Alsop, G. I., Archer, S. G., Hartley, A. J., Grant, N. T. & Hodgkinson, R. (eds) 2012. Salt Tectonics, Sedimentsand Prospectivity. Geological Society, London, Special Publications, 363, 489–501. http://dx.doi.org/10.1144/SP363.23# The Geological Society of London 2012. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics



Fig. 1. (a) Location map of the study area (red dot) and main structural elements after De Jager (2007; image courtesy ofthe Nederlandse Aardolie Maatschappij) and Z3 palaeogeography (after Geluk 2000a) in its vicinity offshore Dutch,modified after van Gent et al. (2011). (b) Zechstein stratigraphy in the Netherlands (after Geluk 2007; based on VanAdrichem-Boogaert & Kouwe 1993–1997; Geluk 2000; TNO-NITG 2004). The red dot marks the projected position ofthe study site. In the right column the position of the seismically imaged stratigraphic units is indicated. Note that onlythe Z3 stringer is visible in seismic reflection data and is fully encased in Z2 and Z3 + Z4 halite.

F. STROZYK ET AL.490



Fig. 2. Depth maps of Top Salt (A), Z3 top stringer (B) and top pre-salt/Base Salt (C) in the study area modified after van Gent et al. (2011). (a) Interpolated interpretation surfaceof the Zechstein Top Salt. Prominent features are the SSW–NNE-trending salt wall in the centre, the adjacent deep rim syncline at the wall’s eastern flank and several largersalt domes and pillows mainly in the NW and SE area (see also Fig. 3a). (b) The interpreted Z3 stringer surface is a highly fragmented (‘floaters’) and seismically invisible in largeparts, especially in the area of the central N–S salt wall as well as in other areas of prominent salt structures. In contrast, the stringer is well-imaged and smoother in, for example,the south-western area. (c) Interpolated interpretation surface of the top pre-salt corresponding to the Base Salt. Note the dominance of SE–NW-trending graben and upthrownblocks and some minor faults trending approximately SSW–NNE. (d) Example of the saltminer’s view on the internal structure of salt: schematic profile through a salt dome afterSeidl (1921). Note the complexity of folding of a continuous stringer layer (black).

3D

SE

ISM

ICS

TU

DY

OF

CO

MP

LE

XIN

TR

A-S

AL

TD

EF

OR

MA

TIO

N491

at RWTH

Aachen on February 19, 2013

http://sp.lyellcollection.org/D

ownloaded from


high-resolution 3D seismic data display a strongfragmentation of stringers (van Gent et al. 2011).Consequently, commercial drilling through theZechstein is seriously hindered by unexpected strin-gers and related pressure kicks form major drillinghazards (Williamson et al. 1997; see also data inKukla et al. 2011). In this study we aim to under-stand the complex geometries of the highlydeformed Z3 stringer in the western Dutch offshore.We discuss our interpretation and the potential to(1) identify and trace the highly deformed intra-saltstringer in 3D seismic data and (2) quantify part ofits deformation pattern compared to what is knownof salt flow regimes both inside and outside majorsalt structures and intra-salt observations in saltmining. The results contribute to an understandingof 3D intra-salt structures and to novel non-destructive prediction methods of intra-salt struc-tures before the creation of underground openings.

Methods

We used the seismic interpretation package Petrel2007 and 2009 (Schlumberger) to study a PSDM(pre-stack depth-migrated) 3D seismic volume ofc. 20 ! 20 km2 area and 3.5 km depth (Fig. 2). Thelateral and vertical minimum resolution is of theorder 20 m. Because of a high acoustic impedancecontrast between the Z3 stringer (carbonate, anhy-drite, clay) and the Z2 and Z3 salts above andbelow, the double-reflector Z3 stringer is reasonablywell imaged in the seismic data. However, there areimportant imaging limitations related to the seismicquality and resolution (frequency content, noiselevel, processing details), but also regarding steeplydipping, thin parts of the stringer (Sleep & Fujita1997; van Gent et al. 2011). Hence, if the thicknessof the stringer is much below the tuning thicknessof c. 30–35 m, it is not visible or has weak contrastand a careful interpretation is required. This also con-cerns the internal structure of the stringer, as theboundary between anhydrite (top) and carbonate(base) is mostly below the resolution of the data. Fur-thermore, the Base Salt and Top Salt are both strongreflectors and can locally lead to mistakes in inter-pretation of stringers in areas where they are closeto the top or the bottom of the salt.

To trace the Z3 stringer we combined differentinterpretation techniques comprising manual horizon

interpretation, 3D autotracking and surface interp-olation. In areas of intense folding and overlapping(stacking) of stringer fragments (see Fig. 2b),additional horizons were implemented. Alterna-tively, a ‘fault interpretation’ routine was carriedout allowing for doubled z-values, which are notallowed using conventional surface interpretation.Based on the resulting high-density point cloud, weinterpolated the top stringer fragments to a surface‘A’ (Fig. 3b) and smoothed it to a surface ‘B’(Fig. 3c). Surface B is similar to the concept of anenveloping surface (Park 1997) whereas in this caseit cuts through the stringer and does not cover it.The surfaces then enable a comparison of the local(surface A) and the regional (surface B) stringergeometry to that of the Top Salt (e.g. Fig. 3b). Asproposed by van Gent et al. (2011) we adopt theconcept of differences in thicknesses, geometriesand structural styles of the bottom and the top reflec-tor being associated with the Z3 carbonate (ZEZ3C)and the anhydrite (ZEZ3A), respectively.

Study area

The study area is located in the Dutch offshore (areaintroduced by van Gent et al. 2011 as ‘western off-shore’; Fig. 2) on the Cleaver Bank High, directlynorth of the Broad Fourteens basin, and is in closeproximity of the Sole Pit Basin and the CentralGraben (Fig. 1a). Although these basins wereinverted in the Cretaceous and Tertiary, the studyarea is located outside the area of erosion and thusappears less affected by those features (e.g. Geluk2000a, 2005; de Jager 2003, 2007). During theLate Carboniferous, the Cleaver Bank High wastectonically active and uplifted. Between thePermian and the Middle Jurassic the Cleaver BankHigh experienced no significant tectonic activity,but during the Late Jurassic–Early Cretaceous theCleaver Bank High was uplifted and deeplyeroded (Ziegler 1990). For more details of theregional settings, the stratigraphy and rheology ofthe Dutch offshore Zechstein, refer to de Jager(2003) and Geluk (2000a, 2005, 2007).

Pre-salt and Top Salt

On a regional scale, mapping of the reflector that rep-resents the base of the salt section or the top of its

Fig. 3. (a) 3D view from south on the interpreted Top Salt surface (see also Fig. 2a) combined to a z-slice of theinvestigated seismic volume in c. 2 km depth. The prominent N–S-trending salt wall and the adjacent rim syncline inthe centre of the study area are most likely responsible for the bulk of the salt drainage in this area. Large salt domes inthe NW and SE and minor salt pillows in the NE and SW area are seen to provide a superimposed, complex saltmovement. (b) 3D south view of the Top Salt (coloured fishnet) and the interpolated Z3 top stringer surface below(surface A). This stringer surface images complex patterns of folds and strictly differs from the Top Salt (see e.g.Fig. 6a). (c) Interpolated stringer surface A (coloured) and the smoothed surface B (grey), which follows the Top Salt.

3D SEISMIC STUDY OF COMPLEX INTRA-SALT DEFORMATION 493



underburden displays SE–NW-striking graben struc-tures and upthrown blocks, which have been associ-ated with the Mesozoic tectonic inversion of theBroad Fourteens basin (van Gent et al. 2011;Fig. 2c). Furthermore, subordinate faults strikingESE–WNW and SW–NE are present (de Jager2003; Schroot & De Haan 2003; van Gent et al.2011; Fig. 2c). These structural features have beenassociated with multiple phases of tectonic move-ments in the pre-salt (e.g. Geluk 2000a, 2005). Domi-nant structural features of the Top Zechstein (Figs 2a& 3a, b) are a large NE–SW-striking salt wall whichhas a listric fault and asymmetric graben at its crest,an asymmetric salt withdrawal area below the down-thrown block and accumulation below the upthrownblock. In addition, several salt domes or pillows canbe identified, of which the largest occur in the NWand SE of the study area (Figs 2a & 3a). ComparingFigure 2a and Figure 2c, salt thicknesses and Top Saltgeometry at regional scale show no clear connectionto tectonic features in the pre-salt units.

The Z3 stringer at regional scale

The study by van Gent et al. (2011) has alreadyshown that the on average 40–50 m thick Z3 strin-ger (Figs 2b & 3b) has a complex structure

dominated by boudinage and folding, frequentlyoffset vertically over more than half of the totalZechstein thickness (Figs 4 & 5). On average theZechstein salt thickness above the stringer is lessthan that below (Figs 4 & 5), and hence the stringermostly occurs close to or at the Top Salt. However,single stringer fragments also occur locally in thecentral to lower salt section and can be of thicknessabove average (i.e. up to c. 70 m in this study area;Fig. 5, left side). For a concept of ‘thicker zones’,see van Gent et al. (2011).

In general, surface B (see section 2) displayslarge-scale folding that follows the Top Salt (white,dashed lines in Figs 4a & 5a) since all structuresin the stringer disharmonic to the Top Salt areremoved due to the smoothening (see Fig. 3c). Onthe smaller scale, the surface A (black, dashedlines in Figs 4a & 5a) images superimposed patternsof complex, constrictional and open to isoclinalfolds with mean wavelengths of 400 m and foldamplitudes less than 200 m, disharmonic to surfaceB (see also Fig. 3c). This images a stringer geometrysimilar to salt mines (Fig. 2d). In many areas there isno continuous reflector even when the stringer isshallow-dipping (Figs 2b, 4b & 5b). This is inter-preted as representing a disruption of the stringerinto individual isolated fragments, especially in

Fig. 4. (a) East–West seismic profile (for location see Fig. 2a) through the study area with the stringer interpolationsurface A (black, dashed line) and the smoothed surface B (white, dashed line) and (b) its interpretation figure. In(b), blue represents the Z2–Z4 salt section between the pre-salt, brown the Basal Zechstein, Rotliegend andCarboniferous and yellow the sedimentary overburden. Note the differences in Z3 stringer geometry west and east of thecentral salt wall related to structural features of the Top Salt.




areas of the central salt wall (Fig. 2b) and salt domesin the NW and SE study area. We assume here thatthe investigated evaporitic sequence was a smoothand closed layer (Geluk 2007) prior to its defor-mation, disregarding other effects on its continuity(e.g. non-deposition, erosion, etc.).

Observations and results: folding

v. complex offsets of the stringers on a

local scale

Given the geometrical complexity of the Z3 stringerin the investigated area, an accurate tracing of thestringer is not always possible. This especiallyapplies for areas where stringer thickness is belowthe resolution of the seismic data (i.e. ,20 m)and/or the stringer is very steep. Hence, from the3D seismic data there is no clear evidence thatgaps between visible stringer fragments are con-nected by thin and steep stringer parts.

Building on the results presented by van Gentet al. (2011), we focus on a small example area (c.400 ! 400 m; Fig. 6) in the south-westernmoststudy area (for location see Fig. 2b). Surface A(Fig. 6a) images a complex pattern of smooth,

open to tight folds. Since our stringer interpretation(dark areas in Fig. 6b) does not fully support a con-nected stringer, folding cannot be accepted as theonly structural process. By comparing the seismi-cally resolved stringer fragments (Fig. 6b) with gra-dient measurements of surface A (Fig. 6c), we seethat locally steeply inclined (i.e. up to 708) stringerparts are imaged. Furthermore, parts that areexpected to be gently inclined (i.e. ,308) are notvisible. These areas can therefore be interpreted as‘real’ gaps most likely representing tectonic boudi-nage (with respect to an initially continuous Z3 eva-porites layer).

Tracing such geometries across some selectedseismic profiles with spacing of 250 m (Fig. 7; pro-files B–D) clearly shows abrupt vertical offsets ofup to 450 m in the stringer (Fig. 7; profile C). Twoconceptual end-member models of this setting areshown in Figure 7e. Differentiation between thesetypes of stringer deformation is not possible at thispoint. The intra-salt structure is much morecomplex than it would be expected from the rela-tively smooth Top Salt and surface B geometry inplaces (see e.g. Fig. 3b). Consequently, such offsetsprovide additional complexity to the stringer andshow that the overall stringer geometry cannot be

Fig. 5. (a) North–South seismic profile (for location see Fig. 2a) slicing through the study area west of the central saltwall (black, dashed line: stringer interpolation surface A; white, dashed line: smoothed surface B) and (b) itsinterpretation figure. Note that some parts of complex stringer geometry may be correlated to the occurrence ofstructures in the pre-salt, for example a graben in the underburden (centre of the profile). Nevertheless, comparing thestringer, the Top Salt and the pre-salt does not show a clear connection of intra-salt deformation to tectonic features inthe underburden and overburden.




explained by simple models of either foldingor boudinage.

Discussion

Regarding intra-salt stringers and their implicationfor evaporite deformation, the factors and processesof great importance for the internal tectonicsand deformational style inside salt structures are(according to Geluk 2000b): rheology and mech-anics of the evaporites; their thicknesses andspatial distribution; the types of salt structures;and the local and regional stress field history. Wehave shown that the structure of the stringer in thestudied part of the Dutch Zechstein section cannotbe easily associated with the Top Salt geometry.Consequently, our data and interpretation implythat the deformation in the salt can be locallymuch higher than it would be expected based onhomogeneous salt rheology and Top Salt geometry.Furthermore, low (salt layers and pillows) and high(domes and diapirs) degrees of halokinesis do notnecessarily correlate with the amount of defor-mation of the stringer (see also examples from Bra-zilian salt basins by Gamboa et al. 2008; Fiduk &Rowan 2012).

Local scale

Starting from our interpretation of the Z3 stringerfolding and disruption (Fig. 3b), detailed obser-vations of the order 10–100 m scale (Figs 6 & 7)imply that complexity of deformation cannot beexplained by models of either (1) folding associatedwith thinning and steepening of parts of the stringeror (2) tectonic boudinage. The first is a likely modelbased on observations from salt mines (Fig. 2d)showing connected and complexly folded layers.The second is imaged in seismic data, but alsoshown from some salt mine examples (e.g. Schleder& Urai 2005; Schleder 2006) and analogue models(e.g. Zulauf & Zulauf 2005). Regarding the firstmodel, isolated, highly offset stringer fragmentsobserved in both the lower and upper parts of thesalt section may represent syncline- and anticline-type fold hinges. Seismically fuzzy areas betweenthe stringer fragments may then be interpreted asthe non-imaged, steep and thin fold limps (seeFig. 7e; right side). Some of these thin and steepstringer parts intersecting seismically imaged frag-ments have been proven by hydrocarbon wells.

They favour a model of complex, superimposed pat-terns of folding being part of the seismically invis-ible stringer. On the other hand, the fuzzy areasbetween stringer fragments may represent realgaps related to tectonic boudinage, locally offsetby vertical throws in the salt (Fig. 7e; left side).

Compared to prior studies investigating stringeroccurrences in salt mines and outcrops, whichshow that intra-salt layer deformation likely com-bines both folding and boudinage on differentscales (e.g. Schleder 2006), the connectivity of astringer is most likely much higher than expectedfrom seismic data interpretation. However, themodels (i.e. boudinage v. folding) cannot be separ-ated at this stage. Based on our interpretation, weassume that the overall folded shape of the investi-gated Z3 stringer, regardless of whether this mayrepresent a continuous or fragmented layer, displayscomplex folding of the salt at different scales(compare Figs 2d & 3b). Furthermore, it impliesthat the deformation in the salt is not necessarilycoupled to deformation in the underburden andthe overburden.

Regional scale

At the regional (kilometre) scale, the central salt walland the large, elongated rim syncline east of it aredominant drivers of salt drainage. Surrounding saltstructures in the NW and SE may be also important,leading to superimposed salt flow regimes(e.g. Geluk 1995, 2005). Common models ofsimple salt flow towards salt structures (e.g.Chemia et al. 2008) do not match the observed strin-ger’s vertical throws also found in areas that appearto be less affected by lateral salt flow (e.g. Figs 5 &7a–c). More complexity is introduced by the differ-ent orientations of stringer offsets (i.e. mainly paral-lel to the central salt wall but also NW–SE, N–S andNE–SW). We therefore hypothesize a vertical com-ponent in salt flow much larger than expected, inaccordance to what is shown in salt mining literature(e.g. Fulda 1928; Bornemann 2008; Fig. 2d).

To provide a test for some of the hypotheses ofhow the Z3 stringer geometry came to be, we firstanticipate possible impacts of structures in the under-burden (i.e. graben and upthrown blocks) as wellas rim syncline development in the overburden.Comparing our measurements of offsets in the under-burden to those of stringer fragments in the saltcolumn (e.g. Figs 4 & 5 and comparing Fig. 2b, c),

Fig. 6. (a) Interpolated surface (surface A) generated from the Z3 stringer interpretation, implying a superimposedcomplex pattern of open to tight folding of the stringer (for location see Fig. 2b). (b) A comparison of the interpolatedstringer surface (a) to the basic stringer interpretation from seismic data: neither folding of a connected stringer surfacenor strict breaking of the stringer to fragments is finally resolved for this area, while a combination of both is most likely.(c) Gradient map of the interpolated stringer surface showing that, compared to (b), the stringer can also be interpreted invery steep parts. With respect to the resolution of the seismic data, these gaps most likely represent boudins.




impacts of tectonics in the underburden are not likelyfirst-order mechanisms of intra-salt deformation onthe larger scale. On a local scale, offsets in the under-burden likely contribute to locally restricted complex3D salt flow. For example, upthrown blocks andgraben structures may result in complex ‘cornerflow’ with increased intensity of the stringer’sfolding and breaking (e.g. Fig. 5).

If comparing structural features in the over-burden to the overall stringer geometry (surfaceA), we propose that the development of rim syn-clines (Fig. 3a) in areas of a less-deformed stringerprovide strong impacts on its deformation. Theresulting large-scale salt depletion may provide acut-off of the salt section preventing further drai-nage of salt (and stringer) to domes and diapirs (asit may apply for the salt structure in Fig. 5; rightside). We therefore conclude that the deformationof the overburden most likely had an impact onthe intra-salt structure on the large scale, whiledeformation in the underburden can be associatedwith some local impacts on the smaller scale (i.e.‘corner flow’). In other words, although pre-salt tec-tonics and overburden sedimentary history and tec-tonics may have had first-order impacts on thestructural features over a regional (kilometre)scale, the complexity of the stringer may only beexplained by much more complex salt flow patterns.This may be related to rheological stratificationin the salt body, which includes highly mobilepotassium–magnesium salt layers in the upperpart of the Z3 salt with bischofite, kieserite, carnal-lite and sylvite (see data in Williamson et al. 1997;Geluk et al. 2007; Urai et al. 2008). The internalmechanical stratigraphy of the Zechstein saltsection is therefore proposed as having had amuch larger effect on controlling the subsequentpatterns of the internal structure than previouslyproposed by Urai et al. (2008).

Another possible mechanism to discuss is gravi-tational sinking of single isolated stringer fragmentsin the salt section (e.g. Koyi 2001; Chemia et al.2008) as it may be interpreted, for example, forthe highly offset stringer in Figure 7c. However,keeping in mind that the main phases of halokinesisin the studied area are Mesozoic and Cenozoicdeformation (Geluk 2000a, 2005), and with respectto average sinking velocities of intra-salt bodies

proposed from numerical (e.g. Chemia & Koyi2008; Li et al. 2012) and analogue models (e.g.Koyi 2001; Callot et al. 2006), all the physicallyseparate stringer fragments would have groundedsince then (van Gent et al. 2011). Based on ourseismic data we suggest that there is no conclusiveevidence for sinking after the end of salt movement.Rather, we propose a model of non-cylindricalsynclinal folds formed during salt flow, and bothseismically invisible fold limps and real gaps dueto boudin fragments can be expected in betweenthe seismically resolved fold hinges. The resultingpattern of stringer fragments finally results fromsuperposed, polyphase folding and boudinage inthe sense of Zulauf & Zulauf (2005), with negligiblecontribution by gravity-induced sinking.

Conclusions

The investigated Zechstein 3 stringer in the Dutchoffshore part of the Southern Permian Basin showsa complex 3D structure as expected from salt minesand outcrops with a wavelength much shorter thanthat of Top Salt and an amplitude much larger thanexpected based on homogeneous salt rheology. Thisis in agreement with the expected rheological layer-ing in the salt, further enhanced by the large contrastwith the stinger and corner flow around upthrownblocks in the pre-salt. Polyphase superimposed pat-terns of brittle and ductile stringer deformationsuggest very different behaviour in extension andshortening. Our data show no conclusive evidencefor significant gravitational sinking of stringer frag-ments after the end of halokinesis. Interpretation ofour data is limited by the fact that thin parts of thestringer in steep orientation are often not wellimaged. Further work comparing well with seismicdata is required to quantify this effect.

We thank the Nederlandse Aardolie Maatschappij (NAM,a Shell operated 50–50 joint venture with ExxonMobil) forproviding the high-resolution seismic data, and especiallyM. DeKeijzer and J. Verbeek for fruitful comments. Wewould also like to thank S. Becker and L. Reuning(RWTH Aachen University) for discussion. We thankreviewers G. Zulauf and M. Geluk for their commentsand suggestions which greatly improved the quality ofthe manuscript.

Fig. 7. (a) Interpolated stringer surface (surface A; for location see Fig. 2b) with an E–W slicing seismic sectionshowing examples of steep stringer offsets deeply incising the surface; (b) (c) and (d) depict a sequence of NW–SEseismic profiles with 250 m spacing showing details (interpretation in white boxes) of the observed steep and deepoffsets in the stringer. (e) Sketches of possible end-member scenarios for the offsets in (d) explaining how such ‘offsets’may look in nature. The first (left) deals with a breaking of the stringer and a subsequent offset of a fragment byvertical flows in the salt. The second (right) images a continuous stringer with a steeply inclined fold that is seismicallynot resolved because of the thin and steep fold limps. Based on observations in salt mines (e.g. Fig. 2d), the secondmodel may be favoured for parts of the stringer not imaged in seismic data.




References

Alsop, G. I., Holdsworth, R. E. & McCaffrey, K. J. W.2007. Scale invariant sheath folds in salt, sedimentsand shear zones. Journal of Structural Geology, 29,1585–1604.

Behlau, J. & Mingerzahn, G. 2001. Geological and tec-tonic investigations in the former Morsleben salt mine(Germany) as a basis for the safety assessment of aradioactive waste repository. Engineering Geology,61, 83–97.

Bornemann, O., Behlau, J. et al. 2008. Standortbes-chreibung Gorleben Teil 3: Ergebnisse der uber- unduntertagigen Geologischen Erkundung des Salinars.Geologisches Jahrbuch Reihe C Heft 73, Hannover.

Burliga, S. 1996. Kinematics within the Klodawasalt diapir, central Poland. In: Alsop, G. I., Blundell,D. J. & Davison, I. (eds) Salt Tectonics. Geo-logical Society, London, Special Publications, 100,11–21.

Callot, J. P., Letouzey, J. & Rigollet, C. 2006. Strin-gers Evolution in Salt Diapirs, insight from AnalogueModels. AAPG International Conference and Exhibi-tion, Perth, Australia.

Chemia, Z. & Koyi, H. 2008. The control of salt supply onentrainment of an anhydrite layer within a salt diapir.Journal of Structural Geology, 30, 1192–1200.

Chemia, Z., Koyi, H. & Schmeling, H. 2008. Numericalmodelling of rise and fall of a dense layer in saltdiapirs. Geophysical Journal International, 172,798–816.

de Boer, H. U. 1971. Gefugeregelung in Salzstocken undHullgesteinen. In: Kali und Steinsalz, 5, 403–425.

De Jager, J. 2003. Inverted basins in the Netherlands,similarities and differences. Netherlands Journal ofGeosciences/Geologie en Mijnbouw, 82, 355–366.

De Jager, J. 2007. Geological development. In: Wong,Th. E., Batjes, D. A. J. & de Jager, J. (eds)Geology of the Netherlands. Royal NetherlandsAcademy of Arts and Sciences, Amsterdam, 5–26.

Fiduk, J. C. & Rowan, M. G. 2012. Analysis of foldingand deformation within layered evaporites in BlocksBM-S-8 & -9, Santos Basin, Brazil. In: Alsop, G. I.,Archer, S. G., Hartley, A. J., Grant, N. T. & Hodg-kinson, R. (eds) Salt Tectonics, Sediments and Pro-spectivity. Geological Society, London, SpecialPublications, 363, 469–481.

Fulda, E. 1928. Die Geologie der Kalisalzlagerstatten. In:Krische, P. (ed.) Das Kali, II. Teil. Enke’s Bibliothekfur Chemie und Technik unter berucksichtiging derVolkswirtschaft 7. Ferdinand Enke. Stuttgart,Germany, 24–136.

Gamboa, L. A. P., Machado, M. A. P., da Silveira, D. P.,de Freitas, J. T. R. & da Silva, S. R. P. 2008. Evapor-itos estratificados no Atlantico Sul: interpretacaosısmica e controle tectono-estratigrafico na Bacia deSantos. In: Mohriak, W., Szatmari, P. & Anjos,S. M. C. (eds) Sal: Geologia e Tectonica, Exemplosnas Basicas Brasileiras. Beca Edicoes Ltda, SaoPaulo, Brasil, 340–359.

Geluk, M. C. 1995. Stratigraphische Gliederung derZ2-(Staßfurt-) Salzfolge in den Niederlanden: Bes-chreibung und Anwendung bei der Interpretation vonhalokinetisch gestorten Sequenzen. Zeitschrift der

deutschen Gesellschaft fur Geowissenschaften, 146,458–465.

Geluk, M. C. 2000a. Late Permian (Zechstein) carbonate-facies maps, the Netherlands. Geologie en Mijnbouw/Netherlands Journal of Geosciences, 79, 17–27.

Geluk, M. C. 2000b. Steps towards prediction of theinternal tectonics of salt structures. In: Geertman,R. M. (ed.) Proceedings of the 8th World Salt Sym-posium, May 2000. Elsevier, Amsterdam.

Geluk, M. C. 2005. Stratigraphy and Tectonics of Permo-Triassic Basins in the Netherlands and SurroundingAreas. Thesis, Utrecht University.

Geluk, M. C. 2007. Permian. In: Wong, T. E., Batjes,D. A. J. & De Jager, J. (eds) Geology of the Nether-lands. Royal Netherlands Academy of Arts andSciences, Amsterdam, 63–84.

Geluk, M. C., Paar, W. A. & Fokker, P. A. 2007. Salt.In: Wong, T. E., Batjes, D. A. J. & De Jager, J.(eds) Geology of the Netherlands. Royal NetherlandsAcademy of Arts and Sciences, Amsterdam, 283–294.

Hubscher, C., Cartwright, J., Cypionka, H.,De Lange, G., Robertson, A., Suc, J. P. & Urai, J.L. 2007. Global look at salt giants. Eos, 88, 177–179.

Jackson, M. P. A., Cornelius, R. R., Craig, C. H.,Gansser, A., Stocklin, J. & Talbot, C. J. 1990.Salt Diapirs of the Great Kavir, Central Iran. Geologi-cal Society of America, Tulsa, Memoir.

Kent, P. E. 1979. The emergent Hormuz salt plugs ofsouthern Iran. Journal of Petroleum Geology, 2,117–144.

Koyi, H. 2001. Modeling the influence of sinking anhy-drite blocks on salt diapirs targeted for hazardouswaste disposal. Geology, 29, 387–390.

Kukla, P. A., Reuning, L., Becker, S., Urai, J. L. &Schoenherr, J. 2011. Distribution and mechanismsof overpressure generation and deflation in the lateNeoproterozoic to early Cambrian South Oman SaltBasin. Geofluids, 11, 349–361.

Li, S., Abe, S., Reuning, L., Becker, S., Urai, J. L. &Kukla, P. A. 2012. Numerical modelling of the displa-cement and deformation of embedded rock bodiesduring salt tectonics: Case study from the SouthOman Salt Basin. In: Alsop, G. I., Archer, S. G.,Hartley, A. J., Grant, N. T. & Hodgkinson, R.(eds) Salt Tectonics, Sediments and Prospectivity.Geological Society, London, Special Publications,363, 497–514.

Littke, R., Bayer, U., Gajewski, D. & Nelskamp, S.2008. Dynamics of Complex Intracontinental Basins.The Example of the Central European Basin System.Springer-Verlag, Berlin–Heidelberg.

Mohr, M., Kukla, P. A., Urai, J. L. & Bresser, G. 2005.Multiphase salt tectonic evolution in NW Germany:seismic interpretation and retro-deformation. Inter-national Journal of Earth Sciences (GeologischeRundschau), 94, 914–940.

Park, R. G. 1997. Foundations of Structural Geology.Chapman & Hall, London, 32–34.

Reuning, L., Schoenherr, J., Heimann, A., Urai, J.,Littke, R., Kukla, P. A. & Rawahi, Z. 2009. Con-straints on the diagenesis, stratigraphy and internal dyn-amics of the surface-piercing salt domes in the GhabaSalt Basin (Oman): A comparison to the Ara Groupin the South Oman Salt Basin. GeoArabia, 14, 83–120.




Richter-Bernburg, G. 1972. Saline deposits inGermany: a review and general introduction to theexcursion. Geology of Saline Deposits, ProceedingsHannover Symposium 1968, Unesco, 275–287.

Schleder, Z., 2006. Deformation mechanisms of natu-rally deformed rocksalt. PhD thesis, Rheinisch-Westfalische Technische Hochschule Aachen.

Schleder, Z. & Urai, J. 2005. Microstructural evolutionof deformation-modified primary halite from theMiddle Triassic Rot Formation at Hengelo, The Neth-erlands. International Journal of Earth Sciences, 94,941–955, http://dx.doi.org/10.1007/s00531–005–0503–2.

Schoenherr, J., Reuning, L., Kukla, P. A., Littke, R.,Urai, J. L., Siemann, M. & Rawahi, Z. 2009. Halitecementation and carbonate diagenesis of intra-salt.Sedimentology, 56, 567–589.

Schroot & De Haan, H. B. 2003. An improved regionalstructural model of the Upper Carboniferous of theCleaver Bank High based on 3D seismic interpretation.In: Nieuwland, D. A. (ed.) New Insights into Struc-tural Interpretation and Modelling. GeologicalSociety, London, Special Publications, 212, 23–37.

Seidl, E. 1921. Schurfen, Belegen und Schachtabteufenauf deutschen Zechsteinsalzhorsten. ArchaologischeLagerstatten – Forschung, 26, Berlin (Geol. L.-A.).

Sleep, N. H. & Fujita, K. 1997. Principles of Geophysics.Blackwell Science, USA.

Taylor, J. C. M. 1998. Upper Permian–Zechstein. In:Glennie, K. W. (ed.) Petroleum Geology of theNorth Sea. Basic Concepts and Recent Advances. 4thedn. Blackwell Science, Oxford, 174–211.

TNO-NITG. 2004. Geological Atlas of the Subsurface ofthe Netherlands e Onshore. TNO-NITG, Utrecht, 103.

Urai, J. L., Schleder, Z., Spiers, C. J. & Kukla, P. A.2008. Flow and Transport Properties of Salt Rocks.In: Littke, R., Bayer, U., Gajewski, D. & Nelskamp,S. (eds) Dynamics of Complex Intracontinental Basins:The Central European Basin System. Springer-Verlag,Berlin–Heidelberg, 277–290.

Van Adrichem-Boogaert, H. A. & Kouwe, W. F. P.1993–1997. Stratigraphic nomenclature of the Nether-lands; revision and update by RGD and NOGEPA.TNO-NITG. Mededelingen Rijks Geologische Dienst,Haarlem, 50, 1–37.

van Gent, H. W., Urai, J. & De Keijzer, M. 2011. Theinternal geometry of salt structures – a first lookusing 3D seismic data from the Zechstein of the Neth-erlands. Journal of Structural Geology, 33, 292–311,http://dx.doi.org/10.1016/j.jsg.2010.07.005.

Wagner, R. H., Winkler Prins, C. F. & Riding, R. E.1971. Lithostratigraphic units of the lower part of theCarboniferous in northern Leon, Spain. Trabajos deGeologıa, 4, 603–663.

Williamson, M. A., Murray, S. J., Hamilton, T. A. &Copland, M. A. 1997. A review of Zechstein drillingissues. SPE Drilling & Completion, 13, 174–181.

Ziegler, P. A. 1990. Geological Atlas of Western andCentral Europe. 2nd edn. Elsevier Scientific Publish-ing Company, The Hague, Amsterdam.

Zulauf, J. & Zulauf, G. 2005. Coeval folding and bou-dinage in four dimensions. Journal of StructuralGeology, 27, 1061–1068.

Zulauf, G., Zulauf, J., Bornemann, O., Kihm, N.,Peinl, M. & Zanella, F. 2009. Experimental defor-mation of a single-layer anhydrite in halite matrixunder bulk constriction. Part 1: geometric and kin-ematic aspects. Journal of Structural Geology, 31, 460.



http://dx.doi.org/10.1007/s00531–005–0503–2

http://dx.doi.org/10.1007/s00531–005–0503–2

http://dx.doi.org/10.1007/s00531–005–0503–2

http://dx.doi.org/10.1007/s00531–005–0503–2

http://dx.doi.org/10.1007/s00531–005–0503–2

http://dx.doi.org/10.1007/s00531–005–0503–2

http://dx.doi.org/10.1007/s00531–005–0503–2

http://dx.doi.org/10.1007/s00531–005–0503–2

http://dx.doi.org/10.1007/s00531–005–0503–2

http://dx.doi.org/10.1016/j.jsg.2010.07.005

http://dx.doi.org/10.1016/j.jsg.2010.07.005


3d seismic study of complex intra-salt deformation: an ... · we used the seismic interpretation...

Documents