Regional variations in the structure of the Permian Zechstein 3 intrasalt stringer in the northern Netherlands: 3D seismic interpretation and implications for salt tectonic evolution

Abstract

The late Permian Zechstein evaporites in the northern Netherlands were exceptionally well imaged in [Formula: see text] of prestack depth migration 3D seismic data. Seismic reflections of a 30–150-m-thick Zechstein 3 anhydrite-carbonate stringer, which was encased in thick layers of rock salt, provided an unparalleled, basin-scale view of the 3D internal structure of a giant salt basin. Seismic data were used to map the regional variation of the intrasalt stringer to analyze its role in deformation styles and salt flow as well as its interaction with the sub- and suprasalt sediments. From our interpretation of the stringer, the salt layers, and the encasing sediments, three regional structural stringer styles can be defined and were analyzed in the context of regional salt kinematics. Our results revealed that the current stringer initially formed a continuous sheet of anhydrite and carbonate, embedded in salt of varying thickness. After the onset of syndepositional gravitational gliding of some of the salt masses and passive salt diapirism triggered by differential loading in the Triassic in other areas, salt flow caused rupture and folding of the stringer on a wide range of scales. The thickness and deformation degree of the individual salt layers controlled the development of regionally distinctive styles of intrasalt structures. Although deformation of the salt and the embedded stringer stopped early on morphologic highs, the basinal areas experienced phases of later activation or reactivation of salt structures and sedimentary basins. This was especially the case during the Late Cretaceous to Early Tertiary plate tectonic reorganization in the Central European plate, causing three-dimensionally complex intrasalt structures observable today.

Evolution of rheologically heterogeneous salt structures: a case study from the NE Netherlands

“…This could have been the case above the basement graben below the study area, where subsalt faulting may have produced gentle depressions in the evolving evaporites. Recent studies show that at least some subsalt faults in the study area were active during ZII and ZIII precipitation (Biehl et al, 2014;Strozyk et al, 2014), providing support for this hypothesis. Mg-enriched residual brines are interpreted to have collected inside the depression of the carnallite-rich ZIII1b layers above the basement graben, in the area where the Veendam Pillow later formed, with bischofite precipitation in local lenses (Fig.…”

“…The ZIIIAC stringer represents the base of the ZIII unit and consists of the gray Salt Clay, overlain by the 0.5-20 m thick Plattendolomit and the 15-130 m thick Hauptanhydrit (Van Gent et al, 2011). As the stringer is thick and encased in rock salt, it produces a high-amplitude reflection in the seismic data (Van Gent et al, 2011;Strozyk et al, 2012Strozyk et al, , 2014.…”

“…The role of high-viscosity, brittle-ductile layers (also called stringers) in salt deformation has been studied using 3-D seismic data (Van Gent et al, 2011;Cartwright et al, 2012;Fiduk and Rowan, 2012;Jackson et al, 2014Jackson et al, , 2015Strozyk et al, 2014), laboratory experiments, analogue models, and numerical modeling. More specifically, these techniques have been used to understand the complex folds, faults, and boudinage of stringers as a result of deformation of the surrounding salt.…”

“…Evaporites like carbonates and sulfates (anhydrite, polyhalite, tachydrite), and the K-Mg chlorides bischofite (MgCl 2 × 6H 2 O) and carnallite (KMgCl 3 × 6H 2 O), are rheologically and mechanically different from the polycrystalline halite and may impact the internal deformation of salt structures (Geluk, 1998;Strozyk et al, 2014). Compared to rock salt, the effective viscosity of K-and Mg-salts is up to three orders of magnitude lower (van Eekelen et al, 1981;Urai, 1983;Urai ,1985;Urai and Boland, 1985;Urai, 1987;Urai et al, 2008;Spiers et al, 1983;Langbein, 1987;Scott Duncan and Lajtai, 1993;Schenk and Urai, 2005), while anhydrite and carbonates have much higher viscosity than rock salt and thus form buckle folds during compression.…”

The effect of salt in dilatant faults on rates and magnitudes of induced seismicity – first results building on the geological setting of the Groningen Rotliegend reservoirs

“…The thickness of the salt is highly variable, ranging from locally possibly close to zero to 1500 m or more in the highest salt domes near the flanks of the field. In most places the salt is currently more than 500 m thick (van Gent et al, 2009;Strozyk et al, 2012Strozyk et al, , 2014Raith et al, 2016). Locally along its eastern border and in the far SW of the field, salt flow has led to almost complete withdrawal of salt in rim synclines.…”