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, anhydrite, clay) of at least 10 m thickness form good reflectors in evaporites, but the structure and dynamics of such ‘stringers’ in the salt movement are poorly understood. In this study, we investigate the intra-salt Zechstein 3 (Z3) stringer from 3D seismic data in an area offshore the Netherlands. Observations show complex deformation including boudinage, folding and stacking. Reflections from thin and steep stringer parts are strongly reduced, and we present different structural models and 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 the stringer fragments follows the shape of Top Salt, but smaller-scale stringer geometries strongly differ from this and imply boudinage. The imaged disharmonic patterns of constrictional folds provide 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 salt flow, different phases and styles of basement tectonics and movement of the overburden.
Classically, the North-Sea Chalk is assumed to have deposited under quiet, homogeneous pelagic conditions with local re-deposition in slumps and slides. However, recently the observation of highly discontinuous reflection patterns on 2D and 3D seismic data from the NW European Chalk Group initiated a revision of some general ideas of chalk deposition, assuming that long-lived, contour-parallel bottom currents exert a primary influence on the development of intra-chalk channels, drifts and mounds. In this study, an alternative explanation is suggested for the formation of many of the significant intra-chalk seismic and stratal discontinuities by interpreting these as being caused by gravity-driven processes developing in response to intense syndepositional tectonics. Submarine mass-transport systems identified in the study area include large-scale slumps, slides, debris flows and turbidites. The latter occur in sinuous channel systems flanked by large master overbanks, with the channel fill exhibiting well-developed secondary banks and overbanks on the respective outer bends of the inner channel thalweg. This first documentation of channelised density-flow deposits in the North-Sea Chalk has important consequences for the interpretation and prediction of re-deposited chalk units, emphasising at the same time the strength of vigorous 3D seismic discontinuity detection for subsurface sedimentary-systems analysis.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.