3D reconstruction of salt movements within the deepest post-Permian structure of the Central European Basin System - The Glueckstadt Graben

Abstract

The Glueckstadt Graben is a prominent structure of the Central European Basin System, where the sedimentary patterns are extensively affected by Permian salt movements. The relations of the sedimentary patterns to salt structures have been analyzed through present-day distributions of sediments. In addition, a three-dimensional backward modelling approach has been applied to determine the original salt distribution in response to the unloading due to sequential backstripping of the stratigraphic layers. The results of the modelling reveal the thickness distribution of the Permian salt for 5 time intervals from the end of the Triassic to present day. Spatial agreement has been found between the development of the depleted zone of the Permian salt through time and the observed distribution of the maximum subsidence for the different stratigraphic units above the salt. The sedimentation centres for each time interval are always located above the zone of reduced or depleted Permian salt. In the central part of the Glueckstadt Graben, the depletion occurred already in the Triassic and perfectly correlates with the thickest Triassic. During the Jurassic, Cretaceous and Tertiary, the areas of depleted Permian salt shifted towards the basin flanks, and the same occurred with the centres of maximum sediment deposition. Thus, the results of the modelling strongly support the conclusion that salt withdrawal has played a major role during the Meso-Cenozoic evolution of the Glueckstadt Graben and that the progressive depletion of the Permian salt layer, from the central part towards the margins, created the large part of the accommodation space for sedimentation in addition to tectonic subsidence. Furthermore, our study has several important implications for salt behaviour in different tectonic settings. In general, the results of modelling indicate a good correlation between the main phases of salt movements and tectonic events in the area under consideration. During the Triassic, the first stage of diapirism in the Glueckstadt Graben occurred within the central part of the basin. Regional extension may have triggered reactive diapirism and caused the formation of the deep primary rim synclines. Once the salt structures had reached the critical size, buoyancy forces supported their continued growth until the Jurassic when extension-induced regional stresses once more affected the Glueckstadt Graben. The results of the modelling indicate very little salt activity during the late Early Cretaceous-earty Late Cretaceous when the area of the Glueckstadt Graben was tectonically silent. Therefore, our study supports the concept of tectonicatly induced salt movements which can be interrupted during the absence of tectonic forces. Salt movements were reactivated in the marginal troughs by compressional forces during the latest Late Cretaceous-Early Cenozoic. Paleogene-Neogene salt withdrawal led to the growth of N-S oriented salt structures mainly at the margins of the basin. This phase of salt tectonics correlates temporally with almost W-E extension. This indicates a renewed change in tectonic regime after Late Cretaceous-Early Cenozoic compression.