ALBERT

Description: A detailed study of the structural and stratigraphic evolution of the Southern Permian Basin during latest Carboniferous to Early Jurassic times, supported by quantitative subsidence analyses and forward basin modelling for 25 wells, leads us to modify the conventional model for the Rotliegend-Zechstein development of this basin. The Late Permian-Early Jurassic tectonic subsidence curves are typical for a Permian to Early Triassic extensional stage that is followed by thermal subsidence. However, a purely extensional model is extremely problematic because active faulting during this time is ''minor' and generally hard to document. Using inverse techniques to model the subsidence curves, we quantitatively show that a significant component of Late Permian and Triassic tectonic subsidence can be explained by thermal relaxation of Early Permian lithospheric thinning, and by delayed infilling of paleo-topographic depressions that developed during the Early Permian. In this interpretation, Stephanian-Autunian wrenching resulted in thermal destabilisation of the lithosphere, deep fracturing of the crust, disruption and erosion of its sedimentary cover and regional uplift of the area of the future Southern Permian Basin. Upon termination of wrench tectonics and associated volcanism, towards the end of the Autunian, the Southern Permian Basin began to subside in response to thermal contraction of the lithosphere. The evolving basin was isolated from the World oceans and had subsided possibly up to some 700 m below their level at the beginning of Upper Rotliegend sedimentation. After catastrophic flooding of this paleo-topographic depression at the beginning of the Zechstein, changing sea level, sedimentation and subsidence rates remained essentially in balance. Although the effects of Triassic rifting overprinted parts of the Southern Permian Basin, its overall subsidence pattern persisted well into the Jurassic. In contrast to the remainder of the Southern Permian Basin, Permian and Triassic crustal extension contributed significantly to the subsidence of the Polish Trough.