Tectonic subsidence modelling of the Polish Basin in the light of new data on crustal structure and magnitude of inversion

The Polish Basin (PB) is one of a set of basins developed on the Paleozoic platform of western Europe in the Late Paleozoic between the Variscan Orogen and the East European Craton (EEC). Its main depocentral axis (the Mid-Polish Trough-MPT) was active during most of the basin development as a maximum subsidence zone with almost uninterrupted sedimentation. The present base of the Permian in the MPTranges in depth from ca. 3000 to 3500 mnear the Baltic coast to up to 8000 m to the southeast. The MPT lies parallel and adjacent to the edge of the EEC and appears to be related to a distinct structural zone within the crust (the Tornquist-Teisseyre Zone-TTZ). Subsidence of the MPTcan be explained in terms of crustal extension/transtension and related lithosphere cooling coupled with the structural predetermination of the underlying TTZ. Tectonic subsidence analysis of the preserved and reconstructed stratigraphic record suggests the occurrence of a Late Permian-Early Triassic "rifting" phase. However, there is a deficit of geologically observable extensional features (faulting) of this age, implying an important relationship between this phase of apparent basin subsidence and earlier post-Variscan, Late Carboniferous-Early Permian tectonism. The match between crustal structure implied by basin modelling studies and available deep seismic sounding (DDS) data is not always clear. This is probably related to the heterogeneous basement, which comprises the outer zone of the Variscan belt in the southwest, EEC crust in the northeast, and a complex of Caledonian/reworked Precambrian crustal blocks in the central part of the basin. Changes to crustal architecture as a result of Alpine tectonics may also play a role. Increased tectonic subsidence rates during Oxfordian-Kimmeridgian times (Late Jurassic) correlate with intensified rifting and wrench activity within the Arctic-North Atlantic rift system and along the northern Tethyan margin. In contrast, accelerating tectonic subsidence beginning in the Cenomanian is a precursor of compressional deformations in the basin that culminated in Alpine-related basin inversion during the latest Late Cretaceous and earliest Tertiary. Taking inversion into account, the maximum depth of the base Zechstein structural surface at the end of the Cretaceous is estimated to have been as much as 5000 m near the Baltic Sea to more than 10000 m in the southeasternmost part of the basin. Because of the erosion of these sediments, however, constraints on Cretaceous subsidence and, in turn, the magnitude and exact timing of Late Cretaceous-Paleogene inversion are poor. © 2002 Elsevier Science B.V. All rights reserved