Evolution of the Rotliegend Basin of northwestern Poland

Abstract

The Rotliegend Basin of northwestern Poland is characterized by a complex structure that reflects syndepositional reactivation of fault systems related to the Teisseyre-Tornquist (TTZ) and Sorgenfrei-Tornquist (STZ) zones. This basin is superimposed on the Caledonian Trans-European Suture Zone and encroaches eastward onto the East European Craton and southwestward onto the Variscan Externides. Latest Carboniferous and Early Permian sinistral wrench movements along the TTZ and STZ, causing disruption and erosional truncation of the Variscan foreland basin and the external Variscan fold-and-thrust belt, were accompanied by the extrusion of voluminous volcanics. During the deposition of the Upper Rotliegend sediments, earlier formed fault systems were recurrently reactivated, controlling the subsidence of an array of troughs and uplift of horst blocks. During deposition of the upper parts of the Upper Rotliegend, when tectonic activity had abated, subsidence and broadening of the Polish Basin was controlled by thermal relaxation of the lithosphere. Analysis of wireline logs, calibrated by cores, and their regional correlations permits to distinguish nine successive Upper Rotliegend depositional cycles. These involve alluvial fan, fluvial, lacustrine, playa-lake and aeolian deposits and are separated by conspicuous lithofacies and/or erosional boundaries. Lithofacies maps developed for each of these depositional cycles allowed to retrace the palaeogeographic evolution of the Polish Rotliegend Basin, with supporting cross-sections providing insight into its structural development. Palaeoclimatic factors, such as rapid humidity changes, combined with tectonic activity, played an important role in the development of the different depositional cycles and their boundaries. Tectonics controlled the development of accommodation space and the lack thereof, as well as uplift and erosion of clastic source areas. The Polish and North German Rotliegend basins were separated during the deposition of the Drawa (Parchim and Mirow) and the earlier part of the Noteć (Rambow and Eldna) formations by the vast area of palaeohigh. Subsequently this high was overstepped by sediments of the upper part of the Noteć (Peckensen and Mellin) Formation, resulting in the coalescence of these basins. A tentative correlation of depositional cycles evident in the Polish and North German Rotliegend basins is presented.