Palaeogeography and sedimentary model of the Kupferschiefer in Poland

The Kupferschiefer in Poland consists of clayshales and shaly, laminated and argillaceous dolomites/limestones, with minor terrigenous and non-laminated carbonate interbeds. In the Kupferschiefer two main microlithofacies types were identified: (1) clayshales and (2) laminated argillaceous dolo- and calcilutites. These microlithofacies are interbedded throughout the Kupferschiefer sequences. Regional microlithofacies distribution and their mutual proportions in the profiles allowed two main palaeogeographical zones of the Kupferschiefer to be distinguished: (A) deep shelf, which comprises the center of sedimentary basin, characterized by lithofacies of low and fairly consistent thickness (20–60 cm), and alternately occurring microlithofacies 1 and 2; and (B) shallow shelf, which comprises marginal areas of the basin, characterized by lithofacies of highly variable thickness (0–170 cm), predominance of microlithofacies 2 and local occurrence of terrigenous and carbonate tempestites. The spatial distribution of the lithofacies indicates that the Kupferschiefer was deposited in a relatively shallow, mud-dominated stratified shelf sea. Deposition of the Kupferschiefer generally took place below fair-weather wave base, in low-energy environment; the deep shelf lithofacies was formed in anaerobic-to-dysaerbic waters mainly below storm wave base, whilst the shallow shelf lithofacies was deposited within storm wave base in dysaerobic-to-aerobic waters. Conditions of oxygenated and agitated waters predominated around basin margins and on intrabasinal elevations, where the Kupferschiefer is lacking. Variability of the Kupferschiefer sequences is attributed to fluctuating redoxcline, which intersected submarine topography. Vertical movements of the redoxcline, related to sea-level fluctuations could account for large lateral shifts of depositional environments along a gently dipping shelf.