Late Cretaceous inversion and salt tectonics in the Koszalin-Chojnice and Drawno-Czlopa-Szamotuly zones, Pomeranian sector of the Mid-Polish Trough

Abstract

Late Cretaceous inversion processes and their relation to salt movements in the Pomeranian sector of the Mid-Polish Trough are described, based on deep boreholes. Two tectonic zones, inverted in the Late Cretaceous, located in the Mid-Polish Trough, were selected for study: the Koszalin-Chojnice Zone situated NE of the present-day Mid-Polish Swell in the Pomeranian Trough, within an area of non-salt anticlines, and the Drawno-Czlopa-Szamotuly Zone located in the Szczecin Trough, SW of the Mid-Polish Swell, in an area of strong salt tectonics. The stratigraphic gaps present indicate that the first pulse of Late Cretaceous inversion might have occurred in the Coniacian-early Santonian in this area. Another pulse can be dated at late Campanian-early Maastrichtian. Intra-Cretaceous stratigraphic gaps reached their maximum areal extent in the Coniacian (Inoceramus involutus Zone) and Upper Campanian (Koszalin-Chojnice Zone). Over large areas, Santonian (mostly upper Santonian) deposits rest upon Turonian (including Inoceramus schloenbachi Zone), and locally on older rocks. The lithofacies maps show that thickness and lithofacies distribution in the Cenomanian was independent of the strike of the Koszalin-Chojnice Zone. Such a dependence began and was accentuated in the Coniacian. Santonian and Campanian clastic deposits, extending along the SW boundary of the Mid-Polish Swell and absent in the SW part of the Pomeranian Trough, suggest local tectonic inversion within the central part of the Mid-Polish Trough.