On geological structure of the Ostrzeszów Hills

Abstract

Specific tectonic structure of sub-Cainozoic substratum played a decisive part in the origin of glaciotectonic deformations in the region of Ostrzeszów; the substratum is complicated here by the occurrence of proven horsts that are manifested by, among others, the occurrence of the oldest members of the Tertiary or even the Triassic - exposed on the land surface. The position of the Odolanów Valley within block-type dislocation zones as well as a region of liltoral sedimentation of Zechstein salt deposits contributed to the appearance of different cover structures with essential participation of halotectonic dislocations due to consecutive epeirogenic movements. When young-Alpine movements affected the area, horsts (of NE-SW orientation) were formed in the axis of the present Ostrzeszów Hills; sedimentation which was taking place in the Poznań Basin situated in the southeastern part of the Fore-Sudetic Monocline was subject to differentiation with respect to these horsts. The horsts were reactivated and even considerably uplifted (though on a local scale) in the time of Pleistocene glaciotectonic deformations. Apart from essential participation of water and differentiated compaction, shallow positive structures of stiff substratum within Cainozoic sediments in the south and a deep valley of the pre-Barycz River of tectonic setting in the north were the main factors that under subglacial conditions stimulated the development of shearing planes. This process resulted in the origin of many glaciotectonic structures within the Ostrzeszów Hills.