Lower Cretaceous succession and biostratigraphy near overthrust plane of Silesian Nappe (Ostravice River Channel, Outer Western Carpathians, Czech Republic)

Abstract

Contact between the Upper Cretaceous rocks of the Subsilesian Nappe and the overthrust Lower Cretaceous rocks of the Silesian Nappe is uniquely exposed at locality Ostravice River Chanell. The deposits of the Silesian Nappe in the zone of overthrust plane that belong to the Hradiště Formation are tectonically affected. The more exact age of the mentioned rocks has never been documented earlier. The most significant stratigraphic data were obtained by the analysis of calcareous nannofossils. The sediments of the Hradiště Formation in the zone of overthrust of the Silesian Nappe belong to two partial tectonic slices. Sediments of slice on the contact between both the Nappes is, according to calcareous nannoplankton, of latest Hauterivian to Early Barremian age. In the area of the rapids, the other slice lying on it is of Late Hauterivian age. Micritic limestones occurring in the Late Hauterivian slice indicate basinal sedimentation above the carbonate dissolution level. Character of intercalated sandstones indicates of its turbiditic origin. Limestone interclasts in layers of gravelly sandstones document the erosion of the Upper Jurassic to early Lower Cretaceous carbonate platform by turbiditic currents. Further up the river, deposits belonging to higher, partial tectonic slices and stratal members of the Silesian Nappe were identified. At the beginning, a small part of the Veřovice Formation of Late Aptian age is exposed. After interruption, a huge outcrop of the Lhoty Formation of Middle and Late Albian age follows and then again the higher part of Hradiště Formation of Early Aptian age.