Eocene Hieroglyphic beds of Silesian Nappe in Western Polish Carpathians – development and foraminiferal record

Abstract

The sedimentation of Hieroglyphic beds of the Silesian Nappe took place between the Lower and Middle Eocene and Upper Eocene within the Carpathian Silesian Basin. These beds are represented by thin-bedded flysch containing – at various stratigraphic positions – sandstone-less complexes with variegated shales and bentonite laminae developed in conditions of calm sedimentation with a limited supply of material from the land. The profiles of Hieroglyphic beds of the Silesian Nappe are diversely developed. Their variability and borderline sequences, transitory into overlying and underlying divisions, are presented. In the Ypressian, during the sedimentation of Hieroglyphic beds, foraminiferal associations with numerous small sized Trochammina developed, which formed in the Silesian Basin after the PETM crisis.  Since the Lutetian, in slightly more favourable conditions, more differentiated associations have occurred, with Reticulophragmium amplectens (Grzybowski), Ammodiscus (Dolgenia) latus (Grzybowski), and Reticulophragmium gerochi Neagu et al., which preferred cool waters, being index fossils for stratigraphy. Hieroglyphic beds developed during an interval of the gradually cooling climate. The gradual decrease in temperature stimulated the transfer of species: in the Eocene associations of Hieroglyphic beds a number of thermophilous forms, whose optimum of development came in the Upper Cretaceous-Paleocene, disappeared whereas new species appeared which prefer cold waters commonly occurring in boreal basins. The deep restructuring of foraminiferal assemblages took place in the Priabonian, when massive numbers of calcareous benthonic and planktonic forms occurred.