Small-sized Trochammina assemblages in deep-water Eocene flysch deposits (Outer Carpathians, Poland) and their palaeoecological implications

Abstract. The global climate change in the early Eocene contributed significantly to the turnover of benthic foraminifera. A major extinction within agglutinated and calcareous forms and the occurrence of opportunistic assemblages resulted. The Trochammina material described here belongs to these post-crisis assemblages. Foraminiferal assemblages with numerous Trochammina species are identified within deep-water Eocene deposits of the Polish part of the Outer Carpathians. Trochammina reach up to 80% of the assemblages, the remainder consists of cosmopolitan agglutinated foraminifera, mainly Bathysiphon, Recurvoides, Paratrochamminoides and Trochamminoides. The low biodiversity (average number of species 24, of genera 15) and the presence of dwarf forms are the main characteristics of the assemblages. These assemblages occur predominantly in shales with numerous organic traces (lower Hieroglyphic beds), deposited in the Silesian Basin (Outer Carpathians) which was on the northern margin of the western Tethys Ocean during the early Eocene (Ypresian, c. 50 Ma). The Trochammina biofacies developed in the Silesian Basin after the Paleocene–Eocene Thermal Maximum crisis, and is dominated by opportunistic forms, mainly represented by mobile epifauna and shallow-water infauna, interpreted as a recolonizing assemblage in a low energy environment.