Biostratigraphical and paleoecological significance of small foraminiferal assemblages of the Silesian (Cieszyn) Unit, Western Carpathians, Poland

Abstract

Biostratygraficzne i paleoekologiczne znaczenie zespołów małych otwornic jednostki śląskiej (cieszyńskiej) w polskiej części Karpat Zachodnich The oldest assemblage of the nonflysch marly sediments (Lower Cieszyn Shales; Tithonian) is dominated by calcareous benthic foraminifera. Some foraminifers are reported here for the first time (Belorusiella wolinensis, Geinitzinita wolinensis, Frondicularia cf. inderica, Lenticulina cf. ambanjabensis, L. ponderosa). The assemblages may be referred to those of the European Platform (neritic zone), but the presence of radiolarians (calcificated) suggest at least the upper bathyal environment o f Cieszyn basin. Foraminifers o f Lower Cieszyn Shales originate from the Malm microfauna following destruction o f north carbonate margins of Tethys, and subsidence of basin o f the Tithonian age. The worldwide regression during the late Tithonian and early Berriasian corresponding to the Neocimmerian orogeny may be responsible for the supply of those neritic forms into the Cieszyn basin. The younger microfossils from the calcareous flysch (pelitic Cieszyn Limestones; Berriasian) and shaly flysch (Upper Cieszyn Shales, Grodziszcze Beds and lower part of Vefovicc Shales; Valanginian-Barremian) are composed of both calcareous and primitive agglutinated foraminifera reflecting an upper to middle bathyal environment. The foraminifera from shaly-sandy deposits - the upper part of the Vefovice Shales, lower and middle part of Lgota Beds (Aptian-AIbian) - consist o f arenaceous species (except for Hedbergella sp. and Cibicides sp.) and correspond to lower bathyal conditions. The described assemblages resemble the coeval faunas o f the Alpine flysch troughs. Two low-oxygen periods in the late Berriasian-Valanginian (assemblage with Pseudoreophax cisovnicensis) and the early Albian (assemblage with Haplophragmoides nonioninoides) have been recognized in the Cieszyn basin.