Ammonites of the geslinianum zone, Upper Cenomanian (BCB)

ENGLISH SUMMARY Ammonite assemblage from the Upper Cenomanian of the Bohemian Cretaceous Basin realtively poorly known. Some species have been described herein for the first time: Thomelites cf. sornayi (Thomel) Euomphaloceras septemseriatum (Cragin) Eucalycoceras pentagonum (Gragin) and Allocrioceras annulatum (Shumard.). These records predominantly come from the M. geslinianum zone sediments developed in the higher parts of the Pecinov member (Uličný et al., 1998) of the Peruc - Korycany Formation. The sediments yielding ammonite assemblage represents the Late Cenomanian transgressive tract, accompanied by anoxic event OAE II = Oceanic anoxic Event II, CTBE) worldwide recorded in sediments and showing an increased content of stable isotope δ13 C. The OAE II is suggested to be connected to marine biota crisis and also the mass extinctionas well. The most affected organisms were benthic forms, due to high anoxic conditions at the bottom of the water column. Morphological features of the shells may, depending on the quality preservation shells (or cores) can be used to paleobathymetric interpretations. Most described species lived at depths of 50-80 m (up to 100m). Pelagic ammonites (i.e. Sciponoceras) lived at depths of up to 50 m. Heteromorphic taxa (Allocrioceras) have occurred at a depth of up to 100 m