Biostratigraphy and the Mid-Jurassic environment from the Ogrodzieniec quarry

Abstract

The uppermost Bathonian and Callovian deposits from the newly exposed section of Ogrodzieniec were studied. The biostratigraphical analysis was based on both ammonite and dinocyst zonations. The uppermost Bathonian Orbis and Discus and the Callovian Herveyi, Jason, Coronatum, Athleta, Lamberti zones were distinguished. State of preservation of ammonites and lack of dinocysts made it impossible to distinguish Koenigi and Calloviense zones of the lowest Callovian. The position of the Bathonian/Callovian boundary was found in the clayey part of the section. Earlier the boundary was thought to be erosional. The new data indicate, however, the presence of continuous sedimentation, with low sedimentation rate, during Discus and Herveyi chrons. The presence of [i]Ctenidodinium combazii[/i] in Orbis, Discus and Herveyi zones shows normal sea conditions in this time. The change of the dinocyst assemblage the Bathonian/Callovian boundary indicates the sea water cooling.