Bio- and chemostratigraphy of the Posidonia Shale: a new database for the Toarcian Oceanic Anoxic Event from northern Germany

Abstract

We present calcareous nannofossil biostratigraphy, calcium carbonate and organic carbon isotope data of two cores drilled in the North German Basin (northern Germany) covering the upper part of the Amaltheenton-Formation (Fm) (upper Pliensbachian) and the Posidonienschiefer-Fm. (Toarcian). Fourteen bioevents spanning the latest Pliensbachian to late Toarcian time interval allowed the identification of the NJ5, NJ6 and NJ7 Zones of the Boreal biozonation. The early Toarcian Oceanic Anoxic Event (T-OAE), identified by the organic carbon isotopic excursion within the Posidonienschiefer-Fm., is constrained by the first occurrences (FOs) of Carinolithus superbus crassus and Diductius constans at the onset of the delta C-13 anomaly. The last occurrences (LOs) of the nannofossil species Crepidolithus granulatus, Parhabdolithus liasicus distinctus, Biscutum finchii and Biscutum grande are detected within the delta C-13 isotopic anomaly. The new biostratigraphic data acquired in the North German Basin are compared to data from sections at higher and lower latitudes to evaluate event reproducibility relative to the delta C-13(org) isotope curve. The FO of C. superbus crassus is an excellent datum to constrain the onset of the T-OAE at supraregional - global scale. Our finding indicates further nannofossil biohorizons within the T-OAE that might be useful at regional scale.