Calcareous nannofossil biostratigraphy of the Grund Formation (Molasse Basin, Lower Austria)

The calcareous nannoplank-ton was studied in samples from the Grund Formation type locality (sections B, F, G and H). Samples from Grund-Windmuhlberg (W1-W4) were further collected and investigated. The nannofossil assemblages are characterized by biostratigraphically important Helicosphaera waltrans, H. walbersdorfensis and the rare occurrence of discoasterids. Although the marker species Sphenolitus heteromorphus is absent in all samples, the composition of nannofossils enables specification of these deposits as Biozone NN5 of Martini (Lower Badenian). Regular presence of H. waltrans, which is usually limited to a short stratigraphic interval within nannoplankton Zone NN5, enables attribution of these sediments to the Helicosphaera waltrans Horizon (Svabenicka 2002).