Mollusc bearing Neogene strata were collectively designated as ”Grund Beds” in the 19^th century. The different lithostratigraphic formations of these Grund Beds were studied in the Austrian Molasse Basin north of the Danube (Alpine-Carpathian Foredeep). Biostratigraphic methods and paleomagnetic measurements revealed that the entire Karpatian Laa Formation spans nannoplankton Zone NN4. It is transgressive on the Lower Miocene, Ottnangian marine sequences. The upper part of the Laa Formation correlates with the first occurrence of Globigerinoides bisphericus and is correlated in the type locality with the reverse Chron C5Cr and the normal chron C5Cn.2n. A distinct unconformity separates the Karpatian and Badenian sequences. The first Badenian transgression of the Molasse Basin resulted in a clastic sequence which, for the time being, has no lithostratigraphic designation. The lower part belongs to nannoplankton Zone NN4, with the first occurrence of Praeorbulina glomerosa glomerosa (Middle Miocene, Zone M5). The upper part of this basal clastic sequence belongs to nannoplankton Zone NN5. A coarse conglomerate, overlying a further unconformity, is interpreted as the transgression horizon of the fine clastic, more than 250 m thick Grund Formation. It spans nannoplankton Zone NN5 and contains Praeorbulina glomerosa circularis. Higher up in the sections, this species occurs together with Orbulina suturalis (plankton Zone M6). Ostracods and molluscs from the Grund Formation is distinctly different from the Karpatian, and indicate an unambiguously Badenian age. The normal paleomagnetic polarity measured in the type locality of the Grund Formation is interpreted as Chron C5Bn.2n. The Gaindorf Formation is coeval with the Grund Formation, developed along the western coast of the Molasse Basin. The more eastern development of the Mailberg Formation stratigraphically corresponds to the upper part of the Grund Formation with the co-occurrence of Po. glomerosa circularis and O. suturalis. In the Mailberg Formation a reverse magnetization is interpreted as correlating with Chron C5Bn.r.