Evolution of the eastern Austrian Molasse Basin - The lower Miocene (Burdigalian) as a key to the understanding of the EA

Sands of the Lower Miocene Traisen Formation in the Lower Austrian Molasse Basin represent a clastic interval correlated with the global sea level drop Bur3 (Burdigalian). Drill cores from OMV-wells in deep parts in the NE show hundreds of meters of pelites with intersections of sands. Profiles of carbonate content, XRD, XRF, whole rock chemistry, clay minerals, calcareous nannoplankton and dinoflagellate cysts of 7 wells were investigated. The Traisen Formation and its equivalents are characterized at their base by an increased clastic input, increasing mica content and decreased calcite content which goes hand in hand with the absence of nannoplankton. Whether the signal is related to a crisis in primary production or to carbonate dissolution remains unclear. These results enable us to define a basinal interval as equivalent to the proximal Traisen Formation which may serve as a key section for the stratigraphy of the deep basinal part influenced by a low salinity crisis that was caused by the closure of the connection to the Upper Austrian Molasse Basin. The closure is probably connected to the Miocene lateral extrusion of the Alps. This isolation may be terminated by the deepening of the Vienna Basin.