Austrian Journal of Earth Sciences Volume 102/2 Vienna 2009 The initial phase of the early Sarmatian (Middle Miocene) transgression. Foraminiferal and ostracod assemblages from an incised valley fill in the Molasse Basin of Lower Austria. Holger GEBHARDT*), Irene ZORN & Reinhard ROETZEL KEYWORDS paleoenvironmental interpretation Middle Miocene Lower Austria foraminifera Geologische Bundesanstalt, Neulinggasse 38, 1030 Wien, Austria; Sarmatian ostracods *) Corresponding author,
[email protected] Badenian Abstract In order to document the foraminiferal and ostracod faunal changes between Badenian and Sarmatian strata, we investigated sam- ples from a sediment core drilled at Hollabrunn in Lower Austria. Lower Badenian strata show typical normal marine, outer shelf to upper bathyal foraminferal and ostracod assemblages also known from other sections in the Molasse and Vienna Basins. The co- occurrence of Praeorbulina glomerosa circularis and Orbulina suturalis indicates a lower Badenian age for these samples, corres- ponding to the mid Langhian Zone M6. The investigated core lacks middle to upper Badenian strata. We were able to identify the Sarmatian samples by 1) index species and 2) by apparently unique autochthonous microfossil assemblages. We found the Sarma- tian foraminiferal index species Nonion bogdanowiczi and Anomalinoides dividens in samples from the upper part of the core and did not find foraminifers or ostracods belonging to lower Sarmatian Elphidium reginum Zone or younger (eco-) Zones. Consequently, the drilled Sarmatian samples belong to the basal Sarmatian Anomalinoides dividens (eco-) Zone. The monospecific occurrence of Au- bignyna perlucida in one older sample, however, suggests an extreme, most likely brackish environment with very different condi- tions from those prevailing earlier during the Badenian.