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During the Ottnangian (Early Miocene) the peripheral Alpine foreland basin was flooded by a shallow sea, which linked the Mediterranean in the south with the Paratethys in the northeast. Since this seaway shows a clear evolution and did not exist uniformly during the period investigated, we reconstructed its palaeogeography and bathymetry for the time of its maximum extent in the German part of the Molasse Basin. For this time interval tidal deposits are known from France and Switzerland towards Austria. A fully non-linear three-dimensional hydrodynamic model has been applied to reconstruct tidal currents and amplitudes. Residual currents are interpreted to represent net transport directions of sediments within the seaway. The model is forced at its open boundaries by semi-diurnal M 2 waves. The sensitivity of the tidal model has been tested, using different tidal amplitudes and phases at the open model boundaries. Based on this, the model indicates high mesotidal ranges, similar to those deduced from outcrops in Switzerland, Germany and Austria. The model suggests a complex system of convergent and divergent currents in the seaway, mainly along circular pathways.

The mass occurrence of turritelline gastropod shells from the Lower Miocene of southern Germany allows for detailed studies of their palaeoecology, transport mechanisms, preservation potentials and the reconstruction of nutrient regimes. Changes in the fabric of the gastropod‐dominated beds are used to reconstruct a generally deepening environment corresponding to the Lower Miocene transgression within the Upper Molasse Sea of the North Alpine Foreland Basin. The sedimentary succession ranges from chaotically arranged, densely packed and near‐shore transported; wave‐influenced deposits showing bimodal shell orientations; more widely dispersed shells showing a uni‐directional orientation; and dispersed shells showing diverse orientations. The shells often show damage to the apex and aperture though it is not clear whether this is due to predation events, pagurisation or abrasion due to transport. An outstanding feature is the replacement of aragonite shells by calcite leading to internal vugs as well as modulating the outer shell surface morphology. The high density of turritelline gastropods indicates a nutrient‐rich palaeoenvironment at the northern edge of the Molasse Sea.

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