Sedimentology and stratigraphy at the rocky coast of the upper Burdigalian Molasse Sea: a case study from Gurlarn near Passau (SE Germany)

This study presents a sedimentological and stratigraphical description of the Gurlarn site near Passau (SE Germany), which exposes an almost completely preserved Ottnangian near-shore succession of the Upper Marine Molasse in direct contact with the crystalline basement of the Bohemian Massif. Sedimentological features indicate quiet depositional conditions in a depression of the crystalline palaeorelief. The sediments were presumably deposited in the form of a basinal mud succession. Deposition most likely resulted from rapid flooding that may have been induced by tectonical subsidence. The macro- and microfaunal assemblages indicate that the Lower Ottnangian part of the section represents a marginal-marine, approximately 20 m deep equivalent of the Neuhofen Beds. This is the first evidence of shallow facies of the Neuhofen Beds, which have previously only been reported from 100 to 200 m deep basinal settings. The Middle Ottnangian part of the section corresponds to the facies of the “Blättermergel” based on the foraminiferal assemblages. The Gurlarn section may exemplify a widespread situation in the Ottnangian of the Molasse Sea, even though no entirely identical deposits are known from elsewhere. All other successions of similar age that yield a corresponding fauna are dominated by coarse-grained, high-energetic deposits or carbonates. Our data provide additional evidence for a single transgressive-regressive sequence in the Ottnangian.