A fourth St. Gallen Formation cycle (?) in the Karpatian Upper Marine Molasse of central Switzerland

The Mauensee section in the Molasse Basin (North Alpine Foreland Basin) of central Switzerland represents one of the best continuously exposed outcrops of the St. Gallen Formation of the Upper Marine Molasse. A similarly well-exposed section is at Schmiedrued, situated about 15 km to the north. Biostratigraphic analysis of mammal and fish faunas shows that both sections are of Early Karpatian age. Palaeoecological analysis of the biota indicates an oligohaline intercalation within the marine part of the sections. This is additionally confirmed by the oxygen isotopic compositions of fish otoliths from the Mauensee section. The overlying marine sequence may represent a fourth cycle in the St. Gallen Formation that might perhaps indicate a Karpatian transgression from the Mediterranean Sea, which has not previously been recognized. Biostratigraphic comparison shows that the sedimentation of the Upper Freshwater Molasse began at the base of the Karpatian in southwest Germany and eastern Switzerland, and in the Middle Karpatian in central Switzerland. The presence of a Karpatian marine sedimentation area in central Switzerland may explain that the terrestrial sedimentation of the Upper Freshwater Molasse began at such different times.