Late Oligocene micromammal teeth (MP28/29) from the Lower Freshwater Molasse (USM) of Chrummorge (Lägern, N-Switzerland)

The small sandpit “Chrummorge” on the Lägern hill (N-Switzerland) was searched for small mammal fossils. Bone fragments and about 100 teeth were retrieved while screen-washing of about 300 kg of Late Oligocene river channel-sands. Sedimentology indicates a probably meandering stream type, which likely followed a more erosional environment with tropical karsts and the formation of bolus-clay and iron ore. Even though, most of the micromammal teeth were rolled due to river transport before sedimentation, it was still possible to identify teeth of biostratigraphical importance, dating this new mammal assemblage to MP28/29 (about 24.6 ± 0.2 Ma). These Late Oligocene river channel sands are the oldest molasse sediments in the Lägern area, and they are in direct contact with Late Jurassic limestone. Thus they add important information for the reconstruction of the regional geological history. [ABSTRACT FROM AUTHOR]