First high-precision U–Pb age from the Pennsylvanian-Permian of the continental Saar–Nahe Basin, SW Germany

The Saar–Nahe Basin is one of the largest intra-continental basins of the European Variscides. It is filled with up to 6500 m thick volcano-sedimentary rocks representing up to 40 million years of late- and post-orogenic basin evolution from the early Pennsylvanian to the late Early Permian. Radioisotopic dating of magmatites as well as intra- and extra-basinal pyroclastic rocks from the study area was carried out mainly during the end of the last century. Here, we present the first high-precision U–Pb CA-ID-TIMS age of 298.7 ± 0.4 Ma for a hitherto undated ash tuff layer of the Altenglan Formation near the middle part of the Pennsylvanian-Permian succession of the Saar–Nahe Basin. Comparative analyses of zircons from the same tuff layer and a closely associated tuff by U–Pb LA-ICP-MS yielded an age of 299.5 ± 2.6 Ma supporting the CA-ID-TIMS result. Based on the new data, the Pennsylvanian-Permian boundary in the study area is close to or even within the Altenglan Formation and overlying Rotliegend formations have to be considered of clearly Permian in age. A recently discovered and globally important fossil tetrapod lagerstaette of the Remigiusberg Formation lying immediately below the Altenglan Formation at the base of the Saar–Nahe Rotliegend is suggested to be of earliest Asselian minimum age.