The formation of Middle and Upper Pleistocene terraces (<i>Übergangsterrassen</i> and <i>Hochterrassen</i>) in the Bavarian Alpine Foreland – new numeric dating results (ESR, OSL, ¹⁴C) and gastropod fauna analysis

Abstract

Until now, reliable chronological classifications based on numerical ages for many Pleistocene fluvial deposits in the Alpine Foreland were rare. In this study, new numeric data (ESR, OSL, 14C) from Middle and Upper (Late) Pleistocene Hochterrassen (high terraces) and Übergangsterrassen (transitional terraces) in the Bavarian Alpine Foreland are presented. The dating results imply that the Hochterrassen gravel sensu stricto were deposited during the penultimate glacial (MIS 6, Rissian), and that underlying older gravel accumulation are predominantly of penultimate interglacial (MIS 7, Riss–Riss interglacial) age. In some areas of the Hochterrassen in the Danube valley south of Regensburg (interglacial Hartinger Schichten, Harting layers), and in some areas of the Rainer Hochterrasse (basal gravel unit I), Hochterrassen gravels are underlain by much older interglacial gravel deposits. These interglacial basal gravel deposits illustrate that the downcutting of these valleys far away from areas of Pleistocene foreland glaciations happened predominantly during warm-temperate interglacial or late-glacial periods. One last interglacial (MIS 5e, Riss–Würm interglacial) Hochterrasse is morphologically preserved in the Isar valley. This Jüngere Moosburger Hochterrasse is composed of the Fagotienschotter (Fagotia gravel, named after the gastropod Fagotia acicularis). The next younger terraces are the Early to Middle Würmian (MIS 5d to MIS 3?) Übergangsterrassen (transitional terraces), whereas the younger one of the two Übergangsterrassen was formed most probably during the Middle Würmian (MIS 3).