Integrated stratigraphy and Ar/Ar chronology of the Early to Middle Miocene Upper Freshwater Molasse in eastern Bavaria (Germany)

A detailed integrated stratigraphic study was carried out on middle Miocene fluvial successions of the Upper Freshwater Molasse (OSM) from the North Alpine Foreland Basin, in eastern Bavaria, Germany. The biostratigraphic investigations yielded six new localities thereby refining the OSM biostratigraphy for units C to E (sensu; Heissig, Actes du Congres BiochroM’97. Mem Trav EPHE, Inst Montpellier 21, 1997) and further improving biostratigraphic correlations between the different sections throughout eastern Bavaria. Radioisotopic ages of 14.55 ± 0.19 and 14.88 ± 0.11 Ma have been obtained for glass shards from the main bentonite horizon and the Ries impactite: two important stratigraphic marker beds used for confirming our magnetostratigraphic calibration to the Astronomical Tuned Neogene Time Scale (ATNTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). Paleomagnetic analysis was performed using alternating field (AF) and thermal (TH) demagnetization methods. The AF method revealed both normal and reverse polarities but proofs to yield unreliable ChRM directions for the Puttenhausen section. Using the biostratigraphic information and radioisotopic ages, the magnetostratigraphic records of the different sections are tentatively correlated to the Astronomical Tuned Neogene Time Scale (ATNTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). This correlation implies that the main bentonite horizon coincides to chron C5ADn, which is corroborated by its radioisotopic age of 14.55 Ma, whereas the new fossil locality Furth 460, belonging to OSM unit E, probably correlates to chron C5Bn.1r. The latter correlation agrees well with the Swiss Molasse locality Frohberg. Correlations of the older sections are not straightforward. The Brock horizon, which comprises limestone ejecta from the Ries impact, possibly correlates to C5ADr (14.581– 14.784 Ma), implying that, although within error, the radioisotopic age of 14.88 ± 0.11 Ma is somewhat too old. The fossil localities in Puttenhausen, belonging to Electronic supplementary material The online version of this article (doi: 10.1007/s00531-006-0166-7) contains supplementary material, which is available to authorized users. H. Abdul Aziz (&) V. Bachtadse Department for Earth and Environmental Sciences, Section Geophysics, Ludwig-Maximilians-University Munich, Theresienstrasse 41, 80333 Munich, Germany e-mail: [email protected] M. Böhme J. Prieto Department for Earth and Environmental Sciences, Section Palaeontology, Ludwig-Maximilians-University Munich, Richard-Wagner-Str. 10, 80333 Munich, Germany A. Rocholl Department for Earth and Environmental Sciences, Section Mineralogy, Ludwig-Maximilians-Universität München, Theresienstrasse 41, 80333 Munich, Germany K. Heissig Bavarian State Collection for Palaeontology and Geology Munich, Richard-Wagner-Str. 10, 80333 Munich, Germany J. R. Wijbrans Department of Isotope Geochemistry, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands A. Zwing Ludwig-Maximilians-University Munich, Leopoldstrasse 3, 80802 Munich, Germany 123 Int J Earth Sci (Geol Rundsch) DOI 10.1007/s00531-006-0166-7