Hochauflösende Chronologie des Unter- und Mittel-Miozän Süddeutschlands
Zusammenfassung der Projektergebnisse
This project has been focused on biostratigraphy, geochronology, palaeoclimatology, and bentonite geochemistry from the Upper Freshwater Molasse of the NAFB. The main results are the following: Morphometric analyses on Megacricetodon species verify the existence of several independent evolutionary lineages within this genus during the Miocene in Southern Germany. The identified lineages are (in stratigraphic order): 1) the M. bavaricus lineage (18- 15 Myr), the M. aff. gregarius lineage (~14.4-13.5 Myr), 3) the M. germanicus lineage (13.5- ~12.8 Myr). The M. bavaricus lineage is characterized, beside size increase, by outline changes through time of both m1 and M1. The M. aff. gregarius lineage immigrates into the area around the end of the climate optimum. The M. germanicus lineage is again an immigrant and cannot be derive from the M. aff. gregarius lineage. The species M. collongensis is not equivalent to the German Early Miocene samples of the OSM A, therefore this name cannot be applied to primitive populations from the M. bavaricus lineage. In contrast, the species M. lappi fits in the outline of the large size population of the M. bavaricus lineage, which confirms earlier morphologic results. This study shows the difficulties to taxonomically assign the small-sized Megacricetodon forms, and the longdistance correlations based on such assignment are to be taken with the highest care. As M. collongensis is not recorded in the NAFB, a correlation with the specimens attributed to the French species in the Iberian Peninsula needs a deeper analysis. The M. bavaricus lineage, although playing a primordial role in the Early-Middle Miocene biostratigraphy in the NAFB, is without detailed analysis of dangerous use in term of long distance correlations. Based on methods developed by Böhme et al. we performed a high-resolution precipitation and continental runoff curve for the Miocene of Central Europe. In contrast to the late Karpatian and the beginning of the Badenian, the Ottnangian and early Karpatian are characterized by pronounced and rapid climatic shifts, which we attribute to a highly dynamic cryosphere of the Southern Hemisphere. The available data indicate that humidity and temperature are generally positively correlated. Three extreme arid events (EAE) with mean annual precipitation (MAP) <200 mm are recognized during this time. A Carpathian-Pannonian provenance of the investigated Bavarian rhyolite tuffs has been deduced from major and trace elements, Nd-Sr isotopes, and 40Ar/39Ar and U/Pb zircon ages. In detail, the data manifest a close genetic relationship with the volcanic fields at Bükkalja and Tokay, NE-Hungary. This parentage implies transport of the plinian tuff particles for more than 850 kms, suggesting that during the Miocene Climate Optimum easterly stratospheric wind circulation was dominant. 40Ar/39Ar and U/Pb dating of glass fragments and single zircons, respectively, indicate that the so-called ―main bentonite‖ is composed of at least three different tuff layers of ca. 15.06, 14.9, and 14.8 Ma. This is in contrast to conventional interpretations which assume a single volcanic pulse as ―main bentonite‖ source. An additional U/Pb age of 14.2 Ma for the bentonite at Bischofzell (Zürich) indicates that volcanic activity in NE-Hungary and easterly stratospheric winds continued for at least another half a million years. A highly significant by-product of the present study is the establishing of a high-accuracy, high-precision age of the Ries impact structure. The age has been derived by dating the three principal impact products (suevite, moldavite tectite, Brockhorizon) by 40Ar/39Ar and U/Pb and combining the results with astrochronological, paleomagnetic and paleontological/biostratigraphic data. The derived impact age of 14.94 ± 0.07 Ma represents an important stratigraphic time marker for the Miocene Molasse sediments and contrasts with recently published and significantly younger ages (14.3-14.6 Ma). Palaeomagnetic investigations of the Kirchberg Formation give results of variable quality. Based on the available data the correlation of the obtained polarity record to ATNTS04 has been achieved by comparing the bio-magnetostratigraphy of this locality to the established chronostratigraphic framework for the eastern and western Bavarian Upper Freshwater Molasse (UFM), resulting in the correlation of the normal interval in Kirchberg to the short normal chron C5D.1n around 17.73 Ma. Our publication of the bio-magnetostratigraphic dating of the oldest hominoid fossil outside Africa has received high international attention and have been highlighted by Nature ('Ancient tooth tells of migration‘, Nature, 7. July 2011, page 8).
Projektbezogene Publikationen (Auswahl)
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(2010). Integrated stratigraphy and 40Ar/39Ar chronology of the Early to Middle Miocene Upper Freshwater Molasse in western Bavaria (Germany). International Journal of Earth Sciences, 99:1859–1886
Abdul-Aziz, H., Böhme, M., Rocholl, A., Prieto, J., Wijbrans, J., Bachtadse, V.
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(2011). Biomagnetostratigraphy and the Environment of the oldest Eurasian Hominoid from the Early Miocene of Engelswies (Germany). Journal of Human Evolution
Böhme, M., Abdul Aziz, H., Prieto, J., Bachtadse, V., Schweigert, G.
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(2011). Miocene precipitation in Europe: Temporal trends and spatial gradients. Palaeogeography, Palaeoclimatology, Palaeoecology 304 (3/4): 212-218
Böhme, M., Winklhofer, M., Ilg, A.
