An integrative palaeoenvironmental and chronostratigraphic study of the Lower Miocene in the North Alpine Foreland Basin – Are global climate signals detectable?

Abstract

Uncertainties in relation to chronostratigraphic correlations have limited our understanding of the possible impact of global-scale climate signals on the epicontinental sediments of the North Alpine Foreland Basin (NAFB). In an effort to resolve the problem, we have carried out a detailed palaeoenvironmental and chronostratigraphic study of an 18-m thick section of the marine, middle Burdigalian Neuhofen Formation (NH Fm) at Mitterdorf (SE Germany). Based on section logging, sampling of microfossils and nannoplankton, and analyses of stable oxygen and carbon isotopes, we demonstrate that significant environmental changes took place during the deposition of the NH Fm at Mitterdorf. In particular, the presence of nannoplankton zones NN3 and NN4 necessitated a re-interpretation of existing magnetostratigraphic data from Mitterdorf. To determine whether the observed environmental changes can be placed in a supra-regional and global context, a new chronostratigraphic framework was established for the study area using a multi-proxy approach based on 3-D modeling, litho-, bio-, and magnetostratigraphy, already available data, and statistical analyses of new and previously published microfossil data. The results reveal that the Mitterdorf section can be correlated with polarity chrons C5Dr.2r and C5Dr.1n and that its age is 17.78–17.65 (vs. 17.65–17.50 Ma or 17.95–17.85 Ma in earlier works). Furthermore, the results show that the deposition of the entire NH Fm took place during the interval from 18.1 to 17.6 Ma, and that the accompanying environmental changes did not occur isochronously across its range. Nevertheless, comparison of literature-based global datasets with our new data indicates that the 3rd order sea level highstand at 17.85 Ma had an impact on the environment of the NH Fm. Furthermore, transition from eutrophic, open marine to mesotrophic, shallow marine conditions at Mitterdorf coincides with minima in orbital eccentricity and global carbon isotope values at 17.67 Ma. Our results are summarized in palaeoenvironmental models of three time-points within the middle Burdigalian in the NAFB.