An integral way to stratigraphy – Are there global climate signals in the North Alpine Foreland Basin?

Abstract

Observed paleoenvironmental fluctuations in the North Alpine Foreland Basin, as one of the largest sedimentary archives of the Oligocene and Miocene are mainly controlled by regional factors. Global climate signals are usually less prominent than local tectonics and sedimentary input, caused by the enclosed paleogeographic setting of the Paratethys. Moreover are stratigraphic concepts still under debate, disabling a precise correlation of observed regional environmental changes to global climate patterns. In this study, a multi-proxy approach is used to achieve an accurate chronostratigraphy of regional formations and to verify whether global signals can be detected in the North Alpine Foreland Basin. Therefore, a detailed paleoenvironmental and biostratigraphic study of an 18 m-thick section of marine Miocene deposits (Neuhofen Formation) was carried out, using micropaleontology, sedimentology and geochemistry. In total 39 samples, yielding 68 foraminifera species and 47 ostracod species were processed together with 32 nannoplankton samples. Additionally, 34 ostracods and 49 benthic foraminifera were used for the analysis Oxygen and Carbon isotopes. Furthermore, 50 samples of six different sites in the Neuhofen Formation were used for statistical analyses of benthic foraminifera to assess supra-regional environmental correlations. Finally, the chronostratigraphic concept of the Neuhofen Formation was revised using magnetostratigraphic data from four sections, nannoplankton biostratigraphy and Sr-Isotope stratigraphy from previous studies as well as 3D-modelling using previous data additionally to 29 drillings. For the hypothesis that regional environmental patterns are correlating with global climate signals, environmental indices of the Neuhofen Formation (Isotopes, Diversity, Infaunalisation, Abundancy) were compared with global isotope values and Milankovic Cycles. The new stratigraphic concept of the Neuhofen Formation yielded an age of 18.1 – 17.6 Ma with a depositional time of 500,000 years. It was shown by a cluster analysis that strong faunal differences exist between the single localities, indicating separate paleoenvironments. These environmental differences are rather caused by regional factors. Occasionally, e.g. at 17.67 Ma, throughout the deposition of shallow marine sediments in the Neuhofen Formation the influence of global climate change can be inferred.