Three-dimensional geological modeling supports a revised Burdigalian chronostratigraphy in the North Alpine Foreland Basin

Abstract

Precise age data are a basic prerequisite for the correlation of a sedimentary succession with the Global Time Scale, which in turn allows one to place its biotic and other data in a global context. In the North Alpine Foreland Basin (NAFB), a patchy distribution of outcrops and uncertainties in the correlation of strata have led to conflicting age models, in particular for deposits of lower Miocene (Burdigalian) age. Here, we present a new three-dimensional geological model of the SE German sector of the NAFB, covering an area of 13,200 km2, which helps to resolve the discrepancies. The dataset comprises lithostratigraphic information from 150 boreholes, supplemented by magnetostratigraphic data from six outcrops. Computer-based 3D modeling was conducted with the open source software QGIS for a 500-m-thick succession comprising units of the Upper Marine Molasse, the brackish Oncophora Fm and the Upper Freshwater Molasse. The results provide new insights pertaining to (1) the isochrony of strata, (2) subsidence, and (3) synsedimentary tectonics. The new data permit us to reliably place the outcrops within the regional lithostratigraphic scheme, thus enabling a new correlation of their magnetic polarities with the Global Time Scale. On this basis, we propose a revised age model for the middle and upper Burdigalian strata in the eastern part of the NAFB, which is supported by previously reported 87Sr/86Sr age data. The model indicates that the succession is substantially—up to 0.8 Ma—younger than earlier publications have suggested. Furthermore, it implies that the two synsedimentary tectonic events discerned may both be related to the large-scale tectonic movements that affected the NAFB during the late Burdigalian.