Chronostratigraphy of clinothem-filled non-marine basins: Dating the Pannonian Stage

Abstract

Clinoforms and clinothems are important and common architectural elements in the sedimentary record of many basins worldwide. The influence that they exert on chronostratigraphic interpretations, however, is often underestimated. This is especially true in non-marine basins, such as the Central European to Central Asian Neogene Paratethyan basins, where chronostratigraphic division and correlation is usually based on fossils of environmentally sensitive molluscs recovered from outcrops of shallow-water deposits. In the subsurface, the diachronous boundary between the foreset and topset parts of the shelf-edge scale clinoforms, where significant lithological and paleontological changes can be observed with the transition from deep to shallow water, was routinely identified with one of the regional stage or substage boundaries, inflicting serious confusion in chronostratigraphy. In the late Neogene brackish lacustrine basin fill of the Pannonian basin (Pannonian Stage, 11.6 to 2.6 Ma), where extended endemic radiation and long-term gradual morphological change in various groups of the biota offer good marker species for high-resolution biostratigraphy, molluscs and dinoflagellate algae are used to establish a clinothem chronostratigraphy. The biozone and clinothem boundaries are correlated with the geological time scale through mammal stratigraphic considerations, magnetostratigraphy, and radiometric dating. For the time being, the beginning of lacustrine deposition at 11.6 Ma and the intervals between 8.8 and 7.1 Ma and 4.6–2.6 Ma are accurately dated in drill cores. These time intervals can be correlated through the dense seismic network across the basin. For other time intervals of the late Miocene and Pliocene, the uncertainty of dating remains high on the order of several 100 kys. • Discrepancy between field- or well-based stratigraphy and clinothem geometry is commonly a source of correlation issues. • Such chronostratigraphic misinterpretations are especially common in the non-marine basins of the Paratethys region. • The endemics-based biostratigraphy of the Neogene lacustrine Pannonian basin was adapted to the seismically imaged clinothem sets. • The clionoform-bounded biochronozones of the Pannonian basin are dated by magnetostratigraphy and radioisotopic dating.