Age duration and depositional history of the Lower Muschelkalk of Winterswijk

Abstract

If one wishes to fully understand the sedimentation of the Lower Muschelkalk and evolution of the Germanic basin during the Middle Triassic, it crucial to know how long the deposition of the Lower Muschelkalk has taken place. While this has been studied for the center of the Germanic basin, this is not the case for sites located at the edge of the basin. This included the Lower Muschelkalk of Winterswijk, for which there is currently no duration known. In the quarry of Winterswijk the Lower Muschelkalk consists of a 40 meter thick deposit of micritic (marly) limestones, interchanges with several claystones and dolostones. A XRF-scan was executed on a core taken right next to the quarry to trace cyclicity within the geochemical composition of the section. The ratios of cycle-periods in the depth domain were compared with known astronomical periods from the Middle Triassic. This indicates that the thick claystone intervals that are present in the Lower Muschelkalk from Winterswijk represent the 405 kyr eccentricity cycle with a high probability. The whole duration of the deposition would then be ± 1 Myr. Comparisons with German Lower Muschelkalk sections strengthen this hypothesis. From geochemical profiles and calculated sedimentation rates it is proposed that astronomical climate forcing induces changes in lithology by sea level rise and fall.