Geochemical analysis of the WINT-UU-21 core to study volcanism during the Late Triassic (Rhaetian) at Winterswijk

Abstract

The WINT-UU-21 core taken at Winterswijk is studied for evidence of environmental change, specifically volcanism, during the late Triassic and the emplacement of the Central Atlantic Magmatic Province (CAMP). The Late Triassic (Rhaetian) part of the core consists of black shale from 23.985 to 20.2 mbs and red and grey clay (mainly red) until 13.55 mbs. Magnetic susceptibility and carbon isotope data combined with Hg, palaeoproductivity proxies, climatic proxies, and redox proxies are used to determine and compare changes during this time interval with other studies. There is a clear negative Carbon Isotope Excursion (CIE) visible in the δ13C data, which matches with the Marshi CIE in other studies. Together with Hg data there is a clear indication that there is indeed volcanism taking place during the sedimentation of the core. The volcanism would have taken place in the lowest part of the Rhaetian that is preserved in the core. The Marshi CIE is used to correlate the Winterswijk core to two sites in northern Germany, which also show the extinction interval known as the Triletes Beds above the Marshi CIE. The lithological transition from shale to clay in the core corresponds to the changes from the Contorta Beds (pre-extinction interval) to the Triletes Beds (extinction interval). As there are other Hg spikes in the core without changes in δ13C it is clear that there is another source of Hg besides volcanism or at least that high Hg concentrations do not mean that there is volcanism taking place. Clear cyclicity likely caused by precession is clearly visible in the Total Organic Carbon (TOC) and climatic proxies used in this study, and slightly less in the magnetic susceptibility. Magnetic susceptibility is not indicative of terrestrial input, as high peaks in the magnetic susceptibility are not accompanied by increases in terrestrial trace elements Fe, Ti and Al. To study palaeoproductivity the enrichment factor of Ba and P are analysed. Both elements are under- enriched compared to the reference shale, but these two elements are not in agreement with each other about the changes in palaeoproductivity through time. This might be due to an outside source of P to the system, as the enrichment factor of P in the extinction interval is not lower than before the extinction interval and anoxia does not seem to play a role in Ba and P recycling. Anoxia is higher in the Contorta Beds than the Triletes Beds, but does not seem to correlate to other changes throughout the core, aside from lower anoxia in the Triletes Beds during drier conditions.