Climate change driven black shale deposition during the end-Triassic in the western Tethys

Several new Triassic–Jurassic boundary sections from the Eiberg Basin (Northern Calcareous Alps, Austria) have been studied at high resolution. We present integrated geochemical and biological proxy data from this western Tethys shelf basin. High-resolution correlation of Kuhjoch, the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic, Hochalplgraben and Tiefengraben shows that the initial and main Carbon Isotope Excursions (CIE) are contemporaneous with first and last occurrences of boundary defining macro- and microfossils. We focus on the end-Triassic initial CIE at the transition from the limestones of the Kössen Formation to the marls of the Kendlbach Formation. This change coincides with a dramatically increased influx of conifer (Cheirolepidiaceae) pollen and increased total organic carbon (TOC) values, succeeded by an acme of green algae (Cymatiosphaera). We present a model in which increased terrestrial organic matter influx is related to enhanced seasonality and increased erosion of the hinterland. Reduced salinity of the surface waters led to the mass occurrence of green algae. Stratification of the water column may have caused anoxic bottom water conditions and black shale deposition during the initial CIE at the base of the Kendlbach Fm.