Geochemical and radiogenic isotope records of the Weissert Event in south Tethyan sediments

Abstract

The Cretaceous marine sedimentary record is characterized by time intervals rich in organic matter correlating with positive carbon isotope excursions, often called oceanic anoxic events. The Weissert Event corresponds to the first such event in the Cretaceous during the Valanginian stage. The associated palaeoenvironmental perturbations, which include increasing marine surface water primary productivity, are hypothesized to have been triggered by volcanic activity from large igneous provinces, and the source of nutrients is not well constrained (continental runoff v. oceanic upwelling). We present isotope ratios of Pb, Sr and Nd, together with concentrations of major and trace elements, for sediments from the central Moroccan margin to test these hypotheses. We demonstrate that the nutrient input was dominated by continental weathering. The source of sedimentary material remained stable during the Valanginian interval and originated from an old source, probably the African Sahara region. The radiogenic isotope signatures do not show a significant contribution of volcanic products from any known Valanginian large igneous province to the geochemical budget of sediments deposited on the central Moroccan margin. Although this does not preclude an impact of volcanic activity on the composition of seawater, it demonstrates that the erupted volumes were not sufficient to affect the deposited sediments. Supplementary material: The Supplementary Table contains three sheets: (1) Central Moroccan Margin, the analytical data generated and analysed during this study; (2) Fig. 8 data, large igneous provinces, the data of known Valanginian large igneous provinces used for comparison; and (3) Fig. 9 and S5 data, source areas, the data of potential surrounding source areas used for comparison, available at https://doi.org/10.6084/m9.figshare.c.6333040 .