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

International audienceThe 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

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

Fig. S3. Trace elements normalized to the upper continental crust values of Rudnick and Gao (2013). (a) In Zalidou, a strong enrichment is observed for Zr (avg. 1.55), Hf (avg. 1.67) and Li (avg. 1.92). (b) In Hole 416A, depletions are observed for Zr (avg. 0.71) and Hf (avg. 0.71); also, a weak enrichment is observed for Cs (avg. 1.42) and Rb (avg. 1.38), and a strong enrichment is observed for Li (avg. 3.66). These are caused by the chemical fractionation of elements occurring during the transport of sediment

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

Fig. S5. Geographic location of the possible source areas for the Essaouira-Agadir Basin (Morocco) and DSDP Hole 416A. (A) Physical map of North Africa showing the African Sahara (delimited by the dashed line), West African Craton, Reguibat Rise, Moroccan Meseta, Saharan metacraton and the Bodélé Depression. (B) Physical map of northwest Morocco showing the location of the Essaouira-Agadir Basin (EAB), Moroccan Meseta to the north, High Atlas to the east and the Anti Atlas to the south and SE

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

Fig. S6. Comparing the initial isotope ratios (i; 135 Ma) of Pb and Sr in the studied successions (Zalidou and Hole 416A) with surrounding possible source areas having reported these isotopes (see also Supplementary Table). The possible sources are the central Sahara Bodélé Depression (Abouchami et al. 2013), Saharan metacraton (Küster et al. 2008) and modern Sahel desert dusts (Kumar et al. 2014)

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

Fig. S2. Location of selected samples (arrows) in Zalidou and DSDP Hole 416A; colors correspond to the pre-Weissert Event (blue), Weissert Event (green) and post-Weissert Event intervals (orange), following Shmeit et al. (2022). In Zalidou, the recognized stages are plotted with, the ammonite biostratigraphy (zones/subzones), calcareous nannofossil biostratigraphy (zones/subzones), sedimentary discontinuities (D0 to D8) and lithology (Reboulet et al. 2022; Shmeit et al. 2022). In Hole 416A, the recognized stages are plotted with, the calcareous nannofossil biostratigraphy (zones/subzones) same as for Zalidou, the lithological units, magnetic anomalies and lithology. Also, in Hole 416A, the Berriasian/Valanginian boundary is fixed following Čepek and Gartner (1980), and the top of the Valanginian stage is fixed following Shmeit et al. (2022). Abbreviations: Berr., Berriasian; Haut., Hauterivian; T. pertra., T. pertransiens; N. prem., N. premolicus; N. neocomiensi., N. neocomiensiformis; B. camp., B. campylotoxus; K. i., K. inostranzewi; S. ver., S. verrucosum; K. pro.; K. pronecostatum; T. c., Tescheniceras callidiscum and magnetic anom., magnetic anomalies