Characterization of lowest oxygen environments within ancient upwelling environments: Benthic foraminifera assemblages

The Upper Campanian Mishash Formation of southern Israel was deposited within the southern Tethys upwelling belt, with sea floors beneath this system characterized by poorly ventilated sediments approaching anoxia. This study was aimed at tracking the oxygen-poor gradient using benthic foraminiferal assemblages of organic-rich carbonates that are devoid of benthic macro-invertebrates and trace fossils. Quantitative data were gathered on foraminiferal faunas from four sections, namely Zin/Saraf, Qazra (Ashosh, Omer) and Qilt, from three basins affected by upwelling. Four distinct benthic foraminiferal assemblages characterize the organic-rich carbonate facies (B-assemblages A-D). These assemblages are distinguished by their species richness and composition, relative abundance, and dominance patterns. The low-diversity buliminid-dominated faunas correlate with high (up to 25 wt.%) total organic carbon levels, and inferred pore water oxygen levels range from nearly anaerobic to dysaerobic (up to 0.1 ml O₂/l). The Zin and Qazra/Ashosh basins in southern Israel have representation of assemblages A and B, indicative of the most oxygen-depleted environments. Assemblages C and D are more common in better ventilated environments, such as the Qazra/Omer basin of southern Israel and the Qilt basin to the northeast. Nonetheless, all these basins have benthic assemblages indicative of low-oxygen pore waters (< 0.1 ml O₂/l) beneath the upwelling belt, in comparison with the open Tethyan system indicated by the Shefela basin of central Israel.