Anoxia-Dysoxia at the Sediment-Water Interface of the Southern Tethys in the Late Cretaceous: Mishash Formation, Southern Israel

Abstract

Anoxic conditions prevailed on the Late Cretaceous seafloor beneath a long-term upwelling system situated across the southern Tethys. In Israel, the acme of this system was during the Campanian, when a suite of characteristic lithofacies (organic-rich carbonate, phosphorite, porcelanite, and chert) was broadly distributed over at least a 250 km wide zone encompassing the paleotopography of the Syrian Arc fold belt and beyond. Stressed faunal associations developed all across this belt. While more ventilated horizons supported molluscan assemblages, laminated sediments with oxygenation levels below 0.1 ml O2/l were macroscopically sterile but were found to support rich foraminiferal microfaunas. These faunas, apparently adapted to near anoxia, are dominated by two highly specialized buliminid species, Neobulimina canadensis and Praebulimina prolixa, in five assemblages that define different levels of oxygen stress. The foraminifera presumably lived below the sediment surface in the pore-water microenvironment, where habitat partitioning depended on food and oxygen resources rather than the nature of the sediment particles. They therefore do not correlate to the sediment type or lithofacies from which they were recovered.