Climate variability and paleoceanography during the Late Cretaceous: Evidence from palynology, geochemistry and stable isotopes analyses from the southern Tethys

Abstract

The Late Cretaceous epoch witnessed significant changes in climate and considerable perturbations in the global carbon cycle, among others leading to Oceanic Anoxic Events (OAEs). Investigating the paleoceanographic setting in the southern Tethys (northern Egypt) is critical for a better understanding of the triggering mechanisms that occurred during deposition as a result of a greenhouse climate. Here we present bulk rock geochemical and stable isotopic proxies from the biostratigraphically well constrained Abu Roash A Member (180 m thick) deposited through the late Coniacian–earliest Campanian in the Abu Gharadig Basin of the north Western Desert of Egypt, to investigate whether there was a record of OAE3 and deposition of organic rich facies or oxic Cretaceous Oceanic Red Beds (CORBs). Paleoclimate in this low-latitude Tethyan setting was investigated, where warm to hot greenhouse climate prevailed based on specific dinoflagellate cyst taxa and regional correlation of the δ18Ocarb trends, despite a long-term temperature fall from the mid–Santonian onwards. Low river discharge and terrigenous input during arid conditions, inferred from elemental geochemistry and clay mineralogy, led to low marine productivity during enhanced carbonate production, and thus triggered low organic matter accumulation. The neodymium isotope signatures from bulk carbonate fractions along with available coupled ocean-atmosphere climate models indicate that the studied area witnessed a westward Tethys circumglobal current. These paleocirculation patterns caused enhanced water mixing, resulting in enhanced water column ventilation. These settings led to the deposition of organic-poor CORBs and the absence of the organic-rich OAE3 deposits.