Middle to upper Eocene dysoxic-anoxic Kuma Formation (northeast Peri-Tethys): Biostratigraphy and paleoenvironments

In the late middle to earliest late Eocene, a vast dysoxic to anoxic basin extended from the Crimea in the West through the northern Caucasus to the Aral Sea in the East, and a huge amount of organic carbon was deposited in the organic-rich sediments of the Kuma Formation. We document the paleo-environmental conditions in the basin using benthic foraminiferal and organic carbon data. Oxygen levels were lowest during the deposition of the middle part of the Kuma Formation, a time of relatively cool climate. We estimate the time of deposition and its duration as ranging from planktonic foraminiferal zones upper P11 through P14, and calcareous nannofossil zones CP13c to lowermost CP15 (∼44-36.5 Ma). We argue that this large-scale storage of organic carbon over ∼7 m.y. resulted from a complex interaction of tectonic and climatic factors, and that it may have influenced the global carbon budget in the ocean-atmosphere system. It probably was at least a contributing factor to the global cooling in the middle Eocene that led to the establishment of ice sheets on the Antarctic continent by the end of the Eocene. © 2003 Geological Society of America.