Late Cenomanian Paleoecological Event OAE 2 in the Sections of the Northern Peri-Tethys (Crimea, Eastern Caucasus): Sediment Structure and Dynamics of their Accumulation

The comparative characteristics of sedimentary successions corresponding to the paleoecological event OAE 2, which are spaced over 1000 km apart within the Crimean–Caucasian region, are present. It is shown that the sediments accumulated during this time span under different sedimentary conditions are featured by the similar structures. The sedimentological, geochemical, and paleoecological analyses, indicate that (1) stable oxygen deficient conditions were not spread in the water column of the paleobasin; they occurred locally in a thin layer of bottom water owing to the oxidation of organic matter accumulated on the seafloor; (2) geochemical anomalies inherent in the TOC-rich horizon extend to the embedding layers that indicate their involving to the paleoecological event. The carbonaceous sediments of OAE 2 formed due to the enhanced nutrients influx from the land during the eustatic transgression caused the dramatic increase in the plankton productivity. The transgression was complicated by frequent sea-level fluctuations of minor magnitude associated with the Milankovitch precession cycles.