The genesis of oolitic carbonates among the sulfate-carbonate-clayey deposits of the Lower Maeotian in the sections of Cape Kazantip was investigated through detailed analysis. Laboratory studies were conducted utilizing a range of analytical techniques, including carbonate chemical analysis, optical polarisation with computer support for photography and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), isotopy, gas chromatography (GCM), electron paramagnetic resonance (EPR), infrared (IR) spectroscopy, and X-ray diffractometry. The chemical composition of the oolitic carbonates was found to be characterizing by the constant presence of dolomite (11.93–40.98%) and clay (2.42–19.40%) components, as well as the most isotopically heavy values of carbonate carbon (2.74–5.40%) among the enclosing carbonates. This indicates the colites formation in saltwater of an extremely shallow coastal lagoon. The presence of gypsum in colite cores and as cement in oolitic carbonates and oolitic conglogravelites has been established, and it has been determined that gypsumification of the sediments occurred at the stage of colite formation. This process took place during a sharp fall in sea level and could be associated with the participation of sulphate ions from meteoric waters in the removal of sediments into the zone of meteoric-vadose conditions, possibly together with gas-fluid seepage. The occurrence of bottom gas-fluid seeps is corroborated by the detection of mineralized extracellular polymeric substance (EPS) in colites, as well as the presence of bacterially induced halite, barite and high-Mn kutnogorite from the dolomite group. Among the carbonate minerals found in colites, low and high-Mg calcites and Ca-dolomite have been identified; the distribution of the latter indicates the primary sedimentary genesis of dolomite micro-crystals in the colite structure.
Antoshkina et al. (Wed,) studied this question.