Formation Conditions of the Lower Meotian Oolitic Carbonates (Cape Kazantip, Crimea)

Abstract

The genesis of oolitic carbonates among the lower Meotian sulfate–carbonate–clayey deposits in the Cape Kazantip sections was investigated. Laboratory studies were conducted using several analytical techniques, such as carbonate chemical analysis, optical polarization microscopy with the computer support for photography and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), isotopy, gas chromatography (GC), electron paramagnetic resonance (EPR), infrared (IR) spectroscopy, and X-ray diffractometry (XRD). The obtained results show that the chemical composition of oolitic carbonates is characterized by the constant presence of dolomite (11.93‒40.98%) and clayey (2.42‒19.40%) components, as well as the isotopically heaviest values of carbonate carbon (2.74‒5.40‰). These indicate the formation of oolites in saline water of an extremely shallow coastal lagoon. Gypsum is present in oolite cores and as cement in the oolitic carbonates and conglogravelites. Gypsification of sediments, which occurred at the stage of oolite formation during a sharp sea level fall, could be associated with the participation of sulfate ions from meteoric waters in the removal of sediments into the meteoric-vadose zone, possibly, together with the gas-fluid seepage. The occurrence of bottom gas-fluid seeps is corroborated by the detection of mineralized extracellular polymeric substance (EPS) in oolites, as well as the presence of bacterially induced halite, barite, and high-Mn kutnohorite of the dolomite group. Carbonate minerals in oolites are represented by low- and high-Mg calcites and Ca-dolomite. Distribution of the latter variety indicates the possibly primary sedimentary genesis of dolomite microcrystals in the oolite structure.