Microspherulites in a biogenic-abiogenic carbonate formation (the lower maeotian carbonates, cape Kazantip, the Kerch peninsula)

The results of the study of calcite microspherulites in carbonate breccia formed at the junction of biohermal and bioclastic limestones (Lower Maeotian, Cape Kazantip, Kerch Peninsula), the nature of which is still being discussed, are presented. The following analytical methods were used: chemical carbonate, gas chromatography, Raman spectroscopy, electron microscopy with EDS, isotope. The studies resulted in the following: the presence in the fossilized biofilms of the pelitomorphic matrix and microspherulites of framboidal pyrite, halite, barite, celestine, dolomite-calcite, hematite and magnetite, which are absent in the other structural components of the breccia. Organic matter (OM) is represented by algal-cyanobacterial matter with a large contribution of the microbial component and an admixture of humic material. The carbonaceous matter in calcite microspherulites is actually characterized by primary unstructured organic matter. The accessory minerals zircon, oligoclase, rutile, neodymium-cerium monazite and vanadium silicide were identified. The formation of microspherulite calcites most likely occurred in the reducing conditions of the lagoon with high salinity in the contact zone of carbonate and microbial muds. The activation of authigenic mineral formation was facilitated by gas-fluid seeps from an active ancient mud volcano.