Authigenic carbonate formation in the ocean

Oceanic authiaenic carbonates are classified according to the origin of carbonate carbon source using a complex methodology that includes methods of sedimentary petrography, mineralogy, isotope geochemistry, and microbiology. Mg-calcite (proto-dolomite) and aragonite predominate among the authipenic carbonates. All authigenic carbonates are depleted in heavy carbon isotope 13 C and enriched in heavy oxygen isotope O-18 (in PDB system), indicating biological fractionation of isotopes during the carbonate formation. Results obtained show that authigenic carbonate formation is a biogeochemical (microbial) process, which involves carbon from ancient sedimentary rocks, abiogenic methane, and bicarbonate-ion of hydrothermal fluids into the modern carbon cycle.