DIRECTIONALITY AND PHASING OF CABONATE ACCUMULATION IN THE EARTH HISTORY

In the geological history of the Earth, there has been a significant change in the composition and areas of formation of carbonate deposits, which reflects the general evolution of methods, paleogeographic and geochemical settings during this time, and different stages in this evolution. At the Archean-Proterozoic boundary, acidic conditions in impounded bodies changed to moderately acidic, which is seen in the appearance of iron carbonates. The second frontier is the Siderian-Rhyacian boundary, when intensive assimilation of CO₂ led to the formation of alkaline conditions in impounded bodies and the accumulation of magnesian carbonates. Carbonate accumulation itself occurred in the impounded bodies of continental block. The third milestone is the Vendian-Cambrian boundary, when skeletal fauna appeared, and carbonate accumulation became largely biogenic. Along with the basins of the continental block, there were new oceanic areas of formation of carbonate sediments, where the skeletons of nekton organisms became a significant supplier of material. The fourth boundary – Paleozoic-Mesozoic one – was the beginning of the accumulation of the proper oceanic deep-water carbonate sediments. The fifth milestone is associated with the Cretaceous period, when oceanic carbonate accumulation sharply increased due to planktonic organisms.