Dolomite-sepiolite interaction in Kashira and Podolsk deposits of platform part of Bashkortostan: possible biogenic origin

The article is devoted to the genesis of microcrystalline dolomites of the Kashira and Podolsk horizons of the Moscow stage, which are oil reservoirs in the western part of Bashkortostan. They form consistent layers of low thickness, traceable for tens of kilometers, which determines the relevance of studying the conditions of dolomite formation. Dolomites are composed of crystals 1-10 µm in size with sulfate inclusions and sepiolite admixture. Sepiolites are developed in the intercrystalline space as the finest threads and films enveloping dolomite crystals. A detailed study of sepiolites with a scanning electron microscope with experiments on partial dissolution of dolomites with acid showed an abundance of bacteriomorphs of sepiolite composition. The distribution of REE and Y in dolomites and host rocks is considered. Good convergence in REE spectra is noted for a number of dolomite samples. As a result of the conducted complex of studies, a conclusion is made about the microbial-induced formation of dolomite and sepiolite in the shallowest part of the sea basin with high salinity.