A complex of modem physical investigations of carbonate crusts covering Lower Miocene bryozoan limestone from the Kazantip Cape showed that bryozoans built a biohermal skeleton due to the synsedimentation of bioinduced cement. The mineral association (Mg-calcite + aragonite) indicates the existence of near-bottom environment typical for gas-hydrate biogenic mineral formation as a result of bacterial methane oxidation during the formation ofbioherms. The presence of bitumen, pyrite, strontianite, barite, kutnohorite and traces of vital activity of carbonate-depositing methanotrophic bacteria in the composition of carbonate crusts is concerned with a significant influence of near-bottom local gas-fluid seeps.