The role of sulfur gas of intense volcanic exhalations is considered as an important source of sulfur in sedimentation basins and as a probable cause of alterations and crises in the Mesozoic ecosystems. In the work sedimentary deposits of different ages and genesis are analyzed, presented in the form of lithological columns with detailed paleontological, mineralogical and geochemical characteristics. The levels in the sections enriched with pyroclastics are compared with the changes in the taxonomic composition of the paleobiota and the distribution of authigenic-mineralogical forms of sulfur. Diagnosis of ash particles in rocks was carried out by direct and indirect signs, for this purpose information was used on the composition of clay minerals obtained through analytical methods of investigation. It is established that significant changes in biotic diversity are often confined to lithostratigraphic levels containing transformed vitroclastic material (in varying degrees). At the same levels, as a rule, elevated concentrations of sulfur are observed. Lowering of paleotemperatures, increasing acidity of soils and sea water, oppression of photosynthetic processes due to emissions of ash and gases led to a significant reduction of the amount of sulfur bacterium, thiobacterium, green bacteria, and as follows the accumulation of hydrogen sulphide. The threshold of biocenoses stability was violated, when these unfavorable conditions supplemented the toxic effect of gases (including H2S), generated during the abiogenic transformation of buried organic matter in meta-catagenesis zones of a sediment strata. [ABSTRACT FROM AUTHOR]