text: In the Black Sea, sapropels are distributed at a depth of 500 to 2200 m, and in different morpholithological zones they have different thicknesses. Deep sea sediments are called the sediments formed outside the zone of influence of hydrogenic factors such as wind-driven waves and internal waves as well as of the transgressive and regressive cycles of the Black Sea basin. Here, under the conditions of relative stagnation, can be observed uninterrupted cross-sections because this area was under the sea level during the entire Pleistocene and Holocene. Deep sea organogenic mineral sediments (DSOMS) are those sediments that contain more than 3% organic carbon. The sapropels form a single horizon with constant thickness typical of the Black Sea basin. Analogues of the sapropels on the continental shelf and the upper part of the continental slope are the green aleurite-pelite, oozes with accumulation of plant detritus and decomposed shells of Mytilus galloprovincialis. The transition from aleurite-pelitic oozes to sapropels is facial. The organic matter in the sapropels is of heterogeneous origin. They are composed primarily of planktogenic organisms (about 80%) and continental organic matter (20%). The planktonic organisms are well preserved in most cases under the conditions of the hydrogen sulfide zone. The main components of the sapropels are the dinoflagellate cysts, diatom algae, coccolithophorids, peridiniales. The mineral part of sapropel muds is represented by a poly-component mixture of clay minerals. The minerals illite and montmorillonite predominate, chlorite and kaolinite occur in subordinate quantities. Individual grains of quartz, feldspar, volcanic glass and others are rarely found among them. Carbonate minerals are mainly represented by calcite and dolomite. It is generally accepted that the main source of hydrogen sulfide in the Black Sea today are the processes of anaerobic decomposition of organic matter by sulfate-reducing bacteria (SRB). The organic substance that is fixed at the bottom of the basin in the form of organogenic-mineral sediments (sapropels) is a product of the mass extinction of the plankton biomass as a result of the Black Sea flood. There is an excess of a huge amount of organic matter, which creates favorable conditions for the development of bacterial sulfate reduction.