ИСТИНА

The South Caspian is one of the largest oil-producing regions within the Caspian Sea. Most of the offshore fields are focused here along with the main geologic oil and gas reserves of Azerbaijan. The development of the discovered fields, prospects and exploration of new ones require detailed study of the Quaternary deposits: their material composition, stratigraphy, thicknesses and other properties. It is necessary to study these issues not only for improvement of the efficiency, provide safe geological prospecting and exploration, but also to solve engineering and geological tasks related to the planned development of discovered oil and gas fields. Study of fauna and stratigraphy of the Quaternary deposits in the South Caspian is important to learn the Quaternary history of the Caspian Sea. The Quaternary time is known for its frequent and abrupt fluctuations in climate, ocean and sea levels, considerable changes in topography, fauna, flora and other natural components of the Earth. The large-scale well drilling in the South Caspian water area provided geological information particularly about ostracod fauna, stratigraphy and litho-facies features of the Quaternary deposits of the studied regions. We investigated the systematic composition and distribution regularities of ostracod fauna from the Quaternary deposits over the vast South Caspian territory, including the stratigraphic role of the fauna and correlation of the data with the coastal –onshore area. Multiple well sections and their enclosed micro- and macro fauna were the study target. When we analyzed and correlated well sections and natural outcrops we used other methods like lithological, macro fauna, radiometric, electric logging, seismic logging as well. The result of our study allowed us to design a detailed stratigraphic chart for the Quaternary deposits of the entire South Caspian basin. For the first time the Quaternary deposits of the South Caspian breakdown with 5 supra horizons, 10 horizons with 7 index species. Index species were identified on the successive change of zonal complexes- biozones. All these subdivisions play a regional role and correlated well with the ones from the adjacent areas of the Caspian region. The paleontological processing of individual ostracod of genera: Leptocythere, Amniocythere, Euxinocythere, others allowed us to identify specific features among them in order to differentiate a new ostracod species. We also highlighted the issues of stratigraphy, facies analysis and thicknesses of the Quaternary deposits in the South Caspian. The analysis of facies, thicknesses and fauna distribution shows that in the Quaternary time the South Caspian region was characterized by rather dynamic paleogeographic settings: along with the active change of the sea bottom topography, salinity and temperature varied considerably and often, as well as the sea level.