BIOSTRATIGRAPHY OF THE CASPIAN NEOPLEISTOCENE

Biostratigraphy of the Caspian Neopleistocene (middle and late Pleistocene) is based on changes in evolutionary patterns and ecological assemblage change of the mollusk genus Didacna Eichwald. The study of peculiarities and patterns in the spatial-temporal distribution of mollusk shells of the genus Didacna Eichwald in the deposits of the middle and upper Pleistocene of the Caspian region showed, that the molluscan fauna represent a complex hierarchical system of faunal assemblages with different taxonomic composition and at different taxonomic levels: faunas, complexes, subcomplexes, associations, distinguished following particular criteria. Based on molluscan fauna, namely on distinguished faunal units at different hierarchical levels, we built a regional biostratigraphic (ecostratigraphic) scheme of the Middle and Upper Pleistocene (Neopleistocene according to Russian stratigraphic sheme) of the Caspian, supplementing and specifying the exisiting schemes. Caspian Middle and Upper Pleistocene (Neopleistocene) represent a Didacna biozone - deposits encompassing the entire stratigraphic interval of this taxon distribution. Based on temporal distribution of faunas, the zone is subdivided into subzones, which become the biostratigraphic basis for establishment of horizons. Interval-zones, characterized by faunal complexes, are used for distinguishing subhorizons. Subcomplexes are used to define beds. Mollusk associations show the facies diversity of these subdivisions. All distinguished stratigraphic units are related to paleogeographic events at variable hierarchical levels (transgression, stage, phase) in the development of the basin. Type localities for faunas, faunal complexes and subcomplexes were suggested for distinguished stratigraphic units. All of them are located in well stratified sections, available for investigation and previously thoroughly studied. Besides malacofauna they contain other fossil remains (ostracodes, foraminifers, pollen, carpologic material etc.), the data on which, as well as on paleomagnetism, absolute chronology, lithology and geomorphology, were taken into consideration for their selection.