STRATIGRAPHY AND THE NEOGENE-QUATERNARY SEDIMENTATION ENVIRONMENT IN THE NORTHWESTERN SHELF AND COAST OF THE TARTAR STRAIT

Abstract

The systematic analysis of geological, geomorphological, lithological, and paleontological data is used along with results of geochronological studies (C 14, TL, and AA dating) to detail the Upper Cenozoic stratigraphy of shelf deposits and to detect their sedimentation environment. As inferred, the sedimentary cover of the shelf comprises a thick sequence of Miocene-Pliocene rocks. The oldest sediments of the terminal Miocene (presumably older than 5 Ma) were deposited here under conditions of a rather cold climate. The lower Pliocene deposits are rich in pollen of the Turgai and subtropical floras, and their beds also yielded molluscan shells, whose stratigraphic range corresponds well to the age interval of 5.1-4.3 Ma estimated on the basis of the diatom flora. The upper Pliocene sediments bear boreal and arctic mollusks associated with periglacial plant remains. Neodenticula koizumi from these sediments suggests that their age interval is 4.3-3.0 Ma. The Eopleistocene strata include two members, one corresponding to the initial cool epoch of this stratigraphic interval and another correlative with the warm episode of the Jaramillo Subchron (1.3-0.79 Ma). The respective diatom assemblage and silicoflagellate Mesocena elliptica substantiate the correctness of the last age range. The Quaternary System of marine sediments in the region is divided into the lower-middle Pleistocene beds and two higher units, one corresponding to the lower-middle part of the upper Pleistocene and another to the Holocene age.