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

The systematic analysis of geological, geomorphological, lithological, and paleontological data is used along with results of geochronologic al studies (C-14, TL, and AA dating) to detail the Upper Cenozoic stra tigraphy of shelf deposits and to detect: their sedimentation environm ent. As inferred, the sedimentary cover of the shelf comprises a thick sequence of Miocene-Pliocene rocks. The oldest sediments of the termi nal Miocene (presumably older than 5 Ma) were deposited here under con ditions of a rather cold climate. The lower Pliocene deposits are rich in pollen of the Turgai and subtropical floras, and their beds also y ielded molluscan shells, whose stratigraphic range corresponds well to the;Ige interval of 5.1-4.3 Ma estimated on the basis of the diatom f lora. The upper Pliocene sediments bear boreal and arctic mollusks ass ociated with periglacial plant remains. Neodenticula koizumi from thes e sediments suggests that their age interval is 4.3-3.0 Ma. The Eoplei stocene strata include two members, one corresponding to the initial c ool epoch of this stratigraphic interval and another correlative with the warm episode of the Jaramillo Subchron (1.3-0.79 Ma). The respecti ve diatom assemblage and silicoflagellate Mesocena elliptica substanti ate the correctness of the last age range. The Quaternary System of ma rine sediments in the region is divided into the lowr-middle Pleistoce ne beds and two higher units, one corresponding to the lower-middle pa ri of the upper Pleistocene and another to the Holocene age.