Study On Sedimentary Facies Of Eastern Of Precaspian Basin

The southeast margin of Caspian basin is controlled by the Ural Ocean’s evolution, the passive continental margin during Silurian to Devonian developed into arc basin during early Carboniferous, and the arc continent accreted to form continental margin basin. From late Carboniferous to early Permian, the northern section of the Ural Ocean has closed and orogeniced to form foreland basin. Ural Ocean’s occlusion has a characteristic that it has gradually closed from north to south. The southern margin of the basin was passive continental margin that facing Tethys during Devonian and early Carboniferous, and formed into a back-arc basin during the late Carboniferous to early Permian, then the solitary land collaged until the late Permian.By a comprehensive analysis of constructing-sequence, the southeast margin of Caspian basin during Carboniferous mainly divided into five second-order sequences which represent Caspian basin’s 5 tectonic-sedimentary evolution phases in Carboniferous, and the 5 phases Corresponding to a change of basin’s marine flooding surface and deposition rate. Meanwhile, they also reflect the structural changes around the basin, revealing the change of sequence stratigraphic framework and structure are in the correlation.The sedimentary facies distribution of Caspian basin’s southeastern margin has a character of east-west zoning and north-south trending. East-west zonation reflects in: during the early Carboniferous sedimentary period,this region mainly developing the continental shelf and open platform facies, and the open platform facies developing in the west section, the continental shelf facies developing in the east. During interim Carboniferous,the eastern and western sections of study area generally developed continental shelf facies, and in the late period the eastern part of Caspian basin developed restricted platform facies. In the late period of Carboniferous,eastern part developed restricted platform facies and evaporate platform facies, the western part mainly developed open platform and restricted platform facies.The tectonic evolution of the basin’s southern margin is closely related to the southern sections’ orogeny during Carboniferous-Permian period. During the early Carboniferous to middle Permian period(Visean- Bashkir-order period),the northern part is Astrakhan-gram remedy guest uplift zone where develops carbonate rocks platform facies, Casa Gan, Tengiz and other areas are located in Nan Enba recessed areas, the area where initial landscape is higher developing carbonate rocks platform facies; the lower mainly developing continental shelf facies muddy Sediments.