Research On Strata And Paleontology Of Late Paleozoic In Bogda Stratigraphic Subregion,East Tianshan Mountains

Based on the project of 1:250 000 regional geological surveying of Sandaoling, the doctoral dissertation did the research on the lithostratigraphic division and correlation in Bogda Stratigraphic Subregion; The study followed or discarded lithostratigraphy units built in the past, re-established lithostratigraphic mapping units in Sandaoling area. The research of biostratigraphy, not only enriched the fossils database, but also improved the stratigraphic time frame, made the geological age of lithostratigraphic units to have an exact basis. The dissertation made the following innovative understanding and progress:1.The brachiopod fossils found in the Dananhu Formation(D1d), such as Leptaenopyxis, Megakozlowskiellina, Megastrophia and Leptoslrophia, are most similar to those which found in the Mangkelu Formation, Tuoranggekudouke Formation, the stratotype of the Dananhu Formation in Hami, so the geological age of Dananhu Formation in the research area should be Emsian Period in Early Devonian;2.The regional geological surveying found:the lithostratigraphy unit was divided into Tousuquan Formation(D2ts) by the past research in the Saerqiaoke area, had big difference with Tousuquan Formation on lithology, facies and metamorphism, so should be redefined. The age data of 450.3±4.3Ma were obtained by LA-ICP-MS zircon U-Pb, the geological age of Saerqiaoke was revised as early Late Ordovician, and was divided into Wuliegai Formation(O3w). The research also found precambrian basement in Saerqiaoke;3.Based on the brachiopod fossils collected in the lower and upper layers in the first section of Heishantou Formation (C1h1), the study built "Leptagonia analoga-Brachythyrina pingguisiformis-Schuchertella radialis" assemblage in the lower layers, and "Brachythyris ovalis-Schellwinella rotundata-Tornquistia borochorensif assemblage in the upper layers. According to the brachiopod fossils, coral fossils found in the second section of Heishantou Formation (C1h2) and k-Ar isotopic age, the age of Heishantou Formation should be Tournaisian-Visean Period in Early Carboniferous;4.The brachiopod fossils of the Jiangbasitao Formation (C1j) are similar to those of the Akshak Formation of Late Carboniferous, but found some elements of early Late Carboniferous, such as Choristites and Paramuirwoodia, can build "Brachythyrina pingguisiformis-Chonetes cf. Sinkiangensis-Pseudosyrinx mylkensis" assemblage, It is believed that the geological age of Jiangbasitao Formation should be late Early Carboniferous, and close to early Late Carboniferous;5.Based on the study of foraminifera found in the limestone belt of the Liushugou Formation (C2/), it was concluded that the foraminiferal characteristics were similar to "Bradyina saucraeforma-Tetrataxis parviconica" sub-assemblage of "Bradyina-Tefrataxis-Palaeotextularia" Assemblage built in the middle and lower layers of Huanglong Formation in the Guangde, upper layers of the Huanglong Formation in the South China, Azigan Formation in the Southwestern Margin of the Tarim Basin, upper layers of the Moscow Stages of the Russian Platform. The Liushugou Formation shoule be a set of sedimentary strata in the Moscow Period of Late Carboniferous.The foraminifera of Qiajiagou Formation(C2qj) in Xialaoba is characterized by the prosperity of Bradyina and Tetrataxis, is similar to the stratotype of the Qijiaogou Formation in the same stratigraphic subregion. Comparing "Tolypammina fortis-Palaeospiroplectammina conspectd’assemblage with "Bradyina concinna-Plectogyra minutd’assemblage built in the lower or upper layers of the stratotype, is most similar to "Bradyina concinna-Plectogyra minutd’assemblage. At the same time, similar to Tahachi Formation in the Tarim Basin and Benxi Formation in the North China. The formation should be a set of deposits in the Kasimovian Period of Late Carboniferous.6.The geological age of the Qijiaojing Formation (dq) should be Late Carboniferous. Comparing the Qijiaojing Formation (dq) lies in synclines show with the Liushugou Formation (C2l) lies in synclines outside in the following aspects:spatial distribution of stratigraphy, lithological and lithofacies assemblage, the change of depositional sequence, contact relationship of stratum, fossils and zircon isotopic age. It is conclued that the Liushugou Formation and the Qijiaojing Formation belong to different facies of the same period, the Ashkala Formation (da) and the Qijiaogou Formation (C2qj) is also.7.In view of the research area has been elevated to land after the Permian, the stratum is no longer zoning. The survey also found unconformity interface in Aerbasyi Formation (P1ae), so divided the Aerbasyi Formation into Shirenzigou Formation (Pi-y) and Santanghu Formation (P1st).The study delimited a set of continental clastic rock for Shirengougou Formation and volcanic rock construction for the Santanghu Formation in the north and south of the Tianshan Mountains consistently.