Midu and Weishan Basin Pleistocene geological characteristics and evolution of the
|School||Kunming University of Science and Technology|
|Keywords||Dextral strike-slip pull-apart basin Terrace sedimentary facies thermo luminescence dating evolution stage Midu Weishan|
Midu and Weishan basins are located in the joint unit of Yangzi quasi-floor (Ⅰ) and Tanggula--Changdu--Lanping--Simao fold lines(Ⅳ), whose tectonic location is extremely complex. Midu basin is located in the North East of the Red River fault zone. Weishan basin is located in the South West of the Red River fault zone, and both two basins belong to slip pull-apart basins.In this paper, Midu and Weishan basin sediments are to study and to gain thermo luminescence dating, and to analyze the uplift rate of the mountains, sedimentary basin formation, evolution of environmental changes and so on.Through a field survey, we discover that in Midu and Weishan basins, on both sides of the mountains between Midu and Weishan mountains, various types of terraces grow, and it is mainly Pleistocene sediments from the loose hair slope Group (Qps) and litho logy is mainly grey, grey-yellow, purple, purple-thick layered rocks, gravel, sandstone and clip-black, gray, Brown clay, rock, siltstone and the amount of the seam. Terraces type is the base terraces.There are totally five development terrace levels among Midu basin, and its distribution is:level I terraceis located to the West of Lengguanying-Xiaojiaying-Qijiaying,the elevation is about 1690m to 1750m, and the TL dating value is 200.48±22.05Ka;level III terrace is located to the West of Dahongqing-Lonhhuasi-Sanjiacun-Sanhezhongcun, the elevation is about 1750m to 1830m, the TL dating value is 239.06±26.30Ka, uplift rate is 0.23m/ka; level IV terraces are mainly located in the basin to the West of Pingan Village, Daluoji and Sanheshang Village. The elevation is about 1900m to 2100m, the TL dating value is 320.85±35.29Ka, uplift rate is 0.59m/ka; level V terrace is on the West side of Dashuping, Xiaoluoji and Tinmushan.The elevation is about 2150m-2250m, the TL dating value is 332.07±36.59Ka, and uplift rate is 0.042m/ka.There are totally four development terrace levels among Weishan basin, and its distribution is:level I terrace is located to the south of Reshuitang, the elevation is about 1661m, and the TL dating value is 118.64±13.05Ka;level IIterrace is located to the West of Nanshancun, xiangxuxiacun, xiangyangzhongcun, the TL dating value is 137.23±15.09Ka, uplift rate is 0.25m/ka; levelⅢterraces are mainly located in Xincun, heshangwan, dongchang, xiaoheli, xiejiacun, qipanshan, shilongshan. The elevation is about 1750m-1900m, the TL dating value is 258.52±28.44Ka, uplift rate is 1.46m/ka; level IV terrace is on the east side of Liqingyuan, xiaohuangbacun, huangbacun. The elevation is about 2050m-2200m, the TL dating value is 511.35±56.25Ka, and uplift rate is 0.86m/ka.Through the uplift rate analysis:Weishan basin and Midu basin watershed areas are between the difference of 50 million years to lifting movement, both sides uplift rate is pretty basic and show a rapid rise early, and a rate slowed later.According to the above analysis shows the Midu basin, a total of 5 time gap uplifting stage, and as to Weishan basin, there are 4 time gap uplifting stage.Midu basin development evolution stages:(1) of 332.07±36.59Ka to 320.85±35.29Ka period for lake sediments, mild climate, shallow water environments such as; (2):320.85±35.29Ka to 239.06±26.30 Ka period for pluvial stacked-fluvial-on the Lake-deep lake-Lake-swamp-Delta phase of depositional environments, divided into two cycles. (3): 239.06±26.30 Ka to 200.48±22.05Ka Lakes coastal deposition during; (4) of 200.48±22.05Ka to 10Ka Lakes coastal-during swamp-Lake and river-lake shore-on the Lake-Lake shore sedimentary environments.Weishan basin evolution stages:(1):511.35±56.25Ka to 258.52±28.44Ka period of alluvial fan deposits. The sedimentary facies were from the bottom up alluvial fans (fan root)- alluvial fans (fan in)-alluvial fans (fan side)-River marsh facies, mild climate, lush vegetation. (2):258.52±28.44Ka to 137.23±15.09Ka period of fluvial deposits. (3):137.23±15.09Ka to 118.64±13.05Ka during the bottom of the lake shore-swamp facies, up there three alluvial fans (fan root)-alluvial fans (fan in)-alluvial fans (fan side) into the product by the fine thicken the type of anti-cyclic sequences, indicating that basin in a tight state; (4): 118.64±13.05Ka to 10Ka period of fluvial deposits.Midu and Weishan basins are strike-slip pull-apart basin, basin, is dextral strike-slip fault zone in the Red River formed under tension.