Quaternary Sedimentary Structural Evolution In The Northwest Of Yili Basin

The Huocheng alluvial-proluvial plain in the northwest of Yili basin has accumulated abundant sediments since the Quaternary,which well records the information of basin mountain process.Based on field observation,section survey and 127 boreholes,combined with ESR,OSL and magnetostratigraphy dating,the thickness contour of Quaternary in the study area is mapped according to three stages of early Pleistocene,Middle Pleistocene and late Pleistocene-Holocene.The overall thickness of the Quaternary is 150-400 m.The thickness of the lower Pleistocene is 40?320 m,distributed mainly between Huocheng-Liushisituan.The thickness of the Middle Pleistocene is 20-240m,distributed mainly between the Liushisantuan-Kedala.The thickness of the upper Pleistocene is 20?140 m,and distributed mainly Horgos-Daxigou-Guozigou and north of Wusun mountain piedmont.This paper reveals the sedimentary characteristics of different periods of Quaternary in the northwest of Yili basin,which provides an important basis for the Quaternary tectonic uplift of Tianshan and the basin mountain process of Yili basin.From the end of Pliocene to the beginning of the Quaternary,the whole crust of Tianshan mountains uplift,and the climate gradually became cold.The lithology of the Xiyu formation is mainly gray white-gray calcareous cemented conglomerate.The material source mainly comes from the Paleozoic strata and granite of the Northern Tianshan Mountains.The typical strata are found in the Hongqiazi and the Fushoushan area.At the end of the early Pleistocene,they were involved in the fold together with the Changjihe group.Wusu group is mainly exposed in Daxigou-Changshanliangzi-Qiatertale in the northeast margin of the basin.The lithology is ice cement gravel accumulation.The south is mainly found in the south of Yamadu,and the lithology is alluvial-proluvial,mainly distributed in front of Wusun mountain.In the late Pleistocene,a large area of gravel layer developed in front of the mountain,which was in unconformity contact with the underlying strata,and turned to the plain area for fine-grained deposition.At the end of the late Pleistocene,Loess accumulation in piedmont hilly area.In addition,there have been three extended events to the basin during Quaternary.At the end of the early Pleistocene,the Xiyu formation and Changj ihe group folded together;at the end of the Middle Pleistocene,the northern margin of Wusun mountain fault was strongly northward thrust,and the Hongshanzui fault was strongly southward thrust since the end of the late Pleistocene.Three extended events to the basin together shaped the current structural landform of the northwest of Yili basin.