Characteristics And Sedimentary Environment Of The Middle-Lower Triassic Strata Of Gande Formation Of North Bayan Har Area Of Qinghai

The research area is located in the southeastern Qinghai Province,south of the Animaqing Mountains.The tectonic of the earth is mainly located in the Hoh Xil-Songpan foreland basin which is in the northwestern part of the Buqingshan-Maduo-Maqin belt,and in the northwestern part of the Qiangtang-Sanjiang orogenic belt.This research is based on the project of collecting and sorting the previous data about the project of "1: 50000 General Survey of Geological and Mineral Resources in Northern Part of Bayan Har,Qinghai Province".Through field investigation and drawing of measured sections,the authors analyze the characteristics of the Triassic Gander Formation in terms of lithology,lithofacies and paleontology fossils in the Triassic Lower Middle Gande Formation,and discuss the geologic age and evolution of sedimentary environment.The main topics of this research are the following aspects:Due to the single nature of Gangde Formation in Youyun area,Beiba,Qinghai,the thickness is huge,the fossils are scarce,the coverage is serious,so it is not easy to divide the formation.Through the field survey of 6 profiles,collation data and comparison and analysis of lithology to determine the stratigraphic features of the Triassic Gander Formation in the Youyun area,Beiba,Qinghai.The thickness of the Triassic Gander Group is believed to be about 1800 m to 3500 m.It is a sedimentary formation of even-pinnacled limestone that is mainly composed of silvery-green cuticle feldspar quartz sandstone and silty sandstone.The study area is sandstone turbidity flow sedimentary sequence,developing deep-sea basin sediments.The larger sandstone and slate ratios are relative nearshore conditions in turbidite deposition heads or fans,While the smaller ratio of sandstone to slate is the middle of sedimentary fan or the edge of sedimentary fan.There are new fossils of plant fossils,Triassic animal fossil ammonites and early Triassic bivalves in Gande Formation in the study area,which can roughly determine the geologic age of the Gander Formation in the Youyun area of Beiba,Qinghai.