Sedimentary Facies Analysis and Sedimentary Environment Reconstruction from Late Permian to Early Triassic of West Qinling Area

Key words: 
• sedimentary facies /
• sedimentary environment /
• west Qinling /
• Late Permian /
• Early Triassic

Abstract: Tongren area of Qinghai province is located on the copulae of Qilian and Qinling orogene, of which the structure evolution history is very famous. A continuous PermianTriassic stratum was found in Longwuhe area during this work. In ascending order, this section is divided into Shiguan Formation of upper Permian, Guomugou Formation and Jiangligou Formation of lower Triassic, while Jiangligou Formation is divided into turbidite Member at the lower and tempestite Member at the upper. Primary PermianTriassic Boundary is definited in this work. Sedimentary sequence, sedimentary facies and sediments indicate the Shiguan Formation of upper Permian and Guomugou Formation of lower Triassic are terrigenous clastic turbidite, while the lower parts of Jiangligou Formation of lower Triassic is intraclast turbidite and upper is tempestite. According to the sedimentary facies and geochemistry of interlayer igneous rock, the Shiguan Formation and Guomugou Formation were located at active hemipelagic continental margin, while the Turbidite Member of Jiangligou Formation was located at steady hemipelagic continental margin. The sea level turns down and the sedimentary environment transited into neritic shelf during the tempestite Member of Jiangligou Formation. Based on the sedimentary facies characteristic, this paper reconstructed the eustatic changes during Late Permian and Early Triassic.