Sedimentary environments of the Upper Triassic Tumengela Formation in the Woruo Mountain area in the Qiangtang Basin,Xizang

This paper focuses on the study of the sedimentary environments of the source rocks from the Upper Triassic Tumengela Formation (T₃t) in the Qiangtang Basin, Xizang, in the light of petrology, geochemistry and sedimentary facies analysis. The sedimentary environments of the source rocks in the Upper Triassic Tumengela Formation is assigned to the delta sedimentary facies. The enrichment of the hydrolytic elements, iron group elements, and the element Fe (Fe/Mn ratios) in the upper sandstones indicates the shallower river mouth to onshore environments. The values of CIA (63.8-79), ICV (0.52-1.4) and Ga/Rb vs. K₂O/Al₂O₃ diagrams show the moderate weathering under the semi-arid to semi-humid climatic conditions. The Sr/Ba ratios are all less than 1 (0.09 to 0.27), indicating the low-salinity and fresh continental sedimentary environments. The V, U and Mo contents also indicate the anoxic-suboxic water environments. The warmer and wetter climates are beneficial to the reproduction of organisms, while the anoxic-suboxic environments are not constructive to the enrichment of organic matter. The low TOC values of 0.76% to 1.46% (mean value is 1.04%) have disclosed that the source rocks should be assigned to the medium-quality source rocks in the study area.