Characteristics and significance of the source rocks from the Lower Permian Zhanjin Formation in the Jiaomuchaka area, Qiangtang Basin, northern Xizang

The tuffaceous source rocks are found to be hosted in the Lower Permian Zhanjin Formation in the Jiaomuchaka area near the central uplift of the Qiangtang Basin,northern Xizang. The integration of abundance, type and maturity of the organic matter in this study has disclosed that the total organic carbon contents in the tuffaceous source rocks range between 0.35% and 0.98%, within the limits of standards coming up to the medium-grade maturity of source rocks. The microscopic examination and element and carbon isotope analyses for the kerogens indicate that the organic matter types are represented by sapropel-humic (II₂ type) and humic (III type). The vitrinite reflectances (Ro) for the source rocks vary from 1.54% to 1.59%. The pyrolytic peak temperatures (T_max) range between 467 and 530℃. Meanwhile, the sapropelinite in the kerogens exhibits brownish yellow in colour. The above-mentioned results show that the thermal evolution of organic matter has now reached up to the higher maturity levels of the source rocks, and thus the source rocks have good hydrocarbon-generating potential in the study area.