Source rock features of the middle-upper Jurassic Lagongtang Formation in Biru Basin,Tibet Plateau

The middle-upper Jurassic Lagongtang Formation,composed mainly of a turbidite depositional system of bathyal-deep sea facies,is characterized by an incomplete Bouma sequence.The statistic data of observations at different parts of the residual basin as well as the measurement and analysis on source rock samples showed that the Lagongtang Formation source rock had a huge accumulative thickness and contained organic matter dominated by typeⅠand type Ⅱ1 kerogens.The source rock was characterized by abundant organic matter with TOC mostly ranging from 0.40% to 1.20%,and a high or even over maturity with Ro mainly varying between 2.0%～5.0%.Under special evolutionary settings of the Tethys tectonic domain,the regional metamorphism and local structural deformation arising from the Mesozoic folding,stacking,thickening and the Yanshanian-Himalayan magmatic and hydrothermal alterations were likely to be the important factors that gave rise to high maturity of the Mesozoic organic matter and regional differences in maturity.Therefore,the paper suggested that the prospecting and assessment on hydrocarbon resources in Tibet Plateau should focus on the influence of the Himalayan tectonic evolution on oil-gas accumulation and preservation.