Thermal evolution history of the Mesozoic marine source rock in the Qiangtang Basin, Tibet

The source rocks in the Qiangtang Basin, a low thermal flow basin with a paleothermal gradient of about 2℃/100m, are the best ones in Tibet residual basins, where four main source rock formations developed. Analysis of the 7761 samples, collected from the 27 petroleum geology lines in Tibet in 1994-1999, shows that the Xiaochaka Formation, Upper Triassic, is in an over maturity stage and the Middle Jurassic Sowa Formation, Xiali Formation and Buqu Formation are in a middle-late stage of oil generation, and a second oil generating process existed in Late Tertiary. All the maturity parameters decrease gradually in cycles from margin to central uplift. The main influential factors of the thermal evolution are: the highest paleo-temperature and the deepest burial depth in relative weak structure in the middle basin; the non-balance pressure in basin margin or nearby fault folder play; the local igneous rock and thermal flow in deep formation.