Oil sand is widely cropped out at Houba region of Sichuan Province. The lower member of the Jurassic Shaximiao Formation is the main oil reservoir, which is composed of sandstone beds stretching towards north-east orientation for as long as roughly 25 km. Tar sand oil contents of cropped and drilled samples range from 0.4% to 3.3%. The characteristics of saturated hydrocarbon component analyzed by GC-MS showed that tar sand oils were severely biodegraded, which was featured by the disappearance of n-alkanes and iso-alkanes. Biomarkers like tricyclic terpane, pregnane and homo-pregnane have relatively high contents. Meanwhile, the content of C29 regular steranes is relatively high compared to its C27, C28 series. Features for both biomarkers and carbon isotope ratios of the Houba oil sand imply that these oils may have originated from Sinian-Cambrian source rocks and had biological sources comprising of algae and bacteria.
