Abstract
The Kashi Sag is an area with abundant gas/oil shows in the Tarim Basin of China. Identification of the sources of its oil and gas sources is important for petroleum exploration. We have applied molecular comparisons of oil sand extracts and two sets of potential source rocks from the Kashi Sag to appraise the source of the oil. The oil sand we studied is from the north limb of the Kelatuo Anticline. One of the potential source rocks is a Middle and Lower Jurassic silt-sand mudstone from Kuzigongsu Profile in the northern part of the basin, and the other is a Lower Carboniferous black shale from the Xilibili Profile in the southern part. The molecular source indicators used are the steranes, terpanes, and sesquiterpenoids in the saturated hydrocarbon fraction and the triaromatic steroids in the aromatic hydrocarbon fraction. Because great differences exist between the molecular compositions of the oil-sand extract and the Middle and Lower Jurassic mudstone, whereas the extract and the Lower Carboniferous black shale are similar, we conclude that the black shale of the Xilibili Profile in the southern part of the basin is the source rock of the sand oil.