The Tertiary saline lacustrine source rocks in oil-gas resources were sampled from exploration wells in western Qaidm Basin（90°10′-92°40＇E, 37°20′- 38°50＇N）in the northwest China, to which chem- ical and mineralogical analyses were performed on trace-element, organic or inorganic matters, pyrite abundance and clay mineral composition. Geochemical indicators were used to determine the sedimentary environment during the age in the region. The concentrations of Cl^- , B and gammacerane show that the water mass was semi-brine to brine. The deposition center was moved northward with a gradual change in salinity. In terms of Fe^2 ＋/Fe^3 ＋ ratio, Pr/Ph ratio, the amounts of S^2- and pyrite, and hopane distribution, the local Tertiary sedimentary environment featured strong reduction. The geochemical and mineral composition of clay suggests that the sedimentary facies of the source rocks was between marginal and central salt lake facies.
Oceanologia Et Limnologia Sinica
Trace element, Clay mineral, Organic matter, Salt lake facies, Sedimentary environment,Eochemistry, Qaidam Basin