Geochemical Characteristics of Hydrocarbon Source Rock and Paleoenvironment Reconstruction in Houjingou Profile of Songliao Basin

Key words: 
• Songliao Basin /
• Nenjiang Formation /
• carbon isotope /
• n-alkanes /
• C₃₀-sterane

Abstract: Different types of source rock of Houjingou profile in Songliao Basin were analyzed in details for understanding the organic geochemical characteristics and the paleoenvironmental significance in Late Cretaceous, which were collected from the upper member 1 of Nenjiang Formation to the lower member 2 of the Nenjiang Formation. The results show that the source of organic matter in the upper member 1 of Nenjiang Formation changed upwardly from hybrids of lake inherent and terrestrial plants to lake endogenous predominance; There were three models in n-alkanes, the co-existence between odd-even preference of high carbon number and even-odd preference of low carbon number, odd-even preference of high carbon number, even-odd preference of low carbon number n-alkanes, respectively; The concentrations of 24-n-propylcholestane, 24-i-sopropylcholestane and dinoflagellate-steranes were 0.09 to 8 μg/g, 0 to 2 μg/g, 0 to 0.3 μg/g, respectively, increasing as the buried depth decrease, all of these indicated marine transgression combined with variations of δ¹³ Corg and C/N values. For the lower member 2 of the Nenjiang Formation, the source of organic matter showed lake inherent and the preservation of organic matter were related with anoxic bottom water and microorganism activities, but the non-marine algaes were also contributed to long-chain alkanes; The concentrations of 24-n-propyl cholestane, 24-i-sopropyl cholestane and dinoflagellate-steranes were 2.8 to 12.5 μg/g, 2.4 to 8.5 μg/g, 0.1 to 0.64 μg/g, respectively. Therefore, the depositional environment of upper member 1 of Nenjiang Formation showed shore lacustrine to transition of shallow lacustrine facies with increasing of marine transgression; The lower member 2 of Nenjiang Formation was turned out to be a semi-deep lake facies to deep lacustrine facies, the concentrations variation of marine algaes C₃₀ sterane indicated that marine transgression marched more than once according to irregular fluctuate.