BIOMARKER COMPOUNDS IN THE SOURCE ROCKS OF UPPER PERMIAN LINXI FORMATION IN WESTERN BINBEI AREA, SONGLIAO BASIN: Characteristics and Implications

The characteristics of biomarker compounds in the source rocks of Upper Permian Linxi Formation are studied, as well as the sources, sedimentary environment and thermal evolution degree of organic matter, based on the gas chromatography and gas chromatography-mass spectrometry. The results show that the source rocks, with organic matter Type Ⅱ, have high organic abundance in the high mature-overmature evolution stage. The (C₂₀+C₂₁)/(C₂₃+C₂₄) tricyclic terpane is 0.12-0.86 (averagely 0.50). The C₂₄ tetracyclic terpene/C₂₆ tricyclic terpene is 0.41-0.72 (averagely 0.54), with the characteristics of typical lacustrine source rocks. The Pr/Ph is mainly 0.16-0.71 (averagely 0.32), indicating a strong reduction-reduction sedimentary environment. The gammacerane/C₃₀ hopane is 0.09-0.35 (averagely 0.21), reflecting the brackish water sedimentary environment. The relation between Pr/nC₁₇ and Ph/nC₁₈, and interrelation of C₂₇-C₂₈-C₂₉ steranes show that the organic matters are the mixed sources of higher plants with lower aquatic organisms like bacteria and algae. The Ts/Tm ratio of 0.18-1.03 (averagely 0.86) and C₃₁αβ22S/(22S+22R) ratio of 0.53-0.62 (averagely 0.58) both show the source rock maturity is high. From the above, it is concluded that the source rocks were formed in the reduction-strong reduction environment of brackish water, and the mixed sources are favorable for the enrichment of organic matters, thus the Linxi Formation has oil-gas exploration prospects.