CHARACTERISTICS AND IMPLICATION OF BIOMARKER COMPOUNDS IN SOURCE ROCKS FROM BEIPIAO FORMATION IN JINYANG BASIN, WESTERN LIAONING PROVINCE

The gas chromatography and gas chromatography-mass spectrometry are combined to study the characteristics of biomarker compounds in source rocks from Beipiao Formation in Jinyang Basin, western Liaoning Province, by analysis of such information as the sources, sedimentary environment and thermal evolution degree of organic matter in rocks. The mass spectrometry of normal-alkanes for source rock samples shows characteristics of mature source rocks dominated by front peak-typed unimodal distribution. The ratios of C₂₉-αββ/(ααα+αββ), varying between 0.35 and 0.58 with mean value of 0.5, indicate that most source rocks are in mature stage, while some have reached the peak or high mature stage. The Pr/Ph ratio (1.0-3.0) shows a weak pristane advantage. According to the cross plot of Pr/nC₁₇-Ph/nC₁₈, the source rocks are dominated by Ⅲ-type. The tricyclic terpane is normally distributed with C₂₀ as the main peak. The content of C₂₄ tetracyclic diterpane is generally high. The ratios of C₂₄ tetracyclic diterpane and C₂₆ tricyclic terpane are basically greater than 1, while the ratios of tricyclic terpane/hopane of source rocks from SZK01 and SZK03 wells less than 0.4. The gammacerane indexes range from 0.02 to 0.30 with average of 0.12. From the above, the source rocks from Beipiao Formation were formed in the brackish water-freshwater shallow water sedimentary environment with partial oxidation, belonging to typical sedimentary facies zones with advanced plant immigration.