GEOCHEMICAL CHARACTERISTICS OF BIOMARKERS EXTRACTED FROM THE LOWER CRETACEOUS COAL MEASURES ROCKS IN JIXI BASIN

By the Gas chromatography and the Gas chromatography-mass spectrogram analysis,the biomarkers in the Lower Cretaceous mud rocks and coals of coal measures from Jixi Basin were studied.The results indicate that n-alkanes in mud rocks show front single-peak type,with the main peak carbons to be C₁₆ or C₁₈.The ratio of Pr/Ph is 2.86～11.22,Pr/n C₁₇ is larger than 1.The n-alkanes in coals show rear single-peak type,with the main peak carbons to be C₂₂ or C₂₃.The ratios of Pr/Ph and Pr/n C₁₇ are 2.86～11.22 and 2.1～3.33 respectively.The values of the OEP and CPI in both mud rocks and coals concentrale on 1.0.The thermal evolution has reached maturation stage.The biomarkers in mud rocks show that the ratio of tricycle terpane plus tetracyclic terpane to C₃₀H is 2.37～3.62.The C₃₁22S/22(S+R),Ts/Tm and G/C₃₀H are 0.57～0.61,0.47～0.81 and 0.11～0.34 respectively.The ααα20R homosteranes in mud rocks appears to be in asymmetrical "V"distribution.The analytic result of the biomarkers show the mud rocks coming mainly from aquatic organisms and depositing in reducing environment with more saline water,which is better for preservation and transformation of organics.The biomarkers in coals show that the ratio of tricycle terpane plus tetracyclic terpane to C₃₀H is lower than that in mud rocks.The ratio of C₃₁22S/22(S+R) is about 0.6,the Ts/Tm and G/C₃₀H are very low.The ααα20R homosteranes of coals appear to be in inverted "L" distribution.The coals are mainly from higher plants,and deposit in oxidizing environment.