Characteristics of biomarkers of the black rock series of Lower Cambrian Niutitang Formation in the Nayong area, western Guizhou, China

With the methods and the measures of GC-MS analysis, authors study the biomarkers of the black shale series of Cambrian Niutitang Formation in the Nayong area of Guizhou Province. The results show that OEP values of the n-alkanes close to 1.00，showing no odd-even carbon dominance. The mean of Pr/ Ph is less than 1, indicating that mineral samples possess phytane dominance. The terpanes distribution patterns of mineral samples are pentacyclic terpanes > tricyclic terpanes > tetracyclic terpanes. The steranes consist mainly of C27-steranes.The average ratio of ΣC27/ΣC29 is 1.41,greater than 1.00.The ratio indicate that the organic matter sources are mainly shallow marine bacteria and algae and other lower aquatic organisms. The average of C32αβ22S/(22S+22R) is 0.59, and the value of Ts /(Ts+Tm) 0.43, the ratio of βα-MO alkyl / αβ - Hopane 0.124, the value of C29 sterane 20S/(20S+20R) 0.39, the ratio of βαββ /(αββ ααα) 0.41.The ratios show that the evolution of organic matter in black shale series of Nayong region is close to or reach maturity. All these characteristics indicate the black shale series of this region is formed in the restore shallow water environment with higher degree of thermal evolution of organic matter， and the parent material is mainly derived from bacteria , algae and other lower hydrobiont.