Characteristics of biomarkers of Ni-Mo ore bed of black shale of Early Cambrian Niutitang Formation in the Zhangjiajie area, northwestern Hunan, China

The black shales are enriched with organic matter in Palaeozoic distributed widely in South China, with multi-metal elements of enrichment in them. In this paper, in terms of molecular paleontology, we studied the characteristics of biomarkers of Early Cambrian Niutitang Formation Ni-Mo ore bed of black shale in the Tianmenshan area, Zhangjiajie, Hunan. And abundant biomarkers, including n-alkanes, isoprenoid, terpanes and steranes, have been detected from the ore bed. They have the following characteristics: ① OEP values of the n-alkanes close to 1.0, showing no odd-even carbon dominance. The ratio of (nC21+nC22)/(nC28+nC29) is 0.7-10.4, with an average of 6.16, indicating a dominant role of light hydrocarbon components. Pristane (Pr) and phytane (Ph) are enriched in samples. The average ratio of Pr/Ph is 0.26, showing phytane dominance. ②According to the relatively abundance, tricyclic terpane > pentacyclic triterpane > quartcyclic terpane. The tricyclic terpane contents of C21,C23 and C24 show the distribution of V shape. The ratio of C24 of the quartcyclic terpane and C26 of the tricyclic terpane is 0.50. The ratio of Ts/ (Tm+Ts) is between 0.40 and 0.43, with the average is 0.42. The value of gammacerane is between 0.10 and 0.17, with the average is 0.13. ③ The sterane characteristics of C27>C29>C28 show the distribution of asymmetrical V shape. The average ratio of C27 and C29 of the sterane is 1.46(>1). Any 4-methyl sterane is detected in the samples. All of the biomarkers indicate the reducing and neritic sedimentary environments of black shales which bacteria, algae (blue-green algae, dinoflagellate, etc.) and low plankton are prosperous.