Abstract
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.
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