湘西北张家界地区早寒武世牛蹄塘组黑色岩系镍钼矿层生物标志物的特征

以湖南张家界天门山地区下寒武统牛蹄塘组底部的黑色页岩镍钼矿层为研究对象，对其进行了生物标志化合物特征的分析。发现该矿层的正构烷烃、类异戊二烯烃、萜类化合物和甾类化合物具有以下特征：①正构烷烃OEP(奇偶优势)接近1.0，无明显奇偶优势；(nC21+nC22)/(nC28+nC29)比值为0.7~10.4，平均为6.16，显示轻烃组分占绝对优势；样品富含姥鲛烷(Pr)和植烷(Ph)，比值平均为0.26，具有植烷优势。②萜烷相对丰度三环萜烷>五环三萜烷>四环萜烷；三环萜烷中C21、C23、C24呈倒V字形分布；C24四环萜与相邻C26三环萜比值为0.50；Ts/(Tm +Ts)比值在0.40~0.43之间，平均为0.42；γ-蜡烷指数介于0.10~0.17之间，平均值为0.13。③规则甾烷呈不对称的 V字形分布，表现为C27>C29>C28的分布特征；C27规则甾烷/C29规则甾烷平均比值为1.46(>1)；检测出一定丰度的4-甲基甾烷。这些特征共同指示了张家界地区早寒武世黑色岩系形成于菌藻类(蓝绿藻、甲藻等)和低等浮游生物大量繁殖的浅海还原环境。

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.