摘要
已有研究结果表明C30~32羊毛甾烷系列存在于下古生界到新生界的沉积地层、原油及沥青样品中,但目前还少有文献从有机地球化学的角度对地质样品中此类标志物的分布及其地球化学意义进行探讨。本文通过对苏北盆地海安凹陷古新统阜二段烃源岩和柴达木盆地西部古近系烃源岩中C30~32 羊毛甾烷系列与其他生物标志物组成特征的系统对比,探讨了此类标志物的生物来源、成因、热稳定性及其地球化学意义。分析结果表明所研究烃源岩中的羊毛甾烷系列基本都与异常偏低的姥植比、正构烷烃系列的偶碳优势、高含量的伽马蜡烷和明显的C35升藿烷优势相伴生,表明咸水、强还原的环境和高盐度的分层水体有利于该类化合物的形成或保存。该系列标志物的浓度与代表真核生物贡献的伽马蜡烷和C27~29甾烷系列的浓度呈正相关关系,而与代表原核生物输入的C14~16补身烷系列和C27~35藿烷系列的浓度呈负相关关系,这一现象说明烃源岩中C30~32 羊毛甾烷系列的生物来源可能是真核生物而非原核生物。此外,不同时代、不同性质地质样品中C30~32羊毛甾烷系列分布特征的相似性,及同一样品中C30~32羊毛甾烷系列的碳数组成与C28~30 4-甲基甾烷系列和C29~31 4, 4-二甲基甾烷系列碳数组成间的离散关系,暗示着它们具有各自独立的生物来源。换言之, 4-甲基甾类不可能是C30~32羊毛甾烷的前身物。在柴达木盆地西部镜质体反射率(Ro)介于0.6%~1.0%之间的咸水湖相烃源岩中均可检测到完整的C30~32羊毛甾烷系列,只有在Ro值达到1.4%的高成熟烃源岩中才消失,这一事实表明此类标志物具有较高的热稳定性,预料它在咸水-盐湖盆地的油源研究中具有较好的应用前景。
Although C30–32 lanostanes have previously been identified in the Paleozoic-Cenozoic sedimentary record, crude oils and bitumen, there have been few studies that systematically discuss or study their distributions, relationships with other biomarkers in geological samples, and their geochemical significance. In this paper, we compare the C30–32 lanostanes and other biomarkers in the Paleogene source rocks from the Haian sag of the Subei basin and the west Qaidam basin, focusing on their source, origin, thermal stability and geochemical significance. Based on the analytical results, we found that relatively abundant and whole C30–32 lanostanes are always accompanied with abnormally low Pr/Ph ratio, even carbon predominance in normal alkanes, and high index of gammacerane and C35 homohopane in the source rocks. The results suggest that the formation of lanostanes requires a kind of saline, stratified and strongly reduced depositional environment. In addition, the concentration of C30–32 lanostanes correlates positively with that of gammacerane and C27–29 steranes, but negatively with that of C14–16 drimanes and C27–35 hopanes in E1f2 source rocks from the Haian sag of the Subei basin. These relationships show that lanostanes in the geological samples were derived from eukaryotes rather than prokaryotes. Notably, that the distributions of C30–32 lanostanes in different source rocks are similar, but the distributions of carbon numbers comprising C30–32 lanostanes, C28–30 4-methylsteranes and C29–31 4, 4-dimethylsterane in the same sample are very different, showing that each has its own independent biological source. Therefore, 4-methylated steroids are not likely precursor of lanostanes. C30–32 lanostanes were still identified in saline lacustrine source rocks from the west Qaidam basin, although their vitrinite reflectance Ro values are about 0.6%–1.0%. However, lanostanes were not been identified in a high mature source rock whose Ro value is approximately 1.40%. This result suggests that lanostanes have relatively higher thermal stability in the geological samples and may have a potential application for oil-source correlations in saline-hypersaline basins.
作者
包建平
申旭
朱翠山
BAO Jian-ping;SHEN Xu;ZHU Cui-shan(Key Laboratory of Oil and Gas Resource and Exploration Technology,Geochemistry Department,Yangtze University,Wuhan 430100,China)
出处
《地球化学》
CAS
CSCD
北大核心
2019年第3期261-275,共15页
Geochimica
基金
国家自然科学基金(41772119,41272169)
