沟鞭藻:24-降胆甾烷的重要生源

DINOFLAGELLATES AS POTENTIAL PRECURSORS OF 24-NORCHOLESTANES

24-降胆甾烷是出现在原油和沉积有机质中的一类重要分子化石,其在地层中的分布与地质时代、古气候和沉积相等有关。国内外研究表明,硅藻是24-降胆甾烷的重要生源。通过研究发现,在缺少硅藻化石的渤海湾盆地济阳坳陷古近系沙河街组湖相沉积中,发育丰富的24-降胆甾烷,且与地层中的沟鞭藻分子化石(三芳甲藻甾烷)和生物化石(囊孢)存在明显相关性。因此可以推测,沟鞭藻是24-降胆甾烷的另一重要生源。由于沟鞭藻和硅藻分布的差异,不同盆地中24-降胆甾烷的来源存在区别。济阳坳陷古近纪气候温暖湿润,沟鞭藻极度繁盛,是24-降胆甾烷的主要贡献者。

Occurring widely in oils and ancient sediments,24-norcholestanes are useful to oil-source correlation and petroleum age evaluation.24-norcholestanes mainly derive from diatoms;however,they are also identified unambiguously from dinoflagellates.Abundant 24-norcholestanes occur in oils and source rocks of the Shahejie Formation,but no diatom fossils have been distinguished from the Shahejie Formation.Thus,other potential precursors might be responsible for these 24-norcholestanes.A correlative relationship between 24-norcholestanes and dinocysts or triaromatic dinosteroids has been observed,revealing that dinoflagellates should be potential precursors of 24-norcholestanes.It seems that 24-norcholestanes come from dinoflagellates and diatoms,respectively,for different basins.Notwithstanding the fact that 24-norsterols have low concentrations in contemporary dinoflagella test,it is concluded that dinoflagellates are key contributors to 24-norcholestanes within subtropical lacustrine sediments of the Eocene-Oligocene Jiyang Depression.