莱阳凹陷莱阳群黑色页岩氧化还原敏感微量元素特征与有机质富集的控制因素

Redox Sensitive Trace Element Compositions of the Shuinan Formation Black Shale in the Laiyang Sag:Controlling Factors of Organic Matter Enrichment

咸化湖盆泥岩和页岩的地球化学特征对咸化烃源岩的形成条件和沉积环境具有重要指示意义。对山东莱阳凹陷下白垩统莱阳群泥岩和页岩的氧化还原敏感微量元素(RSE,包括Mo、Cr、Zn、Cu、Ni、Co、V、As、U和Th)和总有机碳(TOC)进行分析,旨在恢复研究区氧化还原环境和探讨盐湖有机质富集的控制因素。研究结果显示,瓦屋夼组和止凤庄组泥岩的TOC含量较低,RSE没有明显富集,RSE及其比值(U/Th、Cu/Zn、V/Cr和Ni/Co)反映该沉积时期为氧化环境;水南组黑色泥页岩的TOC含量骤增,RSE显著富集,反映该沉积时期为弱还原环境;龙旺庄组和曲格庄组TOC含量迅速减小,RSE含量较低,反映该沉积时期为富氧环境。水南组黑色页岩有机质的富集与古气候、古生产力、古盐度和氧化还原条件等综合因素有关,其中古气候是导致古生产力、古盐度和氧化还原条件等因素变化的主控因素。

The geochemical characteristics of mudstone and shale in the saline lake basin are of great significance to the formation conditions and sedimentary environment of saline Source rock.To reconstruct the redox conditions and explore the controlling factors of organic matter enrichment in the Lower Cretaceous Laiyang Group of the Laiyang Sag,redox sensitive elements(RSEs,such as Mo,Cr,Zn,Cu,Ni,Co,V,As,U and Th)and total organic carbon(TOC)of mudstone and shale from this Group were analyzed.The results show that TOC content of mudstone in the Wawukuang and Zhifengzhuang Formations is relatively low,and that RSEs are not obviously enriched.TOC content of Shuinan Formation black shale increases sharply,and RSEs are enriched significantly,suggesting a weakly reducing environment.TOC content of the Longwangzhuang and Qugezhuang Formations decreases rapidly,and the RSE content is low,suggesting an oxidizing environment.Organic matter enrichment in the Shuinan Formation black shale is likely related to a combination of paleoclimate,paleoproductivity,paleosalinity and redox factors,among which paleoclimate is the main controlling factor of paleoproductivity,paleosalinity and redox conditions.