松辽盆地北部青山口组黑色页岩的地质特征与海水侵入的成因模式

Geological characteristics of black shale of Qingshankou Formation in northern Songliao Basin and genetic model of marion transgression

以松辽盆地青山口组黑色页岩为研究对象,对页岩的岩石学特征、岩相组合、平面分布和有机碳分布规律进行研究,并结合古气候、古盐度、氧化还原环境探讨海侵事件对富有机质页岩的影响。研究认为,盆地东西两大凹陷页岩的地质地化特征存在较大差异:西部齐家—古龙凹陷页岩厚度大,有机碳丰度中—高,粉砂岩、介壳灰岩夹层发育;东部三肇—朝长地区页岩厚度相对薄,有机碳丰度极高,灰岩、白云岩薄夹层发育。白垩纪全球海侵造成青山口组湖海沟通,海水从盆地东南方向侵入造成东西水体盐度不均一、不对称格局。古生物、微量元素和分子标志化合物等证据证明,海侵提升了水体古盐度和古生产力,促进水岩界面的还原环境,为有机质的生产、聚集和保存提供了有利条件。青山口组页岩成因模式为海侵背景下的水体分层模式,可与白垩纪Cenomanian-Turonian期大洋缺氧事件层对标,是白垩纪全球缺氧事件在陆相湖盆的地质响应。

Taking the black shale of Qingshankou Formation in Songliao Basin as the research object,the petrological characteristics,lithofacies association,plane distribution and organic carbon distribution of the shale are studied.The impact of transgression on the formation of organic rich shale is discussed in combination with paleoclimate,paleosalinity and redox environment.Research suggests that the geological and geochemical characteristics of shale in the East and West depressions of the basin are different.In the western Qijia-Gulong sag,the shale is thick,the organic carbon abundance is medium and high,and the siltstone and shell limestone interlayer are developed in the shale.In the eastern Sanzhao-Chaochang area,the thickness of shale is relatively thin,the abundance of organic carbon is very high,and the thin interlayer of limestone and dolomite is developed in the shale.The Cretaceous global transgression caused lake-sea linking of Qingshankou Formation,and the seawater intruded from the southeast corner of the basin,resulting in the uneven and asymmetric salinity pattern in the the basin.The evidence of paleontology,trace elements and molecular marker compounds shows that transgression improves the paleosalinity and paleoproductivity,promotes the reduction of water-rock interface,and provides favorable conditions for the production,accumulation and preservation of organic matter.The genetic model of Qingshankou Formation shale is a water stratification model under the background of transgression.The black shale of Qingshankou Formation can be benchmarked with the Cretaceous Cenomanian-Turonian oceanic anoxic event layer,which is the response of the Cretaceous global anoxic event in the continental lake basin.