雅布赖盆地小湖次凹细粒沉积岩岩相特征与沉积环境探讨

The lithofacies and depositional environment of fine-grained sedimentary rocks of Xiaohu Subsag in Yabulai Basin

通过岩心观察、薄片鉴定、X-射线衍射、有机碳分析等技术,综合矿物成分、有机质含量、沉积构造等因素,对雅布赖盆地小湖次凹新河组下段半深湖—深湖细粒沉积岩岩相进行研究,形成了细粒沉积岩四组分三端元的岩相划分方案。结果表明:新河组下段半深湖—深湖细粒沉积岩发育9种岩相类型,其中以贫有机质块状黏土质细粒长英沉积岩、贫有机质纹层状硅质碎屑型混合细粒沉积岩、贫有机质块状长英质黏土岩、中有机质纹层状硅质碎屑型混合细粒沉积岩、中有机质纹层状长英质黏土岩、富有机质纹层状碳酸盐型混合细粒沉积岩等6种岩相为主。岩相类型与特征反映沉积环境和沉积机理的差异,在前三角洲—半深湖的环境中,波浪增强型沉积物重力流普遍发育,形成纵向上贫有机质块状黏土质细粒长英沉积岩—纹层状硅质碎屑型混合细粒沉积岩—块状长英质黏土岩的叠置,反映水动力渐弱的过程;在半深湖—深湖环境中,水体相对安静,悬浮沉积为主,陆源碎屑输入少,碳酸盐和黏土较发育,形成中—富有机质纹层状混合细粒沉积岩和黏土岩。

Taking the fine-grained sedimentary rocks of the lower Xinhe Formation in Yabulai Basin as a research object,the lithofacies were subdivided using ＂four components-three endmembers＂classification scheme with integrated analysis of minerals,structures and organic carbon content by core observation,thin section identification,X-ray diffraction and organic carbon test.The results showed that there were nine lithofacies types that could be identified in the fine-grained sedimentary rocks of the lower Xinhe Formation,and six of them are mainly developed,which were organic-lean massive clay-rich siltstone,organic-lean laminated siliceous mixed fine-grained sedimentary rocks,organic-lean massive felsic claystone,organic-contained laminated siliceous mixed fine-grained sedimentary rocks,organic-contained laminated felsic claystone and organic-rich laminated carbonate mixed fine-grained sedimentary rocks.The different lithofacies types and characteristics reflected the differences of sedimentary environment and depositional mechanism.In the prodelta to semi-deep lacustrine,the wave-enhanced sediment gravity flows are widely developed,which formed the superimposed deposition combination of organic-lean massive clay-rich siltstone-laminated siliceous mixed fine-grained sedimentary rocks-massive felsic claystone from bottom to top.In the semideep to deep lacustrine,the water was relatively quiet with a small amount of terrigenous clast input,and the carbonate and clays were more developed,forming organic-contained to rich laminated mixed finegrained sedimentary rocks and claystones.