苏北盆地高邮-金湖凹陷古近系阜宁组细粒沉积岩纹层特征与成因

Characteristics and forming mechanism of laminae fine-grained sedimentary rock of the Paleogene Funing Formation in Gaoyou and Jinhu sags,Subei Basin

深水细粒沉积物不仅可作为烃源岩,也可成为非常规油气的储集层。以苏北盆地高邮-金湖凹陷古近系阜宁组阜二段半深湖-深湖水平层理细粒沉积岩为研究对象,通过高精度厘米级岩心观察描述、薄片鉴定、X射线衍射全岩矿物分析、微量元素测试及扫描电镜等手段,分析了岩石纹层特征并尝试探讨其成因。结果表明:高邮-金湖凹陷阜宁组二段半深湖-深湖细粒沉积岩岩性复杂,多种物质组分的混合及叠置形成了不同颜色的纹层。水平层理可根据纹层厚度进一步分为薄纹层状和厚纹层状2类沉积构造,两者的宏观与微观结构、物质组成等均存在差异。纹层成因复杂,但主要受形成和保存2个方面因素影响。在纹层形成过程中,各物质组分的产生与沉淀均具有季节性意义;纹层的保存主要与水体深度有关。

The deep-water fine-grained deposits can be not only the source rock,but also the reservoir of unconventional oil and gas.Combined with high-precision centimeter-scale core observation,thin section identification,X-ray diffraction whole rock analysis,trace element test and scanning electron microscopy(SEM)analysis,the laminae characteristics and the genesis mechanism of semi-deep to deep lake fine-grained sedimentary rocks in the Member 2 of the Funing Formation are investigated in the Gaoyou and Jinhu sags of the Subei Basin.The results show that the semi-deep and deep lake fine-grained sedimentary rocks of the Member 2 of the Funing Formation in the Gaoyou and Jinhu sags are complex in lithology,and the laminae with different colors are formed by the mixture and superposition of various material components.The horizontal bedding developed in the fine-grained sedimentary rocks can be further divided into thin-laminated and thick-laminated sedimentary structures,whose macroscopic,microscopic characteristics and the composition are different.The complex forming mechanism of laminae includes two aspects:Formation process and preservation process.The generation(or the input)and the precipitation of each component have seasonal significance during the formation of laminae,whereas the preservation of the laminae could be mainly related to the water depth in the study area.