黑色岩系中的深源碎屑沉积研究-以新疆三塘湖盆地二叠系芦草沟组为例

Lacustrine black rock series are an important kind of fine-grained sedimentary rocks with abundant organic matter and complex mineral composition. These rocks have been simply considered as mixed deposits of terrigenous clasts and chemical precipitates for a long time due to their extremely fine grain size. Their features of organic geochemistry and reservoir have been well researched; however, the petrology, mineralogy and forming mechanism are relatively ignored. Recently, abundant deep-originated materials derived from volcanic and hydrothermal activities were observed in the black rock series. The influences on deposition, diagenesis, and even hydrocarbon generation and mineralization resulted from the materials has become to an emergent issue to study. Hence, intervals which are dominantly composed of deep-derived materials termed as magmatic-hydrothermal exhalative sedimentary rocks in Permian Lucaogou Formation are the main object of this project, whereas their host rocks, black shale and dolomicrite are the secondary object. Their features of micro petrology and mineralogy, as well as geochemistry and mathematical statistics are going to be observed, analyzed, and calculated. The method of identifying fine-grained terrigenous and deep-derived clasts is going to be established. Based on the study of deposition and early diagenesis, the sedimentary features, as well as the influences on forming mechanism of black rock series caused by deep-derived clasts will be discussed. Finally, expected outcomes may further enrich modern sedimentary theories and guide oil-gas exploration and development.

湖相沉积的黑色岩系是一类组分复杂且富含有机质的重要细粒沉积岩。受限于极细的粒度，这类岩石长期被简单地视为陆源碎屑与内源碎屑和化学沉淀物的混合沉积岩。其储层和有机地球化学特征得到大量研究，但其岩石学、矿物学及形成机理研究较少。近年来研究发现，黑色岩系中发育有丰富的火山及热液喷流的深源碎屑，这些物质的识别与如何参与沉积和成岩作用，甚至生烃、成矿作用急待深入研究。本项目拟以新疆北部三塘湖地区二叠系芦草沟组中富含深源碎屑的岩浆-热液喷流沉积岩夹层为主要研究对象，其围岩-黑色页岩和泥晶白云岩为次要研究对象。重点研究其微观岩石学、矿物学结构构造特征，结合地球化学及数理统计学分析。建立细粒深源碎屑与陆源碎屑在黑色岩系中的识别方法。并从沉积方式与早期成岩作用两方面，探讨湖相沉积环境下，深源碎屑参与的黑色岩系的基础沉积特征及形成机理，进一步丰富现代沉积学理论，为该岩系油气勘探开发提供理论指导。

富有机质黑色泥页岩是我国陆相湖盆一类组分复杂且分布广泛的重要细粒沉积岩。受限于极细的粒度和毫米级纹层，这类岩石长期被简单地视为陆源碎屑与盆内化学沉淀物的混合沉积岩。其岩石学、矿物学及形成机理研究较少。近年来研究发现，这类岩石中发育有丰富的火山及热液喷流的深源碎屑，并且与油气的生成和富集展现出极强的耦合关系。这些物质的识别与如何参与沉积和成岩作用，甚至生烃、成矿作用急待深入研究。本项目以新疆北部三塘湖盆地二叠系芦草沟组中富含深源碎屑的火山-热液喷流沉积岩夹层为主要研究对象，并选择其围岩-黑色泥页岩和泥晶白云岩以及临近的准噶尔盆地吉木萨尔凹陷同层位为次要研究对象。重点研究其微观岩石学、矿物学结构构造特征，结合全岩及原位地球化学及数理统计学分析。建立深源碎屑与陆源碎屑在细粒沉积岩中的识别方法。并从沉积方式与早期成岩作用两方面，探讨湖相沉积环境下，深源碎屑的基础沉积特征及形成机理。项目取得以下研究认识：（1）微观尺度下，在湖相细粒沉积岩中识别出基性、中性及酸性多套火山-热液来源矿物及其岩性组合，重新认识了三塘湖盆地二叠系芦草沟组岩石学、矿物学特征。（2）提出在裂谷型湖盆中，在火山喷发与热液喷流作用共同影响的特殊沉积环境中，持续的源自幔源的热液流体的供给造成的局部的高温，丰富的镁离子与碳酸根离子以及由此造成的微生物活动，共同促进了纹层状泥晶白云石的沉淀。（3）通过将已发现的不同性质与来源的火山-热液喷流沉积岩，并结合芦草沟组中所发现的辉绿岩进行综合研究，初步提出了不同性质岩浆-热液活动共存机理。（4）提出三塘湖盆地及邻区准噶尔盆地吉木萨尔凹陷的二叠系芦草沟组细粒沉积岩型烃源岩形成于地质时期的一个火山-热液沉积系统，其中富含的油气的生成与聚集受该系统影响。上述认识进一步丰富了现代陆内湖相沉积学理论，并为同类型油气勘探开发提供理论指导。