二叠系纹层状微生物白云岩研究—以新疆准噶尔盆地东部为例

Lucaogou Formation of Middle Permian in Jimusar sag, Junggar Basin,Xinjiang, formed in a continental rift lake, was identified as the magma- and mantle-derived hydrothermal exhalative sedimentary rocks. The microbial dolomite with the aggregation of nano-scale spheroids ( 200 to 700nm in diameter), micro-broccoli and micro-kidney shaped, rich in oil, was found for the first time in Lucaogou Formation in this area. Based on the petrology, mineralogy and structures of the dolomite, this project proposes to carry out the detailed study of the micromorphology, major elements, rare elements and isotope analysis of C, O, Sr, Nd of the dolomite, together with the in-situ Pb isotope analysis of the paragenetic alkali feldspar to discuss the origins and the paleosedimentary environments of the dolomite and the paragenetic alkali feldspar, specify the diagenetic evolutions during their burial history, determine the types of microbial dolomite, and compare the dolomite with the hydrothermal exhalative dolomite in same period in Santanghu Basin. At the same time, the simulation experiments of carbonate precepation induced by anaerobic methanogenic metabolic activities will be taken to explore the relationships between the microbes and the oil-bearing dolomite in magma- and mantle-driven hydrothermal envirmonments, the mechanisms and models of microbial dolomite in research area, the features of nanobacteria fossils in ancient rocks, and the relationships between the organic and inorganic dolomite. The research results will provide significant examples in lacustrine dolomite study in geological history in China.

新疆准噶尔盆地吉木萨尔凹陷的二叠系芦草沟组被初步确定为一套形成于陆内裂谷湖相盆地中的岩浆-地幔热液喷流沉积岩系,在其中首次发现了主要由200-700nm的纳米级球粒组成的含油微生物白云岩，同时还有花椰菜状、肾状等形态特征。本课题拟在对该类白云岩进行岩石学、矿物学及其结构构造精细研究基础上，深入开展白云石微形态、主量、微量元素及C、O、Sr、Nd同位素等分析以及对白云石共生矿物碱性长石进行原位铅同位素分析,探讨白云石与碱性长石形成的古环境及物质来源，了解沉积埋藏阶段的成岩变化特征,确定该微生物白云岩的类型，并与三塘湖地区同期的热液喷流型白云岩进行对比研究。开展以本区白云岩为实例的厌氧环境产烷古菌诱导碳酸盐沉淀模拟实验研究,探讨古代富岩浆-地幔热液环境中含油微生物白云石的特征、成因机理及模式、纳米细菌化石特征以及有机、无机白云石之间的相互联系，为我国地质历史时期湖相白云岩研究提供范例。

新疆北部地区的二叠纪芦草沟期发育陆内裂谷型欠补偿湖盆，形成了中二叠统芦草沟组的重要烃源岩系。湖底的火山-热液活动非常频繁，形成一套以深源碎屑为特色的细粒沉积组合，包括薄层、纹层状地幔岩浆-热液喷流沉积岩、微晶白云岩、沉凝灰岩及正常沉积岩等。通过对准噶尔盆地吉木萨尔凹陷、三塘湖盆地中二叠统芦草沟组的系统剖析，探索了火山-热液喷流沉积作用机理及与烃类生成、聚集的关系，建立了完整的陆相湖盆岩浆-热液喷积岩系序列，包括喷爆岩、喷溢岩、喷流岩、喷混岩、喷裂岩及嗜热嗜毒生物岩等。同时还深入刻画了热液矿物组合及地球化学响应特征。认为细粒沉积物由火山-热液晶屑矿物（长石、方解石、白云石、黄铁矿、方沸石等）与自生矿物（石英、水铵长石、泥晶白云石）等的混合而形成。岩浆-热液矿物的主量元素、微量元素、锶同位素、镁同位素均反映出强烈的幔源物质参与的特征；氧同位素、硫同位素显示出湖水参与的特征；强烈正偏的碳同位素暗示了微生物对微晶白云石的形成贡献巨大；而流体包裹体均一温度则揭示成矿流体由低温到高温的动态变化特征，也暗示了岩浆流体与湖水混合的特征。有机地化指标显示岩浆-热液活动区的有机质丰度、生烃潜力指标明显优于正常沉积区。上述研究结果不仅对于探索我国陆相湖盆岩浆-热液沉积作用机理、物质来源有重要理论意义，同时对于深入了解陆相裂谷型盆地油气成因、储层类型、资源分布及扩大勘探方向提供了新思路。