陆内裂谷湖相火山-热液沉积型白云岩研究进展^*

Progress on volcanic-hydrothermal sedimentary dolostone in intracontinental lacustrine rift basin

摘要

以富有机质黑色页岩为代表的页岩油、页岩气资源近年来成为全球范围内油气勘探、开发领域的研究热点。该岩性在中国陆相湖盆中主要为来源复杂的细粒沉积岩,其中发育有一类特殊的纹层状泥晶白云岩。该类白云岩的岩石学、矿物学微观特征和地球化学特征既区别于常见的次生白云石化成因白云岩,又与微生物成因白云岩不同,被定义为一类新型的火山-热液沉积型白云岩。在研读大量国内外文献的基础上,综述了现代湖相白云石全球分布及形成环境特征,并展示了白云岩成因模式研究进展。重点选择了均在拉张构造背景下所形成的三塘湖盆地和准噶尔盆地芦草沟组、酒西盆地下沟组和二连盆地腾格尔组发育的火山-热液沉积型白云岩为研究对象,并进行对比研究。发现该类白云岩的特征: (1)保留有完好的原始微米级纹层结构和微晶晶体,后期受到的成岩作用较弱; (2)与半深—深湖黑色泥页岩互层且缺乏蒸发作用特征,并含有不同比例的火山-热液矿物; (3)锶同位素显示成岩流体具有深源(壳-幔混合)特征; (4)含有丰富的有机物质,并与油气分布展现出较强的耦合关系。最后,提出应加强该类白云岩研究、 利用其蕴含的特殊地质信息进行构造背景示踪及探讨其与油气生成关系。

Abstract

Organic-rich black shales,which represent shale oil and gas resources,have become a research hotspot in the field of oil and gas exploration and development in China and around the world in recent years. These lithologies consist mainly of complexly sourced fine-grained sedimentary rocks in continental lacustrine basins in China,among which a special type of laminated microcrystalline dolostone is developed. The petrological,mineralogical micro-features,and geochemical characteristics of this type of dolostone are distinct from the commonly dolostones formed by dolomitization and are also different from microbial mediated dolostones. Hence,the dolostones have been defined as a new type of volcanic-hydrothermal sedimentary dolostone. Based on extensive review of domestic and foreign literature,this paper summarizes the global distribution and environmental characteristics of modern lacustrine dolomites and presents the research progress on the models of origins of dolostone. The focus is on the comparative study of volcanic-hydrothermal sedimentary dolostones found in the Lucaogou Formation in Santanghu and Junggar Basins, the Xiagou Formation in Jiuxi Basin,and the Tengger Formation in Erlian Basin,all of which are formed in an extensional tectonic setting. Four characteristics are summarized as follows: (1)These dolostones are well-preserved with μm-scale laminated structure and microcrystallized,indicating latterly weak diagenesis. (2)They contain a variety of volcanic-hydrothermal minerals,and are interbedded with semi-deep to deep lacustrine black shale. Evaporite characteristics are lacking. (3)Strontium isotopes indicate that the diagenetic fluid has a deep source(crust-mantle mixed)characteristic. (4)They are rich in organic matters and show a strong coupling relationship with hydrocarbon distribution. Finally,it is recommended to enhance research on this type of dolostone,utilize its unique geological information for tracing tectonic backgrounds,and explore its relationship with hydrocarbon generation as future research directions.

关键词

白云岩成因 / 湖相泥晶白云岩 / 热液沉积 / 黑色页岩 / 裂谷盆地

Key words

dolomite origin / lacustrine microcrystalline dolostone / hydrothermal sedimentology / black shale / rift basin

基金资助

*国家自然科学基金青年项目(编号: 41802120)与陕西省自然科学基础研究计划项目(编号: S2024-JC-YB-1766)联合资助