前寒武系海相白云石胶结物研究现状及展望^*

Precambrian marine dolomite cements: review and perspectives

摘要

海相白云石胶结物在前寒武纪广泛发育,因其多样的形态、复杂的成因及其对前寒武纪海水性质的指示意义,近年来引起了广泛关注。目前对前寒武系海相白云石胶结物的研究主要集中在两个方面,一是基于矿物学特征分析进行成因探讨,二是探索其反映的前寒武纪海水性质。前人对海相白云石胶结物成因的认识包括原生沉淀与次生交代2种观点,但因缺乏可靠的地球化学证据支撑而存在争议,主要体现在对原生沉淀成因白云石胶结物的具体沉淀机理及其相应的海水化学条件仍不清楚,对次生交代成因白云石胶结物的前驱矿物类型也存在较大分歧。为进一步推动海相白云石胶结物的研究,文中首先系统总结了前寒武系海相白云石胶结物的时空分布特征、岩石学、矿物学及地球化学特征,并从原生沉淀、次生交代、生长组合形态3个方面全面回顾和评述了关于海相白云石胶结物成因研究的现状。在此基础上,对未来相关研究提出以下几点展望: (1)基于矿物成核与生长原理,结合微区或原位地球化学分析,开展不同类型海相白云石胶结物成因研究; (2)评估微生物在海相白云石胶结物形成过程中的具体作用; (3)以前寒武系白云石胶结物为载体探索前寒武纪古海洋海水性质的演化,需建立在厘清其成因的基础之上。

Abstract

Marine dolomite cement is widely developed in the Precambrian era,whereas its occurrence in the Phanerozoic is scarce. Precambrian marine dolomite cement has attracted extensive attention in recent years due to its diversity,complex origins,and potential implications for Precambrian seawater chemistry. Research on Precambrian marine dolomite cement mainly focuses on two aspects: one is the formation mechanism through mineralogical analysis,and the other is the investigation into the unique Precambrian‘aragonite-dolomite sea' conditions as reflected by marine dolomite cement. The origin of marine dolomite cement incorporates both primary precipitation and mimetic dolomitization. However,due to a lack of reliable geochemical evidence,there is ongoing controversy in this field. In addition,both the precipitation mechanism of the primary dolomite and the corresponding seawater chemical conditions remain unclear. The identification of precursor minerals for mimetic dolomite is controversial. Based on previous studies,it can be summarized the spatial and temporal distribution,petrological and mineralogical characteristics,and geochemical characteristics. Subsequently,the current research status on the formation mechanism of marine dolomite cements from three aspects,including primary precipitation,secondary replacement,and growth assemblage morphology. Finally,it can be proposed that three aspects should be enhanced: (1)The genesis of diverse types of marine dolomite cements should be investigated based on the principles of mineral nucleation and growth theory,combining with micro area or in-situ geochemical analysis;(2)he specific contribution of microorganisms to the formation of marine dolomite cements requires assessment;(3)To gain a comprehensive understanding of the evolution of Precambrian seawater properties,exploration of the origin of marine dolomite cement is imperative.

关键词

前寒武系 / 海相白云石胶结物 / 拟晶白云石化作用 / 原生沉淀白云石 / 文石—白云石海

Key words

Precambrian / marine dolomite cements / mimetic dolomitization / primary dolomite / aragonite-dolomite sea

基金资助

*国家自然科学基金项目(编号: 42102136,42472156),油气藏地质及开发工程国家重点实验室(成都理工大学)基金项目(编号: 油重 2019017),四川省天然气成藏物质基础青年科技创新团队基金项目(编号: 2022JDTD0004),中国石油天然气股份有限公司科学研究与技术开发项目(编号: 2021DJ0503)联合资助。