四川汉源-峨边地区上震旦统灯影组藻白云岩特征及成因研究

"藻白云岩"术语的提出已有五十年历史,震旦系藻白云岩以其巨大的厚度,精美的原生结构、构造,以及丰富的微生物化石和矿产资源而闻名,但至今其成因仍存在争议。以四川汉源-峨边地区上震旦统灯影组藻白云岩为研究对象,对其宏观的剖面、岩石学、原生构造特征,微观的白云石和微生物化石形态、原生结构特征,以及相应的地球化学特征进行了详细研究。结果表明:研究区灯影组藻白云岩为一套在潮坪和潟湖环境下形成的微生物（碳酸盐）岩的岩石类型组合,以藻黏结型的叠层状、纹层状、葡萄状和均一状（藻）白云岩为主要的次级类型;藻白云岩中主要发育原生的隐晶状微生物白云石和次生的纤维状拟晶白云石,其形成与蓝细菌、硫酸盐还原细菌、中度嗜盐好氧细菌和红藻等微生物的矿化作用密切相关:沉积-同生阶段,主要由微生物诱导矿化作用形成大量纳米似立方体粒状和（亚）微米级片状微生物白云石,同时共（伴）生纤维状文石和高镁方解石;同生-准同生阶段,主要由微生物影响矿化作用形成纳米球粒状和微米级不规则状、球状和卵状微生物白云石,同时纤维状文石和高镁方解石因微生物催化矿化作用和拟晶白云石化作用形成纤维状拟晶白云石;随后微生物白云石与拟晶白云石一起组成具纹层状、叠层状、均一状等构造的藻白云岩。对藻白云岩特征及成因的研究有助于理解微生物-矿物交互作用和过程的复杂性、多样性,也为前寒武纪微生物矿化作用、微生物白云石和拟晶白云石研究提供了新的实例。

Study on Characteristics and Geneses of Algal Dolostone of the Upper Sinian Dengying Formation in the Hanyuan-Ebian Area of Sichuan Province,China

Based on the macroscopic characteristics of profile,petrology and original structures,the microscopic char-acteristics of morphology and original textures of dolomite and microbial fossils and the corresponding geochemical characteristics,this paper studied the characteristics and geneses of algal dolostone of the Upper Sinian Dengying For-mation in the Hanyuan-Ebian Area of Sichuan Province, China. The results show that the algal dolostone is a set of microbialites or microbial carbonates association formed in the tidal flat and lagoon,in which the laminated,stromato-lithic,botryoidal and uniform(algal)dolostones are dominate. There are mainly two different texture and genesis types of dolomites,primary cryptocrystalline microbial dolomite and secondary fibrous mimetic dolomite. The geneses of the two types of dolomites are closely related to microbial biomineralization of Cyanobacteria, sulphate-reducing bacteria(SRB),moderately halophilic aerobic bacteria and red algae. In the precipitation and syngenetic stages, a large amount of nanometre-sized(pene-)cubical granular and(sub-)micron-sized sheeted dolomites is formed by microbially induced mineralization;meanwhile,fibrous aragonite and high-Mg calcite are developed.In the syngenetic and penecontemporaneous stages,nanometre-sized(spherulitic)granular and micron-sized irregular,spherical and o-voidal dolomites are formed by microbially influenced mineralization,in the meantime the fibrous aragonite and high-Mg calcite transform into the fibrous mimetic dolomite through microbially catalysed mineralization and mimetic dolo-mization. Then the microbial and mimetic dolomite form laminated stromatolithic and uniform dolostone together. The research of characteristics and geneses of algal dolostones is useful to comprehend the complexity and diversity of min-eral-microbe interaction and process in this paper, and provides a new example of the investigation of microbial bi-omineralization,microbial dolomite and mimetic dolomite in the Precambrian era.