摘要： 微生物活动导致铁氧化被认为是前寒武纪铁建造和红层形成的重要机制之一,但是地质记录中却鲜有相关证据。针对这一问题,本研究选择华北古元古代末的大红峪组微生物席成因构造(MISS)为研究对象,通过沉积学和矿物学的综合研究,揭示微生物活动在前寒武纪铁循环中的关键作用。研究表明:华北井陉大红峪组发育大量以砂裂为代表的MISS,指示当时潮间带至潮上带广泛发育微生物席;非微生物席层发育大量原位和近距离搬运的海绿石,指示低氧富铁的浅海和孔隙水化学条件,而相邻微生物席层则发生了显著的赤铁矿化,指示相对更氧化的沉积环境。考虑到微生物席层与相邻(厘米级)非微生物席层间微生物活动与矿物组成的明显差异,笔者提出微生物活动可能是导致当时低氧铁化浅海环境局部铁氧化的重要机制。本研究提供了微生物参与Fe²⁺离子氧化的重要证据,对揭示前寒武纪红层和大规模铁建造形成机制具有启示意义。

关键词: 大红峪组, 赤铁矿, 海绿石, 氧化还原, 铁循环

Abstract: Microbially mediated iron oxidation has been considered as one of the most important mechanisms for the formation of Precambrian iron formation and marine red bed. However,the evidence of microbial mediation is rarely recorded through Earth history. To reveal the potential roles of microbes in the Precambrian iron cycling,we chose microbially induced sedimentary structure(MISS)from the late Paleoproterozoic Dahongyu Formation,North China,as target,and conducted a comprehensive investigation in sedimentology and mineralogy. In this formation,sand cracks are the dominated type of MISS,indicating the existence of abundant microbial mats on the intertidal to supratidal zones previously. Microscopic observations show that the non-microbial mat layer contains abundant in situ to shortly transported glauconite,indicating suboxic and iron-rich shallow seawater and porewater chemistry. In contrast,the microbial mats show significant hematization,indicative of more oxygenated conditions. Considering the differences in microbial activity and mineralogy between the microbial mat and adjacent non-microbial mat layers,we propose that microbial mediation is an important mechanism leading to the oxidation of Fe(Ⅱ)in the weakly oxygenated ferruginous shallow seawater. This study provides important evidence for microbial mediation in Fe(Ⅱ)oxidation and may shed light on the formation of Precambrian marine red bed and iron formation.

Key words: Dahongyu Formation, hematite, glauconite, redox condition, iron cycling

中图分类号: 

• P534.41