湖相原生白云石的微生物成因机理探讨

摘要

Recently,with the in-depth research on the microbial dolomite mode,a new perspective on Dolomite Problem has been provided.Previous researches on the origin of microbial dolomite mainly focused on the microbial processes in unconsolidated sediments,which equals to organic penecontemporaneous dolomitization.It differs from bacteria-induced organic primary dolomite in laboratory in mechanism.This study introduces the formation mechanism of microbial dolomite into lacustrine primary dolomite,concluding that it would also precipitate primary dolomite in the interface between lake water and sediment,organic primary dolomite.There is a distinction between lake water and sediment in microenvironment of interface,which can be generally divided into two subenvironments:Aerobic and anaerobic,living with different microflora.According to the subenvironments' characteristics of different lake types,different microorganism species and their various role in the formation of dolomite,three microbial dolomite modes can be distinguished,which are the aerobic oxidation mode,the sulphate reduction mode and the methanogenesis mode.Different modes of the microbial dolomite correspond to different lake environments:The aerobic oxidation mode mainly develops in aerobic,high Mg/Ca,salt water lake/saline.The sulphate reduction mode mostly develops in anaerobic,high Mg/Ca,salt water lake/saline.The methanogenesis mode primarily develops in anaerobic,low Mg/Ca,freshwater lake/salt water lake.Moreover,some stillcontroversial issues on the process of dolomite precipitation will be discussed,such as the changing of pH,the effect of SO42-,the impact of sulfide on dehydration of magnesium hydrate and the environmental factors on the precipitation of microbial dolomite.The deep understanding of microbiogenic of primary dolomite model will provide a new theoretical basis and a new insight for lacustrine dolomite.%近年来,随着对微生物白云石模式研究的不断深入,为解释“白云石问题”提供了新思路.前人对微生物白云石成因研究侧重于微生物对未固结沉积物的改造,即有机准同生白云石化作用,这与实验室中以微生物为媒介形成的“有机原生白云石”在成因机理上存在差异.笔者将微生物白云石机理引入湖相原生白云石成因解释中,认为在湖水—沉积物交界处也会发生微生物成因的原生白云石沉淀,即有机原生白云石.湖水与沉积物交界处的微环境存在明显区别,总体可分为有氧和缺氧2种亚环境,不同亚环境中生活有不同的微生物群落.根据湖泊亚环境特性和微生物种类及其在白云石形成过程中所发挥的作用,可以区分出细菌有氧氧化模式、硫酸盐还原模式和产甲烷模式3种微生物白云石模式.不同模式对应于不同的湖泊环境:细菌有氧氧化模式主要发生于有氧、高Mg/Ca值的咸水/盐湖环境;硫酸盐还原模式主要发生于缺氧、高Mg/Ca值的咸水/盐湖环境;产甲烷模式主要发生于缺氧、低Mg/Ca值的淡水/咸水湖环境.另外,还探讨了pH值变化、SO42-的存在和硫化物对镁水合物脱水的影响以及微生物白云石沉淀的环境因子.对微生物成因的原生白云石模式的深入认识,将为湖相白云石成因研究提供新的理论基础和研究思路.