青海湖湖滩岩的岩石学特征及其形成机制

以青海湖的湖滩岩为研究对象,通过显微镜观察、扫描电镜、矿物阴极发光性观察和电子探针等分析方法研究了湖滩岩的岩石学特征和形成机制.湖滩岩胶结物主要由暗色纹层和文石针组成,识别出五类胶结物晶体和三类胶结物组构.在暗色纹层中,有发现包覆式和缠绕式生长的微生物.微生物对泥晶方解石和黏土矿物起着生物稳定化作用(障积作用、捕获作用和粘结作用).微生物生长过程中的新陈代谢影响了碳酸盐的溶解度,从而导致产生碳酸盐矿物在微生物席内的丝状体之间或沿着丝状体的沉淀作用.从研究湖滩岩胶结物垂向上和横向上的变化规律入手,发现胶结物的类型和组构与水深、温度、盐度、水动力条件有一定关系.破浪带和碎浪带的水深、温度、盐度适宜,为微生物作用最强的水动力带.通过对青海湖湖滩岩中的微生物作用特征及其发育模式的研究,认为湖滩岩中胶结物的形成受到微生物作用的影响较大,从而支持了微生物作用对碎屑岩早期成岩具有重要意义的假设.

The petrological characteristics and formation mechanism of Lake Beachrock in Lake Qinghai

The lake beachrock in Lake Qinghai as the research object, through microscope, SEM, mineral cathode luminance observation and electron probe analysis method to study the characteristics and precocious mechanism of lake beachrock. The beachrock cement is mainly composed of dark grain layers and aragonite needles. There are five kinds of cement crystals and three kinds of cement fabric. There is coating, voluble and conglutinating growth of microbes in the lake beachrock cement. Microorganisms for micritic calcite and clay mineral have a biological stabilization effect(barrier, and the roles of capture and bonding effect). The metabolism in the microbial growth will change the carbonate solubility and resulting in carbonate minerals is produced by the filaments in microbial mat or between precipitations along the filaments. From the lake beach rock cement on the lateral and vertical changes, it is found that the type and texture of the cement are related to water depth, temperature, salinity and hydrodynamic conditions. Water depth, temperature, and salinity are suitable in swash zone and breaker zone where microbial activities arethe strongest. Through the research of microbial characteristics and developmental pattern of beachrock cement in Lake Qinghai, we concluded that cement in the lake beachrock is affected by the microbial action, which support the biological role of clastic rock in early diagenetic hypothesis that it is of great significance.