Abstract

Distribution of carbonate sediments of different composition in the Precambrian section is reviewed. It is shown that calcium carbonates prevailed in the Archean–initial Early Proterozoic, and iron carbonates dominated in the banded iron formations. Dolomites and magnesites were more widespread in the Proterozoic. Such distribution suggests an acid reductive geochemical environment in the Archean–Early Proterozoic, which determined the corresponding character of continental weathering: appearance of dissolved forms of Fe and silica that were transported to ancient oceans and deposited, resulting in the formation of ferruginous–quartzites or jaspilites (banded iron formations). Large-scale and almost explosive development of photosynthesizing cyanobacteria at the Archean–Proterozoic boundary stipulated, first, the utilization of carbon dioxide and, correspondingly, the change of acid environment into alkaline, leading to the formation of magnesian carbonates; and, second, to the appearance of free oxygen.

中文翻译：

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前寒武纪沉积的地球化学环境

摘要

回顾了前寒武纪剖面碳酸盐沉积物的分布。结果表明，碳酸钙主要存在于太古代至原始元古代，而碳酸铁主要存在​​于带状铁地层中。白云岩和镁质岩在元古代较普遍。这种分布表明在太古代-元古生代存在一种酸性还原地球化学环境，这决定了大陆风化的相应特征：溶解形式的铁和硅的出现，这些铁和硅被运到古代海洋并沉积，导致形成铁质石英岩或碧玉（带状铁）。在太古代-元古代界，光合作用蓝细菌的大规模，几乎是爆炸性的发展规定，首先是二氧化碳的利用，以及 相应地，酸性环境变成碱性，导致镁碳酸盐的形成。第二，游离氧的出现。