First occurrence of stromatolites in the Early Archean Moodies Group (3.22 Ga), Barberton Greenstone Belt, South Africa

生物圈已经几乎完全控制了地球表面的系统，但人们仍然不太清楚是哪些机制和主要代谢机制在起作用，这一过程发生的时间和速度，以及对地球的大气、水文和地气圈造成的后果。这在一定程度上是由于生命最早痕迹的岩石记录有限且不完整。本文介绍了巴伯顿绿岩带（BGB）古太古代modies群的浅水硅塑料初步数据，这是最早保存完好的微生物生态系统之一。该单元潮汐相砂岩的干酪质层状，与现代蓝藻席非常相似，已经得到了很好的研究，但由于未知的原因，叠层石被认为在该单元中不存在。2019年，我们发现了cm到dm大小的钙质叠层石碳酸盐丘，其中一些位于生物层状砂岩中明确的流体逸出结构之上。它们是如何形成的？除了由于逸出流体的压力和温度降低而导致方解石的非生物成因沉淀外，矿物沉淀还可以反映出干酪根微生物垫降解产生的气体的代谢利用，例如甲烷化（利用附近光合作用的微生物垫产生的废氧作为氧化剂）、利用浓缩CO2通量的常规含氧光合作用、呼吸、发酵或这些的组合。与碳酸盐结壳互层的碎屑黄铁矿颗粒自面体生长过度的边缘可能表明前者存在额外的基于代谢，可能是微生物硫酸盐还原（MSR）。我们建议通过测量叠层石片层中特定SIMS横截面的δ13C、测量黄铁矿颗粒中的δ34S、对露头和手样中的叠层石形态进行分类以及对相关沉积相进行地质填图来验证这些假设。如果SIMS的结果支持碳酸盐土丘的生物地球化学起源，那么它们将突出早期生命历史中的一种新策略，可能记录地球历史上最早的微生物共生例子之一，甚至可能增加沿古太古代海岸线的已知微生物群落清单。

The biosphere has attained near-complete control over the Earth’s surface systems but it remains poorly understood which mechanisms and dominant metabolisms were responsible, at what time and rate this process occurred, and which consequences for Earth’s atmo-, hydro- and geosphere resulted. This is in part due to the restricted and incomplete rock record of life’s earliest traces. We here present preliminary data from shallow-water siliciclastics of the Paleoarchean Moodies Group of the Barberton Greenstone Belt (BGB), one of the earliest well-preserved microbial ecosystems. Kerogenous laminations from tidal-facies sandstones of this unit, strongly resembling modern cyanobacterial mats, are reasonably well studied, but stromatolites have been thought to be absent from this unit, for unknown reasons. In 2019, we discovered calcareous, stromatolitic carbonate mounds cm to dm in size, some of which top unambiguous fluid-escape structures in biolaminated sandstones. How did they form? Aside from abiogenic precipitation of calcite due to pressure and temperature reduction of escaping fluids, mineral precipitation could also reflect the metabolic utilization of gases from the degradation of kerogenous microbial mats, e.g., methanotrophy (using waste O2 from nearby photosynthesizing microbial mats as oxidant), conventional oxygenic photosynthesis exploiting a concentrated CO2 flux, respiration, fermentation, or a combination of these. Euhedral overgrowth rims of detrital pyrite grains interbedded with the carbonate crusts may indicate the former presence of an additional S-based metabolism, likely microbial sulfate reduction (MSR). We suggest to test these hypotheses by measuring δ13C in selected SIMS traverses across the stromatolitic laminations and by measuring δ34S in pyrite grains, by classifying stromatolite morphologies in outcrop and hand sample, and by geologic mapping of relevant sedimentary facies. If SIMS results supported the biogeochemical origin of the carbonate mounds, then they would highlight a novel strategy in the early history of life, possibly document one of the earliest examples of microbial symbiosis in Earth’s history, and potentially even add to the known inventory of microbial communities along Paleoarchean shorelines.