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系统，但人们仍然不太清楚是什么机制和主要新陈代谢造成的，这一过程发生的时间和速度是什么，以及对地球大气层、水圈和地圈造成了什么后果。这在一定程度上是由于对生命最早踪迹的有限和不完整的岩石记录。我们在这里介绍了巴伯顿绿岩带(BGB)古太古代穆迪群(BGB)浅水硅质碎屑岩的初步数据，这是保存最完好的微生物生态系统之一。这个单元的潮汐相砂岩中的干酪生纹层与现代蓝藻垫层非常相似，研究得相当充分，但由于未知的原因，该单元中没有叠层石。2019年，我们发现了大小为厘米至dm的钙质叠层碳酸盐丘，其中一些在生物分层砂岩中具有明显的流体逃逸结构。它们是如何形成的？除了由于逃逸流体的压力和温度降低而导致方解石的非生物沉淀外，矿物降水还可以反映来自干酪微生物垫降解的气体的代谢利用，例如甲烷营养(使用来自附近光合作用微生物垫的废氧作为氧化剂)、利用集中的CO2通量的传统的氧合光合作用、呼吸作用、发酵或它们的组合。与碳酸盐结壳互层的黄铁矿碎屑颗粒的真面体过度生长边缘可能指示了以前存在另一种以S为基础的代谢，可能是微生物硫酸盐还原作用。我们建议通过测量叠层石纹层中选定的SIMS导线中的δ13C，通过测量黄铁矿颗粒中的δ34S，通过对露头和手样中的叠层石形态进行分类，以及通过相关沉积相的地质填图来检验这些假设。如果SIMS的结果支持碳酸盐土丘的生物地球化学起源，那么他们将突出早期生命历史中的一种新策略，可能记录下地球历史上微生物共生的最早例子之一，甚至可能增加已知的古太古代海岸线微生物群落的清单。

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.