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

南非巴伯顿绿岩带早太古代穆迪群 (3.22 Ga) 首次出现叠层石

• 批准号: 447538422
• 负责人: Professor Dr. Christoph Heubeck
• 金额: --
• 依托单位: Institut für Geowissenschaften
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/447538422?language=en
• 关键词: First; occurrence; stromatolites; Early; Archean

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.

生物圈已经几乎完全控制了地球的表面系统，但人们仍然不太清楚是哪些机制和主要的新陈代谢负责，这一过程发生在什么时间和速度，以及对地球的大气层，水和地圈造成了什么后果。这部分是由于有限的和不完整的岩石记录的生命的最早的痕迹。本文介绍了巴伯顿绿岩带（BGB）古太古代穆迪群浅水硅质碎屑岩的初步资料，穆迪群是最早保存完好的微生物生态系统之一。干酪根纹层从潮汐相砂岩的这个单位，强烈类似于现代的蓝藻垫，是合理的研究，但叠层石已被认为是从这个单位缺席，原因不明。在2019年，我们发现了尺寸为厘米到厘米的钙质叠层石碳酸盐土丘，其中一些位于生物层砂岩中明确的流体逃逸结构之上。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引起的方解石的非生物成因沉淀之外，矿物沉淀还可以反映来自干酪根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O2作为氧化剂）、利用浓缩CO2通量的常规产氧光合作用、呼吸、发酵或这些的组合。自形增生边缘的碎屑黄铁矿颗粒与碳酸盐结壳互层可能表明前存在一个额外的S-为基础的代谢，可能微生物硫酸盐还原（MSR）。我们建议通过测量穿过叠层石纹层的西姆斯导线中的δ 13 C和通过测量黄铁矿颗粒中的δ 34 S，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验证这些假设。如果西姆斯结果支持碳酸盐土丘的地球化学起源，那么它们将突出早期生命史中的一种新策略，可能记录地球历史上最早的微生物共生实例之一，甚至可能增加已知的微生物群落清单沿着古太古代海岸线。