Spatially-resolved isotopic study of carbon trapped in ∼3.43 Ga Strelley Pool Formation stromatolites
Spatially-resolved isotopic study of carbon trapped in ∼3.43 Ga Strelley Pool Formation stromatolites
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对 3.43 Ga Strelley 池组叠层石中捕获的碳进行空间分辨同位素研究
DOI：
10.1016/j.gca.2017.11.028
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发表时间：
2018
影响因子：
5
通讯作者：
Ferralis, Nicola
中科院分区：
文献类型：
--
作者：
Flannery, David T.;Allwood, Abigail C.;Summons, Roger E.;Williford, Kenneth H.;Abbey, William;Matys, Emily D.;Ferralis, Nicola
与酶碳同化相关的碳的大量同位素分馏使生命的远古证据，以及潜在的几条现存代谢途径的早期运行，可以从沉积岩的稳定碳同位素记录中获得。地球的有机碳同位素记录可以追溯到早太古代晚期-古太古代早期：已知最古老的沉积岩的年龄。然而，互补的无机碳库在最古老的单元中代表得很少，而且通常报道的整体有机碳同位素测量没有捕捉到越来越多地从年轻岩石中报道的微尺度同位素不均质性。在这里，我们研究了沉积碳酸盐和有机质最古老的配对产状的同位素组成，它们以白云石和干酪根的形式保存在∼3.43 Ga Strelley Pool组的结构生物特征中。我们在非破坏性元素填图的指导下，使用微采样技术，瞄准了环境中变化最小的碳酸盐相。有机碳同位素值通过空间分辨的整体分析进行测量，并使用二次离子质谱仪来定位捕获在无机碳基质中的有机物质的微尺度结构域。观测到的13C总分馏分数范围从−29到−45‰。我们的数据与对拥有生物叠层石和有机-无机碳对的年轻太古宙岩石的研究一致，显示出比单独固定Rubisco的预期更大的分馏。我们的结论是，在古太古代浅水海洋环境中，除了CBB循环外，有机质还被至少一种代谢作用固定和/或再动员，可能是通过Wood-Ljugdahl途径或甲烷生成-甲烷营养作用。
The large isotopic fractionation of carbon associated with enzymatic carbon assimilation allows evidence for life’s antiquity, and potentially the early operation of several extant metabolic pathways, to be derived from the stable carbon isotope record of sedimentary rocks. Earth’s organic carbon isotope record extends to the Late Eoarchean-Early Paleoarchean: the age of the oldest known sedimentary rocks. However, complementary inorganic carbon reservoirs are poorly represented in the oldest units, and commonly reported bulk organic carbon isotope measurements do not capture the micro-scale isotopic heterogeneities that are increasingly reported from younger rocks. Here, we investigated the isotopic composition of the oldest paired occurrences of sedimentary carbonate and organic matter, which are preserved as dolomite and kerogen within textural biosignatures of the ∼3.43 Ga Strelley Pool Formation. We targeted least-altered carbonate phasesin situusing microsampling techniques guided by non-destructive elemental mapping. Organic carbon isotope values were measured by spatially-resolved bulk analyses, andin situusing secondary ion mass spectrometry to target microscale domains of organic material trapped within inorganic carbon matrixes. Total observed fractionation of13C ranges from −29 to −45‰. Our data are consistent with studies of younger Archean rocks that host biogenic stromatolites and organic–inorganic carbon pairs showing greater fractionation than expected for Rubisco fixation alone. We conclude that organic matter was fixed and/or remobilized by at least one metabolism in addition to the CBB cycle, possibly by the Wood-Ljungdahl pathway or methanogenesis-methanotrophy, in a shallow-water marine environment during the Paleoarchean.