Changes in stable chromium isotopes (denoted as δ⁵³Cr) in ancient carbonate sediments are increasingly used to reconstruct the oxygenation history in Earth’s atmosphere and oceans through time. As a significant proportion of marine carbonate older than the Cambrian is microbially-mediated, the utility of δ⁵³Cr values in ancient carbonates hinges on whether these sediments accurately capture the isotope composition of their environment. We report Cr concentrations (Cr) and δ⁵³Cr values of modern marginal marine and non-marine microbial carbonates. These data are supported by stable C and O isotope compositions, as well as rare earth elements and yttrium (REY) concentrations. In addition, we present data on ancient analogs from Precambrian strata. Microbial carbonates from Marion Lake (Australia, δ⁵³Cr ≈ 0.99‰) and Mono Lake (USA, ≈0.78‰) display significantly higher δ⁵³Cr values compared with ancient microbialites from the Andrée Land Group in Greenland (720 Ma, ≈0.36‰) and the Bitter Springs Formation in Australia (800 Ma, ≈−0.12‰). The δ⁵³Cr values are homogenous within microbialite specimens and within individual study sites. This indicates that biological parameters, such as vital effects, causing highly variable δ⁵³Cr values in skeletal carbonates, do not induce variability in δ⁵³Cr values in microbialites. Together with stable C and O isotope compositions and REY patterns, δ⁵³Cr values in microbialites seem to be driven by environmental parameters such as background lithology and salinity. In support, our Cr and δ⁵³Cr results of ancient microbial carbonates agree well with data of abiotically precipitated carbonates of the Proterozoic. If detrital contamination is carefully assessed, microbialites have the potential to record the δ⁵³Cr values of the waters from which they precipitated. However, it remains unclear if these δ⁵³Cr values record (paleo-) redox conditions or rather result from other physico-chemical parameters.

中文翻译：

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现代和古代微生物岩中的铬同位素系统学

在稳定同位素铬的变化（记为δ ⁵³在远古碳酸盐沉积物铬）越来越多地用于通过时间来重建地球的大气和海洋中的氧的历史。作为海相碳酸盐比寒武纪年长的显著比例微生物介导的，δ的效用⁵³在古碳酸盐铰链Cr值上这些沉积物是否准确捕获它们的环境的同位素组成。我们报告铬浓度（Cr）和δ ⁵³现代边际海洋和非海洋微生物碳酸盐的Cr值。这些数据得到稳定的C和O同位素组成以及稀土元素和钇（REY）浓度的支持。此外，我们介绍了前寒武纪地层的古代类似物的数据。从马里恩湖微生物碳酸盐（澳大利亚，δ ⁵³铬≈0.99‰）和莫诺湖（美国，≈0.78‰）显示显著较高δ ⁵³ Cr值从土地的Andrée集团在格陵兰古代微生物岩（720马，≈0.36相比‰ ）和澳大利亚的苦泉组（800 Ma，≈-0.12‰）。该δ ⁵³ Cr值是microbialite样本内和个人学习网站内均匀。这表明生物参数（例如生命效应）会导致高度可变的δ^53个在骨骼碳酸盐Cr值，不δ诱导变性^53个在微生物岩Cr值。具有稳定的C和O同位素的组合物和REY图案，δ一起^53个在微生物岩Cr值似乎是由环境参数如背景岩性和盐度来驱动。在支持，我们的Cr和δ ^53个古老的微生物碳酸盐岩铬结果与元古代的非生物沉淀碳酸盐的数据吻合。如果碎屑污染仔细评估，微生物岩具有记录δ的电位⁵³从它们沉淀水域的Cr值。但是，目前还不清楚如果这些δ ⁵³Cr值记录（古）氧化还原条件，或者由其他理化参数得出。