Organic and inorganic stable isotopes of lacustrine carbonate sediments are commonly used in reconstructions of ancient terrestrial ecosystems and environments. Microbial activity and local hydrological inputs can alter porewater chemistry (e.g., pH, alkalinity) and isotopic composition (e.g., δ¹⁸O_water, δ¹³C_DIC), which in turn has the potential to impact the stable isotopic compositions recorded and preserved in lithified carbonate. The fingerprint these syngenetic processes have on lacustrine carbonate facies is yet unknown, however, and thus, reconstructions based on stable isotopes may misinterpret diagenetic records as broader climate signals. Here, we characterize geochemical and stable isotopic variability of carbonate minerals, organic matter, and water within one modern lake that has known microbial influences (e.g., microbial mats and microbialite carbonate) and combine these data with the context provided by 16S rRNA amplicon sequencing community profiles. Specifically, we measure oxygen, carbon, and clumped isotopic compositions of carbonate sediments (δ¹⁸O_carb, δ¹³C_carb, ∆₄₇), as well as carbon isotopic compositions of bulk organic matter (δ¹³C_org) and dissolved inorganic carbon (DIC; δ¹³C_DIC) of lake and porewater in Great Salt Lake, Utah from five sites and three seasons. We find that facies equivalent to ooid grainstones provide time‐averaged records of lake chemistry that reflect minimal alteration by microbial activity, whereas microbialite, intraclasts, and carbonate mud show greater alteration by local microbial influence and hydrology. Further, we find at least one occurrence of ∆₄₇ isotopic disequilibrium likely driven by local microbial metabolism during authigenic carbonate precipitation. The remainder of the carbonate materials (primarily ooids, grain coatings, mud, and intraclasts) yield clumped isotope temperatures (T(∆₄₇)), δ¹⁸O_carb, and calculated δ¹⁸O_water in isotopic equilibrium with ambient water and temperature at the time and site of carbonate precipitation. Our findings suggest that it is possible and necessary to leverage diverse carbonate facies across one sedimentary horizon to reconstruct regional hydroclimate and evaporation–precipitation balance, as well as identify microbially mediated carbonate formation.

中文翻译：

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碳酸盐相特定的稳定同位素数据记录了犹他州大盐湖的气候，水文和微生物群落。

碳酸盐湖沉积物的有机和无机稳定同位素通常用于重建古代陆地生态系统和环境。微生物活性和当地水文输入可以改变孔隙水化学（例如，pH，碱度）和同位素组成（例如，δ ¹⁸ ö_水，δ ¹³ Ç _DIC），反过来又有可能影响在碳酸化碳酸盐中记录和保存的稳定同位素组成。然而，这些同生过程在湖相碳酸盐相上的指纹仍然未知，因此，基于稳定同位素的重建可能会将成岩记录误认为是更广泛的气候信号。在这里，我们描述了一个具有已知微生物影响的现代湖泊（例如，微生物垫和微生物岩碳酸盐）中碳酸盐矿物，有机物和水的地球化学和稳定同位素变异性，并将这些数据与16S rRNA扩增子测序社区提供的背景相结合个人资料。具体而言，我们测量氧，碳，和结块碳酸盐沉积物的同位素组成（δ ¹⁸ ö_{碳水化合物}，δ ¹³Ç_{碳水化合物}，Δ ₄₇），以及散装有机物碳同位素组成（δ ¹³ C ^_组织）和溶解的无机碳（DIC;δ ¹³ Ç _DIC湖泊和孔隙水的在大盐湖），犹他从五个网站和三个季节。我们发现，与卵石质岩相等同的相提供了湖泊化学的时间平均记录，反映了微生物活动的最小变化，而微生物岩，碎屑岩和碳酸盐泥显示的局部微生物影响和水文学变化更大。此外，我们发现至少发生一次∆ ₄₇自生碳酸盐沉淀过程中可能由局部微生物代谢驱动，同位素失衡。所述碳酸盐材料（主要是鲕粒，颗粒包衣，泥，内碎屑）产生结块同位素的温度（T（Δ的其余部分₄₇）），δ ¹⁸ ö_{碳水化合物}，和δ算出¹⁸ ö_水与环境水和温度在同位素平衡碳酸盐沉淀的时间和地点。我们的发现表明，有可能而且有必要在一个沉积层上利用不同的碳酸盐相来重建区域水文气候和蒸发-降水的平衡，并确定微生物介导的碳酸盐的形成。