Interpreting the environmental conditions under which ancient microbialites formed relies upon comparisons with modern analogues. This is why we need a detailed reference framework relating the chemical and mineralogical compositions of modern microbialites to the physical and chemical parameters prevailing in the environments where they form. Here, we measured the chemical, including major and trace elements, and mineralogical composition of microbialites from ten Mexican lakes as well as the chemical composition of the surrounding waters. Saturation states of lakes with different mineral phases were systematically determined and correlations between solution and solid chemical analyses were assessed using multivariate analyses. A large diversity of microbialites was observed in terms of mineralogical composition, with occurrence of diverse carbonate phases such as (Mg-)calcite, monohydrocalcite, aragonite, hydromagnesite, and dolomite as well as authigenic Mg-silicate phases (kerolite and/or stevensite). All lakes harbouring microbialites were saturated or supersaturated with monohydrocalcite, suggesting that such a saturation state might be required for the onset of microbialite formation and that precursor soluble phases such as amorphous calcium carbonate and monohydrocalcite play a pivotal role in these lakes. Subsequently, monohydrocalcite transforms partly or completely to aragonite or Mg-calcite, depending on the lake (Mg/Ca)_aq. Moreover, lakes harbouring hydromagnesite-containing microbialites were saturated with an amorphous magnesium carbonate phase, supporting again the involvement of precursor carbonate phases. Last, authigenic Mg-silicates formed by homogenous or heterogenous nucleation in lakes saturated or supersaturated with a phase reported in the literature as “amorphous sepiolite” and with a H₄SiO₄ concentration superior to 0.2 mM. A strong correlation between the alkalinity and the salinity of all the lakes was observed. The observed large variations of alkalinity between the lakes relate to varying concentration stages of an initial alkaline dilute water, due to a varying hydrochemical functioning. In all cases, the size of microbialites in the lakes correlated positively with salinity, (Mg/Ca)_aq ratio and alkalinity. The trace element compositions of the microbialites also varied significantly between the lakes. Detrital contamination of the studied microbialites was the major factor affecting their rare earth elements (REE) + Y patterns. In particular, the microbialites highly affected by detrital contamination showed a high (REE + Y) content and flat (REE + Y) patterns. In contrast, some microbialites poorly affected by detrital contamination showed (REE + Y) patterns with features commonly reported for marine microbialites, such as a superchondritic Y/Ho ratio, enrichment in heavy REE and a negative Ce anomaly. This last observation questions the possibility to infer the marine versus lacustrine origin of a microbialite based on (REE + Y) patterns only. Overall, while microorganisms can impact nucleation processes and textural arrangements in microbialites, we observe that the hydrogeochemical evolution of lakes exerts a primary control over the onset of microbialite formation and the evolution of their chemical and mineralogical composition. Moreover, while changes of all these chemical and mineralogical features upon diagenesis and metamorphism will need to be assessed, the present study, together with recent meta-analyses of modern microbialites, broadens the set of modern references available for comparisons with geological archives.

解释古代微生物形成的环境条件取决于与现代类似物的比较。这就是为什么我们需要一个详细的参考框架，将现代微生物的化学和矿物组成与其形成环境中普遍存在的物理和化学参数联系起来。在这里，我们测量了来自十个墨西哥湖的微生物的化学组成（包括主要元素和微量元素），矿物组成以及周围水域的化学组成。系统地确定了具有不同矿物相的湖泊的饱和状态，并使用多元分析评估了溶液和固体化学分析之间的相关性。就矿物组成而言，观察到了多种多样的微辉石，会出现多种碳酸盐相，例如（Mg-）方解石，单氢方解石，文石，水菱镁矿和白云石，以及自生的Mg-硅酸盐相（软沸石和/或硅镁石）。所有包含微斜沸石的湖泊都被单水方解石饱和或过饱和，这表明可能需要这种饱和状态才能开始形成微斜沸石，并且前体可溶相（如无定形碳酸钙和单水方解石）在这些湖泊中起着举足轻重的作用。随后，单氢方解石部分或全部转变为文石或镁方解石，具体取决于湖泊（Mg / Ca）所有包含微斜沸石的湖泊都被单水方解石饱和或过饱和，这表明可能需要这种饱和状态才能开始形成微斜沸石，并且前体可溶相（如无定形碳酸钙和单水方解石）在这些湖泊中起着举足轻重的作用。随后，单氢方解石部分或全部转变为文石或镁方解石，具体取决于湖泊（Mg / Ca）所有包含微斜沸石的湖泊都被单水方解石饱和或过饱和，这表明可能需要这种饱和状态才能开始形成微斜沸石，并且前体可溶相（如无定形碳酸钙和单水方解石）在这些湖泊中起着举足轻重的作用。随后，单氢方解石部分或全部转变为文石或镁方解石，具体取决于湖泊（Mg / Ca）_aq。此外，含有水菱镁矿的微辉石的湖泊被无定形的碳酸镁相饱和，再次支持了前体碳酸盐相的参与。最后，由在湖泊中饱和或过饱和的均相或异相成核形成的自生镁硅酸盐，文献中报道的相为“无定形海泡石”和H ₄ SiO ₄浓度优于0.2 mM。观察到所有湖泊的碱度和盐度之间都有很强的相关性。由于变化的水化学功能，在湖泊之间观察到的碱度的大变化与初始的碱性稀水的浓度阶段的变化有关。在所有情况下，湖泊中微辉石的大小与盐度（Mg / Ca）_{aq正相关。}比例和碱度。湖泊之间的微辉石的痕量元素组成也有很大差异。所研究的微辉石岩的碎屑污染是影响其稀土元素（REE）+ Y型的主要因素。特别是，受碎屑污染严重影响的微粉岩显示出高（REE + Y）含量和平坦（REE + Y）模式。相比之下，一些受碎屑污染影响较小的微生物岩表现出（REE + Y）模式，具有海洋微生物岩普遍报道的特征，如超软骨质Y / Ho比，重稀土元素富集和Ce负异常。最后的观察结果质疑了推断海军陆战队对战舰的可能性仅基于（REE + Y）模式的微辉石的湖相来源。总体而言，尽管微生物会影响微辉石的成核过程和组织结构，但我们观察到湖泊的水文地球化学演化对微辉石的形成及其化学和矿物组成的演化起着主要的控制作用。此外，尽管将需要评估成岩作用和变质作用后所有这些化学和矿物学特征的变化，但本研究以及对现代微辉石的最新荟萃分析，拓宽了可用于与地质档案进行比较的现代参考资料的范围。