Marine ooids have formed in microbially colonized environments for billions of years, but the microbial contributions to mineral formation in ooids continue to be debated. Here we provide evidence of these contributions in ooids from Carbla Beach, Shark Bay, Western Australia. Dark 100–240 μm diameter ooids from Carbla Beach contain two different carbonate minerals. These ooids have 50–100 μm-diameter dark nuclei that contain aragonite, amorphous iron sulfide, detrital aluminosilicate grains and organic matter, and 10–20 μm-thick layers of high-Mg calcite that separate nuclei from aragonitic outer cortices. Raman spectroscopy indicates organic enrichments in the nuclei and high-Mg calcite layers. Synchrotron-based microfocused X-ray fluorescence mapping reveals high-Mg calcite layers and the presence of iron sulfides and detrital grains in the peloidal nuclei. Iron sulfide grains within the nuclei indicate past sulfate reduction in the presence of iron. The preservation of organic signals in and around high-Mg calcite layers and the absence of iron sulfide suggest that organics stabilized high-Mg calcite under less sulfidic conditions. Aragonitic cortices that surround the nuclei and Mg-calcite layers do not preserve microporosity, iron sulfide minerals nor organic enrichments, indicating growth under more oxidizing conditions. These morphological, compositional, and mineralogical signals of microbial processes in dark ooids from Shark Bay, Western Australia, record the formation of ooid nuclei and the accretion of magnesium-rich cortical layers in benthic, reducing, microbially colonized areas.

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西澳大利亚鲨鱼湾富含有机物的双矿物质类物质记录了生物过程

海洋鲕鱼在微生物定殖的环境中形成了数十亿年，但微生物对鲕鱼矿物形成的贡献仍然存在争议。在这里，我们提供了来自西澳大利亚鲨鱼湾卡尔布拉海滩的鲕鱼中这些贡献的证据。来自卡尔布拉海滩的直径为 100-240 微米的深色鲕鱼含有两种不同的碳酸盐矿物。这些鲕粒有直径 50-100 μm 的暗核，含有文石、无定形硫化铁、碎屑铝硅酸盐颗粒和有机物，以及 10-20 μm 厚的高镁方解石层，将核与文石外皮层分开。拉曼光谱表明核和高镁方解石层中有有机物富集。基于同步加速器的微聚焦 X 射线荧光测绘揭示了高镁方解石层以及球状核中硫化铁和碎屑颗粒的存在。核内的硫化铁颗粒表明过去在铁存在下发生了硫酸盐还原。高镁方解石层内和周围有机信号的保存以及硫化铁的不存在表明有机物在含硫量较少的条件下稳定了高镁方解石。围绕核和镁方解石层的文石皮质不保留微孔、硫化铁矿物或有机富集，表明在氧化性更强的条件下生长。这些来自西澳大利亚鲨鱼湾的暗鲕鱼中微生物过程的形态、成分和矿物学信号，记录了鲕鱼核的形成以及底栖、还原、微生物定殖区域中富含镁的皮质层的增生。