We employ complementary field and laboratory‐based incubation techniques to explore the geochemical environment where siderite concretions are actively forming and growing, including solid‐phase analysis of the sediment, concretion, and associated pore fluid chemistry. These recently formed siderite concretions allow us to explore the geochemical processes that lead to the formation of this less common carbonate mineral. We conclude that there are two phases of siderite concretion growth within the sediment, as there are distinct changes in the carbon isotopic composition and mineralogy across the concretions. Incubated sediment samples allow us to explore the stability of siderite over a range of geochemical conditions. Our incubation results suggest that the formation of siderite can be very rapid (about two weeks or within 400 hr) when there is a substantial source of iron, either from microbial iron reduction or from steel material; however, a source of dissolved iron is not enough to induce siderite precipitation. We suggest that sufficient alkalinity is the limiting factor for siderite precipitation during microbial iron reduction while the lack of dissolved iron is the limiting factor for siderite formation if microbial sulfate reduction is the dominant microbial metabolism. We show that siderite can form via heated transformation (at temperature 100°C for 48 hr) of calcite and monohydrocalcite seeds in the presence of dissolved iron. Our transformation experiments suggest that the formation of siderite is promoted when carbonate seeds are present.

中文翻译：

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微生物驱动盐沼沉积物中菱铁矿的形成。

我们采用互补的现场和实验室孵化技术来探索菱铁矿凝结物活跃形成和生长的地球化学环境，包括对沉积物，固结物和相关孔隙流体化学的固相分析。这些最近形成的菱铁矿凝结物使我们能够探索导致这种不太常见的碳酸盐矿物形成的地球化学过程。我们得出的结论是，沉积物中菱铁矿固结物生长有两个阶段，因为整个固结物中碳同位素组成和矿物学都有明显的变化。孵育的沉积物样本使我们能够探索菱铁矿在一系列地球化学条件下的稳定性。我们的孵化结果表明，当有大量铁源（微生物还原铁或钢铁材料）产生时，菱铁矿的形成可能非常迅速（大约两周或400小时之内）。然而，溶解的铁源不足以诱发菱铁矿沉淀。我们建议足够的碱度是微生物还原铁过程中菱铁矿析出的限制因素，而如果硫酸盐还原是微生物代谢的主要途径，则溶解铁的缺乏是菱铁矿形成的限制因素。我们表明，在溶解的铁存在下，方解石可以通过方解石和单氢方解石晶种的加热转变（在100°C下持续48小时）而形成。我们的转化实验表明，当存在碳酸盐种子时，促进了菱铁矿的形成。