Abstract Stromatolites have been a major focus in the search for ancient microbial life, however, the organic carbon biosignatures of dolomitized stromatolites have not yet been fully characterized or correlated with their dolomitizing conditions. Although dolomitization rarely preserves microbial morphology, the presence of organic carbon can provide valuable information for characterization of fossils' biogenicity, syngenicity, and indigeneity to their host rock. The Cambrian Allentown Formation in New Jersey, USA, is an excellent example of dolomitized stromatolites and thrombolites containing diagenetically modified microbial biosignatures. Based on XRD and EPMA data, the dolomite composition is typically stoichiometric, with varying degrees of cationic ordering. The outcrop underwent early dolomitization in a marginal-marine setting and later burial diagenesis resulting in multi-generational dolomite formation: (1) microspar dolomite formed by early diagenetic replacement at or near the surface, (2) zoned dolomite formed penecontemporaneously with the microspar phase as rhombohedral crystals by infilling primary pore spaces within the microspar matrix. The rhombic crystals continued to grow outward in alternating stages of Fe-enriched and -depleted fluids, which were preserved in zoned rims and revealed by cathodoluminescence, and (3) saddle dolomite formed during late stage deep burial with Fe- and Mn-rich fluids, and occurs as a void-filling, high-temperature phase. Organic carbon, characterized using confocal Raman microscopy, has an exclusive distribution within the microspar dolomite, and the D and G bands' characteristics reveal similar thermal alteration to the host rock, indicating that the mapped organic carbon is indigenous and syngenetic with the Cambrian carbonates. The findings presented in this study reveal organic matter found within microspar of various dolomitized facies deriving from different source pools of organic carbon. This study sheds light on biosignatures in secondary dolostones and may aid biosignature detection in older carbonate rocks on Earth and Mars.

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白云石化寒武系叠层石中有机碳的保存及其对成岩置换碳酸盐岩中微生物生物特征的影响

摘要叠层石一直是寻找古代微生物生命的主要焦点，然而，白云石化叠层石的有机碳生物特征尚未完全表征或与其白云石化条件相关联。尽管白云石化很少能保留微生物形态，但有机碳的存在可以为表征化石的生物成因性、同源性和其寄主岩石的本土性提供有价值的信息。美国新泽西州的寒武纪阿伦敦地层是含有成岩修饰微生物生物特征的白云石化叠层石和凝块石的一个很好的例子。根据 XRD 和 EPMA 数据，白云石的成分通常是化学计量的，具有不同程度的阳离子排序。露头在边缘海相环境中经历了早期白云石化和后来的埋藏成岩作用，导致了多代白云岩的形成：（1）在地表或地表附近早期成岩置换形成的微晶石白云岩，（2）与微晶石相同生形成的分带白云岩通过填充微晶石基质内的初级孔隙空间，作为菱形晶体。菱形晶体在富铁和贫铁流体交替阶段继续向外生长，保留在分带边缘并通过阴极发光显示，以及（3）晚期深埋藏的鞍状白云岩与富铁和锰流体，并作为填充空隙的高温相发生。使用共聚焦拉曼显微镜表征的有机碳在微晶石白云岩中具有独特的分布，D 和 G 带的特征揭示了与主岩相似的热蚀变，表明绘制的有机碳是原生的，与寒武纪碳酸盐岩同生。本研究中提出的发现揭示了在源自不同有机碳源库的各种白云石化相的微晶石中发现的有机质。这项研究揭示了次生白云岩中的生物特征，并可能有助于地球和火星上较老的碳酸盐岩中的生物特征检测。