Although the Monterey Formation has been studied extensively for its petroleum system and Miocene climate insights, debates persist regarding its paleo-redox conditions. Furthermore, its characteristic lithofacies offer a natural laboratory for developing tools to differentiate siliceous and calcareous rocks in deepwater environments. This study evaluated the potential of the Sulfur Index (SI = mg Sorg/g TOC), measured by Rock-Eval 7S, as a proxy for assessing paleoredox conditions by comparing the SI with iron speciation data. Additionally, high-resolution molecular analyses were performed to investigate possible relationships between sulfur compounds and rocks with different carbonate content. The findings indicate higher SI values and higher concentrations of benzothiophenes over dibenzothiophenes in the siliceous lithofacies compared to the calcareous lithofacies. This suggests that the mineral matrix plays a crucial role in influencing the process by which sulfur-rich kerogen undergoes cracking when placed under thermal stress. The SI may support a paleoredox interpretation for the Monterey Formation, differing from previous interpretations based only on iron speciation. This alternative interpretation involves a more extensive water-column euxinia, distinct from the seasonal euxinia suggested in previous work. This study represents a practical and pioneering workflow based on sulfur data derived from Rock-Eval 7S for paleoredox and lithofacies assessments, opening avenues for further research.

中文翻译：

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加利福尼亚州圣玛丽亚盆地蒙特雷组深水层段的古氧化还原和岩相评估：来自有机硫地球化学的见解


尽管蒙特雷组因其石油系统和中新世气候见解而被广泛研究，但关于其古氧化还原条件的争论仍然存在。此外，其独特的岩相为开发在深水环境中区分硅质和钙质岩石的工具提供了一个天然实验室。本研究评估了由 Rock-Eval 7S 测量的硫指数 （SI = mg Sorg/g TOC） 作为通过将 SI 与铁形态数据进行比较来评估古氧化还原条件的潜力。此外，还进行了高分辨率分子分析，以研究硫化合物与不同碳酸盐含量的岩石之间的可能关系。结果表明，与钙质岩相相比，硅质岩相中的SI值和苯并噻吩浓度高于二苯并噻吩。这表明矿物基体在影响富硫干酪根在热应力下发生开裂的过程起着至关重要的作用。SI 可能支持对 Monterey 组的古氧化还原解释，这与以前仅基于铁形态的解释不同。这种替代解释涉及更广泛的水柱 euxinia，与之前工作中建议的季节性 euxinia 不同。这项研究代表了一种实用且开创性的工作流程，基于来自 Rock-Eval 7S 的硫数据，用于古氧化还原和岩相评估，为进一步研究开辟了途径。