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Redox-controlled preservation of organic matter during 'OAE 3' within the Western Interior Seaway

机译：西部内陆海道“ OAE 3”中氧化还原控制的有机物保存

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During the Cretaceous, widespread black shale deposition occurred during a series of Oceanic Anoxic Events (OAEs). Multiple processes are known to control the deposition of marine black shales, including changes in primary productivity, organic matter preservation, and dilution. OAEs offer an opportunity to evaluate the relative roles of these forcing factors. The youngest of these eventsthe Coniacian to Santonian OAE 3resulted in a prolonged organic carbon burial event in shallow and restricted marine environments including the Western Interior Seaway. New high-resolution isotope, organic, and trace metal records from the latest Turonian to early Santonian Niobrara Formation are used to characterize the amount and composition of organic matter preserved, as well as the geochemical conditions under which it accumulated. Redox sensitive metals (Mo, Mn, and Re) indicate a gradual drawdown of oxygen leading into the abrupt onset of organic carbon-rich (up to 8%) deposition. High Hydrogen Indices (HI) and organic carbon to total nitrogen ratios (C:N) demonstrate that the elemental composition of preserved marine organic matter is distinct under different redox conditions. Local changes in C-13 indicate that redox-controlled early diagenesis can also significantly alter C-13(org) records. These results demonstrate that the development of anoxia is of primary importance in triggering the prolonged carbon burial in the Niobrara Formation. Sea level reconstructions, O-18 results, and Mo/total organic carbon ratios suggest that stratification and enhanced bottom water restriction caused the drawdown of bottom water oxygen. Increased nutrients from benthic regeneration and/or continental runoff may have sustained primary productivity.
机译：在白垩纪期间，一系列的海洋缺氧事件（OAE）发生了广泛的黑色页岩沉积。已知有多种过程可控制海洋黑页岩的沉积，包括初级生产力的变化，有机物的保存和稀释。 OAE提供了一个机会来评估这些强迫因素的相对作用。这些事件中最年轻的一次是科尼亚奇亚至桑托尼亚的OAE 3，在包括西部内陆海道在内的浅海和受限海洋环境中导致了长时间的有机碳埋葬事件。从最近的土伦时代到早期的Santonian Niobrara组，新的高分辨率同位素，有机物和痕量金属记录被用来表征所保存的有机物的数量和组成，以及其积累的地球化学条件。氧化还原敏感的金属（Mo，Mn和Re）表明氧逐渐下降，导致富含有机碳（最多8％）的沉积突然发生。高氢指数（HI）和有机碳与总氮之比（C：N）表明，在不同的氧化还原条件下，保存的海洋有机物的元素组成是不同的。 C-13的局部变化表明，氧化还原控制的早期成岩作用也可以显着改变C-13（org）记录。这些结果表明，缺氧的发展对于触发Niobrara组中延长的碳埋藏具有重要意义。海平面重建，O-18结果以及Mo /总有机碳比表明，分层和底部水限制增加导致底部水氧的下降。底栖生物再生和/或大陆径流增加的养分含量可能具有持续的初级生产力。

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