Controls on organic carbon and molybdenum accumulation in Cretaceous marine sediments from the Cenomanian-Turonian interval including Oceanic Anoxic Event 2
Controls on organic carbon and molybdenum accumulation in Cretaceous marine sediments from the Cenomanian-Turonian interval including Oceanic Anoxic Event 2
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包括海洋缺氧事件2在内的塞诺曼期-土伦期白垩纪海洋沉积物中有机碳和钼积累的控制
DOI：
10.1016/j.chemgeo.2011.10.004
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发表时间：
2012
期刊：
影响因子：
3.9
通讯作者：
Dale A
中科院分区：
文献类型：
--
作者：
Dale A
本研究探讨了西部内陆海道横跨塞诺曼—turonian界线段（94.34—93.04 Ma）沉积物中有机碳和钼（Mo）聚集的控制因素，包括海洋性缺氧事件2 （OAE2）。根据现场数据重建沉积物-水界面的碳通量（反映初级生产力的变化）和底水氧浓度（反映保存效应），并用于约束模拟未固结沉积物沉积时地球化学的底栖生物模型。结果表明，在OAE2 （O2~105μM）过程中，活性铁的可用性增加通过(i)抑制硫酸盐还原，（ii）缓冲任何可用的游离硫化物，从而阻止Mo以硫钼酸盐（MoS42−）的形式被封存。在oae2后期（O2~50μM），铁通量的大幅度降低有利于Mo的积累。重要的是，这与含氧的底部水和表面沉积物中高速率的好氧碳降解同时发生，这意味着古海相中较高的Mo埋藏通量并不一定反映水柱内的含氧甚至缺氧条件。研究结果表明，西部内陆海道有机碳的生成和保存都导致了有机碳的富集。更一般地说，结果表明，仔细考虑成岩早期阶段铁、碳和氧循环之间的耦合对于解释现代和古代环境下的地球化学指标至关重要。
This study investigates the controls on organic carbon and molybdenum (Mo) accumulation in sediments deposited within the Western Interior Seaway across the Cenomanian–Turonian boundary interval (94.34–93.04 Ma) including Oceanic Anoxic Event 2 (OAE2). Carbon fluxes to the sediment–water interface (reflecting changes in primary productivity) and bottom-water oxygen concentrations (reflecting preservation effects) are reconstructed from field data and used to constrain a benthic model that simulates the geochemistry of unconsolidated sediments as they were deposited. The results show that increased availability of reactive iron prevents Mo sequestration as thiomolybdate (MoS42−) during OAE2 (O2~105μM) by (i) inhibiting sulfate reduction, and (ii) buffering any free sulfide that becomes available. In the post-OAE2 period (O2~50μM), Mo accumulation is favored by a large reduction in iron flux. Importantly, this occurs in parallel with oxygenated bottom waters and high rates of aerobic carbon degradation in the surface sediments, implying that elevated Mo burial fluxes in ancient marine facies do not necessarily reflect euxinic or even anoxic conditions within the water column. Our findings suggest that both an increase in production and preservation lead to enrichment in organic carbon in the Western Interior Seaway. More generally, the results demonstrate that a careful consideration of the coupling between iron, carbon and oxygen cycles during the early stages of diagenesis is critical for interpreting geochemical proxies in modern and ancient settings.