Evolution of (Bio‐)Geochemical Processes and Diagenetic Alteration of Sediments Along the Tectonic Migration of Ocean Floor in the Shikoku Basin off Japan
Evolution of (Bio‐)Geochemical Processes and Diagenetic Alteration of Sediments Along the Tectonic Migration of Ocean Floor in the Shikoku Basin off Japan
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DOI：
10.1029/2020gc009585
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发表时间：
2021-06
期刊：
影响因子：
3.7
通讯作者：
M. Köster;M. Kars;F. Schubotz;M. Tsang;M. Maisch;A. Kappler;Y. Morono;F. Inagaki;V. Heuer;S. Kasten;S. Henkel
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作者：
M. Köster;M. Kars;F. Schubotz;M. Tsang;M. Maisch;A. Kappler;Y. Morono;F. Inagaki;V. Heuer;S. Kasten;S. Henkel
海底沉积物中的生物地球化学过程与全球元素循环密切相关。为了更好地了解地质时间尺度上地球化学条件的变化，我们调查了国际海洋发现计划第370次考察期间在日本近海南海海槽（Site C0023）钻探的1，180 m深的孔中的沉积物岩心。在其构造迁移从四国盆地到南海海槽在过去的15 Ma，站点C0023经历了沉积，热，地球化学条件的显着变化。通过结合孔隙水，固相和岩石磁性数据，我们证明了从有机碳饥饿的条件下，主要是有氧呼吸到升高的碳埋藏环境，增加沉积发生在2.5Ma。由于营养供应和生产力的增加，有机碳埋藏率更高，可能刺激了有机碳降解过程中厌氧电子接受过程的发生。自20.5 Ma以来，与沟槽式沉积相关的沉积柱温度显著升高了250 °C，这可能会增加有机质的生物利用度，并增强生物甲烷生成。由此产生的反应前沿的变化导致了埋藏后数百万年有机碳匮乏沉积物中铁（氧氢）氧化物成岩转化为黄铁矿。我们还表明，可以作为微生物铁（III）还原的电子受体的大量可还原铁（III）被保留下来，并且仍然可以作为页硅酸盐结合铁。这是第一项研究，显示了（生物）地球化学过程的长期变化的演变沿着洋底的构造迁移，从而改变了沉积后很长一段时间的主要沉积物组成。
Biogeochemical processes in subseafloor sediments are closely coupled to global element cycles. To improve the understanding of changes in biogeochemical conditions on geological timescales, we investigate sediment cores from a 1,180 m deep hole in the Nankai Trough offshore Japan (Site C0023) drilled during International Ocean Discovery Program Expedition 370. During its tectonic migration from the Shikoku Basin to the Nankai Trough over the past 15 Ma, Site C0023 has experienced significant changes in depositional, thermal, and geochemical conditions. By combining pore‐water, solid‐phase, and rock magnetic data, we demonstrate that a transition from organic carbon‐starved conditions with predominantly aerobic respiration to an elevated carbon burial environment with increased sedimentation occurred at ∼2.5 Ma. Higher rates of organic carbon burial in consequence of increased nutrient supply and productivity likely stimulated the onset of anaerobic electron‐accepting processes during organic carbon degradation. A significant temperature increase by ∼50°C across the sediment column associated with trench‐style sedimentation since ∼0.5 Ma could increase the bioavailability of organic matter and enhance biogenic methanogenesis. The resulting shifts in reaction fronts led to diagenetic transformation of iron (oxyhydr)oxides into pyrite in the organic carbon‐starved sediments several millions of years after burial. We also show that high amounts of reducible iron(III) which can serve as electron acceptor for microbial iron(III) reduction are preserved and still available as phyllosilicate‐bound iron. This is the first study that shows the evolution of long‐term variations of (bio‐)geochemical processes along tectonic migration of ocean floor, thereby altering the primary sediment composition long after deposition.