Multi-elemental composition of authigenic carbonates in benthic foraminifera from the eastern Bering Sea continental margin (International Ocean Discovery Program Site U1343)
Multi-elemental composition of authigenic carbonates in benthic foraminifera from the eastern Bering Sea continental margin (International Ocean Discovery Program Site U1343)
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DOI：
10.1016/j.gca.2019.09.025
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发表时间：
2020-01
影响因子：
5
通讯作者：
H. Detlef;S. Sosdian;S. Kender;C. Lear;I. Hall
中科院分区：
文献类型：
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作者：
H. Detlef;S. Sosdian;S. Kender;C. Lear;I. Hall
白令海沉积物代表了特殊的档案，提供了以高分辨率研究过去气候和地球化学的潜力。然而，丰富的微生物来源的碳氢化合物，特别是沿着东白令海大陆边缘，可以阻碍基于钙质有孔虫的古海洋代用品的适用性，由于自生碳酸盐的形成。尽管如此，自生碳酸盐岩也可能具有重建沉积氧化还原环境变化的独特机会。在这里，我们使用了一套来自白令海东部国际海洋发现计划（IODP）U1343站点的浅底动物群底栖有孔虫物种Elphidium batialisSaidova（1961）的单一标本的视觉和地球化学证据，探讨自生碳酸盐对有孔虫微量金属组成的影响。我们的研究结果表明，有孔虫方解石测试作为一个成核模板二次碳酸盐沉淀，改变其地球化学的有机硫酸盐还原和甲烷厌氧氧化导致形成的低镁和高镁方解石，分别。自生碳酸盐可作为有孔虫测试的外部和/或内部的结壳，以测试壁的重结晶形式，或作为有孔虫测试壁内沿沿着天然层片的条带。除了Mg之外，自生碳酸盐还富含U/Ca、Mn/Ca、Fe/Ca和Sr/Ca，这取决于它们形成的氧化还原环境。我们的研究结果表明，特定地点的U/Ca阈值是一个很有前途的工具，以区分成岩蚀变和原始有孔虫样品，利用原生有孔虫地球化学的古海洋重建的重要。与以往的研究一致，在IODP站点U1343有孔虫的U/Mn比增加，根据其程度的成岩蚀变，这表明自生U/Mn的潜在响应，反过来又与沉积氧化还原环境的微生物活动。
Bering Sea sediments represent exceptional archives, offering the potential to study past climates and biogeochemistry at a high resolution. However, abundant hydrocarbons of microbial origin, especially along the eastern Bering Sea continental margin, can hinder the applicability of palaeoceanographic proxies based on calcareous foraminifera, due to the formation of authigenic carbonates. Nonetheless, authigenic carbonates may also bear unique opportunities to reconstruct changes in the sedimentary redox environment.Here we use a suite of visual and geochemical evidence from single-specimens of the shallow infaunal benthic foraminiferal speciesElphidium batialisSaidova (1961), recovered from International Ocean Discovery Program (IODP) Site U1343 in the eastern Bering Sea, to investigate the influence of authigenic carbonates on the foraminiferal trace metal composition. Our results demonstrate that foraminiferal calcite tests act as a nucleation template for secondary carbonate precipitation, altering their geochemistry where organoclastic sulphate reduction and anaerobic oxidation of methane cause the formation of low- and high-Mg calcite, respectively. The authigenic carbonates can occur as encrusting on the outside and/or inside of foraminiferal tests, in the form of recrystallization of the test wall, or as banding along natural laminations within the foraminiferal test walls. In addition to Mg, authigenic carbonates are enriched in U/Ca, Mn/Ca, Fe/Ca, and Sr/Ca, depending on the redox environment that they were formed in. Our results demonstrate that site-specific U/Ca thresholds are a promising tool to distinguish between diagenetically altered and pristine foraminiferal samples, important for palaeoceanographic reconstructions utilising the primary foraminiferal geochemistry. Consistent with previous studies, U/Mn ratios of foraminifera at IODP Site U1343 increase according to their degree of diagenetic alteration, suggesting a potential response of authigenic U/Mn to the microbial activity in turn linked to the sedimentary redox environment.