A multi-proxy approach to constrain reducing conditions in the Baltic Basin during the late Silurian Lau carbon isotope excursion
A multi-proxy approach to constrain reducing conditions in the Baltic Basin during the late Silurian Lau carbon isotope excursion
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DOI：
10.1016/j.palaeo.2021.110624
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发表时间：
2021-08
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影响因子：
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通讯作者：
Chelsie N. Bowman;T. Them;Marisa D. Knight;D. Kaljo;M. Eriksson;O. Hints;T. Martma;J. Owens;Seth A. Young
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文献类型：
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作者：
Chelsie N. Bowman;T. Them;Marisa D. Knight;D. Kaljo;M. Eriksson;O. Hints;T. Martma;J. Owens;Seth A. Young
志留纪是一个动态的时期，其特征是显著的气候和海平面变化，生物危机和碳循环波动。志留纪全球碳循环的最大扰动是Ludfordian中期的碳同位素偏移，称为Lau CIE，这与Lau/Kozlowskii灭绝（LKE）相一致。许多已发表的关于志留纪晚期的研究都描述了生物记录和全球海洋氧化还原条件的变化。有限的工作已经完成，但是，阐明当地古氧化还原条件的变化。在这里，我们使用一套古氧化还原代理研究从哥特兰岛，瑞典的浅陆棚碳酸盐岩序列，从拉脱维亚的深陆棚碎屑岩序列。来自碳酸盐序列的低碘钙比表明存在缺氧水柱，或与附近的还原水团进行了重大交换。铁形态的数据和适度的微量金属富集表明，沉积物的较深的货架上沉积在一个氧气最小的区域与一个refining水柱之前和期间的LKE与硫化物的条件限制的沉积物孔隙水。灭绝后，微量金属浓度（V，Hg，U，Mo）的相对耗尽表明，水柱条件是局部减少。在微量金属浓度的耗尽是同时代与以前报道的全球缺氧和euxinia LKE后的增加，因此，可能会导致全球性的微量金属的下降叠加在当地记录的古氧化还原变化。
The Silurian was a dynamic time characterized by significant climatic and sea level changes, biotic crises, and carbon cycle volatility. The largest magnitude perturbation to the Silurian global carbon cycle was the mid-Ludfordian carbon isotope excursion, termed the Lau CIE, which was coincident with the Lau/Kozlowskii extinction (LKE). Much of the published research on the late Silurian has described changes in the biotic record and global marine redox conditions. Limited work has been done, however, to elucidate the variability in local paleo-redox conditions. Here, we use a suite of paleo-redox proxies to examine a shallow shelf carbonate succession from Gotland, Sweden, and a deep shelf clastic sequence from Latvia. Low iodine-to‑calcium ratios from the carbonate succession suggest an anoxic water column, or significant exchange with nearby reducing water masses. Iron speciation data and moderate trace metal enrichments suggest that the sediments of the deeper shelf were deposited in an oxygen minimum zone with a denitrifying water column before and during the LKE with sulfidic conditions limited to the sediment porewaters. After the extinction, a relative depletion in trace metal concentrations (V, Hg, U, Mo) suggest that water column conditions were locally less reducing. The depletion in trace metal concentrations is coeval with previously reported global increases in anoxia and euxinia after the LKE and, thus, potentially could have resulted from a global drawdown in trace metals overprinted upon the local record of paleo-redox change.