Geochemical evidence for expansion of marine euxinia during an early Silurian (Llandovery–Wenlock boundary) mass extinction
Geochemical evidence for expansion of marine euxinia during an early Silurian (Llandovery–Wenlock boundary) mass extinction
复制标题
DOI：
10.1016/j.epsl.2019.02.023
复制
发表时间：
2019-05
影响因子：
5.3
通讯作者：
Seth A. Young;Andrew Kleinberg;J. Owens
中科院分区：
文献类型：
--
作者：
Seth A. Young;Andrew Kleinberg;J. Owens
反复的生物危机已成为志留纪的标志，三个最重要的海洋周转事件与剧烈的全球环境扰动有关。将这些海洋灭绝事件与正碳同位素（δ 13 C）漂移、古海洋学变化和气候联系起来的因果机制仍然缺乏约束。在这里，我们研究了正δ 13 C漂移在Llandovery/Wenlock边界，和相关的Ireviken灭绝事件。这种正的δ 13 C偏移被解释为反映了全球海洋气候状态的重大变化和有机碳埋藏的增强。利用碳、硫同位素（δ 34 S）和碘（I/Ca+ Mg）代用指标分析了两个古海洋盆地的新地球化学数据，以确定局部和全球的氧化还原条件。两个剖面的高分辨率δ 13 C和δ 34 S数据显示正偏移，表明这些元素循环中的每一个都受到全球扰动，两个系统之间的时间偏移最小。δ 13 C和δ 34 S数据的数值箱模型表明，这些同位素变化可以产生的有机碳和黄铁矿的埋藏，这是最有可能是由于在富氧（缺氧和硫化物）条件下，加强埋藏的显着增加。独立地，I/（Ca+ Mg）值指向局部缺氧的底部沃茨在远端和更深的盆地设置在内华达州之前，期间和之后的Ireviken积极的δ 13 C偏移。I/（Ca+ Mg）值在近端大陆架设置在田纳西州显示相对含氧沃茨在峰值δ 13 C值的开始，之后，底层水氧浓度下降，在整个其余的偏移。这一多代理古氧化还原数据集提供了第一个直接证据，证明志留纪生物事件和正δ 13 C漂移与海洋条件的局部和全球扩张相一致。整合这些地球化学数据的本地和全球规模的变化，海洋氧化还原条件与古生物学数据和证据的海平面上升指向浅滩的缺氧和/或缺氧沃茨到货架上的驱动程序的Ireviken灭绝事件。
Repeated biotic crises have become the hallmark for the Silurian with the three most significant marine turnover events being related to dramatic global environmental perturbations. Causal mechanisms linking these marine extinction events with positive carbon isotope (δ 13 C) excursions, paleoceanographic change, and climate remain poorly constrained. Here, we examine the positive δ 13 C excursion across the Llandovery/Wenlock boundary, and the associated Ireviken extinction event. This positive δ 13 C excursion has been interpreted to reflect a major change in global oceanographic-climate state and enhanced organic carbon burial. New geochemical data from two paleocean basins have been analyzed to determine local and global redox conditions using carbon-and sulfur-isotopes (δ 34 S), and iodine (I/Ca+ Mg) proxies. The high-resolution δ 13 C and δ 34 S data from both sections show positive excursions indicative of global perturbations to each of these elemental cycles, with minimal temporal offsets between the two systems. Numerical box modeling of δ 13 C and δ 34 S data indicates that these isotopic shifts can be generated by significant increases in the burial of organic carbon and pyrite, which are most likely due to enhanced burial under euxinic (anoxic and sulfidic) conditions. Independently, I/(Ca+ Mg) values point to locally anoxic bottom waters in the distal and deeper basinal setting in Nevada before, during, and after the Ireviken positive δ 13 C excursion. I/(Ca+ Mg) values in the proximal shelf setting in Tennessee show relatively oxic waters during the onset of peak δ 13 C values, after which bottom-water oxygen concentrations dropped throughout the remainder of the excursion. This multiproxy paleoredox dataset provides the first direct evidence for local and global expansion of reducing marine conditions coincident with the Silurian biotic event and positive δ 13 C excursion. Integration of these geochemical data for local-and global-scale changes in marine redox conditions with the paleontological data and evidence for eustatic sea-level rise points toward a shoaling of anoxic and/or euxinic waters onto the shelf as a driver for the Ireviken extinction event.