Abstract The Silurian was a time of major climatic transition punctuated by multiple biotic crises and global carbon cycle perturbations. The most severe of these biotic events was the late Silurian (Ludfordian) Lau/Kozlowskii extinction event (LKE) and the associated Lau carbon isotope excursion (CIE). Although the extinction event and Lau CIE are globally documented, the only records thus far of local and global marine paleoredox conditions through this interval are from a single region in Scandinavia. Here we examine four sections along a bathymetric transect of mixed carbonate-siliciclastic sediments from western Tennessee, USA. A novel approach using a multi-proxy dataset combining high-resolution geochemical data and microfacies analyses from multiple localities explores the possibilities of local/regional-scale redox heterogeneities during a time of widespread environmental upheaval on a global scale. Paired positive excursions recorded in carbonate carbon isotopes and carbonate-associated sulfate sulfur isotopes support recent work from carbonate and siliciclastic successions from Scandinavia, suggesting a global enhancement of organic carbon and pyrite burial driven by an expansion of euxinic (anoxic and sulfidic water column) conditions in the oceans during the mid-Ludfordian. Furthermore, positive excursions in organic carbon isotopes and pyrite sulfur isotopes reflect the global changes in redox. Stratigraphic trends in I/Ca ratios imply a local expansion of low-oxygen conditions, with low, but non-zero values during the rising limb and peak of the CIE. The fossil assemblages vary across the shelf and through the CIE interval. Stratigraphic changes in fossil assemblages and I/Ca are closely associated with local and global changes in oxygenation and sea level during the mid-Ludfordian. The collective data indicate significant biotic reorganization in response to changes in marine redox conditions and in conjunction with sea-level variation during the LKE interval, but detailed macroscopic biodiversity is currently unconstrained for this region.

中文翻译：

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晚志留纪（Ludfordian）灭绝事件期间劳伦西亚南部多个地点的综合沉积、生物和古氧化还原动力学

摘要 志留纪是一个主要的气候转变时期，被多次生物危机和全球碳循环扰动打断。这些生物事件中最严重的是志留纪晚期 (Ludfordian) Lau/Kozlowskii 灭绝事件 (LKE) 和相关的 Lau 碳同位素偏移 (CIE)。尽管灭绝事件和 Lau CIE 已在全球范围内得到记录，但迄今为止，该间隔期间局部和全球海洋古氧化还原条件的唯一记录来自斯堪的纳维亚半岛的一个地区。在这里，我们研究了美国田纳西州西部混合碳酸盐硅质碎屑沉积物的测深断面的四个剖面。一种使用多代理数据集的新方法，结合高分辨率地球化学数据和来自多个地点的微相分析，探索了在全球范围内广泛环境动荡时期局部/区域尺度氧化还原异质性的可能性。在碳酸盐碳同位素和碳酸盐相关硫酸盐硫同位素中记录的成对正偏移支持斯堪的纳维亚半岛碳酸盐和硅质碎屑岩序列的近期工作，表明有机碳和黄铁矿埋藏的全球增强是由富氧（缺氧和硫化水柱）条件的扩张驱动的在 Ludfordian 中期的海洋中。此外，有机碳同位素和黄铁矿硫同位素的正偏移反映了氧化还原的全球变化。I/Ca 比率的地层趋势意味着低氧条件的局部扩张，在 CIE 的上升沿和峰值期间具有较低但非零的值。化石组合在大陆架和 CIE 区间内各不相同。化石组合和 I/Ca 的地层变化与 Ludfordian 中期的局部和全球氧化和海平面变化密切相关。集体数据表明，为了响应海洋氧化还原条件的变化以及 LKE 间隔期间海平面的变化，发生了显着的生物重组，但目前该地区详细的宏观生物多样性不受限制。化石组合和 I/Ca 的地层变化与 Ludfordian 中期的局部和全球氧化和海平面变化密切相关。集体数据表明，为了响应海洋氧化还原条件的变化以及 LKE 间隔期间海平面的变化，生物发生了显着的重组，但目前该地区详细的宏观生物多样性不受限制。化石组合和 I/Ca 的地层变化与 Ludfordian 中期的局部和全球氧化和海平面变化密切相关。集体数据表明，为了响应海洋氧化还原条件的变化以及 LKE 间隔期间海平面的变化，生物发生了显着的重组，但目前该地区详细的宏观生物多样性不受限制。