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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Sulfur isotope evidence for low and fluctuating sulfate levels in the Late Devonian ocean and the potential link with the mass extinction event
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Sulfur isotope evidence for low and fluctuating sulfate levels in the Late Devonian ocean and the potential link with the mass extinction event

机译：硫同位素证据表明泥盆纪晚期海洋中硫酸盐含量低且在波动，并且可能与大规模灭绝事件有关

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摘要

High amplitude positive carbon isotope excursions in the Late Devonian, the punctata and Kellwasser events, reflect major perturbations in the global carbon cycle that have been attributed to increased continental weathering and subsequent ocean eutrophication. Despite the comparable carbon isotope anomalies, however, a major extinction has been reported only for the Kellwasser Events, while the punctata Event is marked by low extinction intensity. This study presents multiple sulfur isotope records of carbonate-associated sulfate (CAS) and pyrite from Late Devonian sections in the Great Basin, USA, in order to document changes in the coupled (or decoupled) geochemical cycles of carbon and sulfur during the punctata and Upper Kellwasser events. A positive sulfur isotope shift in both CAS and pyrite accompanies the onset of the punctata Event, but to a larger extent in the latter. As a result, the sulfur isotope offset between CAS and pyrite (Delta S-34(CAS-py)) dropped to less than 10 parts per thousand. In the middle of the punctata Event, a sharp negative delta S-34(CAS) excursion and negative Delta S-34(CAS-py) values coincide with the Alamo impact. Unlike the rapid delta S-34(py) and delta S-34(CAS) oscillations associated with the punctata Event, the Upper Kellwasser was a period of relative stability, except for a brief delta S-34(CAS) drop before the event. Paired sulfur isotope data, aided by a simple box model, suggest that the geochemical cycle of sulfur may have been partly responsible for the contrasting biological responses that define these events. High stratigraphic delta S-34(py) and delta S-34(CAS) variability, coupled with strong reservoir effect, demonstrates a relatively small oceanic sulfate pool existed during the punctata Event. Further, the Alamo impact likely triggered the rapid oxidation of microbially-produced sulfide within this event. The expansion of sulfidic bottom water thus may have been impeded during the punctata Event. In contrast, the lack of a positive shift in delta S-34(CAS) and sizable Delta 34S(CAS-py) values (>15 parts per thousand) throughout the Upper Kellwasser Event imply higher relative sulfate levels. A larger seawater sulfate reservoir may have promoted the development of sulfidic bottom waters in the eutrophic epicontinental seas, increasing biological stress and potentially contributing to the mass extinction. (C) 2015 Elsevier B.V. All rights reserved.
机译：泥盆纪晚期，点状和凯尔瓦瑟事件中的高幅度正碳同位素偏移反映了全球碳循环中的主要扰动，这是由于大陆风化和随后的海洋富营养化增加所致。尽管存在可比的碳同位素异常，但据报道仅Kellwasser事件发生了大灭绝，而点状事件的灭绝强度却很低。这项研究提供了美国大盆地泥盆纪晚期剖面的碳酸盐伴生硫酸盐（CAS）和黄铁矿的多个硫同位素记录，目的是记录点和点期间碳和硫的耦合（或解耦）地球化学循环的变化。上凯尔瓦瑟事件。点状事件的发生伴随着CAS和黄铁矿中硫同位素正迁移的发生，但后者发生的程度更大。结果，CAS和黄铁矿之间的硫同位素偏移量（Delta S-34（CAS-py））降到了少于千分之十。在点事件的中间，急剧的负增量S-34（CAS）偏移和负增量S-34（CAS-py）值与Alamo撞击相吻合。与点状事件相关的快速三角洲S-34（py）和三角洲S-34（CAS）振荡不同，上凯尔瓦瑟河是一个相对稳定的时期，除了三角洲S-34（CAS）在事件发生前短暂下降。成对的硫同位素数据，借助简单的盒模型，表明硫的地球化学循环可能部分负责了定义这些事件的生物反应的对比。高地层δS-34（py）和δS-34（CAS）的高变异性，再加上强烈的储层效应，表明点状事件期间存在相对较小的海洋硫酸盐池。此外，在此事件中，阿拉莫撞击可能触发了微生物产生的硫化物的快速氧化。因此在点积事件期间可能已阻止了硫化底水的膨胀。相比之下，整个上凯尔华沙峰事件中，ΔS-34（CAS）和相当大的Delta 34S（CAS-py）值（>千分之十五）缺乏正向位移，表明相对硫酸盐含量较高。更大的海水硫酸盐储集层可能促进了富营养的上陆大陆海中硫化物底水的发育，增加了生物压力，并可能导致生物大灭绝。 （C）2015 Elsevier B.V.保留所有权利。

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