Isotopic evidence for water-column denitrification and sulfate reduction at the end-Guadalupian (Middle Permian)
Isotopic evidence for water-column denitrification and sulfate reduction at the end-Guadalupian (Middle Permian)
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DOI：
10.1016/j.gloplacha.2014.10.014
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发表时间：
2014-12
影响因子：
3.9
通讯作者：
M. Saitoh;Y. Ueno;Y. Isozaki;M. Nishizawa;K. Shozugawa;T. Kawamura;Jian-xin Yao;Zhansheng Ji;K. Takai;N. Yoshida;M. Matsuo
中科院分区：
文献类型：
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作者：
M. Saitoh;Y. Ueno;Y. Isozaki;M. Nishizawa;K. Shozugawa;T. Kawamura;Jian-xin Yao;Zhansheng Ji;K. Takai;N. Yoshida;M. Matsuo
通过对川北朝田地区瓜达鲁坪-洛平系（中上二叠统）陆架碳酸盐岩总氮和黄铁矿硫同位素组成的分析，阐明了瓜达鲁坪末期海洋中较深双光带（一般深度大于150 m）的环境变化，重点探讨了其与深海缺氧和浅海灭绝的可能关系。在天宫,瓜德鲁普统Maokou形成和早期Lopingian Wujiaping浅水相的形成主要是由生物碎屑灰岩,虽然上面的一部分Maokou形成厚(ca。11米)是由层状的黑色泥岩和燧石disphotic斜率/沉积盆地在缺氧的条件下。深水相茅口组顶部总氮δ15N值较高，可达+ 14‰，表明水体反硝化作用。在同一双光层段，黄铁矿δ34S值持续较低（约为−37‰），表明富硫酸盐水柱中存在硫酸盐还原作用。朝田地区氮硫同位素新记录表明，华南西北部晚瓜达鲁普期缺氧双光带厌氧呼吸增强。活性水柱硫酸盐还原可能导致双光斜坡/盆地上出现含硫深水块体，这是由岩石中黄铁矿铁与高活性铁的高比例（57fe Mössbauer光谱）所支持的。guadalupian末期双光带的厌氧呼吸可能因表层海洋初级生产力的增加而导致氧最小带（OMZ）的扩大而增强；OMZ的扩张可能与深海中长期氧气消耗的开始相对应。朝田地区清晰的地层关系表明，硫质深水在灭绝之前就已经出现，这意味着硫质深水从以前被忽视的两光带上涌至大陆边缘的浅陆架，可能对浅海生物群起到了压力作用。
The total nitrogen and pyrite sulfur isotopic compositions of the Guadalupian–Lopingian (Middle-Upper Permian) shelf carbonates are analyzed at Chaotian in northern Sichuan, South China, to clarify the environmental changes in the relatively deep disphotic zone (generally deeper than 150 m) in the ocean at the end-Guadalupian, focusing on the possible relationships with the deep-sea oxygen depletion and the shallow-sea extinction. At Chaotian, the Guadalupian Maokou Formation and the Early Lopingian Wujiaping Formation are primarily composed of bioclastic limestone of shallow-water facies, although the topmost part of the Maokou Formation (ca. 11 m thick) is composed of bedded black mudstone and chert that was deposited on the disphotic slope/basin under anoxic conditions. Substantially high δ15N values of total nitrogen (up to + 14‰) in the topmost Maokou Formation of the deep-water facies indicate water-mass denitrification. In the same disphotic interval, the consistently low δ34S values of pyrite (ca. − 37‰) suggest sulfate reduction in the sulfate-rich water column. The new nitrogen and sulfur isotopic records at Chaotian indicate the enhanced anaerobic respiration in the oxygen-depleted disphotic zone in the Late Guadalupian in northwestern South China. The active water-column sulfate reduction likely resulted in the emergence of a sulfidic deep-water mass on the disphotic slope/basin, which is supported by the high proportions of pyrite Fe to highly reactive Fe in the rocks shown using57Fe Mössbauer spectroscopy. The anaerobic respiration in the disphotic zone at the end-Guadalupian may have been enhanced by an expansion of the oxygen minimum zone (OMZ) caused by the increased primary productivity in the surface oceans; the OMZ expansion may have corresponded to the onset of prolonged oxygen depletion in the deep sea. The clear stratigraphic relationship at Chaotian shows the emergence of the sulfidic deep-waters preceding the extinction, implying that the upwelling of the sulfidic deep-water from the previously overlooked disphotic zone to the shallow shelves along the continental margin may have acted as a stress to the shallow-marine biota.