Nitrogen and organic carbon isotope stratigraphy of the Yangtze Platform during the Ediacaran-Cambrian transition in South China
Nitrogen and organic carbon isotope stratigraphy of the Yangtze Platform during the Ediacaran-Cambrian transition in South China
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DOI：
10.1016/j.palaeo.2013.12.016
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发表时间：
2014-03-15
影响因子：
3
通讯作者：
Och, Lawrence M.
中科院分区：
文献类型：
--
作者：
Cremonese, Lorenzo;Shields-Zhou, Graham A.;Och, Lawrence M.
为了研究埃迪卡拉-寒武系过渡期的地球化学循环、地层对比和同位素系统学，对华南盆地沿着西-东剖面的6个剖面的碳、氮同位素结果进行了研究。Δ N-15体积值在-3 ‰和+7 ‰之间，而Δ C-13（有机物）值在-21 ‰和-39 ‰之间。在整个盆地，这两个代理人已确定类似的同位素趋势，虽然间断，沉积环境和同沉积细菌发酵的差异可能会造成一些不一致。在扬子地台Pc-C界线以上，无论是浅盆区还是深盆区，都存在氮同位素负值的趋势。这种负的Δ N-15偏移可能是对透光层缺氧和重氮蓝藻和绿色/紫色硫细菌（GSB和PSB）的强烈固氮/同化的响应。小滩剖面和长江三峡地区的一个复合剖面在氮同位素趋势上表现出有意义的相似性，这被解释为水柱中的化学跃层波动，证明了浅台地上覆水的快速混合。使用碳同位素地层学，我们相关的边界地层在整个平台，以测试更广泛的意义，氮同位素的变化。埃迪卡拉-寒武纪过渡期的生物扰动和食物链复杂性的增加可能导致早寒武纪硝酸盐同位素组成和相关池尺寸的更频繁的变化，反映了一个新的生物控制时代的开始。(C)2013爱思唯尔有限公司版权所有。
N and C-org isotope results are presented from six sections along a West-East transect in the South China Basin (SCB) covering both shallow and deeper domains, in order to investigate biogeochemical cycling, stratigraphic correlation and isotope systematics over the crucial Ediacaran-Cambrian transition. delta N-15 bulk values range between -3 parts per thousand and +7 parts per thousand, while delta C-13(org) values range between -21 parts per thousand and -39 parts per thousand. Similar isotopic trends have been identified for both these proxies across the basin, although hiatuses, differences in depositional setting and syn-depositional bacterial fermentation may have caused some inconsistencies. A trend towards negative N isotope values can be recognized above the Pc-C boundary in both shallow and deeper basin realms across the Yangtze platform. This negative delta N-15 excursion is probably a response to photic zone anoxia and intense nitrogen fixation/assimilation by diazotrophic cyanobacteria and green/purple sulfur bacteria (GSB and PSB). The Xiaotan section and a composite section from the Yangtze Gorges area show meaningful similarities in their nitrogen isotope trends, interpreted as chemocline fluctuations in the water column that testify to rapid mixing of water overlying the shallow platform. Using carbon isotope stratigraphy, we correlate boundary strata across the platform to test the wider significance of nitrogen isotopic variations. Increased bioturbation and food-chain complexity across the Ediacaran-Cambrian transition probably led to more frequent variations in nitrate isotope composition and related pool dimension during the early Cambrian, reflecting the beginning of a new more biologically controlled era. (C) 2013 Elsevier B.V. All rights reserved.