High amplitude redox changes in the late Early Triassic of South China and the Smithian–Spathian extinction
High amplitude redox changes in the late Early Triassic of South China and the Smithian–Spathian extinction
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DOI：
10.1016/j.palaeo.2015.03.038
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发表时间：
2014-10
期刊：
影响因子：
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通讯作者：
Yadong Sun;P. Wignall;M. Joachimski;D. Bond;S. Grasby;Si-quan Sun;Chunbo Yan;Liang Wang;Yanlong C
中科院分区：
文献类型：
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作者：
Yadong Sun;P. Wignall;M. Joachimski;D. Bond;S. Grasby;Si-quan Sun;Chunbo Yan;Liang Wang;Yanlong C
早三叠纪是一个温度异常高、碳循环剧烈紊乱、海洋缺氧时有发生的时期。华南南盘江盆地的沉积物为研究这些极端条件下的沉积反应提供了极好的机会，特别是在smith - spathian （S-S）边界的危机期。我们调查了嘉荣的深水段和明塘的浅水段。它们包含一系列相，包括黑色页岩、泥晶灰岩单元和粗灰质碳酸盐岩事件层，其中包括扁平卵石砾岩和角砾岩碎屑，与碎屑浊积岩序列中的混合事件层相似。氧化还原指标（黄铁矿树状体和微量金属）显示，史密斯世晚期广泛的缺氧持续到Spathian早期的novispathodus pingdingshanensisZone，然后在icriospthodus collinsonzone急剧过渡到高氧的“灰岩相”（红色海相地层），记录了“氧反弹”。底栖动物在当地很常见，但多样性低，以薄壳双壳类和介形虫为主，有小有孔虫和特别罕见的鱼类。生物扰动仅在早-中Spathian （I. collinsoniconodon带）Griotte相强烈。缺氧和极高的温度可能严重限制了当时鱼类和小型海洋无脊椎动物的数量。在我们的研究剖面中，流体和海底扇胶结物的存在表明在史密斯纪末期处于高度饱和状态，而不是酸化状态。
The Early Triassic was a time of remarkably high temperatures, large carbon cycle perturbations and episodes of widespread ocean anoxia. The sediments in the Nanpanjiang Basin of South China provide superb opportunities to examine the sedimentary response to these extreme conditions especially during the crisis interval at the Smithian–Spathian (S-S) boundary. We have investigated a deep water section at Jiarong and a shallower water section at Mingtang. These contain a range of facies including black shales, micritic limestone units and rudaceous carbonate event beds that include flat pebble conglomerates and breccia debrites that bear similarities to the hybrid event beds seen in clastic turbidite successions.Redox proxies (pyrite framboids and trace metals) reveal that widespread anoxia in the late Smithian persisted into theNovispathodus pingdingshanensisZone of the early Spathian before a sharp transition to highly oxygenated “griotte facies” (red marine strata) in theIcriospathodus collinsoniZone that records an “oxic rebound”. Benthic faunas are locally common but of low diversity and dominated by thin-shelled bivalves and ostracodes with small foraminifers and exceptionally rare fish remains. Bioturbation was intense only in the early–middle Spathian (I. collinsoniconodont zone) Griotte facies. Anoxia and extremely high temperatures probably played a role in severely restricting the abundance of fish and the small sizes of marine invertebrates at this time. The presence of ooids and seafloor fan cements in our study sections indicates highly saturated conditions rather than acidification at the end of the Smithian.