Ostracods (Crustacea) and water oxygenation in the earliest Triassic of South China: implications for oceanic events at the end-Permian mass extinction
Ostracods (Crustacea) and water oxygenation in the earliest Triassic of South China: implications for oceanic events at the end-Permian mass extinction
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DOI：
10.1080/08120090903002631
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发表时间：
2009-07
影响因子：
1.2
通讯作者：
M. Forel;S. Crasquin;S. Kershaw;Q. Feng;P. Collin
中科院分区：
文献类型：
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作者：
M. Forel;S. Crasquin;S. Kershaw;Q. Feng;P. Collin
介形类（甲壳纲）是底栖生物，以其作为古环境标志物的一致性而闻名。特别是，它们是水充氧水平的可靠指标：滤食性动物在缺氧条件下更常见，而存款饲养者在充氧良好的环境中更常见。在贵州大滨地区二叠纪/三叠纪（P/Tr）界线过渡期，介形类以存款食性动物为主，从二叠纪末开始，经过灭绝水平，到三叠纪初，介形类处于良好的充氧状态。这些结果与桂西北介形虫区系一致。然而，这两个例子与四川的同时代介形类形成对比，四川的介形类在最早的三叠纪显示出低于正常的氧气水平。贵州大浅滩在华南地块南侧的南盘江大盆地中形成一个孤立的台地;广西西北部在附近，处于边缘环境：根据几个已发表的古地理重建，两者在P/Tr边界时代都面临着泛地中海。四川省P/Tr界线过渡岩位于贵州大滨北约600 km处，位于华南地块的特提斯一侧。贵州大浅滩和四川遗址都有最早的三叠纪微生物岩，但它们在结构和成分上有很大的不同。这两个区域之间的差异可能反映了循环海洋沃茨性质的差异，特提斯（四川）的含氧水平降低，与模拟的缓慢循环有关，而泛海拉萨海洋沃茨（贵州大浅滩和广西西北部）的循环更好。这也可能是一个论点，表明低含氧，甚至缺氧，沃茨不是唯一的原因P/Tr边界危机。
Ostracods (Crustacea) are benthic inhabitants well known for their consistent qualities as paleoenvironment markers. In particular, they are reliable indicators of water oxygenation level: filter feeders are more common in poor oxygen conditions, contrasting with deposit feeders, which are abundant in well-oxygenated settings. In the Permian/Triassic (P/Tr) boundary transition in the Great Bank of Guizhou, ostracod species are dominated by deposit feeders, showing well-oxygenated conditions from the latest Permian, through the extinction level into the earliest Triassic. These results are consistent with ostracod faunas from northwest Guangxi Province. However, these two examples are in contrast with coeval ostracods from Sichuan, which show lower-than-normal oxygen levels in the earliest Triassic. The Great Bank of Guizhou forms an isolated platform in the large Nanpanjiang Basin on the south side of the South China Block; northwest Guangxi is nearby, in a marginal setting: both faced the Panthalassa Ocean through the P/Tr boundary times according to several published paleogeographic reconstructions. In contrast, P/Tr boundary transition rocks in Sichuan Province, located ∼600 km north of the Great Bank of Guizhou, lie on the Tethyan side of the South China Block. Both the Great Bank of Guizhou and the Sichuan sites have earliest Triassic microbialites, but these are profoundly different in structure and composition. The difference between the two areas may reflect contrasts in the nature of circulating ocean waters, with reduced levels of oxygenation in the Tethys (Sichuan), associated with modelled slow circulation, in contrast to better circulated Panthalassa ocean waters (Great Bank of Guizhou and northwest Guangxi). This also may be an argument to show that low oxygenated, or even anoxic, waters were not the only reason for the P/Tr boundary crisis.