Variations in Sr and C isotopes and Ce anomalies in successions from China: evidence for the oxygenation of Neoproterozoic seawater?
Variations in Sr and C isotopes and Ce anomalies in successions from China: evidence for the oxygenation of Neoproterozoic seawater?
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DOI：
10.1016/s0301-9268(98)00092-8
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发表时间：
1999-01
影响因子：
3.8
通讯作者：
Yang Jiedong;Sun Weiguo;Wang Zongzhe;Xue Yaosong;Tao Xiancong
中科院分区：
文献类型：
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作者：
Yang Jiedong;Sun Weiguo;Wang Zongzhe;Xue Yaosong;Tao Xiancong
系统采集了华南扬子地区新元古代震旦系海相碳酸盐岩、磷酸盐化石、磷矿和锰矿床样品，获取并研究了C、Sr同位素和Ceanom值数据。这些数据与Nd同位素数据(Yang et al. 1997a, Chem. Geol. 135, 127–133; Yang et al. 1997b, Chinese Sci. Bull. 42, 2072–2075)相结合，详细记录了震旦纪和早寒武世时期中国海水中同位素和Ce异常变化，并显示出显着的变化： δ13C：-4∼+6‰； ϵNd(T)：-4.5～-7.6；87Sr/86Sr：0.7077～0.7087； Ceanom：分别为+0.20∼−0.65。这些变化超过或等于整个显生宙海水的最大变化。震旦纪期间 δ13C 的普遍较高值可能反映了科格埋藏率的增加。反过来，这可能归因于海洋表面的高生产力和沉积速率的上升，这是由于构造作用增强和全球气温上升造成的。 Ceanom值下降的趋势也可能反映了海洋表面有机生产力的增加以及大气和上层海洋中O2浓度的上升。 Nd和Sr同位素研究揭示的最重要的一点是，最强和最广泛的构造运动发生在元古代末期。构造作用引起了古地理的重新排序、全球沉积速率的快速上升和海洋化学的巨大变化，最终导致震旦纪海水中C、Sr、Nd同位素的变化和Ce异常。
Samples of marine carbonates, phosphatic fossils, phosphorites and manganese deposits were systematically collected from the Neoproterozoic Sinian System in the Yangtze Region, South China, and data of C and Sr isotopes and Ceanomvalues were obtained and investigated. These data, combined with Nd isotopic data (Yang et al. 1997a, Chem. Geol. 135, 127–133; Yang et al. 1997b, Chinese Sci. Bull. 42, 2072–2075), provide a detailed record of isotopes and Ce anomaly variations in Chinese seawater during the Sinian and early Cambrian periods, and show significant changes: δ13C: −4∼+6‰; ϵNd(T): −4.5∼−7.6;87Sr/86Sr: 0.7077∼0.7087; Ceanom: +0.20∼−0.65 , respectively. The changes exceed or match the largest in seawater throughout the Phanerozoic. The generally high values of δ13C during the Sinian may reflect an increase in the Corgburial rate. It, in turn, may be attributed to high productivity at the surface of the ocean and a rise in the sedimentary rate, which resulted from enhanced tectonism and a global temperature rise. A trend of declining Ceanomvalues may also reflect an increase in organic productivity at the ocean surface and a rise in O2concentration in the atmosphere and the upper oceans. The most important point revealed by the Nd and Sr isotopic studies is that the strongest and most widespread tectonism took place towards the end of the Proterozoic. The tectonism caused a paleogeographic reordering, rapid rise in the global sedimentary rate and great changes in ocean chemistry, and ultimately led to the variations in C, Sr and Nd isotopes and Ce anomaly in the Sinian seawater.