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Yang, J., Sun, W., Wang, Z., Xue, Y. and Tao, X. (1999). Variations in Sr and C isotopes and Ce anomalies in successions from China; evidence for the oxygenation of Neoproterozoic seawater?. Precambrian Research 93(2-3): 215-233. |
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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 Ce (sub anom) values 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: delta (super 13) C:-4 approximately +6 per mil; epsilon (sub Nd) (T):-4.5 approximately -7.6; (super 87) Sr/ (super 86) Sr:0.7077 approximately 0.7087; Ce (sub anom) :+0.20 approximately -0.65, respectively. The changes exceed or match the largest in seawater throughout the Phanerozoic. The generally high values of delta (super 13) C during the Sinian may reflect an increase in the C (sub org) burial 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 Ce (sub anom) values may also reflect an increase in organic productivity at the ocean surface and a rise in O (sub 2) concentration 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. |
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Keywords
aerobic environment; alkaline earth metals; Asia; C-13/C-12;, Cambrian; carbon; cerium; China; Far East; geochemical anomalies;, isotope ratios; isotopes; Lower Cambrian; metals; Nd-144/Nd-143;, neodymium; Neoproterozoic; organic carbon; oxygen;, paleo-oceanography; paleogeography; paleotemperature; Paleozoic;, Precambrian; productivity; Proterozoic; rare earths; sea water;, sedimentation; sedimentation rates; Sinian; Sr-87/Sr-86; stable, isotopes; strontium; upper Precambrian; variations; whole rock;, Yangtze River, 12 Stratigraphy; 02D Isotope geochemistry |
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Publisher
Elsevier Science
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The Netherlands
(+31) 20 485 3757
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nlinfo-f@elsevier.com |
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