GYIG OpenIR  > 矿床地球化学国家重点实验室
Meishucun phosphorite succession (SW China) records redox changes of the early Cambrian ocean
Ze-Rui Ray Liu;Mei-Fu Zhou
2017
Source PublicationGeological Society of America Bulletin
Volume129Issue:11-12Pages:1554-1567
Abstract

Two early Cambrian phosphorite units from the Meishucun section, SW China, were investigated to decipher the mechanism of phosphogenesis and to understand the redox states of the early Cambrian ocean. Rocks from the lower unit contain abundant -cyanobacterial-like microfossils and radial francolite aggregates, and they have oolitic textures, a negative delta C-13(carb) shift, and kerogen-like rare earth element (REE) patterns. These rocks were derived from degradation of organisms and were subsequently reworked by high-energy water. In contrast, rocks from the upper unit are dominated by stumpy francolite and have high Zn (40185 ppm) and Pb (15-845 ppm) contents and seawater-like REE patterns, indicating that P adsorption and regeneration were mediated by Fe-(oxyhydr) oxides. Phosphorites in this unit were episodically exposed above the wave base and are characterized by bedding structures. Rocks from the lower unit have low V (3-18 ppm) and Cr (7-20 ppm) contents and negative delta Mo-97/95 values, clearly suggesting that the ambient water was oxygenated due to proliferation of cyanobacteria. The upper unit must have formed near a Fe-redox boundary in sediments that allowed the transformation between Fe3+ and Fe2+, consistent with high V (18-55 ppm) and Cr (20-62 ppm) contents, and positive delta Mo-97/95 values in the unit. The oceanic reduction may be attributed to the ca. 535 Ma volcanism and hydrothermal venting in the basin. Similar compositions of phosphorites from the lower unit and equivalents elsewhere indicate that the early Cambrian phosphogenesis was controlled mainly by proliferation of primary producers. Given that shallow water above the wave base can be well mixed and in equilibrium with atmospheric oxygen, the subsequent reducing environment in the ocean recorded in the upper unit may have been a global phenomenon.

Indexed BySCI
Language英语
Document Type期刊论文
Identifierhttp://ir.gyig.ac.cn/handle/42920512-1/8017
Collection矿床地球化学国家重点实验室
Affiliation1.Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong, China
2.State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
Recommended Citation
GB/T 7714
Ze-Rui Ray Liu;Mei-Fu Zhou. Meishucun phosphorite succession (SW China) records redox changes of the early Cambrian ocean[J]. Geological Society of America Bulletin,2017,129(11-12):1554-1567.
APA Ze-Rui Ray Liu;Mei-Fu Zhou.(2017).Meishucun phosphorite succession (SW China) records redox changes of the early Cambrian ocean.Geological Society of America Bulletin,129(11-12),1554-1567.
MLA Ze-Rui Ray Liu;Mei-Fu Zhou."Meishucun phosphorite succession (SW China) records redox changes of the early Cambrian ocean".Geological Society of America Bulletin 129.11-12(2017):1554-1567.
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