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DOI	10.1111/gbi.12342
	Cr isotopic insights into ca. 1.9 Ga oxidative weathering of the continents using the Beaverlodge Lake paleosol, Northwest Territories, Canada
	Toma J.; Holmden C.; Shakotko P.; Pan Y.; Ootes L.
发表日期	2019
ISSN	14724677
起始页码	467
结束页码	489
卷号	17 期号:5
英文摘要	The ca. 1.9 Ga Beaverlodge Lake paleosol was studied using redox-sensitive Cr isotopes in order to determine the isotopic response to paleoweathering of a rhyodacite parent rock 500 million years after the Great Oxidation Event. Redox reactions occurring in modern weathering environments produce Cr(VI) that is enriched in heavy Cr isotopes compared to the igneous inventory. Cr(VI) species are soluble and easily leached from soils into streams and rivers, thus, leaving particle-reactive and isotopically light Cr(III) species to build up in soils. The Beaverlodge Lake paleosol and two other published weathering profiles of similar age, the Flin Flon and Schreiber Beach paleosols, are not as isotopically light as modern soils, indicating that rivers were not as isotopically heavy at that time. Considering that the global average δ53Cr value for the oxidative weathering flux of Cr to the oceans today is just 0.27 ± 0.30‰ (1σ) based on a steady-state analysis of the modern ocean Cr cycle, the oxidative weathering flux of Cr to the oceans at ca. 1.9 Ga would have likely been shifted to lower δ53Cr values, and possibly lower than the igneous inventory (–0.12 ± 0.10‰, 2σ). Mn oxides are the main oxidant of Cr(III) in modern soils, but there is no evidence that they formed in the studied paleosols. Cr(VI) may have formed by direct oxidation of Cr(III) using molecular oxygen or H2O2, but neither pathway is as efficient as Mn oxides for producing Cr(VI). The picture that emerges from this and other studies of Cr isotope variation in ca. 1.9 Ga paleosols is of atmospheric oxygen concentrations that are high enough to oxidize iron, but too low to oxidize Mn, resulting in low Cr(VI) inventories in Earth surface environments. © 2019 John Wiley & Sons Ltd
关键词	igneous rock isotopic composition lake ecosystem lithostratigraphy molecular ecology oxidant oxidation paleosol Proterozoic redox conditions weathering Alberta Beaverlodge Canada Flin Flon Manitoba Northwest Territories Ontario [Canada]Schreiber Beach chromium chemistry geology lake Northwest Territories oxidation reduction reaction paleontology sediment soil Chromium Isotopes Geologic Sediments Geology Lakes Northwest Territories Oxidation-Reduction Paleontology Soil
语种	英语
来源机构	Geobiology
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/133249
推荐引用方式 GB/T 7714	Toma J.,Holmden C.,Shakotko P.,et al. Cr isotopic insights into ca. 1.9 Ga oxidative weathering of the continents using the Beaverlodge Lake paleosol, Northwest Territories, Canada[J]. Geobiology,2019,17(5).
APA	Toma J.,Holmden C.,Shakotko P.,Pan Y.,&Ootes L..(2019).Cr isotopic insights into ca. 1.9 Ga oxidative weathering of the continents using the Beaverlodge Lake paleosol, Northwest Territories, Canada.,17(5).
MLA	Toma J.,et al."Cr isotopic insights into ca. 1.9 Ga oxidative weathering of the continents using the Beaverlodge Lake paleosol, Northwest Territories, Canada".17.5(2019).