Comparative Cr and Mn speciation across a shore-to-reef gradient in lagoon sediments downstream of Cr-rich Ferralsols upon ultramafic rocks in New Caledonia
نویسندگان
چکیده
Ferralsols upon ultramafic rocks are among the most Cr-enriched soils at Earth surface. Weathering and erosion of these represents a major source Cr for coastal sediments downstream settings. Although mainly occurs as Cr(III)-bearing chromite Fe-(hydr)oxides in rocks, several evidences oxidized Cr(VI) relation with Mn-oxides have been reported. Regarding high solubility toxicity this latter species, thorough characterization Mn crystal-chemistry tropical sedimentary settings is needed to evaluate potential threat towards biodiversity environments. In study, we determined speciation across shore-to-reef gradient lagoon one largest lateritized regolith New Caledonia that contains up 5 wt% Cr2O3. Chromium K-edge XANES data emphasized absence indicated hosting by clay minerals close shore, whereas Cr-bearing goethite dominated reef. Manganese Mn?carbonates The lack detection was considered explain studied sediments. This result thus suggests that, despite their shallow character can favor occasional re-oxidation top-layer re-suspension events, Cr-rich appear rather favorable sequestration less mobile toxic Cr(III) form. However, reverse trends observed from shore reef between contributions speciation, well decrease Cr/Ti ratio, suggest fraction could released water column partial weathering during transport gradient. point emphasizes hazard still represent exceptional ecosystems Ferralsols, detectable Cr(VI). It calls further studies aimed better evaluating stability mineral phases early diagenesis
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ژورنال
عنوان ژورنال: Journal of Geochemical Exploration
سال: 2021
ISSN: ['1879-1689', '0375-6742']
DOI: https://doi.org/10.1016/j.gexplo.2021.106845