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TitleIron loss during continental weathering in the early Carboniferous period recorded by karst bauxites
AuthorLing, KORCID logo; Wen, H; Fan, HORCID logo; Zhu, X; Zhang, Z; Grasby, S EORCID logo
SourceJournal of Geophysical Research, Earth Surface vol. 128, issue 4, 2023 p. 1-15, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20230111
Mediapaper; digital; on-line
File formatpdf
Lat/Long WENS 105.0000 115.0000 30.0000 20.0000
Subjectsgeneral geology; bauxite; iron; weathering; Carboniferous; Permian; Cretaceous; Cenozoic
Illustrationslocation maps; photographs; plots; images
ProgramGEM2: Geo-mapping for Energy and Minerals Western Arctic, Pearya Terrane, North Ellesmere
Released2023 03 22
AbstractSignificant iron (Fe) loss can occur during continental weathering and efflux to the ocean via runoff, historically affecting global Fe cycling and marine ecosystems. Here, we report extremely low Fe content in early Carboniferous (ca. 340 Ma) bauxites in southwestern China. These bauxites were formed by redeposition of terrestrial soils along the paleo-continental margin of the western South China Plate in warm climates. The bauxites contain high d 56Fe (-0.17 per mil to +1.15 per mil) values with a negative correlation between Fe2O3 and d 56Fe, indicating that a substantial amount of Fe(III) was reduced to isotopically light dissolved Fe(II) and effuxed to the ocean via reductive dissolution under anoxic conditions. The low Corg content and low FeHR/FeT, Mo/Al, U/Al, and V/Al ratios of bauxite suggest that this reduction process occurred during the pedogenic (continental weathering) rather than the depositional/diagenetic stage of karst bauxite formation. Most of the dissolved Fe(II) were rapidly re-oxidized to Fe(III) and transported toward the paleo-continental margin forming iron ores with d 56Fe values around zero -0.13 per mil to +0.16 per mil). The negative correlation between Al2O3 and Fe2O3 contents in global karst bauxites suggests common Fe loss processes during continental weathering in geological periods favoring karst bauxite formation, such as during the Carboniferous, Permian, and Cretaceous periods and the Cenozoic era. Karst bauxite may thus provide a record of Fe loss during continental weathering and act as an indicator of enhanced Fe flux to oceans.
Summary(Plain Language Summary, not published)
This work was examining paleo-climate controls on the formation of bauxite and iron ore deposits in order to develop a better exploration model for such resources.

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