Dating of weathering profiles by radioactive disequilibria: contribution of the study of authigenic mineral fractions

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• 作者：Dequincey ; Olivier ; Chabaux ; Franç ; ois ; Clauer ; Norbert ; Liewig ; Nicole ; Muller ; Jean-Pierre
• 关键词：weathering profile ; laterite ; geochronology ; radioactive disequilibrium ; Rb-Sr ; profil d'alté ; ration ; laté ; rite ; gé ; ochronologie ; dé ; sé ; quilibres radioactifs ; Rb-Sr
• 刊名：Comptes Rendus de l'Academie des Sciences Series IIA Earth and Planetary Science
• 出版年：1999
• 出版时间：May, 1999
• 年：1999
• 卷：328
• 期：10
• 页码：679-685
• 全文大小：592 K

文摘

Soil isotopic dating is important for understanding mass transfers related to rock weathering. Here we evaluate a method including TIMS analyses of (²³⁴U/²³⁸U) activity ratios on < 0.2 μm fractions of a Cameroon laterite. Variations of the (²³⁴U/²³⁸U) ratios with depth show (1) significant (²³⁴U/²³⁸U) disequilibrium at the bottom of the pedological units, and (2) progressive returns towards secular equilibrium above. These results suggest that U fractionation occurs at the base of the units and that the analysed fractions probably evolve as closed/restricted systems within each unit. From these data, an overall age of 1.5 Ma may be proposed for the development of this laterite.