首页|Systematics of U-Th disequilibrium in calcrete profiles: Lessons from southwest India

Systematics of U-Th disequilibrium in calcrete profiles: Lessons from southwest India

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  • NSTL
  • Elsevier
Pedogenic carbonates (calcretes) have often been proposed as possible markers of the pedogenetic processes in soils under semi-arid climate. However, precise chronological constraints on, their formation are required in order to investigate the climatic and paleo-environmental conditions that prevailed during and after their formation, and to improve our understanding of the, physical and chemical conditions that promoted their development and preservation. Moreover, these authigenic calcium carbonate precipitates provide us with an interesting test of the U-Th radioactive disequilibrium dating method, the reliability of which has been demonstrated extensively in aragonitic corals and calcitic continental speleothems, but which remains much more questionable in highly porous, chemically and mineralogically complex media such as soil profiles. We report here U-238-U-234-Th-230 radioactive disequilibrium analyses measured by Thermo-Ionization Mass Spectrometry in calcretes from two sites in southwest India. Since calcretes are impure carbonates mixed with various amounts of parent rock and weathered minerals, all ages must be computed using the isochron technique, involving the extraction of several coeval subsamples from the same soil horizon and U-Th analyses after total dissolution (TSD) method, in order to correct for the detrital component. Th-232 is usually used as index of the detrital contamination, and the isochron age is derived from the isotopic composition (Th-230/U-238; U-234/U-238) of the pure authigenic carbonate end-member of the mixing line.

U-seriesIsochronCalcreteImpure carbonateWeathering profileSouthwest India

Durand, N.、Hamelin, B.、Deschamps, P.、Gunnell, Y.、Curmi, P.

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Aix Marseille Univ, CNRS, IRD, CEREGE,Europole Mediterraneen Arbois, BP80, F-13545 Aix En Provence, France

Univ Lyon, Lumiere Lyon 2, UMR 5600, Environm Ville Soc, 5 Ave Pierre Mendes France, F-69976 Bron, France

Agrosup, UMR 1347, Agroecol, BP 86510, F-21000 Dijon, France

2016

10.1016/j.chemgeo.2016.06.026

Chemical geology

Chemical geology

EIISTP
ISSN：0009-2541
年,卷(期)：2016.446
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