Lead isotope signatures of Holocene fluvial sediments from the Loire River valley

Philippe Négrel (1) , Wolfram Kloppmann (1) , Manuel Garcin (1) , Denis Giot (1)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

The distribution of Mn, V, Th, Pb and isotopes of Pb in the labile fraction of sediments from a channel infill in the Middle Loire alluvial plain are used to highlight some aspects of the basin evolution over the period from 0 to 10 ka BP. The acid extractable matter (AEM) in the sediment samples is variable in amount and in trace element contents. Iron-Mn oxyhydroxides are the principle trace element carrying phase in the labile fraction and carbonates are a secondary carrier. Vanadium and Pb originate from the weathering of silicates and are used as a silicate erosion rate index in the fluviatile record. Most of the AEM data plot along a general trend between 3 endmembers (basalts, Cretaceous carbonate rocks and granites) in the relationship between 207Pb/206Pb and 206Pb/206Pb. These endmembers have been mixed in various proportions depending on natural Holocene inputs (erosion, volcanic events) or human influences (mining and smelting of ore).

Domaines: Sciences de la Terre

Philippe Négrel, Wolfram Kloppmann, Manuel Garcin, Denis Giot. Lead isotope signatures of Holocene fluvial sediments from the Loire River valley. Applied Geochemistry, 2004, 19 (6), pp.957-972. ⟨10.1016/j.apgeochem.2003.11.004⟩. ⟨hal-03784143⟩