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Contribution de l'approche sédimentologique à la reconstitution de l'histoire des sols. Définition de traceurs pédologiques et application sur des sédiments lacustres de montagne (Maurienne, Savoie, France).

Abstract : Soil is a natural body occurring at the interface between the lithosphere, atmosphere and biosphere. As a result, the physical and chemical properties of soils evolve with time, and the reconstruction of their history represents a key to understand past environmental changes. Palaeolimnological techniques such as sediment geochemistry can be used to investigate changes in vegetation history by providing information about catchment soil development. However, due to the lack of conservative pedosignatures, there have been few attempts to reconstruct soil changes from the paleorecord. The main objective of the present work is to reconstruct the soil and environmental history from lake sediments of two small lake basins of the Maurienne Valley in the French Alps. Two main issues arise in using the sedimentary approach: i) the geochemical differentiation of different soil processes and soil types, which controls the identification of tracers; ii) the conservative behaviour of these tracers during sediment mobilisation, transport and accumulation in aquatic systems. In a first step, podzolization and chemical weathering processes were assessed on present day soils using a broad geochemical approach. Normalized REE patterns provide a precise tracer of the degree of weathering of materials whereas the proportions of organic-bound Al and Fe provide a sediment tracer to reconstruct the intensity and degree of podzolisation. Then, the same tracers were assessed on the two investigated lake sediment sequences (Loup and Thyl lakes). Evidence of changes is preserved in both sediment records which render possible the reconstruction of aspects of soil genesis from lake sediments. The resulting proxy records, spanning ca. 4 500 yr at the Thyl lake and ca. 13500 yr at the Loup lake, indicate that progressive and regressive pedogenesis occurred after deglaciation. Loup environment and soil history is characterised by a progressive and stable evolution leading to present day old growing forests and Podzol soil type. On the other hand, Thyl record is much contrasted: the progressive setting of the mixed cembra pine ecosystem associated with podzolisation process is followed by abrupt and rapid secondary processes that could result from drastic transformation of the plant cover with changes in fire regimes.
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Submitted on : Monday, March 16, 2009 - 10:48:05 PM
Last modification on : Friday, November 6, 2020 - 3:28:58 AM
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  • HAL Id : tel-00367597, version 2
  • PRODINRA : 249877

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Brice Mourier. Contribution de l'approche sédimentologique à la reconstitution de l'histoire des sols. Définition de traceurs pédologiques et application sur des sédiments lacustres de montagne (Maurienne, Savoie, France).. Sciences de la Terre. Université de Savoie, 2008. Français. ⟨tel-00367597v2⟩

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