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Caractérisation et calibration des flux organiques sédimentaires dérivant du bassin versant et de la production aquatique (Annecy, Le Petit Lac). Rôles respectifs de l'Homme et du Climat sur l'évolution des flux organiques au cours des 6000 dernières années

Abstract : The calculation of organic fluxes deriving from both the catching area and the sedimentation basin has
been realized by the mean of a combined petrographic (palynofacies) and pyrolytic (Rock Eval) approach, on a
core sampled in the center of Annecy lake (Petit Lac) recovering the six last millenia. The calibration of
sedimentary organic markers has been possible by studying with the same methods, the different types of organic
matter on the sites where they are produced (water column, geological substratum and soils from the catching
area).
The evolution of the organic markers allowed to show that the six last millenia could be separated into
two main periods of sedimentation during which Humans have influenced or have not influenced the
sedimentary organic supplies.
- From the upper Neolithic to the Middle-Age, the action of Humans on the forest cover does not seem
to act directly on the variations of the organic sedimentary fluxes which are mostly dependent on the climatic
variations.
- From 1100 cal. AD, period of the monastic installation in the French Alps, the allochthonous
sedimentary fluxes increase by a factor of 4, corresponding to the intense phase of forest clearings and cultures.
This is also the case for the autochthonous organic fluxes underlining that the Human activity may also have an
impact on the variations of the trophic level of the lake.
Although the Human impact mostly marks this last period of sedimentation, the organic fluxes, between
1100 cal. AD and nowadays, are also under the control of the natural climatic variations. This is particularly
marked during the Little Ice Age for the aquatic organic fluxes, sensitive to the variations of temperature and
luminosity. The lowest lacustrine productions coincide precisely with the minimums of solar activity (Wolf,
Maunder, Dalton et Spörer). Similar concordances also occur from 3800 cal. BC to 1100 cal. AD.
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Submitted on : Friday, September 6, 2002 - 8:06:36 AM
Last modification on : Thursday, March 5, 2020 - 6:48:57 PM
Long-term archiving on: : Tuesday, September 11, 2012 - 5:50:30 PM

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  • HAL Id : tel-00001635, version 1

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Hervé Noël. Caractérisation et calibration des flux organiques sédimentaires dérivant du bassin versant et de la production aquatique (Annecy, Le Petit Lac). Rôles respectifs de l'Homme et du Climat sur l'évolution des flux organiques au cours des 6000 dernières années. Géologie appliquée. Université d'Orléans, 2001. Français. ⟨tel-00001635⟩

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