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Contrôles climatique et sismo-tectonique de la sédimentation lacustre dans l'avant pays alpin ( Lac du Bourget) durant le quaternaire récent. (Alpes françaises)

Abstract : An integrated study of lake Le Bourget sedimentary infill from high resolution seismic reflection data, side scan sonar data and short corings is presented and compared to lake Geneva seismic stratigraphy. These new data enable to define the climatic and seismo-tectonic influences on lacustrine sedimentation in the NW Alps since the Würmian glaciation. Correlation between seismic stratigraphies and available chronological data releaved two fluctuations of the Isère and the Rhône glaciers at approximatily 35000 and 20000 y BP. In lake Le Bourget the last deglaciation of the Isère glacier was fast, and induced a Late Glacial infill (from 15000 to 10000 y BP) mainly dominated by glacial meltwater discharge through subglacial streams, subaerial streams and then alluvial streams once the glacier retreated out of the watershed. But lake Geneva being directly related to the Rhône glacier and located closer to the Inner Alps, its infill mainly resulted from subglacial streams and glacio-lacustrine sedimentation associated to several glacier fluctuations till the end of the Late Glacial period. The Holocene sedimentation is then dominated by an authigenic production in lake Le Bourget and in the " Petit lac" of Lake Geneva, whereas in the " Grand lac " most of the terrigeneous supply is trapped in the Rhône and Dranse fan delta. NW-SE strike-slip jurassian faults (Culoz and Col du Chat faults) affecting the Northern and Southern parts of lake Le Bourget, favoured glacial erosion and developped continuous deformation within Late Glacial sediments, but also triggered a large earthquake-induced slide and in situ liquefaction that induced a basin collapse during the Late Glacial-Holocene transition. The present sedimentation of lake Le Bourget and its evolution since the last millennium is established by means of side scan sonar mapping, surficial sediment samples calibration, as well as textural and mineralogical analyses realized on a set of short cores (1 m long). The chronology is based on the extrapolation of the sedimentation rate defined for the last century by Lead 210 and Cesium 137 dating, and calibrated by the main historical events (floods, earthquakes, human developments). The Little Ice Age induced a strong increase in floods events between the 17th and 19th centuries, mainly during the Maunder sun spot minimum (1650-1720 AD). A 45 years cyclicity is highlighted by spectral analysis of different deep sedimentation proxies, sampled every centimeter (clay mineral, carbonates) or millimeter (lamination). A 4 to 5 years cyclicity in the lamination is also clearly identified during the Sporer sun spot munimum (1450-1550 AD). Earthquake-induced disturbances during the main historical events located close to lake Le Bourget are presented , and a regional extension is discussed. The Late Glacial-Holocene seismo-tectonic instability mainly triggered gravity reworking phenomena and the development of homogenites (or seiche deposits) during major events. The acoustic signature of a prehistorical seiche deposit and the sedimentological signatures of an historical seiche deposit produced by the 18/02/1822 earthquake, highlight the influence of the lake water body oscillation (seiche effect) on the downslope evolution of earthquake-triggered slides.
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https://tel.archives-ouvertes.fr/tel-00723721
Contributor : Pascale Talour <>
Submitted on : Monday, August 13, 2012 - 11:28:58 AM
Last modification on : Thursday, November 19, 2020 - 3:54:26 PM
Long-term archiving on: : Friday, December 16, 2016 - 5:49:32 AM

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  • HAL Id : tel-00723721, version 1

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Emmanuel Chapron. Contrôles climatique et sismo-tectonique de la sédimentation lacustre dans l'avant pays alpin ( Lac du Bourget) durant le quaternaire récent. (Alpes françaises). Géomorphologie. Université de Lille 1, 1999. Français. ⟨tel-00723721⟩

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