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| Titel |
Transient sediment supply in a high-altitude Alpine environment evidenced through a 10Be budget of the Etages catchment (French Western Alps) |
| VerfasserIn |
Romain Delunel, Peter van der Beek, Julien Carcaillet, Didier Bourlès, Fritz Schlunegger |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250075704
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| Zusammenfassung |
| Although 10Be concentrations in stream sediments provide useful synoptic views of
catchment-wide erosion rates, they cannot be used to identify the intrinsic spatial variability
of erosion and sediment discharge within a catchment. Therefore we measured 10Be
concentrations (n = 19) of different morphologic features and detrital material resulting from
high-altitude erosion processes that ultimately feed the sediment routing system.
We focussed on the Etages catchment (~14 km2, Ecrins-Pelvoux massif, French
Western Alps), located within the altitudinal range where periglacial and especially
frost-controlled processes are the most efficient. This catchment also hosts a small
cirque-glacier, which is a relict from the Little Ice Age (LIA) glacial advance. Thus, this
basin allows identifying the glacial influence on 10Be concentrations in stream
sediments.
10Be concentrations vary from ~0.1Ã10Ë5 to 4.5Ã10Ë5 atoms g-1 in the Etages catchment,
while displaying consistent 10Be signature within each representative source. 10Be contents
of glacial materials vary from 0 (i.e. undistinguishable from procedural blanks) close to the
present-day glacier position to ~0.3Ã10Ë5 atoms g-1 towards the LIA moraines. Debris-flow
material collected at different catchment levels has slightly higher 10Be concentrations
(~0.4-0.7Ã10Ë5 atoms g-1). Regolith material collected close to the highest crests
(morphologic features currently affected by frost-cracking processes) carries much higher
concentrations (~1.3-1.8Ã10Ë5 atoms g-1), while bare rock surfaces are also characterized by
relatively high and heterogeneous 10Be concentrations ranging from ~1.4 to 4.5Ã10Ë5 atoms
g-1. Finally, stream sediments collected along the main stream and at the catchment outlet
carry 10Be concentrations of only ~0.2Ã10Ë5 atoms g-1, without any downstream
trends.
We interpret these 10Be concentration measurements combining a geomorphological map
and surface 10Be production-rate estimates within a mass-balance model. We show that the
10Be signature of sediments exported from the Etages catchment does not fulfil the
steady-state equilibrium required for inferring catchment-wide denudation rates. Most
important, the 10Be concentrations measured in the alluvial sediments along the
stream reflect the glacial material signature, showing that the Holocene variability in
denudation has not imprinted on the 10Be concentration of the trunk stream yet
and implying a strong transient state in this high-elevation catchment of the Alps. |
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