Geophysical methods for mapping Quaternary sediment thickness: Application to the Saint-Lary basin (French Pyrenees) |
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Institution: | 1. Géosciences Environnement Toulouse, UMR CNRS–IRD–Université de Toulouse, Observatoire Midi-Pyrénées, 14, avenue Édouard-Belin, 31400 Toulouse cedex, France;2. BRGM, direction régionale Midi-Pyrénées, 3, rue Marie-Curie, 31527 Ramonville-Saint-Agne, France |
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Abstract: | This study aims at mapping the sediment infill thickness in the Saint-Lary basin (Aure valley, French Pyrenees). For this purpose, we combine passive seismic and gravity surveys. The resonance frequencies of the sediment body are retrieved from seismic ambient measurements, while the gravimetric survey shows negative residual anomaly of about ?3 mGal in the basin. Both methods reveal unexpected but consistent bedrock shape. The southern Saint-Lary basin appears deeper than its northern part, with maximal infill thickness of about 300 m and 150 m, respectively. Valley cross sections show regular and smooth “U”-shape in the southern Saint-Lary basin, in contrast to an irregular and asymmetric pattern in the northern basin. This basin shape may be related to Quaternary fluvio-glacial carving processes especially controlled by a regional fault (the Soulan fault), variations in bedrock hardness, and preferential ice flow paths. |
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Keywords: | Quaternary geology Pyrenees Sediment-filled basin Geophysics Geomorphology |
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