Geometría y depósitos de las cubetas glaciolacustres del Pirineo

Abstract

Six lacustrine Quaternary basins of glacial origin from the Pyrenees have been studied by using both geomorphological methods and electric soundings. The localities studied are glacial overdeepened basins (Esterri d'Aneu, Noguera Pallaresa valley; Benasque, Esera valley and Bono, Noguera Ribagorçana valley), proglacial lacustrine basins formed by a morainic-ridge obstruction (Seminari de Vilaller, Noguera Ribagorçana valley), juxtaglacial lacustrine basins formed also by a morainic obstruction (Taüll, Noguera de Tor valley) and lacustrine basins formed by bedrock faulting of the slopes after glacial wastage (Basses d'Ules, Garona valley). The high contrast between the resistivities from the bedrock and the Quaternary deposits allows us to determine not only the thickness of the Quaternary deposits but also the several Quaternary units by using electric soundings. Generally three Quaternary units are present over the paleozoic bedrock: a basal glaciolacustrine unit with a low resistivity, a middle fluviodeltaic unit of variable resistivity though higher than the resistivity from the glaciolacustrine unit, and an upper alluvial and/or fluviotorrential unit with high resistivities. The thickness of the Quaternary deposits is very variable, ranging from more than 300 meters in the Esterri d'Aneu overdeepened basin to a few meters in the Basses d'Ules basin.