Palaeoenvironments of the Late Miocene Prüedo Basin: implications for the uplift of the Central Pyrenees

Abstract

The nature, structure and extent of a palaeo-basin sedimentary infill exposed in the Aran valley (Central Pyrenees) was studied by combining stratigraphical and biostratigraphical analyses and an audio-magnetotelluric survey. The basin developed on top of a pre-existing peneplain and was formed by the North Maladeta Fault activity. The fluvio-palustrine sequence filling the basin was at least 100 m thick. Specimens of the taxon Hippuris cf. parvicarpa Nikitin were identified for the first time in a European palaeoflora. The palynological and carpological analyses allowed us to (1) constrain the age of the basin infill as Vallesian (11.1-8.7 Ma), (2) characterize the vegetation of the belt surrounding the basin as a mainly temperate to warm-temperate assemblage, and (3) estimate the palaeoaltitude of the site at between 700 and 1000 m, which leads to an altitude change of 900-1200 m for the North Maladeta Fault downthrown block and 1640-1640 m for the upthrown block. These data allowed us to estimate the regional uplift of the area at between 0.08 and 0.19 mm a−1. The different exhumation values obtained by other researchers for sites located at both sides of the North Maladeta Fault are in agreement with its activity as a normal fault since the Late Miocene.