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. Supplementary materials Details of the data acquisition, processing and modelling for the Porera profile are available at www.geolsoc.org.uk/SUP18551.
Highlights
The fluvio-lacustrine records are very valuable sedimentary archives of geological processes
Neogene lakes preserved in high mountain environments are especially relevant to the orogenic histories, since the generalized enhanced erosion during Quaternary times has left almost no witnesses of the geological history occurred between the end of the orogenic maximum and the emplacement of the Quaternary glaciers
The material recovered so-far consists in a few tens of mm-sized fruits and seeds from samples 1a, 4a, 4d, which are mostly deformed and partly abraded. This makes identification very difficult, because very few carpological data have been published on the Neogene of the Pyrenees area
Summary
The fluvio-lacustrine records are very valuable sedimentary archives of geological processes. Neogene lakes preserved in high mountain environments are especially relevant to the orogenic histories, since the generalized enhanced erosion during Quaternary times has left almost no witnesses of the geological history occurred between the end of the orogenic maximum and the emplacement of the Quaternary glaciers. 1900 m elevation that are “hanged” approximately 400 m above the current level of the river incision. In this high mountain environment, where almost no recent deposits have been preserved, the Prüedo sediments partly maintain their depositional geometry, which contrast with the highly deformed hard bedrock in which the basin was formed (Fig. 2). The post-orogenic (i.e., post-Oligocene) sedimentary cover has been almost completely eroded away by the emplacement of consecutive glacial and river systems during the Quaternary times. Besides the Prüedo sediments, and several yuxtaglaciar deposits generated during the Penultimate Glacial maximum (Bordonau, 1992), the only post-orogenic sediments described in the Central Pyrenees are those generated during or after the Last Glacial maximum
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