INCISÃO FLUVIAL EM TRIBUTÁRIOS DO RIO DOURO, UPLIFT REGIONAL E CONTROLO LITOLÓGICO NA EVOLUÇÃO DOS PERFIS LONGITUDINAIS

Abstract

In this paper it’s analyzed some longitudinal profiles of Douro river tributaries. These streams flow through a landscape strongly influenced by variations in bedrock lithology, fault structures (e.g. Vilariça fault) and a base-level lowering history (tectonic uplift / eustatic). The Douro tributaries display an upstream concave up reach and a downstream rejuvenated profile separated by a transient knickpoint/knickzone. The upstream concavity up reach reflects a relict graded profile, of probable Piacenzian – Gelasian age, while the rejuvenated profile, represents the on-going transmission of several incision waves, linked to the Pleistocene - present stage of fluvial incision. Downstream projection of the relict graded profile was used to estimate the maximum fluvial incision at the stream mouth and the equivalent crustal uplift. The amount of incision ranges from ca 400 m in Côa river up to more than 600 m in the Paiva river, reflecting the differential uplift of the Meseta surface and the Central Plateaus. Incision rates calculated assuming ca of 2,5 to 1,8 Ma for the beginning of the incision are consistent with the amount of the uplift estimated in early works.