Geographic distribution of Quaternary periglacial heritage in Portugal and Madeira

Abstract

Aricle in French.

ORIGINAL TITLE: Repartition geographique des heritages periglaciaires Quaternaires au Portugal et a Madère

Under the current climate, there are a few surface indicators of cryonival morphogenesis on the summit areas of the mountains in northern and central Portugal, and even in the Madeira highlands. However, Quaternary periglacial heritage are far more prominent in shaping the landscape, both in terms of their extent and their distinctive characteristics. In the Minho mountain ranges of northern Portugal, two altitudinal zones can be distinguished. The higher zone, located above 1000 meters, features typical slope deposits formed by frost weathering—more or less stratified and washed depending on the case (tending toward groizes or stratified arenaceous materials), although chaotic block formations are not excluded. The lower zone, approximately between 1000 and 700 meters, is mainly characterized by sheets of block deposits with a fine matrix and no defined structure, found on the slopes of large valleys. These formations appear to have resulted from mass wasting linked to snowmelt-related debris flows. The mountains of central Portugal exhibit similar characteristics, though with less clearly defined altitudinal zonation due to differences in lithological context.

Deposits of the groizes type and block sheets are also observed at higher elevations in Madeira. The most typical cryonival formations among Quaternary relics are restricted to altitudes comparable to those found in the Moroccan Atlas Mountains at the same latitude. Only the apparently cryonival formations along Portugal’s coastal zone between the Mondego River and Cape St. Vincent—present complex paleoclimatic challenges (such as the question of a Würmian coastal desert) or chronological uncertainties (could some of these deposits be attributed, at least in part, to the Riss glaciation?).