O Quaternário, a Morfologia Cársica e o Património Ambiental. Exemplos no sector Setentrional do Maciço de Sicó

Lúcio Cunha


In the main Portuguese calcareous massifs, the karstic process, which led to the formation of unique landforms and landscapes, nowadays considered of high heritage value, was a long and complex process in which the Quaternary represents only a very small part of the time involved.

Considering only the calcareous massifs of the Westem Portuguese Mesocenozoic Border, if we except the calcareous tufas (and especially the largest outcrop, the Tufas of Condeixa) which were formed well into lhe Quaternary, the karstic forms (Karren, dolines, small caves) that developed there therefore being very recent, in the remaining calcareous rocks the karstic process began in the Jurassic period, and was marked by phases of different intensity at the mercy of tectonic changes, and especially of the successive bioclimatic environments registered in the region. 80th in the Calcareous Massif of Extremedura and in the Sicó Massif  the Quaternary seems to have been essentially the setting for the exhumation of paleoforms, some pre-cretaceous, others perhaps tertiary, a1 the same time as a karstic retouching of the calcareous surfaces thus uncovered was taking place.

In spite of this, the most spectacular Landforms, those which have an incontestable heritage value and often correspond to the best known image or these massifs, have the indelible mark of the fluvio-karstic and karstic processes that developed in the Qunternary.

Following the raising of the massifs, and depending on the sandstone coverings progressively mobilized since cretaceous times, which at the beginning of the Quaternary still had, if not a continuous nature, at least larger and thicker extension than the ice remains that can be seen today, conditions were created for the development of the networks of rivers responsible for spectacular canyons, such as, in the case of Sicó, the canyons of Poios, Vale das Buracas and Vale da Grota. Other small canyons, perhaps more worthy of the name, given the almost absolute verticality of their sides, as is the case of the canyon of  Rio dos Mouros which was only one of the reasons for the establishment of the Roman city of Conimbriga, despite being perhaps more recent,were born for the same reasons.

An important part of the geological interest of these fluvio-karstic canyons arises from the shape of their sides, and especially from the «buracas», shapes of surface karst which seem to be linked to processes of frost shattering and dissolution under the action of cold climates. Short, almost vertical sectors (the «penas»), openings under rock (the «buracas») and debris of various origins are, without a shadow of doubt, quaternary marks on the sides of the fluvio-karstic canyons and other scarped slopes which contribute a great deal to the valorization of the landscape.

The same is true of formations of two other types, authentic signatures of  karstic shaping: the karren, responsible for the «stony desert»)with which classic karst is identified, and the caves which are valuable in themselves because of the beauty they enclose, the challenges they lay down and also, particularly, because of their importance in the process of water circulation and storage. In this case, it was also in the

Quaternary that the responsible processes evolved, for the integral sculpture of many karren formations as for the finishing touches seen in them, this was the time that permitted the final restructuring of the network of galleries wl1ich lay out lhe hydrological functioning of the karst of today.

This article discusses the importance of the processes that took place during the Quaternary in the

construction of the karstic landscape, with particular influence on the formations which, for their genetic specificity, spectacular nature and singularity represent more in terms of environmental heritage.

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