The Sicó Massif: Morphostructural Aspects, Hydrology and Karstification

Abstract

The geomorphological setting of the Sicó massif (western-central Portugal) is the result of a long-term evolution under the control of tectonics and climate. The bedrock lithology is composed by a thick and generally continuous carbonate succession from the Lower and Middle Jurassic. Post-Jurassic tectonic deformations were responsible for the progressive uplift, fragmentation and intense internal block-faulting of the Sicó massif, leading to its present-day configuration: a set of dolomitic hills, marly-limestone depressions and limestone mountains/plateaus. Most of the observed morphologies are erosional landforms, with monogenetic or polygenetic origin, mainly generated by the action of fluvial and karstic processes, which often occur under the control of the lithology and geological structure. Some periglacial and depositional karst features (rock-shelters with associated relict cryonival deposits and calcareous tufa/travertine outcrops, respectively) also occur, providing good evidence of the influence of variable climatic conditions during the Quaternary. The presence of a discontinuous Meso-Cenozoic siliciclastic cover influenced fluvial and karstic processes (with cryptokarstic evolution) that interacted and still interact in the construction of a sui generis karst/palaeokarst landscape, with the related forms that coexist in a complex system, resulting from a polyphase and polygenic evolution. Many of the karst and fluvio-karst landforms that characterize the Sicó massif present high value in terms of geoheritage, as well as an intrinsic potential for the local development.