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The Limestone Massif of Estremadura
Abstract
The karst landscapes of Portugal are confined to the sedimentary basins where there are uplifted limestone rocks. The most important limestone massif is the Limestone Massif of Estremadura (LME) located in the Western Sedimentary Basin that contact by an overthrust fault with the active Tagus River sedimentary basin. Although there are other limestone massifs in Portugal, they are smaller and have less developed karst landforms. What makes the LME special is the thickness of the limestone, its high content of calcium carbonate and tectonic uplift of the entire massif in relation to the surrounding areas. No permanent river cuts across the limestone mass, and the water circulation is subterranean. For this reason, most of great karst springs are located along the LME borders, principally in the eastern side, near the tectonic contact with the impermeable sediments of the Tagus Basin. In this chapter, the main geomorphological units within the LME are characterized: three anticline mountains, two plateaus and three tectonic depressions in graben structures. Examples of the main types of karst landforms according to dimension are presented, namely: large karst landforms (poljes, big uvalas, karst canyons or amphitheatre head valleys), medium karst landforms (dolines, dry valleys, karst springs or waterfalls) and small karst landforms (karren features or swallow holes). Among this set of karst landforms, some show a particular value and should be preserved as geoheritage and geomorphosites. Two cases are the polje of Minde and the Fórnia amphitheatre head valley that contains valuable remnants of relict slope deposits from Quaternary cold periods.
... No domínio do Maciço Hespérico, alguns afloramentos de mármores, dolomitos, calcários dolomíticos silicificados, brechas e mineralizações no contacto com rochas carbonatadas, também se apresentam carsificadas (Feio, 1952;Crispim, 2010). Seja como for, e ocupando uma porção muito exígua do território nacional (~5%), as unidades morfo-estruturais mais expressivas, tanto no que diz respeito à especificidade do relevo superficial, assim como à presença de sistemas de cavidades em profundidade, são aquelas que se desenvolvem na dependência dos afloramentos carbonatados do Jurássico Médio (Cunha, 1996;Crispim, 2010;Dimuccio, 2014;Cunha & Dimuccio, 2014;Cunha et al., 2020;Rodrigues, 2020). Carso(s) comparativamente menos evidentes na paisagem, mas igualmente importantes, sobretudo de um ponto de vista hidrogeológico e geoquímico, podem ser reconhecidos, também, em rochas carbonatadas mais ou menos impuras do Jurássico Inferior e Superior, do Cretácico e do Neogénico, assim como em tufos calcários e travertinos do Quaternário (mais detalhes nas revisões de Cunha, 1996;Crispim, 2010;Dimuccio, 2014) (Fig. 1). ...
O hidrogeólogo e geomorfólogo Alexander Klimchouk (1956-2023) dedicou grande parte da sua vida profissional ao estudo da espeleogénese hipogénica, ou seja, de uma tipologia muito específica de atuação dos processos de carsificação em profundidade, ligada a uma recarga hídrica per ascensum. É aqui proposto um modelo cartográfico preliminar que evidencia os principais setores da Orla-Meso-Cenozoica Ocidental de Portugal potencialmente capazes de manifestar indícios de espeleogénese hipogénica.
... Karst formations occupy a considerable area of the Portuguese territory [43,44]. The Maciço Calcário Estremenho-MCE (Estremenho Karst Massif) is located in Southwest Europe and Central Western region of Portugal ( Figure 1A,B) and is an uplifted Jurassic limestone massif unit of the Lusitanian Basin hosting a very complex karst aquifer system, which is made up of several subsystems, each one related to a different perennial karst spring. ...
... Karst formations occupy a considerable area of the Portuguese territory [43,44]. The Maciço Calcário Estremenho-MCE (Estremenho Karst Massif) is located in Southwest Europe and Central Western region of Portugal ( Figure 1A,B) and is an uplifted Jurassic limestone massif unit of the Lusitanian Basin hosting a very complex karst aquifer system, which is made up of several subsystems, each one related to a different perennial karst spring. ...
Climate change may increase the vulnerability of aquifers to contamination through extreme precipitation and extended drought periods. Therefore, the understanding of groundwater ecosystem dynamics is crucial, with bacterial assemblages playing a major role in biogeochemical cycles. The present research describes a geospatial study targeting the bacterial community structure of groundwaters from the largest karst aquifer in Portugal (the Maciço Calcário Estremenho), integrating hydrogeochemical and bacterial diversity data. A total of 22 samples were analyzed from a set of 11 geographically sparsely distributed groundwater sources in dry vs. wet seasons. The 16S rRNA gene barcoding data revealed bacterial community variability across samples in space and time. The phylum Proteobacteria was dominant across all samples (from 44 to 92% of total sequence reads), mainly represented by the classes Alphaproteobacteria (orders Sphingomonadales, BD7–3, Rhizobiales and Rhodospirillales), Betaproteobacteria (orders Burkholderiales, Rhodocyclales, Nitrosomonadales), Gammaproteobacteria (orders Pseudomonadales, Xanthomonadales, Alteromonadales, Legionellales) and Deltaproteobacteria (orders Myxococcales, Spirobacillales). Variation in the bacterial community was primarily attributed to parameters such as redox conditions (DO, ORP), Fe, Mn, SO4, PO4, Sr and Cl, but also some minor and trace elements (Al, V, Cr, Cu, Pb). Our results provide novel insights into bacterial diversity in relation to groundwater hydrogeochemistry. The strong dominance of OTUs related to bacterial taxa associated with nitrification/denitrification also highlights a potentially important role of these assemblages on nutrients (nitrogen sources) and groundwater quality dynamics at this karstic aquifer system. Moreover, the integration of bacterial assemblages information is emphasized as central for water quality monitoring programs.
... Most of these sinkholes are blocked or obstructed, and they have been examined primarily through the lens of geomorphological heritage (e.g. Brilha & Pereira, 2020;Rodrigues, 2020), rather than being comprehensively assessed as potential geohazards. The hazard mapping of karst phenomena along the Algarve coast, as presented by Forth et al. (1999), stands as an exception. ...
In Portugal, scholarly attention towards geohazards has grown significantly since the 1980s, with various analytical methods employed to study these phenomena, including physically-based models, data-driven models, and heuristic techniques. The published research has contributed to a better understanding of the underlying processes, but also includes the assessment of susceptibility, probability, and magnitude of hazardous events. Some studies have extended into risk analysis, considering exposure, asset valuation, and vulnerability, encompassing both physical and social dimensions. Geohazards are concentrated primarily in the western and southern coastal areas of mainland Portugal, particularly in regions like Lisbon, the Lower Tagus Valley, and the Algarve. These areas face multiple geohazard threats, including earthquakes, tsunamis, coastal erosion, floods, flash floods, and landslides. In the remaining parts of mainland Portugal, the inland North and Centre regions are more prone to landslides and soil erosion, while the Alentejo is comparatively safer but still faces a significant risk of soil erosion, contributing to the threat of desertification. Within the Atlantic islands, Madeira exhibits a notable susceptibility to landslides, flash floods, and coastal erosion, whereas the Azores islands encompass a wide spectrum of geohazards, comprising active volcanoes, earthquakes, tsunamis, landslides, flash floods, and coastal erosion.
... This geomorphological unit encompasses the Candeeiros (610 m) and Aire (679 m) mountain ranges and, in between the two, the Santo António and São Mamede plateaus (Fig. 6). Located roughly 75 to 110 km north of Lisbon, the ECM is the most important limestone massif of Portugal (Rodrigues 2020). ...
Sidewalks are not a trivial topic. They are a fundamental element of streets, the main public spaces in urban environments. In modern cities, paving materials are mostly artificial. In Portugal, stone-paved sidewalks are still prevalent and quite characteristic. Walking down a street, you do not need to lift your eyes off the ground to know you are in Portugal. In nineteenth-century Lisbon, a new type of pavement was introduced, the calçada portuguesa, the Portuguese artistic pavement mainly made with white and black limestone or basalt. This pavement is examined herein. More than simply highlighting its geological components, the different meanings and values of the calçada will be discussed from a semiotic perspective. It will also be debated how this geocultural heritage asset became key in shaping the city’s image. How it boosted Lisbon’s memorability, thus generating a strong sense of place among its inhabitants. So much so that these days the calçada patterns are everywhere, from table ware to post stamps, and even on socks. And yet, the long-term survival of the artistic pavement may be in peril. To ensure its preservation, the calçada portuguesa was recently included in the Portuguese Cultural Heritage list, a crucial step towards UNESCO world heritage status. However, in the document ratifying its newly attained status, the geological component of the pavement is mostly neglected. To maximize the conservation effort, the many meanings and heritage values of the calçada, namely the geological ones, should be actively involved, this work hopefully contributing to this end. Available online at https://rdcu.be/cUwk6
Predictive spatial analysis in archaeology refers to the use of geostatistical and computational techniques to assess the relationships between the distribution of archaeological sites and the environmental context. It is increasingly becoming an essential tool in scientific-academic research and rescue archaeology. In the interconnection between these two working contexts, this study aims to explore the advantages of applying an inductive approach, combining Geographical Information Systems (GIS) and geostatistical methods, to identify areas with different degrees of probability for the preservation of the Palaeolithic record in the lower valley of the Lis River (Leiria region, central Portugal). Topographic, hydrographic, geological, and geomorphological data were collected, processed, and integrated into a spatial database, using a GIS, to define the environmental conditioning factors. After applying a spatial multicollinearity procedure, slope, topographical position index, cost-weighted distance to access the watercourses, heat load index and lithology were chosen as input variables for the predictive modelling. Archaeological data, corresponding to the location of known Palaeolithic sites, were also retrieved from the official records. Three models were implemented using regression and multi-criteria methods; for Model 1 a Generalised Additive Model (GAM) was applied, while for Model 2 and Model 3 two distinct combinations of Probabilistic Frequency Ratio (PFR) and Analytic Hierarchy Process (AHP) were used. The spatial cross-tabulation between the obtained predictive maps and the location of the known Palaeolithic sites shows that all the models are acceptable. However, the combinations of PFR + AHP seem to evidence greater efficacy compared to the GAM. Model 3 offers the best performance (90%), followed by Model 2 (87%) and Model 1 (68%). Possible sources of inaccuracies in the input data and the spatial modelling results were critically discussed. Model 3 generated the most robust and reliable predictive prototype map. The maps produced can serve local and regional agencies as a complement and aid decision-making in public policies for spatial planning, and in the conservation/management of cultural heritage. These cartographic representations can provide quicker identification of areas of interest, for example, in the context of rescue archaeology, along with a substantial reduction in time and costs for project promoters, as well as helping in the environmental impact assessments.
Com a pretensão de classificar a escarpa dos Arrifes do Maciço Calcário Estremenho como património geomorfológico de relevância nacional, apresenta-se neste trabalho uma sistematização dos locais de interesse geomorfológico que lhe conferem singularidade e que contribuem para a sua valorização patrimonial. Do relevante património associado à escarpa, encontram-se os mais notáveis exemplos de geomorfologia estrutural e cársica, dos quais se destacam, pelo seu valor científico e didático-pedagógico, o sistema cársico da nascente do Almonda, o complexo flúvio-cársico do Alviela, o polje incipiente do Vale da Serra, os megalapiás do Pedrógão e do Chão da Serra, os afloramentos em que é possível observar o cavalgamento dos Arrifes, entre outros valores geomorfológicos, geológicos, ecológicos e culturais.
ABSTRACT The purpose of this paper is to present the systematization of the geomorphological interest sites which contribute for the uniqueness of Arrifes fault scarp in the Estremadura Limestone Massif as geomorphological heritage of national importance. There were inventoried 36 geomorphosites, including the most interesting examples of structural and karstic geomorphology with great scientific, didactic and geoturistic value. The more relevants sites are the Almonda karstic system associated with the spring of the Almonda River; the Alviela spring system, the incipient polje of Vale da Serra, the megakarren of Pedrógão and Chão da Serra, among other geomorphologic, geologic, ecologic and cultural values.
Les karsts portugais présentent des problèmes géomorphologiques, spéléologiques, hydrogéologiques et d'aménagement. Trois aspects essentiels sont envisagés : 1) la présentation des principaux travaux scientifiques publiés, en particulier depuis le travail pionnier d'Alfredo Fernandes Martins en 1949, sur le massif calcaire de l'Estremadura, qui a posé les bases des études de géomorphologie karstique au Portugal ; 2) la description des caractéristiques les plus importantes des principaux massifs karstiques de la bordure méso-cénozoïque occidentale (Estremadura et Sico) ; 3) la proposition de futures voies de recherches afin d'arriver à une compréhension plus détaillée et plus intégrée des karsts portugais.
The importance of scale during the different steps of geomorphological mapping is a well-discussed issue within the scientific community. Nevertheless, in association with the growing importance of geomorphosite assessment, evaluation, promotion and preservation, the use of different scales is yet to be clearly defined, especially because of the differences in spatial scale of the geomorphological phenomena. When talking about scale in geoheritage assessment, one must take into account the evaluation procedure. Based on previous methods we have outlined four major questions connected to the problematic of scale : What do we get by applying large scale geomorphological mapping ? Will it be reasonable to evaluate simultaneously micro and macro forms ? Should they be assessed separately by using different methods ? Which parameters should be considered ? Using the particular example of Fórnia, located at the Estremadura Limestone Massif, this paper discusses the process of geomorphological heritage evaluation and the problems resulting from its application on large scale surveys, emphasising its connection to site preservation.
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