Geomorphological Map of the Salento Peninsula (southern Italy)

Transcription

1 Journal of Maps, 2007, Geomorphological Map of the Salento Peninsula (southern Italy) FRANCESCO FORTE and LUIGI PENNETTA Sezione di Geografia fisica e Geomorfologia Dipartimento di Geologia e Geofisica, Università di Bari via E. Orabona 4, Bari, Italy; geoforte@libero.it (Received 21 st July 2006; Accepted 20 th February 2007) Abstract: A geomorphological map of the Salento peninsula is presented at a 1:120,000 scale. The map was compiled by combining the available geological and geomorphological information with data derived from: (a) Digital Terrain Model interpretation, (b) an analysis of aerial photographs at a 1:33,000 scale and (c) a geomorphological fieldwork. The Salento peninsula, the southeast portion of the Apulia region in southern Italy, shows peculiar geological and geomorphological characteristics: it is a karstic area, nearly flat, with subsiding zones (Graben) between small ridges (Horst). They were originated by tectonic stresses, resulting in scarps of normal faults and, therefore, in macroscale structures. In addition, some exogenous (meso- and microscale) landforms were originated on the Graben structures, where there are permeable miocenic, pliocenic and pleistocenic sediments with muddy-clayey strata and others which stand on carbonatic substratum, represented by limestone, dolomitic limestone and dolomite, main lithologies of the Horst structures. The results are presented on the map, using a geographic information system (Arcview software). In addition, a digital terrain model, produced from a spatial analysis of contour lines, provides a general topographical setting. ISSN

2 1. Introduction In the past, a methodical investigation based on the recognition of specific landforms has been performed by many authors, in varying scientific areas (Mastronuzzi and Sansò, 2002; Giuliani, 2000; Beccarisi et al., 2003; Parise and Pascali, 2003; Selleri et al., 2003; Delle Rose et al., 2004), including a geomorphic sketch map (Ricchettti, 1988). The principal purpose of this research is to map micro-, meso- and macroscale landforms of the Salento peninsula, using literature data and data derived from a digital terrain model (DTM), analysis of aerial photographs and geomorphological fieldwork. The Salento peninsula, the southeast portion of the Apulia region in southern Italy, covers 7,000 km 2 and stretches over 150 km between the Ionian and Adriatic seas. The peninsula includes two extreme geographical points: the Punta Palasca, near Capo d Otranto and the Punta Rstola, near Capo Santa Maria di Leuca, in the final strip of the Apulia region. 2. Geological and Climatic Settings The Salento peninsula is a flat area with low elevations above sea level: in fact, it is characterized by small ridges, the so-called Serre salentine. They were originated by tectonic stresses acting during the Cretaceous period until the Upper Pleistocene period, mainly along SSE-NNW and SSW-NNE directions, resulting in scarps of normal and transcurrent faults and the anticlines of Nociglia-Galatina (Ambrosetti et al, 1984). Geologically, the substratum of the Salento peninsula is a carbonatic shelf, 6,000 m thick, represented by limestone, dolomitic limestone and dolomite strata, originating from the Jurassic to the Upper Cretaceous (Maastrichtian) periods (Ricchetti, 1988). In the areas between the ridges, there are permeable miocenic, pliocenic and pleistocenic sediments with muddy-clayey strata which stand on limestone, dolomitic limestone and dolomite (Ciaranfi et al., 1988; APAT-DDS, 2004; Tropeano et al., 2004). With regard to the climate of the Salento peninsula, it can be defined as mediterranean. The main winds are hot: the Scirocco, SE wind, very humid because it comes from the eastern basin of the Mediterranean sea and the Libeccio, SW wind, drier because it releases its humidity on the mountains of Sicily and Calabria, before reaching the western coast of Salento. In the summer, instead, NNW wind occurs more frequently 174

3 (Carrozzo and Ruggero, 1989). The annual rainfall is not homogeneous, registering in the eastern part a mean value of 790 mm/year and, in the western part, only 590 mm/year. However, the average rainfall has strongly decreased, giving rise to a long period of drought; Zito (1989) demonstrates that drought periods of 50 consecutive days occur very frequently in the summer months. Actually, therefore, the climatic characteristics of the Salento peninsula can be defined as almost semi-arid (very high temperatures and insufficient rainfall): the dryness is concentrated in summer, whereas the rainfall, the primary cause of flood occurrences, is concentrated in autumn-winter, rarely at the end of summer (Arnell, 1999). 3. Methods The data available for this study encompassed: Geological map of Murge and Salento (Ciaranfi et al., 1988); Land use map of the Project Corine-Land Cover (Project Corine-Land Cover, 2000); Past studies of parts of the Salento peninsula (Giuliani, 2000; Mastronuzzi and Sansò, 2002; Beccarisi et al., 2003; Parise and Pascali, 2003; Selleri et al., 2003; Delle Rose et al., 2004). The geomorphological fieldwork, aerial photographs and DTM analyses, play important roles in mapping landforms and their characteristics: particularly, geomorphological fieldwork and DTM analysis have been carried out in order to have a preliminary overview of the topography and lithology of the Salento peninsula. The geomorphological analysis was carried out was follews: 1. Direct mapping during geomorphological fieldwork 2. Indirect mapping using: Interpretation of aerial photographs DTM analysis 175

4 Data from the geomorphological fieldwork was based on direct topographical analysis and, therefore, on the determination of (micro- and mesoscale) landforms. They were processed and transferred from digital photographs to topographical maps at a 1:25,000 scale. Also, aerial photographs at a 1:33,000 scale, acquired during aerial surveying in May 2000, have helped to identify tectonic structures and macroscale exogenous landforms. Information obtained from aerial photographs completes the geomorphological fieldwork. Finally, a DTM was interpolated using ESRI ArcView from original 5 m contour lines, with a cell size of 100 m. This allowed visualisation of the general topographical setting of the Salento peninsula. All the digitised landforms were exported as shapefiles and compiled in a single geomorphological map. 4. Results and Discussion The methodology adopted for geomorphological analysis has given very interesting results that show how many landforms have been conditioned by geological substratum and tectonics. An example is given by an old drainage network, distinguished in two kinds: the first is an endoreic drainage network, comprising relatively wider and hierarchized streams, the so-called Asso, which flows on impermeable sediments. It is asymmetric, aligned along a SSE-NNW direction and stands on the Graben between the Casarano-Galtone ridge and the Nociglia-Galatina anticline. The second is an exoreic drainage network, independent and deep, represented by small but not hierarchized streams which flow from the Horst structures nearer to the coast towards the Ionian and Adriatic seas (Forte et al., 2005, 2006). Karstic phenomena, composed of 280 natural sinkholes, 1,172 dolines with a range of variable density from 0 to 7 per square kilometer and 223 caves, are located more frequently on carbonatic substratum of the Horst structures, represented by limestone, dolomitic limestone, and dolomite, less frequently on miocenic, pliocenic and pleistocenic sediments which characterize the Graben structures (Ricchetti, 1988; Mastronuzzi and Sansò, 1991; Giuliani, 2000; Beccarisi et al., 2003; Parise and Pascali, 2003; Selleri et al., 2003; Delle Rose et al., 2004). Recent huge dunes, located in the coastal areas of the E and W parts of the peninsula, show that the wind energy is very high and coastal landforms, such as marine terraces, represent old sea level stillstands, occurred during the Pleistocene period 176

5 (Mastronuzzi and Sansò, 2002). In addition, detailed geomorphological fieldwork along the coast allowed mapping of receding (beaches and cliffs) and advancing (beaches) areas. The Corine-Land Cover Project (2000) has provided land use data to represent regions of infrastructure, such as quarries, wharfs and breakwaters. With regard to gravitational landforms, topplings and falls, resulting from marine erosion, occur frequently along the coast and, rarely, below ridges characterized by colluvial fans and debris heaps. In these areas, alluvial fans, resulting as stratum deposits, represent sedimentation landforms, made by old drainage networks, whose waters flowed underground to develop the karstic caves. The landforms of the Salento peninsula are set into a landscape of Horst and Graben structures, characterized by subsiding areas and tectonic scarps, marked on the geomorphological map with symbols of strike and dip of fault. 4. Conclusions The landscape complexity, represented by subsiding areas and small ridges, and the distribution of complex and different exogenous landforms are justified by geological substratum and tectonic characteristics. Such analysis represents a very important basis in order to carry out any kind of environmental study but it should be completed with other more detailed data. Software The software used for geological and geomorphological mapping was ArcView GIS. The DTM was produced as a triangular irregular network (TIN) from original contour lines. 177

6 Acknowledgements The authors thank the technicians of the Municipal Technical Offices for their interest and the technicians of the SIT (Sistema Informativo Territoriale) Office of Lecce Province for their help obtaining digital aerial photographs. Special thanks to the librarians of Sigismondo Castromediano Library of Lecce Province and Library of Geology and Geophysics Department, University of Bari, for their availability, obtaining information about the geological and geomorphological characteristics of the study area. References AMBROSETTI, P., BARBERI, F., BARTOLINI, C., BOSI, C., CARRARO, F., CIARANFI, N., MEZZANI, L., PANIZZA, M., PAPANI, G. and ZANFERRARI, A. (1984) Mappa Neotettonica d Italia, scala 1:500,000. CNR - Progetto Finalizzato Geodinamica, Sottoprogetto Neotettonica. APAT-DDS (Agenzia per la Protezione dell Ambiente e per i servizi Tecnici, Dipartimento Difesa del Suolo) (2004) Carta geologica d Italia interattiva (Fogli 203, 204, 213, 214, 215 e 223), scala 1:25,000, Roma, Italy [online]. Available from: ARNELL, N. W. (1999) The effect of climate change on hydrogeological regimes in Europe: a continental perspective. Global Environmental Change, 9, BECCARISI, L., CACCIATORE, G., CHIRIACÒ, L., DELLE ROSE, M., GUIRI, F., MARRAS, V., QUARTA, G., RESTA, F. and SOLOMBRINO, P. (2003) Le Vore di Barbarano: note descrittive e speleogenesi. Thalassia Salentina, 26, CARROZZO, M. T. and RUGGERO, L. (1989) Descrizione climatica e paleoclimatica della Puglia. In Proceedings of the First Workshop Clima, Ambiente e Territorio nel Mezzogiorno, Taormina, Italy, pp

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