Imp.De Waele et al. GEOSITES AND LANDSCAPE EVOLUTION OF THE TACCHI: AN EXAMPLE FROM CENTRAL-EAST SARDINIA Jo De Waele, Felice Di Gregorio, Roberto Follesa & Giuseppe Piras Department of Geology, Via Trentino 51, 09127 Cagliari - E-mail: geoam@unica.it ABSTRACT: J. De Waele et al., Geosites and landscape evolution of the Tacchi: an example from central-east Sardinia. (IT ISSN 0394- 3356, 2005). The Tacchi area is a landscape unit located to the south of the Gennargentu mountains in the central-eastern part of Sardinia, mainly characterised by table-like carbonatic Mesozoic mountains, locally named "Tacchi", unconformably overlaying a Paleozoic peneplain constituted of Cambro-Silurian silty and sandy shales. The Tacchi are the result of a complex geologic history, deriving from a unique and widespread Jurassic carbonatic cover that was split up in clods due to epirogenetic movements, faulted, uplifted or lowered and successively eroded and isolated by fluvial processes. The palaeo-geography and the evolution of this landscape can be explained using several different geosites of the area, such as the San Giorgio Gorge, the Su Marmuri cave and the Monte Tisiddu Tacco that, united in a network of geosites, can bring to an improvement of the tourist offer of this interesting area. Besides these geosites many other places of geological interest such as the Riu Pardu river and its abandoned villages of Gairo vecchio and Osini vecchio (partially destroyed by phenomena of hydrogeologic hazard during the XXth century and especially following an exceptional rainfall in October 1951), several waterfalls and travertine deposits can be mentioned, completing an already rich and varied landscape. The Project aims to the conservation of the geodiversity and the multiple valences present in the territory, and comprises the valorisa- tion of the sites of geological interest in line with the principles of a sustainable development. This valorisation foresees the realisation of a local network of geosites connected to the system of Natural Monuments instituted by the Regional Law 31/1989, the arrange- ment of equipped pathways, the elaboration of explicative documents and panels in which geology, geomorphology, karst landscape, biology, archaeology and human settlements and processes are described. Some panels will be focalised on the reading of the land- scape and its evolution (Lecture du paysage) in which geological, geomorphological and environmental aspects collimate to form an educational model of great suggestion. This proposal of valorisation of these geosites, grouped in a network, could well be applied to other areas, and the Authors hope that the regional and local stakeholders will, in the near future, participate in the geo-environmental preparation of their territory, giving an important service to the many tourists that come and visit the Tacchi area. RIASSUNTO: J. De Waele et al., Geositi e evoluzione del paesaggio dei Tacchi: un esempio dalla Sardegna centro orientale. (IT ISSN 0394-3356, 2005). L'area dei Tacchi è un'unità di paesaggio situata a Sud del massiccio del Gennargentu (Sardegna centro-orientale), caratterizzata dalla presenza di altopiani carbonatici Mesozoici, conosciuti con il nome locale di "Tacchi" o "Tònneri", che coprono in discordanza il pene- piano Paleozoico costituito da metarenarie e metasiltiti di età Ordoviciano-Cambriana. I Tacchi sono il risultato di una complessa evolu- zione geologica e derivano da un'unica ed estesa copertura carbonatica Giurassica suddivisa in vari frammenti a seguito di movimenti epirogenetici Plio-Pleistocenici dai quali vennero fratturati, sollevati o abbassati e successivamente erosi e isolati da processi fluviali, gravitativi e meteorici. La paleogeografia e l'evoluzione di questi paesaggi possono essere spiegate in maniera eloquente osservando diversi geositi di questa regione, quali la Gola di San Giorgio, la Grotta di Su Marmuri e il Tacco di Monte Tisiddu che, collegati a rete possono creare un forte motivo di richiamo per un turismo naturalistico e culturale per questa regione dell'interno della Sardegna. Oltre a questi geositi il territorio contiene altri validi temi di interesse geologico e geomorfologico come la Valle del Riu Pardu e i suoi villaggi abbandonati di Gairo ed Osini Vecchio (parzialmente distrutti da frane avvenute nel XX secolo e soprattutto dopo le forti piogge nell'ottobre del 1951), diverse cascate temporanee e depositi di travertino o di terre rosse di decalcificazione e valli sospese che com- pletano il richiamo verso questo paesaggio di per sé già ricco e vario. La presente ricerca ha come obiettivo la conservazione della geodiversità e delle molteplici valenze di questo territorio e si propone la valorizzazione dei geositi di maggiore interesse in linea con i principi dello sviluppo sostenibile. Tale valorizzazione prevede la realizza- zione, d'intesa con le Autorità locali, di una rete locale di geositi connesso con il sistema dei Monumenti Naturali istituiti dalla Legge Regionale 31/1989, la costruzione di sentieri equipaggiati, l'elaborazione di cartografia tematica e pannelli esplicativi nei quali geologia, geomorfologia, paesaggio carsico, fauna, flora ed archeologia vengono illustrati in forma chiara ed accessibile secondo i criteri di una corretta divulgazione scientifica. In particolare alcuni di questi pannelli saranno focalizzati alla lettura del paesaggio nella quale gli aspetti geologici, geomorfologici ed ambientali collimino a delineare un modello evolutivo di notevole interesse per l'educazione ambientale e nello stesso tempo di grande suggestione dal punto di vista percettivo. La proposta di valorizzazione di tali geositi, raggruppati in una rete, è concepita per integrarsi con l'insieme dei beni geografico-fisici presenti nelle aree limitrofe. Tutto questo potrà contribuire a fornire un servizio importante ai numerosi turisti che visitano le coste e che possono trovare nei paesaggi dei Tacchi itinerari geotematici di grande interesse. Keywords: Tacchi, Karst, Jurassic, Dolomitic limestones, Geosites, Ogliastra. Parole chiave: Tacchi, Carso, Giurese, Calcari dolomitici, Geositi, Geoturismo, Sardegna. Il Quaternario Italian Journal of Quaternary Sciences 18(1), 2005 - Volume Speciale, 213-222 the area of Ulassai and Osini, in the central-eastern part of Sardinia. The three chosen sites are the San Giorgio Gorge, the Su Marmuri show cave and the Monte Tisiddu Taccu (Fig. 1). Aside the description of these geological monu- 1. INTRODUCTION In this study, performed in the framework of the National Project on Geomorphological sites, the Authors describe the three most important geosites of 214 J. De Waele et al. Fig. 1 - Site orientation. Area di ricerca. ments the Authors propose the conservation of the multiple valences present in the territory, comprising the valorisation of the sites of geological interest in line with the principles of a sustainable development, also through the realisation of a local network of geosites connected to the system of Natural Monuments institu- ted by the Regional Law 31/1989. This proposal of valorisation of these sites of geo- logical and geomorphological interest, grouped in a local network, could well be applied to other areas ending up with the realisation of a Regional System of Geosites, and the Authors hope that the regional and local stakeholders will, in the near future, participate in the correct geo-environmental management of their ter- ritory, giving an important service to the cultural educa- tion of the local people and to the many tourists that come and visit the Tacchi area and the central-eastern coast of Sardinia. 2. METHODOLOGY Geosites and geomorphosites have in some way been recognised as cultural heritage by the “Convention of the Protection of World’s Culture and Nature” signed by almost 160 countries and adopted by UNESCO during the general conference of Paris in 1972. This Convention gave also birth to the World Heritage List of those sites that have “exceptional uni- versal value” from a historical, artistic or scientific point of view. From the end of the 70’s beginning of the 80’s the first inventories of “naturalistic sites” are produced in Italy. In this first phase, that can easily be defined preli- minary, the study and the cataloguing of geological sites does not have well defined and univocal rules. In 1991 the first European meeting on Geosites is held at Digne-les-Bains (France) during which the “Declaration of Rights of the Earth’s Memory” is presented. In the same occasion the methodology for the systematic sur- vey of geological and geomorphological sites on a regional scale is also proposed by Barca & Di Gregorio (1991) with the aim to assure a uniform study and eva- luation of such sites. At this scope a file sheet is propo- sed that is subdivided in four sections: 1) identification, 2) main and integrative parameters of evaluation, 3) degree of scientific and historic-cultural importance, 4) state of use and tutelage. The file sheet is also charac- terised by the presence of an extract of topographical map and further information on the geographical loca- tion. The Authors suggest to arrive at a objective way of survey that do not take too much into account the aesthetic criteria normally used in describing natural sites. Contemporary Casto et al. (1991) produce a type of sheet file used for the cataloguing of geosites and geomorphosites in the provinces of Rome and Rieti. This sheet file, even though containing a precise loca- tion of the described sites and containing also two new elements, such as photographs of the site useful to evaluate modification and or destruction, and a brief description, seems to be too subjective and too depen- dant on the surveyor (Marchetti, 1999; Poli, 2003). From the second half of the 90’s the studies and the methodologies continuously improved and also on a national level starts to form the idea of making a uniform methodology and to construct a sheet file based on the positive earlier experiences made in various Italian regions. The new sheet files for identifi- cation and classification are conceived and realised in order to be inserted in GIS systems, in the framework of regional, national and international projects for geosi- tes census. Since 1996 the International Union of Geological Sciences (IUGS) started the GEOSITES research pro- gram in the framework of UNESCO (Wimbledon, 1996). Finally, in august 2001, during the IVth International Conference of the International Association of Geomorphologists, the Working Group “Geomor- phological sites: research, assessment and improve- ment” has been instituted, taking experience from the Italian national COFIN Project "Geosites in the Italian Landscape: research, evaluation and valorisation". It is in the framework of all these activities that the term “geomorphosites” has been coined (Panizza, 2001) and that new methodologies for cataloguing have been propo- sed (Carton et al., 2003). A sheet file elaborated by the Agency for the Protection of the Environment and Territory (APAT, former National Geo- logica Service) and by the Centre for Documentation of Geosites of the University of Genoa, still under experimenta- tion, has been used in this paper. This sheet file is subdivi- ded in fourteen sections further subdivided in sub-sections, and accompanied by a second so- called “specialistic” sheet file. The presence of sub-sections in most of the sections enhances the comprehension of the geosi- tes giving a more detailed infor- mation. This new type of sheet file, a part of being the most recent and most developed one, is also the one the better sati- sfies the requirement both for the analysis and the input of geomorphosite data, and has also been adopted for the sur- veying of sites in Sardinia. 3. GEOLOGY OF THE TACCHI REGION The Tacchi area is a land- scape unit located to the south of the Gennargentu mountains in the central-eastern part of Sardinia. This unit is mainly cha- racterised by table-like carbona- tic Mesozoic plateaus, locally named "Tacchi", overlaying with 215Geosites and landscape ... an unconformity the Palaeozoic basement constituted of Middle Cambrian-Ordovician quartzitic-micaceous metasandstones, quartzites, quartzitic phyllites and metasiltstones (Gennargentu Formation) peneplained during Permian-Triassic (Fig. 2). This long continental period is clearly identified by the local presence of fer- ruginous phyllites with limonite nodules generally named "Ferro dei Tacchi", in the past cultivated for the iron content (Marini, 1984). The beginning of the Jurassic succession is cha- racterised by a more or less well preserved succession of continental fluvial, delta and lacustrine sediments composed of a quartzite conglomerate, sandy and clayey lenses and, in some places, containing lignite seams or clays with vegetal remains (Barca & Palmerini, 1973; Fazzini et al., 1974). According to Dieni & Massari (1985) these sediments are comparable to the complete succession described at Genna Selole and attributed to Bajocian-Bathonian (Genna Selole Formation). Palynological studies of these sequences also suggest the age of the black clays with plant remains to be Bajocian-Bathonian (Del Rio, 1985). This continental Fig. 2 - Stratigraphic column of the sedimentary sequence of the Tacchi in Central-East Sardinia. Colonna stratigrafica della sequenza sedimentaria dei Tacchi nella Sardegna centro-orientale. 216 J. De Waele et al. Fig. 3 - Geolo- gical and geo- m o r p h o l o g i c a l map of the study area with the three geosites. Carta geologica e geomorfologi- ca dell'area di studio con i tre geositi. 217Geosites and landscape ... 218 J. De Waele et al. sequence is immediately followed by a marine succes- sion of dolomitic limestones, in the lower part disposed in well stratified decimetric and metric beds and upwards becoming more massive, upon which are locally preserved about 30 meters of white coralline and oolithic limestones for a total thickness of over 300 meters. Recently the lower dolomitic succession has been attributed to the Dorgali Formation, mostly of Bathonian-Callovian age, while the uppermost more calcareous part represents sediments of the Monte Tului and Monte Bardia Formations of Callovian- Kimmeridgian age (Barca & Costamagna, 2000, Barca et al., 2000a; 2000b). This unique and widespread Jurassic carbonatic cover emerged form the sea at the end of Mesozoic and during Tertiary the landscape started evolving with the formation of valleys with prevalent direction NNE-SSW that eroded the surrounding Palaeozoic mountains. These palaeo-valleys are still recognisable on top of many Tacchi where large closed depres- sions contain remnants of fluvial deposits with meta- morphic and quartzite elements (e.g. polje of San Giorgio) and suspended valleys occur along the bor- ders of the Tacchi. Towards the end of Tertiary the fluvial erosion of the Palaeozoic metamorphosed sediments, enhanced by the epirogenetic movements of the Alpine orogeny, started cutting the dolomitic limestone plateau in several separated blocks along the major tectonic directions (NNW-SSE, NNE-SSW and E-W), causing an inversion of relief. From this period to now the individual Tacchi started evolving separately and the karst features show slight diffe- rences even between neighbouring table-mountains. From a geomorphological point of view the Tacchi of Osini and Ulassai are mainly characterised by multiple kar- stic forms such as sinkholes, dry valleys, larger depressions (macrodolines), caves, stone forests and other spectacular r u i n - l i k e e r o s i o n a l k a r s t i c forms; grykes, solution pans, karren and other minor karst phenomena are less developed (Marini & Ulzega, 1973; Bianco & De Waele, 1992; Ardau & De Waele, 1999; Bartolo et al., 1999). The valleys that divide the Tacchi, some of which have rapidly evolved since Pliocene (Ulzega & Marini, 1977), are characterised by unstable flanks where landslides have repea- tedly occurred in concomitance with heavy rainfalls (e.g. Rio Pardu) (Maxia et al., 1973; Ciccu et al., 1994; Ginesu, 1999). 4. THE GEOSITES The most typical landform of the region is the so-called Taccu or Tonneri, table-like car- bonatic mountain being the result of the geomorpholo- gic processes that have changed the landscape since Tertiary. These geomorphic testimonies constitute the remains of a continuous dolomitic limestone platform that covered most part of central-east Sardinia, cut in many independent outcrops situated at varying heights by tectonic movements and erosion and forming a typi- cal example of inversion of relief. At the basis and along the borders of these mountains, in some places, the Jurassic transgression sediments of the Genna Selole Formation can be observed and the traces of the ancient excavations for lignite can still be seen along the path that runs at the basis of Tisiddu. On the contact of dolomitic limestones and Palaeozoic basement many karst springs are situa- ted, most of which are used for the orchards or for public fountains (Ardau et al., 1993). In figure 3 a geolo- gical and geomorphological map of the region is given in which the three geosites are clearly reported. One of the most typical Tacchi is Monte Tisiddu near Ulassai; this carbonatic plateau, with a surface of about 1.5 km2 and walls of 50 to 100 m height, is con- trolled by the Forestry Department, and shows intere- sting and spectacular karstic landforms such as sinkho- les, caves etc. (Bianco & De Waele, 1992) (Fig. 4). There are only four pathways that allow to ascend the carbonatic plateau, while along almost the entire perimeter of Tisiddu vertical walls form a natural inac- cessible barrier. These ancient tracks can be followed by hikers and allow to make walks of scientific and didactic interest in a mostly uncontaminated nature and with diversified and unusual panorama's on the underlying Riu Pardu and Riu Ulassai valleys and on the villages of Ulassai and Jerzu. Once on Tisiddu the land- Fig. 4 - Monte Tisiddu Tacco: A panoramic view from Bruncu Cococcia towards the Northwest: on the first plan to the left the vertical walls of Bruncu Casteddu (Monte Tisiddu) and in the background the other smaller Tacchi of Jerzu, all covering the Palaeozoic basement profoundly incised by the Tertiary and Quaternary valleys (Photo Jo De Waele). Tacco di Monte Tisiddu: Vista panoramica da Bruncu Cococcia verso Nordovest; in primo piano sulla sinistra si vedono le pareti verticali di Bruncu Casteddu, mentre sullo sfondo si notano gli altri piccoli tacchi di Jerzu, che coprono anch'essi il basamento paleozoico intensa- mente inciso da valli terziarie e quaternarie (Foto Jo De Waele). scape is dominated by karstic landforms such as doli- nes, dry valleys, caves and karst pinnacles. From the highest top of the mountain (Bruncu Matzeu, 957 m a.s.l.) a spectacular and widespread view stretches from the Tyrrhenian Sea to the Gennargentu mountains, while the nearby Tacco of Ulassai dominates the Riu Pardu valley. The river Pardu flows along a NW-SE alpine fault and deeply cuts the Palaeozoic basement. This rapid deepening by erosion is related to the Plio-Quaternary uplifting of the whole area that also caused the capture of Rio Pardu approximately 3 km downstream of Ulassai. This capture determines an abrupt change of direction from NW-SE to NE-SW. The rapid geo- morphologic evolution of the valley has caused mass movements, mainly along tension cracks, provoking a whole generation of Quaternary landslides (Ulzega & Marini, 1977; Arisci et al., 2000). The most impressive of these tension cracks is the San Giorgio Gorge, across which passes a road that connects the village of Osini with the carbonatic high plateau rich in karst forms, interesting endemic flora and archaeological remains (Fig. 5). The San Giorgio Gorge forms the natural gateway to the plains of the karstic Tacco of Ulassai and is one of the Island's Natural Monuments instituted by the Regional Law n°31/1989. In this narrow gorge, wide only 8 m in some places for a height of 40 m, have been found archaeological remains of a roman settlement. Some pathways lead up into the mountain to the eastern flank of this tension crack from where the panorama dominates the entire Riu Pardu valley with its abandoned villages of Gairo and Osini (partially destroyed by landslides during the XXth cen- tury and particularly after exceptional rainfalls in October 1951), the reconstructed new villages and ancient and recent landslides and rockfalls. A cou- ple of hundreds of meters to the north, along the high dolomite walls of the Taccu, a suspended valley testimonies an ancient Late-Tertiary hydrography. But the most important proof of an ancient drainage basin on the Tacco is the enor- mous sinkhole and underground river passage of the Su Marmuri cave near Ulassai, open to public from April to October and accounting for more than 20,000 visitors/year (Fig. 6). The cave entrance is characterised by a collapse doline which has uncovered a very big natural tunnel. After a descent of almost 40 meters along a stairway con- structed in the late 50's the cave passage becomes hori- zontal and is characterised by a angular development caused by the intersection of fractures along which the underground river has eroded forming this gigantic tunnel. The enormous natural underground river pas- sage of Su Marmuri ends deep into the carbonatic plateau after 219Geosites and landscape ... Fig. 5 - San Giorgio gorge: Spectacular view of the dolomite peak at the centre of the gorge, isolated by tension cracks, around which the tarmac road that connects the village of Osini with the karstic plateau of Tacco of Ulàssai turns (Photo Jo De Waele). La gola di San Giorgio: Vista spettacolare del picco dolomitico che si erge al centro della gola, isolato da tension cracks, attorno al quale gira la strada asfaltata che collega l'abitato di Osini con l'altopiano carsico del Tacco di Ulàssai (Foto Jo De Waele). a total length of almost 900 meters. In the median part of the cave the floor is constituted of thousands of rim- stone pools (Fig. 6), followed by a giant room with impressive flowstones, stalagmites and stalactites. Close to the entrance lay two fresh-water lakes nearby which hibernate more than 10,000 bats (Miniopteris schreibersi NATT.) during winter. Besides this colony of bats, among the greatest known on the island, the cave is very important for its cave dwelling fauna with rare endemic Arthropods such as the Beetle Ovobathysciola gestroi FAIRMAIRE (the first troglobius animal discovered by Raffaello Gestro in Sardinia at the end of the 19th century) and the Chilopod Lithobius doderoi SILVE- STRI, both of which are typical of the Tacchi region (Bartolo et al., 1983; De Waele, 1996; Bartolo et al., 1999). 220 Fig. 6 - Plan of the Su Marmuri cave that takes its name from the characteristic concretioning (marble), with the environmental monito- ring system proposed by Ardau & De Waele (1999) (Survey by Gruppo Speleo-Archeologico Nino Businco Ulàssai). Pianta della grotta di Su Marmuri con il sistema di monitoraggio proposto da Ardau & De Waele (1999): la grotta prende il nome dal- l'abbondante e massiccio concrezionamento. (Rilievo dal Gruppo Speleo-Archeologico Nino Businco Ulàssai). J. De Waele et al. 5. PROPOSAL OF CONSERVATION AND VALORISA- TION Monte Tisiddu, the gorge of San Giorgio and the Su Marmuri cave constitute all together an extraor- dinary example of the Tertiary-Quaternary landscape evolution of the Mesozoic carbonatic platform that cha- racterise the central eastern part of Sardinia: the first, with its dolines, the dry valleys and the karst pinnacles as a testimony of a well developed and mature surface karst; the second representing the tectonic and gravita- tional phenomena and correlated to the fragmentation of the borders of the forming carbonatic plateaus and the third emblematically testifying the underground karst evolution that started before the fragmentation of the emerged carbonate platform. To protect and to valorise these three geosites the Authors propose the crea- tion of a local network of geolo- gical monuments, connected to a regional System that was star- ted with the institution of the Regional Natural Monuments of the Regional Law 31/1989. For these purposes a program of detailed geological-stratigraphi- cal and geomorphological sur- vey has been foreseen that aims to put in evidence their intrinsic characteristics, essential for their appropriate valorisation and a management compatible with their effective carrying capacity, in particular for the Su Marmuri cave where a meteoro- logical study will monitor the subterranean environment. After this phase, in collabo- ration with the local Authorities, illustrative material will be pre- pared (booklets, CD Rom, synthetic thematic maps, etc.) in order to document the elements of interest of these geological landscapes and geosites and, ultimately, a series of explicative panels, containing the educatio- nal information, and signals will be positioned to enable their correct utilisation. Aside these initiatives, anyhow, for some of these geo- sites (Monte Tisiddu, Gorge of San Giorgio) it will be necessary to enforce the measures of pro- tection of the territory and the landscape, and also the forma- tion of local guides that are pre- pared to explain the interest and the importance of these sites and of the network of geo- morphological sites in a regional and in a national context. ACKNOWLEDGEMENTS This research has been performed in the framework of the National Project COFIN 2001-2003 "Geositi nel Pae- saggio italiano" which local re- search group is co-ordinated by 221 Fig. 7 - Su Marmuri cave: "Galleria delle Vaschette"(Passage of the Gours) in the central part of the cave has developed along a NW-SE fracture, is characterised by vertical and rectilinear walls widened by underground fluvial erosion processes, and its floor is at present completely covered with thousands of gours filled with water, some of which still contain cave pearls (Photo Gabriela Pani). La grotta di Su Marmuri: "Galleria delle Vaschette", nella parte centrale della cavità è impostata su una frattura NO-SE e si caratterizza per le pareti rettilinee e verticali allargate da processi d'erosione fluviale. Il pavimento è completamente ricoperto da migliaia di vaschette riempite d'acqua, alcune delle quali contengono perle di grotta (Foto Gabriela Pani). Geosites and landscape ... Prof. Antonio Ulzega and Prof. Felice Di Gregorio of the University of Cagliari. The Authors would like to thank André Ozer and an anonymous referee for their useful comments and advice. REFERENCES ARDAU F. & DE WAELE J. (1999) - Geosites of the Tacchi area (central-east Sardinia, Italy) - In: D. Barettino, M. Vallejo & E. Gallego (eds.), Towards the Balanced Management and Conservation of the Geological Heritage in the New Millenium, Madrid, pp. 87-93. ARDAU F., BIANCO L., DE WAELE J. & VERNIER A. 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