Hydrogeological research of karst areas in Sardinia is often hindered by the discontinuity of superficial runoff and as a consequence the difficulty in performing dye tests. Recent combined speleological and hydrogeological surveys have brought to important scientific results in the carbonatic massif of Supramonte (Central-East Sardinia) where hydrological input and output points are well known and easily monitored. Not the same can be said for the adjacent Gulf of Orosei coastal karst area where inputs and outputs are relatively well known but difficult to monitor. From a geological point of view the Gulf of Orosei is characterised by a Mesozoic sedimentary sequence covering a crystalline Palaeozoic basement composed of granites and metamorphic rocks. The Mesozoic sequence starts with transitional alluvial-lacustrine conglomerates, sandstones and marls of the Genna Selole Formation (Bajocian-Bathonian) immediately followed by greyish dolostones, fossiliferous limestones and oolithic limestones, deposited in more or less shallow water characterised by coral reefs, back- and fore-reef and inner continental shelf environments (Bathonian- Berriasian). The whole Mesozoic sedimentary sequence has been folded and faulted during tertiary according to main N-S, NW-SE and NE-SW directions. The overall monocline eastwards tilted structure of the Gulf of Orosei greatly influences the hydrogeological asset, showing a general tendency for underground water to flow from West to East. Water flows in through various sinkholes in the western part of the area and flows out of the system through several submarine resurgences, the most famous of which are Bue Marino, Cala Luna, Bel Torrente and Ispignadorgiu springs. In the Southern part, where the granite basement crops out close to the sea, two other outflows are known, s’Erriu Mortu and Olcoé caves. Besides direct infiltration in the carbonate aquifer, some of the water is allogenic, coming from the Palaeozoic basement to the West. The best example is given by the Codula Ilune drainage basin, introducing water in to the Codula Ilune karst system through several sinkholes. Some dye tests have enabled to reveal at least partially the hydrogeological asset of the coastal aquifer, but especially the central-southern area remains a rebus. Recent cave surveys, carried out along the coast by German and Italian cave divers and in the contact area at almost 1000 m altitude by French and Sardinian cavers, have enabled to discover several active and very long submarine karst springs and contact-sinkholes that have induced to organise new dye tests. This paper resumes the hydrogeology of this important aquifer based on past researches and on the new data derived both from cave surveys and from dye tests.
The hydrogeological rebus of the coastal karst of Orosei (East Sardinia, Italy) / De Waele J.. - STAMPA. - 2:(2008), pp. 524-527. (Intervento presentato al convegno 14th International Congress of Speleology, della Union International de Spéléologie, il più importante congresso speleologico al mondo che si organizza ogni 4 anni. tenutosi a Kalamos, Greece nel 21-28 August 2005).
The hydrogeological rebus of the coastal karst of Orosei (East Sardinia, Italy).
DE WAELE, JO HILAIRE AGNES
2008
Abstract
Hydrogeological research of karst areas in Sardinia is often hindered by the discontinuity of superficial runoff and as a consequence the difficulty in performing dye tests. Recent combined speleological and hydrogeological surveys have brought to important scientific results in the carbonatic massif of Supramonte (Central-East Sardinia) where hydrological input and output points are well known and easily monitored. Not the same can be said for the adjacent Gulf of Orosei coastal karst area where inputs and outputs are relatively well known but difficult to monitor. From a geological point of view the Gulf of Orosei is characterised by a Mesozoic sedimentary sequence covering a crystalline Palaeozoic basement composed of granites and metamorphic rocks. The Mesozoic sequence starts with transitional alluvial-lacustrine conglomerates, sandstones and marls of the Genna Selole Formation (Bajocian-Bathonian) immediately followed by greyish dolostones, fossiliferous limestones and oolithic limestones, deposited in more or less shallow water characterised by coral reefs, back- and fore-reef and inner continental shelf environments (Bathonian- Berriasian). The whole Mesozoic sedimentary sequence has been folded and faulted during tertiary according to main N-S, NW-SE and NE-SW directions. The overall monocline eastwards tilted structure of the Gulf of Orosei greatly influences the hydrogeological asset, showing a general tendency for underground water to flow from West to East. Water flows in through various sinkholes in the western part of the area and flows out of the system through several submarine resurgences, the most famous of which are Bue Marino, Cala Luna, Bel Torrente and Ispignadorgiu springs. In the Southern part, where the granite basement crops out close to the sea, two other outflows are known, s’Erriu Mortu and Olcoé caves. Besides direct infiltration in the carbonate aquifer, some of the water is allogenic, coming from the Palaeozoic basement to the West. The best example is given by the Codula Ilune drainage basin, introducing water in to the Codula Ilune karst system through several sinkholes. Some dye tests have enabled to reveal at least partially the hydrogeological asset of the coastal aquifer, but especially the central-southern area remains a rebus. Recent cave surveys, carried out along the coast by German and Italian cave divers and in the contact area at almost 1000 m altitude by French and Sardinian cavers, have enabled to discover several active and very long submarine karst springs and contact-sinkholes that have induced to organise new dye tests. This paper resumes the hydrogeology of this important aquifer based on past researches and on the new data derived both from cave surveys and from dye tests.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
