Holecene sea-level chamges and palaeoclimatic reconstruction in central-north Sardinia: preliminary results

For its relative stability during Quaternary (from the isotopic stage 5 about 125,000 years ago) and the presence and fairly good conservation of several palaeo-environmental indicators Sardinia and its continental shelf constitute a key area in the Mediterranean for palaeoclimate and sea-level change studies. Even though many factors influence sea level rise such as global warming, land subsidence, isostatic movements etc. a careful and combined use of several markers can give useful and reliable information. At present, many markers can be used for the reconstruction of the past climate, and several of these have already been applied in Sardinia. First of all classic and submarine geomorphology can help in understanding environmental change at a large scale (ANTONIOLI et alii, 2000). Submerged ancient coastlines (beachrocks) have been detected all around the Island at different depths, and many of these have been studied from a geomorphological and sedimentological point of view (BRAMBATI & DE MURO, 1992). In some areas where sedimentary carbonates are lacking in the geological sequence (e.g. the granitic northern Sardinian coast) the study of the carbonatic cements of the beachrocks allows to date isotopically the interphases of Sea Level stationarity and to find out the conditions in which these carbonates precipitated in the intertidal zone (age of the ancient shorelines, palaeo temperatures of the Sea surface, variations of sedimentary alimentation by rivers, etc.) (DE MURO & ORRÙ, 1997). Six samples of beach rocks sampled in the Bonifacio Strait (La Maddalena) at depths ranging from -40m to 0 below present sea level are currently under study. Speleothems are another powerful tool for palaeo-climate reconstruction of Late Quaternary (ANTONIOLI et alii., 1998): in fact, isotopic studies using C14 and U/Th dating combined with stable isotope analysis (oxygen and carbon) allow reliable palaeo-temperature and sea-level oscillation reconstructions. Earlier palaeo-climate researches at Alghero have revealed and age of 4,623 B.P. for a stalagmite sampled at -1m b.p.s.l. in Grotta Verde cave (ANTONIOLI et alii., 1994) and 165,000 B.P. for a stalagmite sampled at -52 b.p.s.l. in Grotta di Nettuno cave (ANTONIOLI & MUCEDDA, 2003). The presence of marine biological markers grown upon submerged speleothems allow an even more detailed analysis of sea level rise: a very good example is given by the serpulids. Many other biological markers, such as Dendropoma, Vermetids etc. can also be used for Holocene climate reconstruction. Finally, also archaeology can be a useful tool in reconstructing palaeo-environments, especially for sea level fluctuation studies in coastal areas where archaeological remains can indicate sea level low stands (ANTONIOLI et alii, 2000)