SESS 1_160211.pub Il Quaternario Italian Journal of Quaternary Sciences 24, (Abstract AIQUA, Roma 02/2011), Congresso AIQUA Il Quaternario Italiano: conoscenze e prospettive Roma 24 e 25 febbraio 2011 CLIMATIC AND ENVIRONMENTAL CHANGES OF THE SANTA GILLA LAGOON (CAGLIARI) DURING THE HOLOCENE Anna Maria Porcu, Antonietta Cherchi, Paolo E. Orrù & Paola Pittau Dipartimento Scienze della Terra, Università degli Studi di Cagliari Corresponding author: A. M. Porcu ABSTRACT: Porcu A. M. et al., Climatic and environmental changes of the Santa Gilla Lagoon (Cagliari) during the Holocene. (IT ISSN 0394-3356, 2011) Through the study of two boreholes was possible to reconstruct the environmental and climate evolution of the last 10,000 years B.P. of the Santa Gilla Lagoon. The data obtained are based on microfauna and palynomorphs analysis, integrated with geochemical analysis carried out on foraminifera calcareous shells. Radiometric analysis were also per- formed to obtain a well-defined geochronology scale of sedimentary succession. RIASSUNTO: Porcu A. M. et al.: Variazioni climatiche e ambientali della Laguna di Santa Gilla (Cagliari) durante l’Olocene. (IT ISSN 0394-3356, 2011) Attraverso lo studio di due sondaggi a carotaggio continuo è stato possibile ricostruire l’evoluzione ambientale e climati- ca degli ultimi 10.000 anni B.P. della Lagna di Santa Gilla. I dati ottenuti sono basati sull’analisi della microfauna e dei palinomorfi, integrati con analisi geochimiche effettuate sui gusci calcarei dei foraminiferi. Sono state inoltre compiute analisi radiometriche per ottenere una scala geocronologica ben definita della successione sedimentaria. Keyword: Foraminifera, Palynology, stable isotope analyses Parole chiave: Foraminiferi, Palinologia, analisi isotopiche  Multidisciplinary study on the marine and continen- tal microfacies from two boreholes of the Santa Gilla Lagoon allowed to reconstruct the environ- mental, climate and vegetation changes that oc- curred in the Gulf of Cagliari during the Holocene. Palynologic (pollen and spores analyses), micro- paleontologic (benthic foraminifers) and isotopic data (δ18O and δ13C) over the past 10.000 years B.P. from this transitional-coastal sequence show a series of shift leading to the establishment of dif- ferent climatic conditions. The investigated ar- chives included lagoonal organic shales, Posidonia peat and coastal, fine and medium sandstone. Radiocarbon dating and multiproxy analyses were performed on 30 meters of succession. The radio- metric analysis allowed to date the sedimentary series, placing the beginning of the lagoon silting process from moments immediately after the Younger Dryas (ORRÙ et al., 2004; ANTONIOLI et al., 2007) and to compare the sedimentary succes- sion to the Northern European chronostratigraphy. The coastal sediments are the reservoir of biologi- cal and lithological information on mutual relations continent-sea. Any sea level change, both eustatic and isostatic and tectonic, left its marks on the fos- sil faunal and microfaunal composition. Through the foraminifera study and according to the knowledge on their ecology (SGARELLA & MON- CHARMONT ZEI, 1993; CIMERMAN & LANGER, 1998; FIORINI & VAIANI, 2001), have been detected envi- ronmental characteristics that have occurred dur- ing the lagoon filled. Benthic foraminifer associa- tion were identified and assembled into five main eco-groups that have shown the transition from lagoonal environment (10.000-9.000 years B.P.) to marine sublittoral with a very close lagoon (9.000- 3000 years B.P.) and then return to the lagoonal but with marine influences (3.000-250 years B.P.) and re-opened to the sea (250 years B.P.-actual). Any climatic change, if it exceeds a certain thresh- old, gives a change in the vegetation which is re- corded in coeval sediments by the palynological record. The sequence of sporo-pollen spectra pro- vides the vegetation evolutionary pattern of the source area of the studied basin. The palynological study allowed the vegetation spectra reconstruc- tion (REILLE, 1992; REILLE, 1995; REILLE, 1999) showing five phases and a sub-phase, marked by an appreciable evolution in terms of frequency curves that represent the stages of the vegetation dynamics of last 10,000 years under the climate influence. The vegetational response to the ame- lioration of the climate in the Early Holocene (9.800 -7.600 years B.P.) resulted in the spread of the Ericaceae macchia (First phase) and the setting of the Quercus forest between 7.700-7.600 years B.P. (sub-phase). This was followed by a shift to- ward drier and more open vegetation mainly repre- sented by Chenopodiaceae (Second phase) at 7.600-7.200 years B.P. At 7.200-4.800 years B.P. a more persistent peak in deciduous Quercus val- ues signal a reestablishment of wetter conditions and the maximum extension of the Quercus forest (Third phase). Alternated drier (Chenopodiaceae) 51 - 53 52 F ig .1 , g eo ch ro no lo gi ca l, ch ro no st ra tig ra ph ic , o f t he p al eo te m pe ra tu re s, p al eo ve ge ta tio n, p al eo en vi ro nm en ta l, an d pa le oc lim at ic s ch em e of th e st ud ie d su cc es si on s. S ch em a ge oc ro no lo gi co , c ro no st ra tig ra fic o, d el le p al eo te m pe ra tu re , p al eo ve ge ta zi on al e, p al eo am bi en ta le , e p al eo cl im at ic o de lle s uc ce ss io ni s tu di at e A.M. Porcu et al. 53 Ms. received: Testo ricevuto il and wetter phase with developpement of Quercus orest even in the coastal plains followed. The last Chenopodiaceae arid and cold phase (Fifth phase) fitted with the Little Ice Age (216±100 years B.P.). Because eustatic changes are not always depend on climate, but climate change almost always pro- duce eustatic changes, the integrated study of mi- crofauna and continental flora provides a much valuable investigation means in the evolution re- construction of coastal areas and climate evolution of a region. Climate change producing water temperature and salinity variations, which are recorded in the la- goon from microfaunas through the relation changes of oxygen and carbon isotopes. The isotopic analysis (δ18O and δ13C) were carried out on the shells of two species of foraminifera, Ammonia tepida and Elphidium granosum, good indicators of lagoon and estuarine environments (CRONIN et al., 2005). Were obtained two types of scales for each species: a multi-decadal scale and a multi-centennial scale, obtained by the method of 5-point running average. The long-term variability of δ18O values (multi-centennial, 200- 400 years, time-scales) indicate a variable positive trend from 9.450 to 7.500 years B.P. approxi- mately, and a negative trend from approximately 7.100 to 2.000 years B.P. The multi-centennial time-scale of the δ13C values indicates a variable decreasing negative trend from 10.00- to 7.700 years B.P., that we regard reflecting increasing salinity waters culminating with the remarkable marine rising of the Holocene Optimum Climati- cum. Higher δ13C negative values from 7.500 to 3.850 years B.P. are regarded as indicative of higher precipitation with higher organic influx of terrestrial origin; whereas the succeeding higher δ13C values up to 1.850 A.D. are indicative of in- creasing water salinity. Variable amplitude fluctua- tions at multi-decadal time-scale, 20-30 years, are superimposed on these long-term trends.     REFERENCES ANTONIOLI F., ANZIDEI M., LAMBECK K., AURIEMMA R., GADDI D., FURLANI S., ORRÙ P.E., SOLINAS E., GAS- PARI A., KARJNJA S., KOVAČIĆ V. & SURACE L., (2007) - Sea level change during the Holocene in Sar- dinia and in the North-eastern Adriatic (Central Medi- terranean sea) from archaeological and geomor- phological data. Quarternary Science Review 26, 2463 –2486. CIMERMAN F. & LANGER M. R. (1991) - Mediterranean foraminifera - Ljubljana, Slovenska akademia, 118 pp., 93 pls. CRONIN T. M., THUNELL R., DWYER G. S., SAENGER C., MANN M. E., VANN C. & SEAL R. R. 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