"A palaeoenvironmental reconstruction from Isla de los Estados (Argentina) based on diatom analyses"

FERNÁNDEZ, M.; BJÖRCK, S.; UNKEL, I.; RABASSA, J.; WOLFARTH, B.;

Santiago de Chile

Congreso; International Geological Congress on the Southern Hemisphere; 2007

A palaeoenvironmental reconstruction from Isla de los Estados (Argentina) based on diatom analyses M. Fernández1,2, I. Unkel1, S. Björck1, J. Rabassa *2,3, B. Wolfarth4 (1)Geobiosphere Science Centre, Quaternary Sciences, Lund University, Sweden (2)Centro Austral de Investigaciones Científicas (CADIC), Ushuaia, Argentina (3)Universidad Nacional de la Patagonia-San Juan Bosco, Sede Ushuaia (4)Department of Geology and Geochemistry, Stockholm University, Sweden * Presenting Author’s email: jrabassa@gmail.com Climate change since the Last Glacial Maximum (c. 20,000 years B.P.) has modified the environments of Patagonia, Tierra del Fuego and Isla de los Estados. Many palynological studies from south Patagonia describe a fluctuating climate since the deglaciation beginning with cool and dry conditions and with the onset of more humid conditions in the early Holocene (Rabassa et al., 1989a, b). The first hunter-gatherer societies that arrived in this southernmost part of the world had to adapt to the complexity and dynamics of this landscape (Borrero et al., 1998; Miotti and Salemme, 1999). The mobility of these groups was limited by the availability of natural resources, mainly water. In order to understand the variability of the archaeological record on a local and regional scale, we will use lake sediments from northern Isla de los Estados to create a continuous and detailed environmental reconstruction based on changing diatom assemblages from lake sediments deposited since the last deglaciation. This type of study is the first to be carried out in this part of South America. By using diatom analysis we will be able to reconstruct past variations in pH, salinity, nutrient status, water level changes and marine transgressions. These results will be combined with other paleoecological techniques such as geochemistry. The chronology is based on 14C dating. Preliminary results show the frequent occurrence of Fragillaria construens var. venter at the transition from varved clays to organic lake sediments around 16,000 cal. yrs B.P., indicating shallow water depths/arid conditions around this time.