Recent sediments of the eastern Lago Fagnano (Tierra del Fuego, Argentina): geochemistry, mineralogy and their implication for environmental studies

CAFFAU, M; PRESTI, M.; LENAZ, D.; ZECCHIN, M.; LODOLO E.; TASSONE, A.

Torino

Congreso; VIII Forum Italiano di Scienze della Terra; 2011

Federazione Italiana di Scienze della Terra

Lago Fagnano is located in a tectonic depression developed along the Magallanes-Fagnano transform fault, a major segment of the South America-Scotia plate boundary. It is 110 km long and its width varies from 2.8 to 9.7 km, and has a maximum water depth of 206 m. The tectonic structure of the Lago Fagnano formed presumably during the Paleogene, and its morphological setting was subsequently modified by glacial erosion, especially during the Late Quaternary. During a joint Italian-Argentinean acquisition campaign (March 2010) funded by the Italian Ministry of Foreign Affairs, a total of 30 sediment samples were taken from three piston cores collected on the bottom of the easternmost part of Lago Fagnano, in the vicinity of the Rio Turbio inlet. Piston cores CF-1B, CF-3A and CF-F were retrieved at water depths of 20.4 m, 19.8 m and 36 m, respectively, and recovered 80 cm, 92 cm and 90 cm of lacustrine deposits. These sediments have been investigated for their mineralogy (X-ray powder diffraction) and geochemistry (rare earth elements, along with major redox-sensitive elements), with the aim of evaluating the suitability of these proxies for environmental studies. Sedimentological and mineralogical analyses showed that these samples are characterized by a silty-clayey fraction that is mainly constituted by quartz, feldspar and clay minerals. Chondrite-normalised rare-earth elements patterns are similar to those of the lighter upper continental crust, with some depletion of heavy rare earth elements. The analytical results lead to the conclusion that mineralogy and geochemistry provide key clues to the understanding of this depositional environment.