Paleointensity Studies on Holocene-Pleistocene Sediments from Escondido Lake, Argentina

SINITO, A.M.; GOGORZA, C.S.G.; LIRIO, J.M.; NUÑEZ, H.; CHAPARRO, M.A.E.; VILAS, J.F.

República Checa

Congreso; 8th International Meeting on paleo, Rock and Environmental Magnetism; 2002

PALEOINTENSITY STUDIES ON HOLOCENE-PLEISTOCENE SEDIMENTS FROM ESCONDIDO LAKE, ARGENTINA Ana M. Sinito(1), Claudia S.G. Gogorza(1), Juan M. Lirio(2), Héctor Nuñez(2), Marcos Chaparro(1), Juan F. Vilas(3) (1) IFAS - UNCPBA - CONICET, Pinto 399, (7000) Tandil, Argentina (asinito@exa.unicen.edu.ar) (2) IAA, Cerrito 1248, Bs. As., Argentina (liriojm@yahoo.com) (3) CONICET-Lab. D. Valencio-UBA C. Universitaria, P.2, 1428 Bs. As., Argentina (vilas@.glg.fcen.uba.ar) This paper presents the first relative paleointensity record for Holocene-Pleistocene times in Argentina. Samples came from four cores obtained from bottom sediments of Escondido Lake. The age interval of the studied sediments was determined, by AMS radiocarbon dating in former works, between 19,000 calibrated years and present. Two different facies were recognized on Escondido Lake: a basal glaciolacustrine facies named “Elpalafquen Lake” facies, corresponding to sediments from a large proglacial lake, and a younger organic rich lacustrine facies named “Escondido Lake” facies, corresponding to sedimentation under no direct influence of glaciers. Intensity of natural remanent magnetization, magnetic susceptibility; saturation isothermal remanent magnetization; anhysteric remanent magnetization, anhysteric susceptibility and remanent coercitive field were measured in order to analyze the reliability of the sediments as paleointensity recorders and to carry out normalization of natural remanent magnetization by several methods. Anhysteric remanent magnetization seems to be the best normalization parameter, but good agreement is observed between the profiles with the different normalization. The different behavior observed between the two facies in the paleointensity records was analyzed on basis of the dissimilar sedimentation regimes. In order to compare them, they are re-normalized by their mean values to obviate this difference. Smoothed deflections around the mean value are observed along the profile, with extreme values between 16,000 and 17,000 calibrated years.