Holocene-Pleistocene Geomagnetic Secular Variations Recorded on Sediments from El Trébol Lake, SouthArgentina

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

República Checa

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

HOLOCENE – PLEISTOCENE GEOMAGNETIC SECULAR VARIATIONS RECORDED ON SEDIMENTS FROM EL TRÉBOL LAKE, SOUTH ARGENTINA   Claudia S. G. Gogorza(1), María A. Irurzun(2), Ana M. Sinito(1), Juan M. Lirio(3), Héctor Nuñez(3), Juan F. Vilas(4) (1) IFAS - UNCPBA - CONICET, Pinto 399, (7000) Tandil, Argentina (cgogorza@exa.unicen.edu.ar) (2) UNCPBA , Pinto 399, (7000) Tandil, Argentina (airurzun@exa.unicen.edu.ar) (3) IAA, Cerrito 1248, Bs. As., Argentina (liriojm@yahoo.com) (4) CONICET-Lab. D. Valencio-UBA C. Universitaria, P.2, (1428) Bs. As., Argentina (vilas@.glg.fcen.uba.ar)     Paleomagnetic and sedimentological studies carried out on six cores, about 11 m long, from the bottom sediments of El Trébol Lake (southwestern Argentina) are described. This lake is geologically related to the set of lakes of glacial origin located in western Patagonia. Using several magnetic studies, the predominance of pseudo single/single domain magnetite as main carrier. The pairs of magnetic susceptibility and intensity of remanent magnetization profiles show a good correlation with the sedimentological macroscopic descriptions. The stability of the natural remanent magnetization was investigated by alternating-field demagnetization. Within-lake correlation was based on lithology, magnetic susceptibility and intensity of remanent magnetization. Radiocarbon dating from earlier studies have enabled us to construct a secular variation record for the past 17,500 years. The declination and inclination logs show a significant anomaly between 13,500 and 17,500 yr b.p. These results suggest the possibility that an excursion of the geomagnetic field was recorded. Excursions at about this time have been recorded in several other parts of the world.