Holocene-Pleistocene PSV from Escondido Lake, Argentina: Imprints of an Excursion at about 14,000 Calibrated Years

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

Hanoi (Vietnam)

Congreso; 9th Scientific Assembly of IAGA (International Asociation of Geomagnetism and Aeronomy); 2001

IAGA

Paleomagnetic and sedimentological studies carried out on four cores, about 10m long, from the bottom sediments of Escondido Lake (southwestern Argentina) are described. This lake is geologically related to the set of lakes of glacial origin located in western Patagonia. The pairs of magnetic susceptibility and intensity of remanent magnetization profiles show a good correlation with the sedimentological macroscopic descriptions, and also with those of shorter cores previously studied. The stability of the natural remanent magnetization was investigated by alternating-field demagnetization. One sample of each five were chosen as pilot samples, which were demagnetized successively until 70mT peak and the stable remanent magnetization was isolated. Most of the samples showed no systematic change in the direction of their remanent magnetization during AF demagnetization; few of them showed a viscous magnetization, probably picked up in laboratory fields, which could easily be removed by AF demagnetization at about 15 mT. Within-lake correlation was based on the magnetic susceptibility and intensity of remanent magnetization, because the patterns of these parameters showed similarity for every core. Radiocarbon dating from earlier studies have enabled us to construct a secular variation record from South Argentina for the past 20,000 years. The individual measurements were stacked and transformed to a time-scale to produce type-curves. The declination and inclination logs show an anomaly at about 14,000 calendar years. These results suggest the possibility that a geomagnetic excursion of the geomagnetic field was recorded. Excursions at about this time have been recorded in the same area and in several other parts of the world.