Geomagnetic Secular Variations 0-6500 yr. as Recorded By Sediments from Lakes of South Argentina

GOGORZA, C.S.G.; SINITO, A.M.; VILAS, J.F.; CREER, K.M.; NUÑEZ, H.

GEOPHYSICAL JOURNAL INTERNATIONAL

Blackwell Sinergy

Lugar: Londres; Año: 2000 p. 787 - 798

0956-540X

Abstract Regional type curves depicting secular variations of declination and inclination through the last 6500 calendar years constructed for south-western Argentina (about 41°S, 71°30’W) by stacking paleomagnetic data derived from lake sediment cores are described and analyzed. The record from four lakes already studied, El Trébol, Brazo Campanario, Moreno and Escondido are integrated. Within-lake correlation had been based on the magnetic susceptibility (c) and intensity of the natural remanent magnetization (NRM). Inter-lake correlation was derived also from c and intensity of NRM, also taking into account declination and inclination patterns and a set of radiocarbon age determinations to remove any ambiguities. The secular variation (SV) of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector. The spectrum obtained from spectral analysis shows major peaks at periodicities of about 3700 and 1500 years for inclination data and major peaks at periodicities of about 2500 and 1200 years for declination data. In order to test the stability of the obtained periodicities, spectral analysis has been applied to every 3500 yr. time span at intervals of 500 yr. for both records. Patterns of circularity noted in the SW of Argentina during the last 6300 years appear to recur with a near constant interval of about 2000 years. Both open and closed loops are associated with clockwise and counterclockwise circularity. Key  words: Holocene, paleomagnetism, secular variations, lake sediments, South America.