Relative Paleointensity of the Geomagnetic Fiels 12-20 kyr. from Sediment Cores, Lake Moreno (Patagonia, Argentina)

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

Fort Lauderdale, EEUU

Congreso; Joint Assembly: “A Meeting of the Americas”, American Geophysical Union; 2008

American Geophysical Union

We conducted a detailed study of natural remanence and rock magnetic properties on sediments cores from lake Moreno (South-Western Argentina). Based on these measurements, we constructed a paleosecular variation (PSV) record (Irurzun et al., 2008) and a relative paleointensity stack for the period 11-21 $^{14}$C.   The Declination and Inclination logs of the characteristic remanent magnetization for the cores as function of shortened depth are obtained. The data from all cores were combined to obtain a composite record using the Fisher method. Comparison between stacked inclination and declination records of lake Moreno and results obtained in previous works, lake Escondido (Gogorza et al., 1999; Gogorza et al., 2002) and lake El Tr\'{e}bol (Irurzun et al., 2008), shows good agreement. This agreement made possible to transform the stacked curves into time series that spans the interval 11 and 21 $^{14}$C kyr B.P.   Rock magnetic properties of the sediments cores showed uniform magnetic mineralogy and grain size, suggesting that they were suitable for relative paleointensity studies. The remanent magnetization at 20mT (NRM$_{20mT}$) was normalized using the anhysteric remanent magnetization at 20mT (ARM$_{20mT}$), the saturation of the isothermal remanent magnetization at 20mT (SIRM$_{20mT}$) and the low field magnetic susceptibility {\k}. Coherence analysis showed that the normalized records were not affected by local environmental conditions. The recorded pseudo-Thellier paleointensity was compared with records obtained from conventional normalizing methods. Comparing the paleointensity curves with others obtained previously in other lakes in the area has allowed us to reach reliable conclusions about centennial-scale features.