ROCK-MAGNETIC AND PALEOMAGNETIC STUDIES ON SEDIMENTS FROM LAGUNA CHALTEL (PATAGONIA, ARGENTINA)

C. S. G. GOGORZA; IRURZUN, M.A.; P. PALERMO; A. M. SINITO; MICHAEL FEY; CHRISTIAN OHLENDORF; B. ZOLITSCHKA

Puerto Vallarta

Congreso; Reunión Anual de la Unión Geofísica Mexicana 2012; 2012

Unión Geofísica Mexicana

Abstract: We have performed paleomagnetic and rock magnetic studies on four short sediment cores from Lake Chaltel (Patagonia, Argentina) (49º57´S 71º06´W). Measurements of intensity and directions of Natural Remanent Magnetization (NRM), magnetic susceptibility (k), isothermal remanent magnetization, saturation isothermal remanent magnetization (SIRM), back field and anhysteretic remanent magnetization at 100 mT (ARM100mT) were performed and several associated parameters calculated (ARM100mT/k and SIRM/ ARM100mT). Also, as a first estimate of relative magnetic grain-size variations, the median destructive field of the NRM (MDFNRM), was determined. Stability of the NRM was investigated by alternating-field demagnetization (AF). Most of the samples show no systematic change in the direction of their remanent magnetization during AF demagnetization; few of them have a viscous magnetization, which could easily be removed by AF demagnetization at about 10 mT. Rock magnetic properties document that the main carriers of magnetization are ferrimagnetic minerals, predominantly pseudo-single domain magnetite.A total of nine samples was dated by AMS 14C techniques at thePoznan Radiocarbon Laboratory, Poland. Radiocarbon ages were calibrated with the southern hemisphere calibration curve (SHCal04, McCormac et al., 2004) using the software CALIB 5.0.1 (Stuiver and Reimer, 1993; Stuiver et al., 2005) and are given as calibrated years before present (cal. BP). A basal age of 4616 cal. BP is obtained for the core CHA-04-4.The NRM as well as declination and inclination logs of the characteristic remanent magnetization for all samples as function of calibrated ages were obtained. The new paleomagnetic inclination and declination record from Lake Chaltel since 4700 cal. BP is compared with the closest available records, including lacustrine records from further north in Argentina (lakes El Trébol, Moreno and Escondido) and Laguna Potrok Aike.Our new results represent a step forward in constructing a reference PSV curve for SW of Argentina that can be used to date sedimentary sequences. These results can also be used to improve the reliability and accuracy of global geomagnetic field models.