Preliminary paleoclimatic data from sediments of laguna Chaltel

IRURZUN, M. A.; GOGORZA, C. S.; SINITO, A.M.; FEY, M.; OHLENDORF, CHRISTIAN; ZOLITSCHKA, BERND

Mérida

Congreso; 12th Scientific Assembly; 2013

International Association of Geomagnetism and Aeronomy

Sequences of lake sediments are good sources ofpaleoclimatic information because they provide continuous records of magnetic parameters and detailed records of paleoclimatic changes. This study was carried out on bottom cores collected from Laguna Chaltel, an almost circular lake located in Patagonia,Argentina (49.9º S 71º W). The following measurements were performed: magnetic susceptibility at low frequency (specific ? , and volumetric, k) and high frequency; isothermal remanentmagnetisation (IRM) in increasing steps up to 1.2T, reaching the saturation (SIRM); back-field, in growing steps until cancelling the magnetic remanence; anhystereticremanentmagnetisation (ARM), with a direct field of 0.01mT and a peak alternating field of 100 mT. Associated parameters also were calculated: S (IRM300mT/SIRM), coercivityremanent (B) and frequency-dependence magnetic susceptibility (F factor). On selected samples, hysteresis curves were measured and the hysteresis parameter ratios, HCR/HC and MRS/MS were calculated.A model using magnetic grain size,concentration and mineralogy, previously applied to Laguna PotrokAike to infer lake level changes, was a used in Laguna Chaltel. The results indicate a trend to increase the lake level from 3950 to 500 cal. BP with few pulses of relative high lake level between 3900 and 300 cal. BP. A high concentration of low coercivityminerals with coarse magnetic grain size is observed at 4000 cal. BP, suggesting a dry event/lowest lake level for the last 4700 cal. BP in the area.