Magnetic characterization of sediments from La Brava Lake (Buenos Aires Province, Argentina)

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

Foz do Iguazu

Congreso; American Geophysical Union (AGU) - Meeting of the Americas; 2010

American Geophysical Union (AGU)

This study was carried out on bottom cores collected from Lake La Brava, Argentina (37º 52´S 57º 59. W). This elongated and shallow lake, of tectonic origin, has a surface area of about 4.5 km2. Four long cores were recovered in water depths of about 3.4 m using a push corer. The sedimentological description shows the presence of silt, clay and tephra layers. In order to characterize the sediments, a series of rock magnetic studies were conducted. The following measurements were carried out: magnetic susceptibility (mass-specific X, and volumetric, k); intensity of the natural remanent magnetization (NRM); isothermal remanent magnetization (IRM) in increasing steps up to 1.2 T, reaching the saturation (SIRM); back-field, in growing steps until canceling the magnetic remanence; anhysteretic remanent magnetization (ARM100mT), with a direct field of 0.1, 0.5 and 0.9 mT and a peak alternating field of 100 mT. Associated parameters were also calculated: S-ratio (IRM-300mT/SIRM), %soft IRM ((SIRM-IRM-40mT)*100/SIRM), coercivity of remanence (BCR), anhysteretic susceptibility (kARM) and the inter-parametric ratios: ARM100mT/k, ARM100mT/SIRM, kARM/k, kARM/SIRM and SIRM/k. Separation of magnetic phases using an experimental method (IRM-AF demagnetization) and thermal demagnetization of SIRM was carried out.