PRELIMINARY ROCK MAGNETIC AND BIOPROXIES RESULTS FROM A SHORT SEDIMENT CORE OF LAGUNA LA BARRANCOSA (BUENOS AIRES, ARGENTINA)

ROMINA ACHAGA, CLAUDIA S. GOGORZA, FRANCISCO CIANFAGNA, FERNANDA MONTES DE OCA, SOFÍA PLASTANI, MARÍA J. ORGEIRA, CECILIA LAPRIDA

Montevideo

Congreso; Latinmag 2013; 2013

We present preliminary results of rock magnetic and paleomagnetic studies, and bioproxy analyses of short sediment cores collected from the bottom of Laguna La Barrancosa (36.95° S 56.85° W). Two short cores (TBBA1, 81 cm; TBBA2, 66 cm) were collected using a Livingstone piston corer during the 2012 southern summer. The cores show centimetre-scale lamination and frequent textural variations. Measurements of intensity and directions of Natural Remanent Magnetization (NRM), magnetic susceptibility, isothermal remanent magnetization, saturation isothermal remanent magnetization (SIRM), back field and anhysteretic remanent magnetization at 100 mT (ARM) were performed and several associated parameters calculated (ARM/k, SIRM/ARM and SIRM/ARM). Also, as a first estimate of relative magnetic grain-size variations, the median destructive field of the NRM (MDFNRM), was determined. The stability of the NRM was analyzed by alternating field demagnetization. Rock magnetic analysis suggests that the main carriers of magnetization seem to be ferrimagnetic minerals, predominantly pseudo single domain magnetite. Bioproxy analyses allow inferring that hydric balance has increased over the last 100 years, and especially since 1990 AD.