Preliminary Results of Magnetic Measurements on Stream-Sediments from Buenos Aires Province Argentina

CHAPARRO, M.A.E.; GOGORZA, C.S.G.; BIDEGAIN, J.C.; SINITO, A.M.

Hanoi (Vietnam)

Congreso; 9th Scientific Assembly of IAGA (International Asociation of Geomagnetism and Aeronomy); 2001

IAGA

The great urban area from northeast of Buenos Aires Province (near La Plata City) is exposed to an important anthropogenic influence, mainly due to industrial activity. We have special interest in the stream sediments from this region. Two water streams were chosen (Arroyo Pescado (P) y Del Gato (G), tributaries of the La Plata River), both of them with similar characteristics, although with different contribution of pollutants. Six sites were sampled in these water streams, and fourteen sediment cores (each of them about one meter long) from the stream bottom were taken out. Magnetic measurements and geochemical studies were carried out on the samples. Among the magnetic parameters, specific susceptibility (X), X frequency-dependence (XFD%), X temperature-dependence (curves of X vs. T), Natural Remanent Magnetisation (NRM), Isothermal Remanent Magnetisation (IRM), Saturation IRM (SIRM), coercivity of remanence (BCR), S ratio and SIRM/X ratio were studied. In this work stage (preliminary results) interesting results were obtained. The X readings yield higher values for sites G (32.1-95.4 x10-8 m3 kg-1) than for sites P (17.3-18.9 x10-8 m3 kg-1), these ones and NRM results have shown a good correlation. The SIRM values for these sites show a similar behavior to the X results (sites G between 1740-28410 m A m-1 and sites P between 534-3061 m A m-1). In relation to S ratio and BCR, both parameters are coherent with the predominance of ferrimagnetic materials for sites G. The increase of the magnetic parameters is also consistent with the content of “heavy metals” (Cr, Pb, Zn, Cd, Fe, Cu, Ni) detected in earlier geochemical studies.