Resumo

BIDEGAIN, J.C.  e  RICO, Y.. Magnetic mineralogy and susceptibility records in Quaternary sediments of normal (Brunhes) and reverse (Matuyama) polarity in the Juarez quarry, Buenos Aires Province. Rev. Asoc. Geol. Argent. [online]. 2004, vol.59, n.3, pp.451-461. ISSN 0004-4822.

Sediments exposed in the Juárez quarry of Buenos Aires Province (34°57'10''S and 57º53'00'' W), belong to the Pleistocene and Holocene. The sedimentary units are those of the Ensenada and Buenos Aires formations and the so-called Post-Pampean. The Ensenada Formation has reversed polarity (Matuyama) at the bottom of the exposed sequence and normal polarity (Brunhes) at the upper part, while the Buenos Aires Formation and Post-pampean sediments are of normal polarity (Brunhes). The highest susceptibility values were obtained in loess of the Ensenada Formation (189 x 10^-8 m³/kg), and the lowest in sediments belonging to the Buenos Aires Formation (11 x 10^-8 m³/kg) and in hydromorphic paleosols of the Ensenada Formation (30 to 50 x 10^-8 m³/kg), both associated with climatic conditions of higher relative humidity. An increase in magnetic values in the coarse- to medium-silt fractions reflects the dominance of vigorous winds as the main carrier of ferromagnetic minerals during arid periods (glacial periods). The frequency-dependent susceptibility (F factor) varies between 0 % and 6,45 %. The highest values, obtained in intensively weathered horizons (interglacial periods), are, however, intermediate compared with those of Siberia and China. This property allows us to suggest the existence of a third model of susceptibility behaviour related to changes of Quaternary paleoclimate: that of strong winds modified by pedological processes at middle latitudes.

Palavras-chave : Buenos Aires Formation; Ensenada Formation; Paleomagnetism; Paleoclimate; Paleoenvironment.

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