Abstract

BIDEGAIN, Juan Carlos; JURADO, Sandra S.  and  GOMEZ SAMUS, Mauro l.. Magnetoestratigraphy in a Pleistocene loess-paleosoil sequence in Marcos Paz, Buenos Aires Province. Rev. Asoc. Geol. Argent. [online]. 2011, vol.68, n.4, pp.606-614. ISSN 0004-4822.

Late Cenozoic sediments exposed in a quarry in the locality of Marcos Paz (Buenos Aires province) are studied from a stratigraphic and paleomagnetic point of view. The whole sequence, with the exception of the recent soil, belongs to the Pleistocene and is integrated by clayey silts, partly sandy and also by a layer of fine sand. Eleven different depositional/postdepositional units, numbered from unit 1 to 11 downwards, were determined. The units 1, 2 and 3 at the upper part of the geological section should be assigned to Brunhes (< 0.78 Ma). Below a depth of 6 meters the reverse polarity zone corresponds to Matuyama (> 0.78 Ma). Matuyama Magnetozone includes some subzones of normal polarity that should be assigned to the Subchron Jaramillo (0.99 Ma) and to the Subchron Olduvai (1.9 Ma). The reverse polarity levels determined at the bottom of the profile should be assigned to the lower Matuyama (> 1.9 Ma). The highest susceptibility values are recorded in the less pedogenized sediments (400 x 10^-5) while the lowest values are always obtained in gley horizons (30 x 10^-5). The data support the wind-vigor magnetoclimatological model although damped by pedogenesis and weathering as it was established previously.

Keywords : Buenos Aires; Pleistocene; Loes; Paleosols; Magnetoestratigraphy.

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