Abstract

Magnetoestratigrafía en sucesiones del Cenozoico Tardío del area de Sierras de Balcarce, Tandilia. Rev. Asoc. Geol. Argent. [online]. 2016, vol.73, n.4, pp.588-607. ISSN 0004-4822.

Based on geological and paleomagnetic studies a stratigraphic ordering of Neogene-Quaternary deposits in the Sierras de Balcarce area is proposed. Two stratigraphic sections are presented in this contribution. One corresponds to a quarry situated in the southern slope of Sierra Bachicha, the other to a roadside section in the locality of Ramos Otero. In the field, several lithological units were recognized and described and a paleomagnetic sampling was performed. By the application of conventional paleomagnetic laboratory techniques, it was possible to establish magnetic polarity zonations. The magnetozone of the upper part in both sections was assigned to the Brunhes Polarity Chron (<0.781 Ma) and is basically composed composed of two lithostratigraphic units. The youngest one is an aeolian sandy loam -probably deposited during the Last Glacial Maximum- lying discordantly on top of an older unit. The latter is of fluvial origin and contains abundant CaCO3; its age would be less than 450 Ka. Below, through an unconformity, we found deposits with loessoid aspect and psefitic dispersed materials, well represented in the section of Sierra Bachicha. They are interpreted as distal colluvial deposits. Several polarity changes have been recorded in them. The youngest polarity change, at the top of the unit, would have a minimum age of Brunhes-Matuyama Boundary (0.781 Ma), and the oldest, placed at the base of the quarry, would have a minimum age of Middle Matuyama-Olduvai Boundary (1,778 Ma). Although older ages are not discarded, the studied sediments are younger than 3.2 Ma.

Keywords : Paleomagnetism; Quaternary; Balcarce; Brunhes; Matuyama.

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