Abstracts of Symposium 55 and some papers from other related Symposia.

Paleoenvironment Information Obtained from Magnetic Measurements in Pampean Loess and Soils

Paulina NABEL. Conicet, Museo Arg. de Ciencias Naturales, Av. Angel Gallardo 470, Buenos Aires (1405), Argentina.

Quaternary environment changes in Pampean Region, have been recorded in different natural files. Loess, paleosoils, sea level changes, as well as faunal and palynological studies, give information about the natural dynamics of this region.

Geologists, geophysists, biologists, soil scientists as well as others, are making in Argentina important efforts to improve our knowledge about Pampean environmental evolution, with the aim to distinguish natural dynamics from anthropogenic effects.

Among them, magnetostratigraphic as well as magnetic susceptibility studies were carried out. On account of the first of them, it was possible to change, in the early eighties, the general assumption in Argentina, about the age of the Quaternary Sediments, in two orders of magnitude (from ten thousands to millions of years).

As a result of this chronological approach, it was also possible to give an accurate time setting oh the Hisisa Geosol from Ensenada Formation, located at the end of Matuyama Chron. Loess deposits characterize the Brunches Chron onset in this region, 730 Ka ago, suggesting a change to dryer and probably cooler environmental conditions.

Magnetic susceptibility measurements carried out in Pampean loess-paleosoils sequences, show a tight relation with the sedimentological changes. Although these changes, as it is broadly known, reflect the environmental changes, they present a different trend than those observed in other regions. Our studies point out that it has to be regionally checked. With that purpose, we start the study of present magnetic signatures of Pampean soils. Geomorphological settings and magnetic mineralogy are key questions.

However magnetostratigraphic as well as magnetic susceptibility studies in Pampa Region are undoubtedly useful to Quaternary environmental studies, scale problems, field work and sampling procedures, here discussed, seem to be the main limiting factors for reliable application of magnetic measurements to environmental studies.

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