CONICET | Buscador de Institutos y Recursos Humanos

The Pampa plain is represented by a sequence of Upper Quatemary eolian formations interbedded with paleosols. The Pampean Eolian System is the most important morphosedimentary system of the region. It is formed by a sand sea in central Argentina (180,000 km²) and a loess belt to the northeast (2,000 km long and 250-300 km wide). Several paleopedological studies on Quatemary loess-paleosols sequences of Pampa were carried out in the last few years, some of them with the participation of european specialists. A micromorphological approach was used by some authors to identify paleosols, who also provided a reliable chronological framework for the investigated sequences. However, the major part of the studies are not really integrated on a regional scale because such paleosols were differentiated along isolated sites, sometimes with strong influence of local conditions (e.g. profiles located at accessible gullies responding to a micro-climate of fluvial belts instead of the main environmental conditions of the large plain). The paleoenvironmental reconstruction provided by paleosol studies should be based on a coherent stratigraphic framework and a correct geomorphic analysis; nevertheless both have been frequently disregarded by paleopedologists. This contribution seeks to reconstruct the environmental scenarios occurred on the Pampean Eolian System during the Upper Quaternary by means of the integration of own data with the available results produced by other authors in the region. The research focuses on widespred field data and is used for integrating the geomorphologic, stratigraphic and sedimentologic information with the recent paleopedologic advances. In a first approximation of the analysis, large geomorphological environments are discriminated. These comprise: the Pampean Ranges piedmont, the coastal belts and the inland plains. Significant differences registered between loess / eolian sand - paleosols sequences are explained by their geomorphological position. It is more difficult to discriminate microclimatic influences for paleosols developed in fluvial belts, closed depresions, etc. The most important result deduced from the comparison of the large geomorphological environments is the existence of two strong soil forming periods in the last interglacial - glacial cycle. Pedogenic processes as argillan / ferriargillan illuviation, horizon differentiation, pedoturbation, hydromorphism and calcification among others, were produced under such humid periods generating extensive paleosols of regional distribution. The soil developed during the Hypsithermal period of the Holocene (8,500-3,500 yr.B.P.) is a distinct pedostratigraphic marker identified in the main geomorphological units of both the loess belt and the sand sea, and even out of the Pampa plain. The buried soil (Alfisol) was developed on top of the loess/eolian sand (OIS 2) and it is represented by a moderately developed Bt horizon. In general, the soil was truncated and it is covered by an eolian formation (late Holocene in age). In a minor geomorphological unit (fluvial valleys of the region) that soil forms an accretionary pedocomplex of argillic horizons separated by the accumulation of Andean volcanic ash, mainly concentrated by alluvial processes. The main differences between the buried soil and the paleosoil correlated to OIS 5a are the significant mobilization of iron and the degree of development (larger in this one). In all major environments of the region, the older soil underwent a more important erosion. The OIS 3 period has a weaker although regionally important pedogenic signal. The soil developed during the Hypsithermal period of the Holocene (8,500-3,500 yr.B.P.) is a distinct pedostratigraphic marker identified in the main geomorphological units of both the loess belt and the sand sea, and even out of the Pampa plain. The buried soil (Alfisol) was developed on top of the loess/eolian sand (OIS 2) and it is represented by a moderately developed Bt horizon. In general, the soil was truncated and it is covered by an eolian formation (late Holocene in age). In a minor geomorphological unit (fluvial valleys of the region) that soil forms an accretionary pedocomplex of argillic horizons separated by the accumulation of Andean volcanic ash, mainly concentrated by alluvial processes. The main differences between the buried soil and the paleosoil correlated to OIS 5a are the significant mobilization of iron and the degree of development (larger in this one). In all major environments of the region, the older soil underwent a more important erosion. The OIS 3 period has a weaker although regionally important pedogenic signal. The soil developed during the Hypsithermal period of the Holocene (8,500-3,500 yr.B.P.) is a distinct pedostratigraphic marker identified in the main geomorphological units of both the loess belt and the sand sea, and even out of the Pampa plain. The buried soil (Alfisol) was developed on top of the loess/eolian sand (OIS 2) and it is represented by a moderately developed Bt horizon. In general, the soil was truncated and it is covered by an eolian formation (late Holocene in age). In a minor geomorphological unit (fluvial valleys of the region) that soil forms an accretionary pedocomplex of argillic horizons separated by the accumulation of Andean volcanic ash, mainly concentrated by alluvial processes. The main differences between the buried soil and the paleosoil correlated to OIS 5a are the significant mobilization of iron and the degree of development (larger in this one). In all major environments of the region, the older soil underwent a more important erosion. The OIS 3 period has a weaker although regionally important pedogenic signal. The soil developed during the Hypsithermal period of the Holocene (8,500-3,500 yr.B.P.) is a distinct pedostratigraphic marker identified in the main geomorphological units of both the loess belt and the sand sea, and even out of the Pampa plain. The buried soil (Alfisol) was developed on top of the loess/eolian sand (OIS 2) and it is represented by a moderately developed Bt horizon. In general, the soil was truncated and it is covered by an eolian formation (late Holocene in age). In a minor geomorphological unit (fluvial valleys of the region) that soil forms an accretionary pedocomplex of argillic horizons separated by the accumulation of Andean volcanic ash, mainly concentrated by alluvial processes. The main differences between the buried soil and the paleosoil correlated to OIS 5a are the significant mobilization of iron and the degree of development (larger in this one). In all major environments of the region, the older soil underwent a more important erosion. The OIS 3 period has a weaker although regionally important pedogenic signal.

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