Abstract

MORETTI, Lucas Martín; RODRIGUEZ, Darío Martín; ANGELINI, Marcos Esteban  and  MORRAS, Héctor José María. Soil genesis in an alluvial piedmont in the Chaco region of Salta Province. Cienc. suelo [online]. 2012, vol.30, n.2, pp.161-172. ISSN 1850-2067.

The aim of this study was to evaluate the soil-landscape relationships and the physico-chemical and mineralogical composition of different soils within the alluvial fan of Del Valle river, in the western part of the Chaco region in the Salta Province, Argentina. Six groups of soils with distinct characteristics were identified. Medium to coarse-textured Ustipsamments and Haplustolls were found on elongated gently convex sandy accumulations, drainage networks and plains of the proximal section of the alluvial fan. The medium-textured Argiustolls and Haplustalfs are mainly developed on stabilized plains in the intermediate section, while fine-textured Haplusterts characterize swamp environments between intermediate and distal sections of the fan. Mineralogical analyses were performed by X-ray diffractometry (XRD) and Magnetic Susceptibility (MS) measurements. The XRD on total soils samples showed variations in the proportion of quartz, feldspars, muscovite and accessory minerals among the profiles, reflecting the heterogeneity of their parent materials. Moreover, according to the mineralogical composition of the clay fraction, two types of parent materials, possibly related to different source areas, were distinguished: I) one containing high proportions of smectite and illite, where Ustipsamments, Haplustolls and Haplusterts are developed; and II) another one with a lower proportion of expansive minerals and dominance of illite, corresponding to the C horizons of Argiustolls and Haplustalfs. The Magnetic Susceptibility of the Vertisol showed an opposite trend to that of the Argiustoll, Haplustalf and Typic Haplustoll, reflecting different physical-chemical conditions between those soil types, while the MS of the Entisol and Entic Haplustolls varied irregularly with depth in accordance to the heterogeneity of their sedimentary layers. This study summarizes new results and interpretations about the origin, composition and distribution of soils in a region where this information is still scarce.

Keywords : Geomorphology; Soils; Mineralogy; Salta Province.

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