A new soil-landscape approach to the genesis and distribution of typic and vertic argiudolls in the rolling pampa of Argentina

Abstract

The Rolling Pampa is one of the several subregions of the large Pampa plains in central Argentina. The most extensive and representative soils in the area are Typic Argiudolls, together with a smaller proportion of Vertic Argiudolls occurring mainly on relief tops and upper slope facets in a strip close to the Paraná - Río de la Plata fluvial axis. According to the traditional interpretation, the vertic soil properties are due to a combination of finer parent materials resulting from granulometric selection during eolian transport from the south-western Andean sources and intense smectite formation in a more humid eastern sector of the Pampa. A new sedimentological and geopedologic approach explains more accurately the development and spatial distribution of the main soils in the subregion. According to this, smectitic sediments coming from northern sources in the Paraná basin were deposited in the Rolling Pampa and later covered by illitic loess sediments from south-western Andean sources. In a subsequent humid period in the Holocene, the illitic sediments were eroded and the smectitic sediments were exposed on the upper parts of the undulating relief. As a consequence, Typic Argiudolls developed on the illitic and volcanoclastic Andean sediments, while vertic soils evolved in higher positions of the landscape on the smectitic sediments of older age and different origin.