Sedimentological characteristics of fluvial environments in the subtropical Chaco plain (Argentina)

Acta geológica lilloana 22 (1-2): 2010

Abstract

The Eastern sector of the Chaco plain is drained by autochthonous rivers, regulated by the low slope and the subtropical climate. The regional geomorphology is determined by the mega-alluvial fan, belonging to the Bermejo River. Some of the paleochannels that flow from this unit result into rivers whose chemical characteristics are under the influence of particular local saline soils. Framed within a wetland environment of regional and international interest, these rivers have a great environmental importance. The present contribution is an approach to the understanding of the local hydrosedimentologic dynamics, through the study of two typical river systems of the region. For this purpose, samples were taken from the liquid phase, as well as bed and suspended loads, in different hydrological periods. The material was analyzed in the laboratory by standard techniques; the results of grain size, organic matter and hydrochemical features revealed a particular identity in each water system. However, in both rivers particle size uniformity was observed, with a value of over 50% in abundance of fine materials. Similarly, the suspended load had an analogous behavior in the two rivers, according to which they are inversely correlated with the flow and content of dissolved salts.