The definition of the western boundary of the Guarani Aquifer System (Gran Chaco, Argentina): technical or conventional?

Abstract

Unlike the eastern, northern and southern borders of the Guarani aquifer system (GAS), which extends beneath considerable regions of Argentina, Brazil, Paraguay and Uruguay, the western boundary, within the Gran Chaco, has no clear hydrogeologic definition that can be recognized at either the surface or subsurface. For this reason, the precise location of the aquifer in this area is open to many different possibilities, depending upon the factors or interests involved. Thus technical specialists have proposed locations that include or exclude, according to their own criteria, large sections of the Argentine Gran Chaco, the management and use of which, from an administrative point of view, imply diverse economic consequences.

The Lomadas de Otumpa, located near the border between the Santiago del Estero and Chaco provinces, are gently sloping hills, rising to a height of no more than 110 m above the wide expanse of surrounding plains comprising the Gran Chaco. They trend NNE and are 200 km long and from 20 to 80 km in width, reflecting the presence of the regional Otumpa alignment. The Lomadas de Otumpa are clearly defined at the surface and thus they allow a geographical boundary to be imposed on the GAS sequences according to: i) their notable structural features at the surface, and ii) the close matching of the thinning and/or absence of the associated sedimentary record underground.

Because the definition of the limits of the GAS has an influence on its evaluation, management, use and conservation, both at a technical and administrative level, it is of great importance to ascertain its hydrogeologic boundaries.