Geophysical study applied to the evolution of the geothermal resource in the southeastern Entre Ríos

Abstract

The Guarani Aquifer System is a large transboundary groundwater reservoir shared by Brazil, Uruguay, Paraguay, and Argentina. It forms part of the Parana and Chacoparanense sedimentary basins. The geological units related to this system are the Triassic-Jurassic eolian and fluvial sandstones of the Piramboia and Botucatu formations, and the Serra Geral Basalts which present clastic intercalations (Solari Member). This effusive Cretaceous complex covers the sandstones and provides a high-confinement degree. This aquifer is one of the most important fresh groundwater reservoirs in the world. Geoelectrical methods were used to describe the geometry of the geological units and to determine the depth of the crystalline basement, the presence of intercalated clastic deposits, and the existence of thermal waters in the southeast of the Entre Rios province, Argentina. Geoelectrical models were obtained from a set of fourteen vertical electrical soundings carried out in the vicinity of Gualeguaychú, Aldea San Antonio, Concepción del Uruguay, and San José towns. These models indicate that the basement is at a depth of around 900 m, except in those places where the sedimentary sequence does not appear, in which case it is found between 800 and 670 meters. Analyzing all the features and the results obtained, we conclude that the main factor determining the presence of the sediments which contain the Guarani Aquifer System in this area is the structural setting which is directly related to the depth of the crystalline basement.