Hydrogeology of the Mercosul aquifer system in the Parana and Chaco-ParanaBasins, South America, and comparison with the Navajo-Nugget aquifer system, USA

The giant Mercosul aquifer system consists of Triassic-Jurassic eolian-fluv io-lacustrine sandstones confined by Cretaceous basalt flows, and it covers about 1,195,500 km(2) (461,583 miles(2)) In South America. The aquifer sys tem encompasses all of the Parana Basin and part of the Chaco-Parana Basin and is one of the world's largest. The eolian Botucatu Sandstone and its eq uivalents form an important part of this system. Maps of structure, thickne ss of overlying rocks, and water temperature, and a potentiometric map, all based on 322 wells, define hydrogeologic characteristics and provide the b asis for establishing guidelines for the long-term equilibrium use of this important multinational aquifer system. The Mercosul aquifer system is divi ded into two domains - the larger and better understood Parana Basin and th e smaller and less well understood Chaco-Parana Basin. Most of the northern part of the Parana Basin has axially-directed groundwater flow, whereas th e southern part of the aquifer discharges mostly to the southwest into the Corrientes Province of Argentina, with negligible discharge into the Atlant ic Ocean. The Mercosul aquifer system is conservatively estimated to have b een flushed at least 180 times since deposition. Various factors are respon sible for this flushing, including appreciable rainfall since the end of th e Cretaceous Period, probable uplift of the basins' borders in Late Cretace ous time, simple basin geometry, long-term riverine and groundwater flow to the southwest (ancestral and present Parana River Systems), and stable cra tonic setting. Key hydraulic properties of the Mercosul aquifer system are compared to tho se of the eolian Jurassic Navajo-Nugget System of the western United States . The results demonstrate the importance of tectonics and climate on the ev olution of sub-continental aquifer systems.