The groundwater age of the Argentine aquifers: A review and paleoclimate insight

Abstract

Argentina is a large country in South America, spans from the tropical latitude S 26°15′ to the subpolar latitude S 53°38’, and longitudinally from the Atlantic coast to the Andes range in the West. Such extensive geographical coverage includes diverse climatic and geological conditions, fostering a multitude of aquifers with varying hydrogeological attributes. Groundwater dating is an underdeveloped discipline in Argentina, but several studies have been conducted. These studies are delineated across various aquifer typologies, namely: 1) Sedimentary aquifers in Eastern Patagonia, 2) Alluvial aquifers in the middle Andes area; 3) Shallow aquifers in the Pampa region; 4) Confined intermediate aquifers in the Pampa region; 5) Fractured aquifer in crystalline rocks; 6) the confined sandstones of the Guaraní aquifer; 7) Deep confined aquifers in the Pampa region. Most of the studies are based in the classical tracers, 3H and 14C, with only a few employing other traces such as CFCs, 4He and 81Kr. In almost all the studies only an apparent age (piston flow model) is provided. Only two papers include the analysis of the residence time distribution. Considering the apparent ages, groundwater ranges from young in shallow unconfined aquifers, or fractured aquifers in crystalline rocks, to very old groundwater with an age of 1.2 Ma in the deep thermal aquifers. Groundwater which radiocarbon age corresponds to the Upper Pleistocene period, exhibits a depleted isotopic composition that correlates with colder temperatures in a sequence of glacial periods.