Lithological and geomorphological controls in the development of wet meadows associated with basaltic plateaus of Argentinean Patagonia

Abstract

Arid and semi-arid regions constitute an area where approximately 20% of the global population lives and the groundwater represents the only source of fresh water supply in many cases. In Extra-Andean Patagonia, located in the south extreme of South America, the landscape dominated by basaltic plateaus is associated with wet meadows, which are the only source of fresh water for rural inhabitants in a region characterized by arid conditions. The aim of this work was to define the geological and geomorphological controls that condition the formation of wet meadows associated with basaltic plateaus in a sector of the Extra-Andean Patagonian. For this, fieldworks were carried out that included geological profiles, rock sampling and geomorphological description of the sectors associated with wet meadows. The perennial character of wet meadows is supported by lithostratigraphic, structural and geomorphological controls that regulate the recharge, storage, flows and discharge of the groundwater that sustains them. The subhorizontal position of the basaltic plateau and the presence of fractures allow the rapid infiltration of rainwater that recharges the aquifers. The lithology, structure and paleorelief of the underlying rocks to the basalts determine the storage and flow of groundwater. Despite the great extension of the basalt plateaus and their homogeneity, there are different geological-geomorphological combinations in the underlying rocks that give rise to a great variety of controls of the water flows that sustain the wet meadows. The data obtained provide new information for the knowledge of wetlands and water resources in arid environments such as Extra-Andean Patagonia, where wet meadows provide water supply of local people, livestock and vegetation, constituting a relevant ecosystem service.