Isotopic and chemical variations of groundwater in the deep aquifer of the Ombucta Formation, Bahia Blanca, Argentina

Stable isotopes and 14C data on Bahia Blanca basin, Ombucta Formation are presented. Previous hydrochemical and geological studies led to the conclusion that Ombucta aquifer is recharged by water rising through fractures and diaclases from underlying paleozoic rocks. This up movement occurs along a section coincident with the regional tectonic alignment that crosses Bahia Blanca city in W-E direction. Water penetrating this formation moves northward and southward with different velocities, as inferred from thermal and hydraulic gradients. 14C isochrones agree with isochloride curves and the correlation between water ages and stable isotopes values suggest colder climatic conditions prevailing when water infiltrated. Meteoric origin of groundwater and catchment area location at Sierras Australes are confirmed by these results. (author). 20 refs, 9 figs, 2 tabs