Influence of structural features on groundwater occurrence in an intermontane valley of the Ventania fold-and-thrust belt (Buenos Aires, Argentina)

Abstract

Intermontane aquifers in fold-and-thrust belts commonly exhibit strong structuralcontrols that govern groundwater occurrence, storage, and flow paths. This studyevaluates the influence of structural features on groundwater distribution in theintermontane valley of San Andrés de la Sierra, located within the western sector of theVentania System. The objective was to determine how folding, faulting, and basementtopography condition the geometry and heterogeneity of the local phreatic aquifer. Toachieve this, a multidisciplinary approach integrating field observations, well censusdata, borehole cuttings analysis and geoelectrical methods were applied. Ten verticalelectrical soundings and one electrical resistivity tomography profile were performed,and six geological–hydrogeological cross sections were constructed to definesubsurface architecture. Results show that both VES and ERT data reveal markedlateral and vertical resistivity contrasts, reflecting abrupt changes in aquifer thicknessand basement depth, along with a discontinuous fine-grained aquitard interdigitatedwithin the aquifer deposits. The geometry of the basement surface is controlled byplunging folds and faults consistent with the regional structural framework of theVentania fold-and-thrust belt. The aquifer is hosted within colluvial–alluvial depositsthat reach thicknesses of up to 137 m, but thin rapidly toward the quartzite outcropsthat bound the valley. The strong spatial variability in aquifer thickness, along with thepresence of the aquitard layer and the upper fractured sections of the basement, hasdirect implications for groundwater exploitation. These findings demonstrate thatgroundwater occurrence is strongly conditioned by local structural features, producinga highly heterogeneous aquifer system. This complexity highlights the need for higherdensity geophysical surveys to improve subsurface characterization in similarmountain-front environments.