CONICET | Buscador de Institutos y Recursos Humanos

New information about the distribution, geometry, structure, extension and facies variations of theuppermost stratigraphic sequences (particularly the Holocene) of the southern coastal plain of theRío de la Plata was obtained by using geophysical methods. This is the first study performed in theregion to investigate the shallow stratigraphic characteristics through continuous geophysicalsurveys. Methods used were georadar (GPR), electrical resistivity tomography (ERT) and seismicsurface waves (SSW), complemented with short drillings. Two transects perpendicular to thecoastline were selected on the basis of the previous geological knowledge of the region andaccessibility. GPR was used in order to obtain a dense sampling of the near subsoil, whereas ERT andSSW were used in parts of the transects for resolving ambiguous trajectories of the detected GPRhorizons. The geophysical results were jointly interpreted, and validated and complemented by theinformation from the drillings. Two major geophysical horizons were identified; the lower one islocated between 5 and 2 meters below surface and progressively shallows inland, which representsthe late Pleistocene-Holocene boundary; the upper one, located at variable depths of 2 m to 0.70 mbelow surface, represents the base of the Holocene beach ridges system in the region. They delimitthree units, the lower one corresponding to the top of the Pampean deposits, the middle onerepresenting the basal Holocene sandy layer, and the upper one corresponding to the beach ridgessystems and related inter-ridge, tidal deposits. In this way, the applied methodology allowed todetermine the extension of the Holocene sedimentary sequences, the relation between theHolocene sequences and its substratum, and the spatial distribution and geometrical characteristicsof partially buried beach ridges and associated inter-ridges deposits. The applied methodology andthe obtained geophysical-response patterns can be useful for future investigations of other regionswith similar ground characteristics