Geology of the Río de la Plata and the surrounding areas of Argentina and Uruguay related to the evolution of the Atlantic margin

An integrated study of geological and geophysical data of the Río de la Plata region and its relation to the evolution of the Atlantic passive margin is herein described. This characterization is based on the available geological and geophysical information and on the correlation of the southern end of the best-known Santa Lucía Basin in Uruguay to the Salado Basin in Argentina, and their connection through the Quilmes Trough. Furthermore, a new Meso-Cenozoic depocenter is characterized and identified as Recalada Trough, subparallely aligned to the Quilmes Trough and separated from it by the Magdalena-Montevideo High. Both sedimentary fillings present ENE-WSW trending main axes and reach an average thickness of almost 2000 m. This suggests an evolution from a triple junction where interconnected extensional arms developed, which have had common Mesozoic tectosedimentary histories related to the early opening of the Atlantic Ocean. Based on the geophysical and geological evidence, the previously accepted existence in the Río de la Plata of a first-order structural feature along the international border between Argentina and Uruguay, associated to an ENE-WSW trending tectonic high, identified as Martín García, is unjustified. The tectonic evolution of the Atlantic margin in front of the Río de la Plata estuary is the consequence of a long deformation history starting in the Precambrian up to recent times. Each Precambrian, Paleozoic, Mesozoic and Cenozoic tectonic scenario adds different weak trends on the continental crust, which control the evolution of the sedimentary depocenters. The presence of these tectosedimentary records influence the bathymetric control of the Río de la Plata and the dynamics of the recent estuarine deposits. The Meso-Cenozoic sedimentary infill is estimated to comprise considerable ranges of sandstones and conglomerates associated with faulted blocks of the crystalline basement, with expected petrophysical conditions oscillating in the order of 12%-15% of effective porosity and with expected traps of the stratigraphic and combined (closing against faulting) type, and overlapped by fine sediments with excellent quality as seals. The economic significance of these sedimentary volumes lies in their yet unexplored potential as natural fluid reservoirs (hydrocarbons and groundwater), of great importance due to their strategic position near the large urban areas of Buenos Aires and Montevideo.