Abstract The emerged part of the Río de la Plata estuary is characterized by striking coastal geomorphic features. Aerial and satellite images, field observations of the outcrops, shallow boreholes, radiometric dating of sand and shells and Ground Penetrating Radar surveys were analysed. The main sedimentary features are: a large coastal barrier (up of 220 km long), old coastal lagoons, attached beach ridge (about 210) sets distributed along 170 km, the Ibicuy sand body variously interpreted as a reworked shoal/island or delta, and cheniers. The tidal flats and the modern Paraná Delta are located in the centre and on the right side of the inner estuary. The height of the estuarine coastal barrier represents the maximum flooding surface (MFS) of the last transgression at about 6000 aBP. Other main sedimentary forms developed as a falling stage systems tract (FSST) during the sea-level drop between the aforementioned date and the present. The sea surface was about 5 m above sea-level in the inner part of the estuary during the middle-Holocene. This MFS was subsequently followed by a continuous and slow sea-level fall that controlled the generation of the large sedimentary forms developed in the innermost part of the Río de la Plata Estuary.

Abstract The San Rafael Block is included as a part of the pre-Andean region, in the southern sector of the Argentine Precordillera–Cuyania terrane, within the western Gondwana margin. The Río Seco de los Castaños Formation (Upper Silurian–Lower Devonian) is one of the major marine-siliciclastic pre-Carboniferous units, and is interpreted as a distal to proximal silty platform-deltaic system. The dominant sedimentary processes were wave and storm action and the source areas were located to the east, close to the study area. The rocks are mainly of immature arkosic sandstones showing both recycled orogen and continental block provenances. Sedimentological characteristics of conglomerate-filled channels and an organic-matter-rich bed are described. X-ray diffraction analyses of the clay minerals from the sequences show that very low-grade metamorphic conditions acted during the Early Carboniferous. Geochemical analyses indicate moderate to strong weathering, and potassium metasomatism. Zr/Sc ratios lower than 22, no important enrichments of Zr, Th/Sc ratios, high Sc and Cr concentration and the Eu-anomalies indicate a provenance from a less evolved upper continental crust. T DM ages and ɛ Nd are within the range of the Mesoproterozoic basement and Palaeozoic supracrustal rocks from the Precordillera–Cuyania terrane. Probable sources, tectonic setting and land–sea interactions are discussed.