Neodymium and lead isotope values in sediment samples were used to interpret sediment transport and source rocks on the Southeastern South American upper margin. The sediments of the Argentinian margin exhibit an average ɛ_Nd value of −1.9, indicating the influence of the Andean rocks as sediment sources. Sediments from the Río de La Plata estuary show an average ɛ_Nd value of −9.6 which is similar to that of the Southern Brazilian Upper Margin. Finally, sediments of Southeastern Brazil, which are associated with the transport of the Brazil Current exhibit an average ɛ_Nd of −13.0. The Pb isotope signatures also confirm the differentiation of source rocks in the sedimentation of the study area. In addition, Pb isotopes helped to establish the extent of the influence of the Río de La Plata on the sedimentation of the Southern Brazilian margin. In terms of Pb isotopes the sediments from the Río de La Plata estuary and Southern Brazil are more radiogenic than those of Southeastern Brazil and the Argentinian margin.