Age and geological history of the Amazon River revisited by provenance of Cenozoic sedimentary rocks of the Foz do Amazonas Basin (Brazil)

Reconstructing the geological history of the Amazon River and its drainage basin is fundamental for understanding the geological evolution of South America and the origins of Amazonian biodiversity. However, suitable sedimentary records for reconstructing the evolution of the Amazon River have remained scarce, with most available data derived from deep-sea settings (e.g., the Ceará Rise) and, more recently, from the continental shelf/Foz do Amazonas Basin (FAB). Here, we present the first U–Pb dating of detrital zircons from Paleogene to Pleistocene sedimentary rocks of the FAB, based on samples obtained from industrial wells. Combined with major and trace element geochemistry and Sm–Nd isotopic data of the clay-size fraction, this dataset provides an unprecedented opportunity to track sediment provenance shifts through time and offers new insights into the evolution of the Amazon River system. Paleogene sediments display a cratonic origin, with low radiogenic ƐNd(0) values (-20.1 to -19.1) and zircon populations that point to sedimentary sources in the Amazon Craton, in the Gurupi Belt, and in the Borborema Province. Our results further document a provenance shift to Andean derived sediments in the northern fan, supported by a shift to radiogenic ƐNd(0) values (-20.2 to -11.9) and Andean-sourced Paleozoic and Meso-Cenozoic zircons at 14.3 Ma as indicated maximum depositional ages (MDA) and maximum likelihood ages (MLA). We interpret this sharp transition of sediment sources as the onset of a transcontinental river drainage. The presence of Andean sediments in the northern part of the Foz do Amazonas Basin suggests an active North Brazil Current during the Early–Middle Miocene, given that the Amazon canyon and deep-sea fan are located further east. It also suggests that the Middle Miocene Pebas system in western Amazonia was connected to the Atlantic Ocean, acting as a continental scale biogeographic corridor. The presence of Brazilian Orogen (500–700 Ma) and Cariris Velho Orogen (∼1.0 Ga) zircons in the analyzed sediments suggests that the Borborema province was one of the main sources of the FAB during the Plio-Pleistocene. Finally, our provenance dataset suggest that present-day drainage basin of the Amazon River was much younger than previously thought.