Provenance of Pliocene and recent sedimentary deposits in western Amazônia, Brazil: Consequences for the paleodrainage of the Solimões-Amazonas River

Abstract

Integrated data on paleocurrents, the morphology of detrital minerals and zircon grains, chemical compositions and U–Pb geochronology, reveal that the flow of the modern Solimões-Amazonas River has changed from west to east since the Plio–Pleistocene. This finding is supported by several lines of evidence, including paleocurrent directions and detrital mineral assemblages in the Içá Formation and in recent sediments. The Içá Formation, which was most likely deposited during the Pliocene, has NE and SE paleocurrents, a high proportion of stable detrital mineral assemblages and U–Pb zircon ages that we interpreted as being derived from the Amazonian craton (e.g., the Rondonian-San Ignácio and Sunsas-Grenvillian geochronologic provinces) and neighboring provinces, including the Neoproterozoic to Cambrian Brazilian Pampean mobile belts. A small proportion is derived from the Cambrian to Silurian Famatinian continental arch. Another source is the Precambrian and Paleozoic basement from the Andes cordillera, which includes several metamorphic inliers in Colombia, Peru and Bolivia. The overlying recent deposits have different provenances and are characterized by a more variable detrital assemblage with zircon grains that are enriched in trace elements and depleted in Si and have Mesoproterozoic ages. In our interpretation, the erosion of the Iquitos Arch after deposition of the Içá Formation allowed the westward expansion of the Solimões-Amazonas system in the Plio-Pleistocene.