Provenance of Miocene-Pleistocene siliciclastic deposits in the Eastern Amazonia coast (Brazil) and paleogeographic implications

Abstract

During the middle Miocene onshore basins and platforms along Eastern Amazonia coast experienced a massive increase in siliciclastic input. Their deposition was in part concomitant with continental scale geodynamic events including the establishment of the transcontinental Amazon River, the biggest sea-level fall since the Cretaceous, and post-rift tectonism. To better understand the climatic and tectonic control of these deposits and complement the landscape evolution history of Eastern Amazonia we present the first detrital zircon U-Pb ages and Sr-Nd isotopic data for these strata. Compared to suspended particulate matter in the modern Amazon River and core data from the Amazon Fan, the Miocene-Pleistocene onshore deposits have 87 Sr/ 86 Sr and εNd(0) isotopic compositions that dismiss the transcontinental Amazon River characteristic Andean fingerprint. Additionally, detrital zircon U-Pb ages do not present the distinctive Andean Mesozoic-Cenozoic detrital zircon age population. Instead, our results show a predominantly Pre-Cambrian isotopic signature. In the Eastern Marajó Basin, reworked Cretaceous sedimentary rocks and Neoproterozoic granites from the Gurupi Belt were the primary sources. Meanwhile, in the Bragantina Platform, age distribution patterns indicate reworking of the Paleozoic Parnaíba and Cretaceous Grajaú basins sedimentary rocks being the main sources and crystalline basement rocks from the São Luís Craton and Gurupi Belt being subordinated sources. These findings discard the development of the transcontinental Amazon River as the source of middle Miocene siliciclastic influx in the studied area. In fact, our data highlights that those distinct tectonic settings show different depositional histories along the Eastern Amazonian coast, probably controlled by the combination of sea level fall and tectonic reactivations during the Neogene . • First provenance study of Eastern Amazonia Neogene coast deposits. • Sr-Nd isotopes and detrital zircon U-Pb ages dismiss Andean sources. • Crystalline basement and reworked sedimentary rocks were the main sources. • Updated Neogene geodynamic evolution for the Eastern Amazonia coast.