Provenance of the Middle Miocene Barreiras Fan Delta in the Onshore Pará-Maranhão Basin, Northern Brazil

Abstract

The demise of the carbonate platform in the Brazilian Equatorial Margin has been related to the progradation of massive siliciclastic inflow from the Cratonic Amazon River during the middle Miocene. The sediment plume did not influence the eastern portion of this drainage, including the Bragantina Platform andthe Marajó Basin, the onshore Pará-Maranhão Basin. The provenance signatures of these tectonic segments have been demonstrated in siliciclastic coastal deposits of the Barreiras Formation, whose progradation caused the suppression of the Oligocene-Miocene carbonate platform. Our provenance study is based on clast morphology, quartz cathodoluminescence, and heavy minerals of mainly Barreiras alluvial-fluvial deposits, using new and published facies data. This study opens a window of opportunity to investigate, for the first time, the proximal facies combined with paleocurrents exposed only in this area of Brazil. The restricted occurrence of proximal facies indicates an exceptional potential for preservation related to subsiding regions generated by reactivated faults in the Gurupi Belt. Provenance data indicate the strong influence of metamorphic source rocks with minor volcanic and plutonic contributions from the southeastern and southern of the Bragantina Platform and eastern Marajo Basin. Respectively, two heavy minerals assemblages were found: 1) staurolite, metamorphic quartz, and angular clasts; and 2) abundant zircon, kyanite, tourmaline, mixed quartz (metamorphic, plutonic, and volcanic), and rounded clasts. The assemblages are associated with São Luís Craton, mainly crystalline rocks from Gurupi Belt. In addition, the proximal facies of the Bragantina Platform provide rich staurolite concentration and angular clasts indicating near source area; the uplifted Marajó Basin during the middle Miocene contributed with reworked sediments containing rounded clasts and ultrastable minerals related to Silurian-Cretaceous rocks. This work complements the previous paleoenvironmental reconstruction for the Barreiras deposits, including the most robust proximal facies interpretation contributing to understanding sediment dispersion during the middle Miocene, reinforcing previously defined source areas.