Complex depositional environments on a siliciclastic-carbonate platform with shallow-water turbidites: The Natividade Group, central Brazil

• Published in: Journal of South American earth sciences 2021-04, Vol.107, p.102939, Article 102939
• Main Authors: Toscani, R., Campos, J.E.G., Matos, D.R., Martins-Ferreira, M.A.C.
• Format: Article
• Language: English
• Subjects: Mixed platforms; Natividade group; Paleo-mesoproterozoic basins; Shallow water turbidites
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2020.102939

The Natividade Group is a Paleo-Mesoproterozoic metasedimentary sequence outcropping in the external zone of the Northern Brasília Belt, western margin of the São Francisco Craton, Brazil. The present study delimited eleven sedimentary rock types grouped into four rock assemblages: i) Sand-Silt-Carbonate; ii) Sand-Conglomerate; iii) Sand, iv) Silt-Clay. A geological map for the region was produced, and six stratigraphic columns were composed. Based on the descriptions of rock types and on lateral variation of rock assemblages, it was possible to establish four depositional environments for the Natividade Group, including mixed platform (siliciclastic-carbonate deposition), internal siliciclastic platform, open-marine siliciclastic platform, and a shallow water turbidite (mass flow slope deposition). The mixed platform was controlled by the basement paleogeography, which allowed the deposition of carbonates in warm, agitated, and clean, shallow water conditions in parallel to deposition in deeper water setting, where thin siliciclastic sediments were deposited. The siliciclastic internal platform consists mostly of quartzite, originating from sandy sediments, probably indicating deposition dominated by bedload currents under shallow water shoreface conditions. The open-marine siliciclastic platform is dominated by fine-grained sediments, indicating deepening water conditions under lower shoreface conditions below the fair-weather wave base. Shallow water turbidite occurs in the southern parts of the study area. The elevated paleorelief in the southeast of the Natividade basin is considered as the provenance area providing suitable slope environments for density flow initiation. The basin was shallower in the southern portion with a predominance of carbonate and gravitational flux deposits and deeper to the north, evidenced by the northward predominance of fine-grained sediments. Finally, the study shows that the Natividade Group was deposited in a basin controlled by thermo-flexural subsidence. •First shallow water turbidite identified in the Brasilia Fold Belt.•Paleogeography controls mixed carbonate-siliciclastic deposition and turbidite source areas.•Geological map of Natividade Group and different columns at distinct basins regions.•Regional geophysical data delimit the Natividade Basin main source areas.