Provenance of deep-water reservoir sandstones from the Jubarte oil field, Campos Basin, Eastern Brazilian Margin

Abstract

The provenance of the Maastrichtian deep-water reservoir sandstones from the Jubarte oil field (Campos Basin, eastern Brazil), was studied using an integrated approach that included quantitative petrography, conventional heavy mineral analysis, garnet mineral chemistry and zircon geochronology. The reservoirs are predominantly coarse, poorly-sorted sandstones with feldspathic composition derived from uplifted basement terrains. The fourth- and fifth-order depositional sequences analyzed show no major variations in composition or in provenance through time. However, variations in apatite:tourmaline presents potential to be used as a parameter for sandstone correlation within the field. The composition of heavy minerals indicates derivation from high temperature and low-to-medium pressure aluminous metapelitic rocks, from granites and subordinate mafic rocks, derived from the Cabo Frio Tectonic Domain and the Oriental terrain of Ribeira orogen, characterizing a supply route from SW to NE. The low ZTR index, as well as the absence of low-grade stable heavy minerals and of metasedimentary rock fragments, suggest that by the end of Cretaceous all supracrustal, low-grade terrains had already been totally eroded, and that plutonic, infracrustal rocks were exposed, similarly to the present situation. The integration of the compositional and textural aspects suggests a tectonically active source area, located relatively close to the basin. The active tectonic uplift of the basement terrains provided a large volume of coarse, poorly-sorted sediments carried directly from mountain streams and alluvial fans to deep water. The high frequency shifts in apatite:tourmaline values support a direct derivation of the deep-water sandstones from adjacent alluvial systems with short but differential exposure to weathering. The voluminous deposition of such coarse-grained and immature turbidites under the general transgressive conditions of the Maastrichtian indicates a tectonic, rather than eustatic control on their deposition, with important implications for the exploration of similar reservoirs in Campos Basin and in similar basins of eastern Brazilian margin.