The South Atlantic margin developed on Archean stable cratons consisting of hard and resistant rocks and partly on the Neoproterozoic mobile belts composed of less resistant metamorphic rocks. The Precambrian basement of the Santos Basin is exposed as the Araçuaí Belt along the Brazilian coast, most notably in the inselbergs of Rio de Janeiro, of which Sugarloaf Mountain is the most iconic. The ancient rocks consist of a Neoproterozoic to Cambrian high-grade metamorphic core of granites and gneisses, formed during the collision of Gondwana in the Pan-African-Brasiliano orogeny. Basalts similar to the Paraná and Etendeka traps, exposed to the west in the Paraná Basin, have been found underlying the Santos Basin. The Tristan da Cunhahotspot, known as the Tristan hotspot, is considered the driver behind the formation of these flood basalts. During the Early Cretaceous, the former continent Gondwana, as southern part of Pangea, starting to break-up, resulting in a sequence of rift basins bordering the present-day South Atlantic. The Pelotas-Namibia spreading commenced in the Hauterivian, around 133 million years ago and reached the Santos Basin to the north in the Barremian. Seafloor spreading continued northwards to the Campos Basin in the Early Albian, at approximately 112 Ma. Five tectonic stages have been identified in the Brazilian basins:
Oil reservoirs include formations deposited during the Aptian and pre-Aptian continental rift phase, of post-salt Albian-Cenomanian shallow-water marine carbonates and deepwater sandstones, and in turbidites of the open marine drift phase of Late Cretaceous and early Tertiary ages. The Namorado Field "location was selected based on seismic interpretation of a structural high at the top of the Macaé Formation " at a depth of about, and the reservoirs are marine turbidite deposits transgressing over the Albianlimestone shelf. The stratigraphy starts with basalt flows dated at 120 Ma, overlain by the Lagoa Feia Group, consisting of the organic-rich lacustrine "green shales" followed by lacustrine limestones and continental sandstones and conglomerates, transitioning into marine sediments with evaporites, limestones, and limestone altered dolomites. The shallow marine limestones of the Macaé Formation follow, then the Namorado turbidite sandstones, and finally the Campos Formation, consisting of the turbidite sandstone Carapebus Member and the prograding slope and shelf Ubatuba Formation.
Exploration
The off-shore oil exploration in the Campos Basin began in 1968. The first exploratory well was drilled in 1971. The first field to be discovered was Garoupa in 1974, at a shallow water depth of, followed by Namorado in 1975 in of water. The first oil production started in 1977 from Enchova Field, at a water depth of. The largest fields, listed by their year of discovery year, include Linguado, Carapeba, Vermelho, Marimba, Albacora, Marlim, Albacora-Leste, Marlim Sul, Marlim Leste, Barracuda, Caratinga, Espadarte, Roncador, Jubarte, Cachalote, and Badejo. The largest Marlim field is located in the northeast of the basin, offshore in water depths ranging from. By 2003, 41 oil and gas fields were discovered, which ranging at distances from from the coast and at water depths varying from. Of these fields, 37 are being developed by Petrobras. By 2003, the oil production from the basin had reached 1.21 million barrels per day. The production comes from a variety of reservoirs including siliciclastic turbidites, fractured basalts, coquinas, calcarenites. The total cumulative production from the Campos Basin by 2003 was 3.9 billion barrels of oil with remaining reserves of 8.5 billion barrels. In February 2010, a new 65 million barrel discovery was made by Petrobras near the Barracuda oil field.
