Panorama aereo Itajai Balnerio Cambriu 2006 06

The Santos Basin ( pt, Bacia de Santos) is an approximately large mostly offshore

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsiden ...

. It is located in the south

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

, some southeast of Santos,

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. The basin is one of the Brazilian basins to have resulted from the break-up of

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...

since the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145& ...

, where a sequence of rift basins formed on both sides of the South Atlantic; the Pelotas, Santos, Campos and Espírito Santo Basins in Brazil, and the Namibia, Kwanza and Congo Basins in southwestern Africa. Santos Basin is separated from the

Campos Basin The Campos Basin is one of 12 coastal sedimentary basins of Brazil. It spans both onshore and offshore parts of the South Atlantic with the onshore part located near Rio de Janeiro. The basin originated in Neocomian stage of the Cretaceous perio ...

to the north by the Cabo Frio High and the Pelotas Basin in the south by the Florianópolis High and the northwestern boundary onshore is formed by the Serra Do Mar coastal range. The basin is known for its thick layers of

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

that have formed structures in the subsurface due to

halokinesis upright=1.7 Salt tectonics, or halokinesis, or halotectonics, is concerned with the geometries and processes associated with the presence of significant thicknesses of evaporites containing rock salt within a stratigraphic sequence of rocks. This ...

. The basin started forming in the Early Cretaceous on top of the Congo Craton as a rift basin. The rift stage of the basin evolution combined with the arid Aptian climate of the southern latitudes resulted in the deposition of evaporites in the Late Aptian, approximately 112 million years ago. The phase of rifting was followed by a thermal sag phase and drift stage in the widening of the South Atlantic Ocean. This process led to the deposition of a more than thick succession of clastic and carbonate sediments. One of the largest Brazilian sedimentary basins, it is the site of several recently (2007 and later) discovered giant oil and gas fields, including the first large pre-salt discovery Tupi (8 billion barrels), Júpiter (1.6 billion barrels and 17 tcf of gas), and Libra, with an estimated 8 to 12 billion barrels of recoverable oil. Main

source rock In petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been depo ...

s are the lacustrine shales and

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...

s of the pre-salt Guaratiba Group and the marine shales of the post-salt Itajaí-Açu Formation. Reservoir rocks are formed by the pre-salt Guaratiba

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...

s and

microbialites Microbialite is a benthic sedimentary deposit made of carbonate mud (particle diameter < 5 μm) that is formed with the mediation of microbes. The constituent carbonate mud is a type of

seals Seals may refer to: * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impress an emblem, used as a means of a ...

, as well as the shales of the post-salt sedimentary infill. In 2014, the total production of only the sub-salt reservoirs accumulated to more than . In 2017, the Santos Basin accounted for 35% of Brazil's oil, with the northern neighbour Campos Basin at 55%.

Etymology

The Santos Basin is named after the coastal city of Santos in the state of

São Paulo São Paulo (, ; Portuguese for ' Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaW ...

Description

The Santos Basin is a mostly offshore sedimentary basin across the

Tropic of Capricorn The Tropic of Capricorn (or the Southern Tropic) is the circle of latitude that contains the subsolar point at the December (or southern) solstice. It is thus the southernmost latitude where the Sun can be seen directly overhead. It also reac ...

, bordering from north to south the Brazilian states of

Rio de Janeiro Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the state of the same name, Brazil's third-most populous state, and the second-most populous city in Brazil, after São Paulo. Listed by the GaWC as a b ...

, Sáo Paulo, Paraná and Santa Catarina.Constantino et el., 2016, p.200 The basin covers an area of approximately ,Clemente, 2013, p.18 and is bounded in the north by the Cabo Frio High, separating the basin from the

and the Florianópolis High and

Fracture Zone A fracture zone is a linear feature on the ocean floor—often hundreds, even thousands of kilometers long—resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on e ...

, separating the Santos Basin from the Pelotas Basin.Contreras, 2011, p.1 Along the Brazilian coast, the basin is bounded by the Serra do Mar and stretches from Cabo Frio in the northeast to

Florianópolis Florianópolis () is the capital and second largest city of the state of Santa Catarina, in the South region of Brazil. The city encompasses Santa Catarina Island and surrounding small islands, as well as part of the mainland. It has a populat ...

in the southwest. The city of

is located at the coastal edge of the Santos Basin in the northern portion, Santos, Guarujá and the islands of Ilhabela in the central area and Itajaí and

Balneário Camboriú Balneário Camboriú () is a coast beach city in the Brazilian southern state of Santa Catarina. The city, with its steep hills dropping down to the sea, is popular amongst South Americans. The main ocean boulevard is called ''Avenida Atlânti ...

in the south of the basin. Within the basin, several highs are located. The Outer High, in the distal part of the Santos Basin, is the most prominent and extensive intra-basinal high with an approximate area of . The Outer High is likely a segmented series of rift fault-block shoulders which were uplifted and eroded during the Late Barremian.Gomes et al., 2009, p.3 The climate of the onshore stretch of the basin ranges from

tropical savanna climate Tropical savanna climate or tropical wet and dry climate is a tropical climate sub-type that corresponds to the Köppen climate classification categories ''Aw'' (for a dry winter) and ''As'' (for a dry summer). The driest month has less than of ...

(Aw),

tropical monsoon climate An area of tropical monsoon climate (occasionally known as a sub-equatorial, tropical wet climate or a tropical monsoon and trade-wind littoral climate) is a tropical climate sub-type that corresponds to the Köppen climate classification category ...

(Am) and

tropical rainforest climate A tropical rainforest climate, humid tropical climate or equatorial climate is a tropical climate sub-type usually found within 10 to 15 degrees latitude of the equator. There are some other areas at higher latitudes, such as the coast of southe ...

(Af) to a

humid subtropical climate A humid subtropical climate is a zone of climate characterized by hot and humid summers, and cool to mild winters. These climates normally lie on the southeast side of all continents (except Antarctica), generally between latitudes 25° and 40° ...

(Cfa). The onshore portion of the Santos Basin is in the

Serra do Mar coastal forests The Serra do Mar coastal forests is an ecoregion of the tropical moist forests biome. It is part of the Atlantic Forest of eastern South America. This ecoregion has an outstanding biodiversity consisting of flora, mammals, birds, and herpetofaun ...

ecoregion of the

Atlantic Forest The Atlantic Forest ( pt, Mata Atlântica) is a South American forest that extends along the Atlantic coast of Brazil from Rio Grande do Norte state in the northeast to Rio Grande do Sul state in the south and inland as far as Paraguay and th ...

biome. On the islands of the Superagüi National Park in the Santos Basin, the

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

critically endangered Superagüi lion tamarin (''Leontopithecus caissara'') has its restricted habitat.

Tectonic history

The

South Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe a ...

margin developed on Archean stable

craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...

s consisting of hard and resistant rocks and partly on the Neoproterozoic mobile belts composed of less resistant

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, caus ...

s.Clemente, 2013, p.3 The

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of th ...

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 The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...

high-grade metamorphic core of

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

s and gneisses, formed during the collision of Gondwana in the

Pan-African Pan-Africanism is a worldwide movement that aims to encourage and strengthen bonds of solidarity between all Indigenous and diaspora peoples of African ancestry. Based on a common goal dating back to the Atlantic slave trade, the movement exte ...

- Brasiliano orogeny.Owen, 2014, p.36 Basalts similar to the Paraná and Etendeka traps, exposed to the west in the Paraná Basin, have been found underlying the Santos Basin.Peate, 1997, p.220 The

Tristan da Cunha Tristan da Cunha (), colloquially Tristan, is a remote group of volcano, volcanic islands in the South Atlantic Ocean. It is the Extreme points of Earth, most remote inhabited archipelago in the world, lying approximately from Cape Town, Sou ...

hotspot, known as the

Tristan hotspot The Tristan hotspot is a volcanic hotspot which is responsible for the volcanic activity which forms the volcanoes in the southern Atlantic Ocean. It is thought to have formed the island of Tristan da Cunha and the Walvis Ridge on the African Plat ...

, is considered the driver behind the formation of these flood basalts.Beasley et al., 2010, p.31 During the

, the former continent

, 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 The Hauterivian is, in the geologic timescale, an age in the Early Cretaceous Epoch or a stage in the Lower Cretaceous Series. It spans the time between 132.9 ± 2 Ma and 129.4 ± 1.5 Ma (million years ago). The Hauterivian is preceded by th ...

, around 133 million years ago and reached the Santos Basin to the north in the

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is preceded ...

. 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:Contreras, 2011, p.7 # Pre-rift stage -

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretace ...

# Syn-rift stage -

to Late Barremian # Sag stage - Late Barremian to Late Aptian # Post-rift stage - Early to Middle Albian # Drift stage - Late Albian to

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

The sag phase in the Santos Basin was characterised by

thermal subsidence In geology and geophysics, thermal subsidence is a mechanism of subsidence in which conductive cooling of the mantle thickens the lithosphere and causes it to decrease in elevation. This is because of thermal contraction: as mantle material cools a ...

and generated restricted depocentres with relatively uniform water depths, ranging from . The Late Aptian climate was arid with high evaporation rates which triggered hypersaline conditions in these marginal sag basins. This resulted in the accumulation of thick layers of evaporites along the Brazilian and southwestern African continental margins, a process continuing towards the north later in the Cretaceous.Contreras, 2011, p.8 The deposition of the lowermost of salt in the Aptian would have taken approximately 20,000 to 30,000 years.Bryant et al., 2012, p.51 With the continental break-up of the Santos and Campos Basins from the opposite

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...

and Kwanza Basins, oceanic circulation returned during the post-rift stage. The drift phase since the Late Cretaceous produced a thick sequence of clastic and carbonate deposits. Differential thermal regimes and sediment loading of these units produced

; salt movement in the

subsurface In geology, bedrock is solid rock that lies under loose material (regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bedr ...

. The resulting salt diapirs, listric and

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

s and various salt-related structures produced several stratigraphic and combined stratigraphic-structural traps for hydrocarbon accumulation in the Brazilian and southwest African offshore. During the phases of halokinesis, dated to the Albian to

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pala ...

, several areas of the now deep water distal part of the Santos Basin were exposed to subaerial conditions and suffered erosion. The distal parts of the basin were affected by E-W to NW-SE oriented shortening, sub-perpendicular to the Brazilian margin.Alves et al, 2017, p.319

Stratigraphy

The basement of the Santos Basin is composed of

s and

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

es of the Araçuarí Belt that formed at the western boundary of the Congo Craton. The erosion resistant metamorphic and magmatic rocks are exposed in the Serra do Mar, forming the edge of the Santos Basin along the Brazilian coast. The total stratigraphic thickness of the sediments in the Santos Basin has been estimated at and has been described in detail by Clemente in 2013.Clemente, 2013, p.20

I - Guaratiba Group (Hauterivian-Aptian, pre-salt sequence)

The Guaratiba Group is thick and includes four formations, from old to young the Camboriú, Piçarras, Itapema and Barra Velha Formations. The group is equivalent to the Lagoa Feia Group of the Campos Basin. ;Camboriú Formation The Camboriú Formation is thick and includes the

basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...

ic rocks with a basin–wide distribution. The basalts are dark green to dark grey, holocrystalline, medium grained, with an ophiolitic texture. The main components are

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more p ...

and

augite Augite is a common rock-forming pyroxene mineral with formula . The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees. Characteristics Augite is a solid solution in the pyroxene group ...

, usually fresh, non-altered. Half-graben sedimentation

;Piçarras Formation The Piçarras Formation is thick and consists of clastic and carbonate rocks. The formation includes reddish polymictic conglomerates, with clasts of basalt and

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...

in a clay-sandy matrix. It also includes white, reddish lacustrine

coquina Coquina () is a sedimentary rock that is composed either wholly or almost entirely of the transported, abraded, and mechanically sorted fragments of the shells of mollusks, trilobites, brachiopods, or other invertebrates. The term ''coquin ...

s (shelly limestones) and sandstones,

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

s and shales of stevensite composition. Its age, based on the

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

assemblages, is Hauterivian to Aptian. The conglomerates and sandstones of the formation are representative of an

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. ...

environment. The coquinas represent a shallow lacustrine

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

. Similar to the Atafona Formation of the Campos Basin, the sandstones, stevensite-bearing siltstones and shales represent an alkaline lacustrine environment affected by volcanic activity. The shales represent deeper lacustrine waters in more distal areas. The alternation of the two

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

implies a series of alluvial progradation-retractions into the Cretaceous carbonate lakes. The low textural and compositional maturity of conglomerates and sandstones implies the basin was supplied from areas close to the basin margins.Clemente, 2013, p.21 ;Itapema Formation The Itapema Formation is several hundreds of metres thick and consists of calcirudites (limestones) and dark shales. The calcirudite limestones consist of fragmented bivalve shells, frequently

dolomitized Dolomitization is a geological process by which the carbonate mineral dolomite is formed when magnesium ions replace calcium ions in another carbonate mineral, calcite. It is common for this mineral alteration into dolomite to take place due to e ...

and silicified. In more distal sections, the formation consists of dark organic matter rich shales. In the well 1-RSJ-625, the formation includes of radioactive shales interbedded with carbonates. These facies are thought to represent a lacustrine environment. The organic matter-rich shales are one of the main source rocks of the Santos Basin. This formation is correlative with the Coqueiros Formation in the Campos Basin. The age of the Itapema Formation is Barremian to Aptian. ;Barra Velha Formation The Barra Velha Formation is approximately thick. In the proximal sections, the formation comprises limestones of stromatolites and laminated microbialites. In the distal sections, it is composed of shales. Interbedded with the laminated microbialites there are limestones with packstone and grainstone textures made up of

algal Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

clasts and bioclasts (fragmented ostracods). The carbonates frequently are partly or completely dolomitized. These facies represent a transitional continental and shallow marine environment. The age of this formation has been estimated to be Late Barremian to Aptian. It is correlative with the Macabu Formation in the Campos Basin, as both are typified by laminated microbialites and stromatolites. These limestones are one of the sub-salt reservoirs in the Santos Basin.

II - Ariri Formation (Late Aptian, salt sequence)

The Ariri Formation is in the thick and may be up to thick in other areas of the basin. It is predominantly composed of evaporites. The formation is characterized by thick intervals of white

halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...

, associated with white anhydrite, ochre greyish calcilutites, shales and marls. The sedimentary environment probably was restricted marine including mudflat sabkhas, evolving under an arid climate. The ostracod assemblages of this formation indicate a neo-Algoas age (local time scale).

III - Camburi Group (Albian-Cenomanian, lower post-salt sequence)

The Camburi Group is up to thick and includes three formations,

, Guarujá and

Itanhaém Itanhaém is a municipality in the state of São Paulo in Brazil. It is part of the Metropolitan Region of Baixada Santista. The population is 103,102 (2020 est.) in an area of 601.85 km². The elevation is 4 m. Location The name Itanhaém ...

.Clemente, 2013, p.22 ;Florianópolis Formation The Florianópolis Formation is thick in the type oil well, and consists of reddish, fine to coarse-grained sandstones with a clay matrix, reddish

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

ceous shales and siltstones. These clastic units are thought to represent alluvial environments distributed along the western Brazilian basin margin, along the Santos Hinge Line. These alluvial environments were gradational towards the east, with the shallow marine carbonates of the Guarujá Formation, and further to the open basin with the siltstones of the Itanhaém Formation. Biostratigraphical data and its relations with the Guarujá Formation point towards an Albian age. Bandon marsh national wildlife refuge

;Guarujá Formation The Guarujá Formation is thick and consists of oolitic

calcarenite Calcarenite is a type of limestone that is composed predominantly, more than 50 percent, of detrital (transported) sand-size (0.0625 to 2 mm in diameter), carbonate grains. The grains consist of sand-size grains of either corals, shells, oo ...

s, which laterally grade to greyish ochre and brownish grey calcilutites and grey marls. These facies are interbedded with the alluvial clastics of the Florianópolis Formation. The Guarujá name is restricted to the lowest limestone intercalation, previously named Lower Guarujá by Ojeda and Ahranha in Pereira and Feijó (1994). The microfacies indicate a tidal flat to shallow

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into '' coastal lagoons'' (or ''barrier lagoons ...

and open carbonate platform depositional environment. The age based on

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

and

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...

is Early Albian. ;Itanhaém Formation The Itanhaém Formation is thick and consists of dark grey shales, silts and light grey marls, ochre-brown calcisilts and subordinated sandstones. These facies change laterally into the coarse clastics of the Florianópolis Formation. Facies analysis indicates a marine environment ranging from sub-littoral (inner neritic) and more rarely to pelagic (outer bathyal) conditions. The age based on planktonic foraminifera and pollen is Early Albian.

IV - Frade Group (Turonian-Maastrichtian, middle post-salt sequence)

The Frade Group is thick and includes three formations: Santos, Itajaí-Açu and Juréia. They predominantly comprise turbidites.Clemente, 2013, p.23 ;Santos Formation The

Santos Formation The Santos Formation ( pt, Formacão Santos) is a geological formation of the Santos Basin offshore of the Brazilian states of Rio de Janeiro, São Paulo, Paraná and Santa Catarina. The predominantly conglomeratic sandstone formation with inte ...

is thick and consists of reddish lithic conglomerates and sandstones, interbedded with grey shales and reddish clays. These facies are interbedded and change laterally into the Itajai-Açu and Juréia Formations. The sedimentary environment is thought to be transitional continental to marginal marine, ranging from alluvial to

braided river A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, ''aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment ...

s and deltas. Biostratigraphic data indicate a Late Cretaceous age (Cenomanian-Maastrichtian). ;Itajaí-Açu Formation The Itajaí-Açu Formation is thick and comprises a thick interval of dark grey clayey rocks, interbedded with the clastics of the Santos and Juréia Formations. Within this formation, the Ilhabela Member includes the turbiditic sandstones occurring along the section. The sedimentary environment is thought to be marine talus to open basin. Biostratigraphic data from palynomorphs, calcareous

nanofossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s and planktonic foraminifera indicate a Late Cretaceous age (Cenomanian-Maastrichtian). Ostracod2 hg

;Juréia Formation The

Juréia Formation The Juréia Formation ( pt, Formacão Juréia) is a geological formation of the Santos Basin offshore of the Brazilian states of Rio de Janeiro, São Paulo, Paraná and Santa Catarina. The predominantly shale with interbedded siltstones and fine ...

is thick and includes a succession of clastics between the coarse facies of the Santos Formation in the west and the fine-grained clastics of the Itajai-Açu Formation in the east. The formation is characterized by dark grey to greenish and brown shales, dark grey siltstones, fine-very fine sandstones and light ochre calcisilts. The depositional environment is thought to be of a marine platform setting. The age based on palynomorphs and calcareous nanofossils is Late Cretaceous (Santonian-Maastrichtian). Two new

species were identified in the drilling cuttings of wells drilled into the Santonian-Campanian section, '' ?Afrocytheridea cretacea'' and '' Pelecocythere dinglei''.Piovesan, 2010, p.177

V - Itamambuca Group (Cenozoic, upper post-salt sequence)

Itamambuca Group is thick and includes four formations, Ponta Aguda, Marambaia, Iguape and

Sepetiba Sepetiba is a neighborhood in the West Zone of Rio de Janeiro, Brazil, surrounded by Santa Cruz and Guaratiba, and by the Sepetiba Bay. It occupies an area of 1,162.13 ha, and has a population of 35,892 (according to Instituto Brasileiro de ...

. ;Ponta Aguda Formation The Ponta Aguda Formation is up to thick and consists of conglomerates, coarse to fine-grained sandstones interbedded with siltstones and shales. The dominant facies are coarse to fine-grained

quartzitic Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...

sandstones. They range from reddish to grey, usually with calcite cements. Intercalated are reddish to light grey claystones and siltstones. They represent a

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

to shallow marine environment.Clemente, 2013, p.24 ;Iguape Formation The Iguape Formation is thick and consists of bioclastic calcarenites and calcirudites, containing

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...

, echinoids,

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...

s, foraminifera, fragmented shells, and algae remains. They are interbedded with grey-greenish clays, siltstones, marls and variegated grey fine-to-medium grained conglomerates. These facies are interbedded with and change laterally to the Marambaia Formation. The depositional environment is thought to be a marine carbonate platform, influenced by the arrival of alluvial clastics in the most proximal areas. Biostratigraphic data from planktonic foraminifera, calcareous nanofossils and palynomorphs indicate a Tertiary age.

;Marambaia Formation The Marambaia Formation is thick and consists of grey shales and light grey marls interbedded with fine-grained turbiditic sandstones. This formation in places can be found cropping out at sea bottom. The depositional environment is thought to be talus and open marine basin. Biostratigraphic data indicate a Tertiary age. ;Sepetiba Formation (Pleistocene) The Sepetiba Formation is the uppermost formation in the Santos Basin. It has a variable thickness due to the proximal erosion of the uppermost part. The formation consists of whitish grey fine to coarse grained carbonitic sands. They are

feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) felds ...

-rich,

glauconitic Glauconite is an iron potassium phyllosilicate (mica group) mineral of characteristic green color which is very friable and has very low weathering resistance. It crystallizes with a monoclinic geometry. Its name is derived from the Greek () me ...

s consisting of

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of marine and freshwater Mollusca, molluscs that have laterally compressed bodies enclosed by a shell consisting of two hing ...

fragments and foraminifera. The depositional environment is thought to be coastal. The stratigraphy following the classifications by Vieira 2007, Kiang Chang 2008 and Contreras 2011 is:

Basin analysis

4D Basin analysis of the Santos Basin has revealed insights about the interplay among the elements and processes of the petroleum system to assess

potential (vertical and horizontal distribution), thermal evolution of the source rocks, transformation ratio, hydrocarbon generation and charge, timing of migration, oil origin, quality, and volume of petroleum in the main reservoirs. In a basin modeling study performed in 2008 and 2009, a detailed facies model from the pre-salt section was built based on well data and conceptual models from seismic interpretation associated with previous knowledge of the tectono-sedimentary sequences of the Santos Basin. The predicted vitrinite map, integrated with all data, indicates that the Coquinas source rock in most of the eastern half area is in the main oil window, whereas the western half is in the late oil/wet gas generation window. In terms of transformation ratio, the Barremian and Aptian source rock systems in the area reached 70% to 80% today where the main depocentres are. The charge and accumulation simulation model for the pre-salt province suggests a potential reserve in the Cluster area of Santos Basin much larger than that reported, getting numbers to 60 billion barrels of oil reserves.Mello et al., 2009, p.47

Oil and gas exploration

Exploration in the Santos Basin started in the 1970s. Between 1970 and 1987, 59 dry wells were drilled, with one discovery in Santonian turbidites in 1979, Merluza Field. From 1988 to 1998, 45 wells were drilled in the basin providing small discoveries, with the of oil equivalent Tubarão Field discovered in 1988. Eighty-one wells were drilled from 1999 to 2005, leading to the discovery of the Mexilhão Field. Exploration boomed between 2006 and 2012, with 166 wells and the giant Tupi field (8 BBOE), discovered at the Tupi prospect in 2006. In 2013, the Sagitário Field was discovered in the sub-salt carbonates at a water depth of and a

true vertical depth True vertical depth'is the measurement of a straight line perpendicularly downwards from a horizontal plane. In the petroleum industry, true vertical depth, abbreviated as TVD, is the measurement from the surface to the bottom of the borehole ...

of .Juarez, 2013, p.1 In 2014, the pre-salt reservoirs of the Santos Basin produced more than .Moczydlower, 2014, p.34 Thanks to the pre-salt production, compensating for the declining post-salt production, the total oil production of Brazil rose above in April 2016.Oddone, 2017, p.5 The Lapa Field, originally named Carioca, was taken in production in December 2016.Ribeiro da Silva & Pereira, 2017, p.136 In 2017, the Santos Basin accounted for 35% of Brazil's oil, with the Campos Basin at 55%.Brazil Draws Auctions Calendar, Confirms Santos Basin Most Attractive Area
/ref> In the same year, 76 blocks were open for bidding in the Santos Basin.Petersohn, 2017, p.18

Etymology

Description

Tectonic history

Stratigraphy

I - Guaratiba Group (Hauterivian-Aptian, pre-salt sequence)

II - Ariri Formation (Late Aptian, salt sequence)

III - Camburi Group (Albian-Cenomanian, lower post-salt sequence)

IV - Frade Group (Turonian-Maastrichtian, middle post-salt sequence)

V - Itamambuca Group (Cenozoic, upper post-salt sequence)

Basin analysis

Oil and gas exploration

Oil and gas fields in the Santos Basin

See also

References

Bibliography

Brazil general

Santos Basin geology

Santos Basin exploration

External links