The Guaratiba Group is 4,200 metres (13,800 ft) 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 40 metres (130 ft) thick and includes the basaltic 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 and augite, usually fresh, non-altered.

Piçarras Formation
The Piçarras Formation is 990 metres (3,250 ft) thick and consists of clastic and carbonate rocks.
The formation includes reddish polymictic conglomerates, with clasts of basalt and quartz in a clay-sandy matrix.
It also includes white, reddish lacustrine coquinas (shelly limestones) and sandstones, siltstones and shales of stevensite composition.
Its age, based on the ostracod assemblages, is Hauterivian to Aptian.

The conglomerates and sandstones of the formation are representative of an alluvial environment.
The coquinas represent a shallow lacustrine environment.
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 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.

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 and silicified.
In more distal sections, the formation consists of dark organic matter rich shales.
In the well 1-RSJ-625, the formation includes 110 metres (360 ft) 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 300 to 350 metres (980 to 1,150 ft) 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 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.
The Guaratiba Group is 4,200 metres (13,800 ft) 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 40 metres (130 ft) thick and includes the basaltic 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 and augite, usually fresh, non-altered.
Piçarras Formation
The Piçarras Formation is 990 metres (3,250 ft) thick and consists of clastic and carbonate rocks. The formation includes reddish polymictic conglomerates, with clasts of basalt and quartz in a clay-sandy matrix. It also includes white, reddish lacustrine coquinas (shelly limestones) and sandstones, siltstones and shales of stevensite composition. Its age, based on the ostracod assemblages, is Hauterivian to Aptian.
The conglomerates and sandstones of the formation are representative of an alluvial environment. The coquinas represent a shallow lacustrine environment. 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 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.
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 and silicified. In more distal sections, the formation consists of dark organic matter rich shales. In the well 1-RSJ-625, the formation includes 110 metres (360 ft) 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 300 to 350 metres (980 to 1,150 ft) 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 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.
Santos Basin