# Açu Formation

The Açu Formation is an Early Cretaceous (Albian) geologic formation of the Potiguar Basin in Ceará, northeastern Brazil. The formation comprises coarse-grained sandstones deposited in a fluvio-deltaic environment. The Açu Formation, belonging to the Apodi Group, has provided fossils of an indeterminate rebbachisaurid.

## Description

The Açu Formation was deposited in a passive margin setting, overlying the Alagamar Formation and is overlain by the Jandaíra Formation. In the petroleum producing Potiguar Basin, the formation is a reservoir rock.

## Fossil content

The following fossils were reported from the formation:
| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |

### Dinosaurs
#### Sauropods

Sauropods of the Açu Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes |
| Rebbachisauridae indet. | Indeterminate | Ceará | Albian | Vertebrae | |
| Tiamat | T. valdecii | Ceará | Albian to Cenomanian | Caudal vertebrae | A titanosaurian sauropod; closely related to Andesaurus delgadoi. |
| Titanosauria Indet. | Indeterminate | Ceará | Albian | Osteoderm | |

#### Theropods

Theropods of the Açu Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes |
| Abelisauridae Indet. | Indeterminate | Ceará | Albian | Teeth & Completed Femur | |
| Baryonychinae Indet. | Indeterminate | Ceará | Albian | Tooth | A spinosaurid theropod |
| Carcharodontosauridae Indet. | Indeterminate | Ceará | Albian | Vertebrae | |
| Megaraptora Indet. | Indeterminate | Ceará | Albian | Vertebrae | |
| Paraves Indet. | Indeterminate | Ceará | Albian | Vertebrae | A maniraptoran theropod |
| Spinosaurinae Indet. | Indeterminate | Ceará | Albian | Tooth | A spinosaurid theropod |

### Crocodylomorphs

Crocodylomorps of the Açu Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Peirosauridae Indet. | Indeterminate | Ceará | Albian | Insolated Tooth | | |

### Fish

Fish of the Açu Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes |
| Arganodus | A. tiguidiensis | Ceará | Albian | Teeth | A ceratodontid lungfish |
| Ceratodus | C. brasilensis | Ceará | Albian | Teeth | A ceratodontid lungfish |
| Bawitius | B. bartheli | Ceará | Albian | Scales & Tooth | A bichir |
| Distobatus | D. potiguarense | Ceará | Albian to Cenomanian | | A distobatid hybodont |
| Lepisosteidae Indet. | Indeterminate | Ceará | Albian | Scales & Tooth | |
| Mawsonia | M. gigas | Ceará | Albian to Cenomanian | | A mawsoniid coelacanth |
| Pycnodontiformes Indet. | Indeterminate | Ceará | Albian | Teeth | |
| Tharrhias | T. castelhanoi | Ceará | Albian | Scales | A gonorynchiform fish |
| Tribodus | T. limae | Ceará | Albian to Cenomanian | | A hybodont shark |
| Vidalamiinae Indet. | Indeterminate | Ceará | Albian | | |

### Crustaceans

Crustaceans of the Açu Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Unusuropode | U. castroi | Ceará | Albian | | A isopod | |

### Molluscs
#### Bivalves

Bivalves of the Açu Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Brachidontes | B. sp. | Ceará | Albian | | A mytilid mussel | |
| Mytilus | M. rosadoi | Ceará | Albian | | A mytilid mussel | |

#### Gastropods

Gastropods of the Açu Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Gastropoda Indet. | Indeterminate | Ceará | Albian | | | |

### Echinoderms

Echinoderms of the Açu Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Echinodermata Indet. | Indeterminate | Rio Grande do Norte | Albian | | | |

### Plants

Plants of the Açu Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Palmoxylon | P. sp. | Rio Grande do Norte | Albian | | | |