Earth:Açu Formation

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Açu Formation
Stratigraphic range: Albian
~112–100 Ma
TypeGeological formation
Unit ofApodi Group
UnderliesJandaíra Formation
OverliesAlagamar Formation
Lithology
PrimarySandstone
Location
Coordinates [ ⚑ ] : 5°48′S 38°06′W / 5.8°S 38.1°W / -5.8; -38.1
Paleocoordinates [ ⚑ ] 11°54′S 10°54′W / 11.9°S 10.9°W / -11.9; -10.9
RegionCeará
CountryBrazil
ExtentPotiguar Basin
Açu Formation is located in Brazil
Açu Formation
Açu Formation (Brazil)

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.[1]

Fossil content

The following fossils were reported from the formation:[2]

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 Images
Rebbachisauridae indet.[3] Indeterminate Ceará Albian Vertebrae
Tiamat[4] T. valdecii Ceará Albian to Cenomanian Caudal vertebrae A titanosaurian sauropod; closely related to Andesaurus delgadoi.
Titanosauria Indet.[5] Indeterminate Ceará Albian Osteoderm

Theropods

Theropods of the Açu Formation
Genus Species Location Stratigraphic position Material Notes Images
Abelisauridae Indet.[6] Indeterminate Ceará Albian to Cenomanian Teeth & Completed Femur
Baryonychinae Indet. Indeterminate Ceará Albian Tooth A spinosaurid theropod
Carcharodontosauridae Indet. Indeterminate Ceará Albian Vertebrae
Megaraptora Indet. Indeterminate Ceará Albian Vertebrae
Noasauridae Indet. Indeterminate Ceará Albian to Cenomanian Teeth
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
Candidodontidae Indet.[7] Indeterminat Ceará Albian to Cenomanian
Itasuchidae Indet. Indeterminate Ceará Albian to Cenomanian
Peirosauridae Indet. Indeterminate Ceará Albian Insolated Tooth
Sphagesauria Indet. Indeterminate Ceará Albian to Cenomanian

Fish

Fish of the Açu Formation
Genus Species Location Stratigraphic position Material Notes Images
Arganodus A. tiguidiensis Ceará Albian Teeth A arganodontid lungfish
Ceratodus C. brasilensis Ceará Albian Teeth A ceratodontid lungfish
Bawitius B. bartheli Ceará Albian Scales & Tooth A bichir
Distobatus[8] D. potiguarense Ceará Albian to Cenomanian A distobatid hybodont
Lepisosteus[9] L. sp. Ceará Albian to Cenomanian Scales & Tooth A gar
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

Bibliography

References

  1. ↑ Maraschin et al., 2010, p.87
  2. ↑ Açu Formation at Fossilworks.org
  3. ↑ Paulo Victor Luiz Gomes da Costa Pereira; Ingrid Martins Machado Garcia Veiga; Theo Baptista Ribeiro; Ryan Henrique Bezerra Cardozo; Carlos Roberto dos Anjos Candeiro; Lilian Paglarelli Bergqvist (2020). "The path of giants: a new occurrence of Rebbachisauridae (Dinosauria, Diplodocoidea) in the Açu Formation, NE Brazil, and its paleobiogeographic implications". Journal of South American Earth Sciences 100. doi:10.1016/j.jsames.2020.102515. Bibcode: 2020JSAES.10002515P. 
  4. ↑ Pereira, P. V. L. G. C.; Bandeira, K. L. N.; Vidal, L. S.; Ribeiro, T. B.; Candeiro, C. R. A.; Bergqvist, L. P. (2024). "A new sauropod species from north-western Brazil: biomechanics and the radiation of Titanosauria (Sauropoda: Somphospondyli)". Zoological Journal of the Linnean Society 202 (4). doi:10.1093/zoolinnean/zlae054. http://publication.plazi.org/id/FFE8FF8FFFE5FFB95E2E353FFFD4486B. 
  5. ↑ Pereira, P.V.L.G.C.; Marinho, T.S.; Candeiro, C.R.A.; Bergqvist, L.P. (2018). "A new titanosaurian (Sauropoda, Dinosauria) osteoderm from the Cretaceous of Brazil and its significance". Ameghiniana 55 (6): 644–650. doi:10.5710/AMGH.26.08.2018.3168. 
  6. ↑ Ribeiro, T. B.; Vecchietti, L. F.; Candeiro, C. R. A.; Canale, J. I.; Bergqvist, L. P.; Brito, P. M.; Pereira, P. V. L. G. C. (2025). "Overabundance of abelisaurid teeth in the Açu Formation (Albian-Cenomanian), Potiguar Basin, Northeastern Brazil: morphometric, cladistic and machine learning approaches". Journal of Vertebrate Paleontology: e2487366. doi:10.1080/02724634.2025.2487366. 
  7. ↑ Albuquerque, A. S.; Pinheiro, A. E. P.; Ribeiro, T. B.; Bergqvist, L. P.; Pereira, P. V. L. G. C. (2025). "Crocodyliform diversity of the Açu Formation (Albian–Cenomanian), Potiguar Basin, Brazil: geographical distribution and palaeobiological implications". Papers in Palaeontology 11 (4). doi:10.1002/spp2.70027. Bibcode: 2025PPal...1170027A. 
  8. ↑ Brito, P. M.; Veiga, I. M.; Dutheil, D. B.; Bergqvist, L. P. (2025). "First occurrence of Distobatus Werner, 1989 (Elasmobranchii: Hybodontiformes) in the middle Cretaceous (Albian–Cenomanian) of Brazil: Taxonomic and biogeographical implications". Cretaceous Research 171: 106119. doi:10.1016/j.cretres.2025.106119. 
  9. ↑ Costa, V. P. G.; Aureliano, T.; Santos, C. L. A.; Ghilardi, A. M. (2025). "The oldest occurrence of Lepisosteus (Ginglymodi: Lepisosteiformes: Lepisosteidae) in Gondwana". Historical Biology: An International Journal of Paleobiology: 1–8. doi:10.1080/08912963.2025.2504475. 



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