Açu Formation

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Not to be confused with Itajaí-Açu Formation.
Açu Formation
Stratigraphic range: Albian
~112–100 Ma
TypeGeological formation
Unit ofApodi Group
UnderliesJandaíra Formation
OverliesAlagamar Formation
Lithology
PrimarySandstone
Location
Coordinates5°48′S 38°06′W / 5.8°S 38.1°W / -5.8; -38.1
Approximate paleocoordinates11°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

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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

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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

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Sauropods

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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

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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

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

Fish

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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[7] D. potiguarense Ceará Albian to Cenomanian A distobatid hybodont
Lepisosteus[8] 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

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

Molluscs

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Bivalves

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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

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

Echinoderms

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

Plants

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

Bibliography

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  • Gomes da Costa Pereira, Paulo Victor; Ribeiro, Theo Baptista; Brusatte, Stephen Louis; Dos Anjos Candeiro, Carlos Roberto; da Silva Marinho, Thiago; Paglarelli Bergqvist, Lilian (2020), "Theropod (Dinosauria) diversity from the Potiguar basin (Early-late Cretaceous Albian – Cenomanian), Northeast Brazil" (PDF), Cretaceous Research, in press 104517, doi:10.1016/j.cretres.2020.104517, hdl:20.500.11820/849a673d-9aa1-4b8e-be0c-f630af8a5d5e
  • Maraschin, Anderson; Mizusaki, Ana Maria P.; Vasconcelos, P.M.; Hinrichs, Ruth (2010), "Depositional age definition of the Açu Formation (Potiguar Basin, northeastern Brazil) through 40Ar-39Ar dating of early-authigenic K-feldspar overgrowths", Pesquisas Em Geociencias, 37: 85–96, doi:10.22456/1807-9806.22649, retrieved 2020-06-18

References

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  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 102515. Bibcode:2020JSAES.10002515P. doi:10.1016/j.jsames.2020.102515. S2CID 212916577.
  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.
  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. ^ 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. 106119. doi:10.1016/j.cretres.2025.106119.
  8. ^ 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.