Açu Formation - Wikiwand

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.

TypeGeological formation

Unit ofApodi Group

UnderliesJandaíra Formation

OverliesAlagamar Formation

Quick facts Type, Unit of ...

Açu Formation
Stratigraphic range: Albian ~112–100 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Unit of	Apodi Group
Underlies	Jandaíra Formation
Overlies	Alagamar Formation
Lithology
Primary	Sandstone
Location
Coordinates	5.8°S 38.1°W / -5.8; -38.1
Approximate paleocoordinates	11.9°S 10.9°W / -11.9; -10.9
Region	Ceará
Country	Brazil
Extent	Potiguar Basin
Açu Formation (Brazil)

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

More information Sauropods of the Açu Formation, Genus ...

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

More information Theropods of the Açu Formation, Genus ...

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

More information Crocodylomorps of the Açu Formation, Genus ...

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

More information Fish of the Açu Formation, Genus ...

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

More information Crustaceans of the Açu Formation, Genus ...

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

Molluscs

Bivalves

More information Bivalves of the Açu Formation, Genus ...

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

More information Gastropods of the Açu Formation, Genus ...

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

Echinoderms

More information Echinoderms of the Açu Formation, Genus ...

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

Plants

More information Plants of the Açu Formation, Genus ...

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

Bibliography

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

[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]
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) e70027. Bibcode:2025PPal...1170027A. doi:10.1002/spp2.70027.
[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. 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.