Açu Formation

Not to be confused with Itajaí-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.

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

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

• 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: Article 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