Açu Formation

Açu Formation
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°48′S 38°06′W / 5.8°S 38.1°W
Approximate paleocoordinates	11°54′S 10°54′W / 11.9°S 10.9°W
Region	Ceará
Country	Brazil
Extent	Potiguar Basin
	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]

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.

Sauropods of the Açu Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Rebbachisauridae indet.^[3]	Indeterminate
Tiamat^[4]^[5]	T. valdecii			Caudal Vertebrae and Osteoderm	a titanosaurian sauropoda; closely related to Andesaurus delgadoi.

Theropods of the Açu Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Abelisauridae Indet.	Indeterminate
Carcharodontosauridae Indet.	Indeterminate
Maniraptora Indet.	Indeterminate
Megaraptora Indet.	Indeterminate
Spinosauridae Indet.	Indeterminate

Turtles of the Açu Formation
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Apodichelys	A. lucianoi					A pelomedusid turtle

^ Maraschin et al., 2010, p.87
^ Açu Formation at Fossilworks.org
^ Gomes da Costa Pereira et al., 2020
^ 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.
^ 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. doi:10.1093/zoolinnean/zlae054.