Guabirotuba Formation
Stratigraphic range: Late Mid Eocene (Divisaderan) ~42–38 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Underlies	alluvium
Overlies	Cambrian basement
Thickness	60–80 m (200–260 ft)
Lithology
Primary	Mudstone, sandstone
Other	Conglomerate
Location
Coordinates	25°30′S 49°18′W / 25.5°S 49.3°W / -25.5; -49.3
Approximate paleocoordinates	27°30′S 39°48′W / 27.5°S 39.8°W / -27.5; -39.8
Region	Paraná
Country	Brazil
Extent	Curitiba Basin
Type section
Named for	Guabirotuba, Curitiba
Named by	Salamuni & Bigarella
Year defined	1962
Guabirotuba Formation (Brazil)

The Guabirotuba Formation is a late Middle Eocene (Divisaderan in the SALMA classification) geologic formation of the Curitiba Basin in Paraná, Brazil. The formation crops out in and around the city of Curitiba and comprises mudstones and sandstones deposited in a fluvial floodplain environment.

The 60 to 80 metres (200 to 260 ft) thick formation has provided several fossil mammals, and indeterminate side-neck turtle fossils, and indeterminate terror bird fossils. A newly described species of Cingulata; Proeocoleophorus carlinii was also found in the formation.

Description

The Guabirotuba Formation was first described by Riad Salamuni [pt] and João José Bigarella [pt] in 1962. The geologists named the formation after Guabirotuba [pt], a neighborhood of Curitiba, the capital of Paraná State.^[1] The formation is the lowermost sedimentary unit in the 3,000 square kilometres (1,200 sq mi) Curitiba Basin, a Cenozoic continental rift basin of southeastern Brazil,^[2] overlying Cambrian basement comprising gneisses, amphibolites and migmatites of the Atuba Complex and metasediments of the Açungui Group.^[3][4]

Lithologies

The 60 to 80 metres (200 to 260 ft) thick Guabirotuba Formation comprises a basal conglomerate,^[5] mudstones and sandstones,^[3] deposited in a fluvial floodplain environment.^[2][6]

The sediments of the formation contain between 0.24 and 2.61% heavy minerals.^[7] Heavy mineral analysis on the very abundant zircons, abundant epidote, common tourmaline and kyanite and rare rutile has provided insight in the paleocurrents of the fluvial environment, with predominant flow directions towards the northwest and east-northeast.^[8]

Age

The age of the formation has been a matter of debate, with early descriptions assigning the formation to the Miocene to Pliocene,^[6] but after the discovery of a mammal fauna described by Sedor et al. in 2017, the age of the formation has been defined as late Middle Eocene, or "Barrancan", which is a sub-age of the Divisaderan South American land mammal age,^{[note 1]} ranging from approximately 42 to 39 Ma.^[10][11]

Paleontological significance

The Guabirotuba Formation is one of few formations in Brazil providing Paleogene mammal faunas, between the older Tiupampan Maria Farinha Formation of the Parnaíba Basin and the Itaboraian Itaboraí Formation of the Itaboraí Basin in Rio de Janeiro State, and the younger Tinguirirican Entre-Córregos Formation of the Aiuruoca Basin and the Deseadan Tremembé Formation of the Taubaté Basin.^[2]

Fossil content

Fossils recovered from the formation include:^[12]

Class	Group	Fossils	Images	Notes
Mammals	Dasypodidae	Machlydotherium sp.		[12]
		Meteutatus sp.		[12]
		Parutaetus sp.		[12]
		Utaetus sp.		[12]
		Astegotheriini indet.		[12]
		Euphractinae indet.		[12]
	Cingulata	Proeocoleophorus carlinii		[12]
	Notoungulata	Oldfieldthomasiidae indet.		[12]
		Notopithecidae indet.		[12]
	Astrapotheria	Astrapotheria indet.		[12]
	Paucituberculata	Palaeothentoidea indet.		[12]
	Sparassodonta	Nemolestes sp.		[12]
	Theriiformes	Argyrolagoidea indet.		[12]
Birds	Phorusrhacidae	Phorusrhacidae indet.		[13]
Reptiles	Turtles	Pleurodira indet.		[14]