Tiourarén Formation

The Tiourarén Formation is a geological formation in the Agadez Region of Niger whose strata were originally thought to be Early Cretaceous. However, re-interpretation of the sediments showed that they are probably Middle or Late Jurassic (Bathonian-Oxfordian) in age.^[1][2] Other works suggested it reaches the Barremian.^[3] It is the uppermost unit of the Irhazer Group. Dinosaur remains & other vertebrates are among the fossils that have been recovered from the formation.^[4] Originally part of the "Argiles de l'Ihrazer", the Tiouaren Formation primarily comprises reddish to purple siltstones with occasional marls, limestones, and scarce channel sandstones.^[1]

Tiourarén Formation
Stratigraphic range: Middle or Late Jurassic 170–145 Ma PreꞒ Ꞓ O S D C P T J K Pg N (Suggested post Bathonian, reaching either Oxfordian or even Barremian)
Map showing dinosaur localities around Agadez, Niger
Type	Geological formation
Unit of	Irhazer Group
Underlies	Tazolé Formation (Tegama Group)
Overlies	Irhazer Shale
Thickness	~350 m (1,150 ft)
Lithology
Primary	Siltstone, mudstone
Other	Sandstone, marl, limestone
Location
Coordinates	16.5°N 7.8°E / 16.5; 7.8
Approximate paleocoordinates	8.2°N 2.5°E / 8.2; 2.5
Region	Agadez
Country	Niger
Extent	Iullemmeden Basin
Type section
Named for	Tiourarén hill, Agadez
Named by	Moody R.T.J. & Sutcliffe P.J.C.
Tiourarén Formation (Niger)

Description

Black Flag Lake near Kalgoorlie Australia, an Equivalent of the Tiourarén Formation

The formation comprises reddish, almost solid mudstones, which also shows grey and white streaks, probably caused by alternating oxidative and reducing environments. Stromatolites are intermittently found in calcareous layers, while indications of semi-arid to arid conditions such as desiccation cracks and caliche horizons have been reported.^[5] Other lithology includes green or grayish clays, marls, dolomite beds with chert, and phosphatic sandstone limestones.^[6] At Agadez this section is invaded by channels of coarse feldspathic sandstones with limestone nodules and fine, ripple-marked sandstones, featuring green and purple clays with intercalations of cherty limestone beds in the uppermost sequence. The sandstone component increases eastward, and the formation wedges out between the underlying Agadez Sandstones and the overlying Tegama Group.^[6]

The formation suggests a low-energy setting with expansive floodplains, temporary shallow lake development, and calcrete horizon interchanged with swamps, with seasonal flooding from a meandering, shallow river system dominated by overbanked silt. Many sandstone channels are composed of reworked sand grain-sized pebbles of mudstone, supporting the view of a predominantly low-relief environment.^[2] This latter feature is suggested by the widespread occurrence freshwater ostracod accumulations and rarer unionid bivalve shells.^[5] Local sedimenst were very affected and influenced by large scale faulting.^[7]

The Early Cretaceous dating for the Tiouaren Formation was based on vertebrate fossil evidence, specially Mawsoniidae coelacanths (referred without evidence to Mawsonia lavocati), while other taxa like Hybodus? sp. and Lepidotes? sp., are either dubious or have a suggested wide temporal distribution and invertebrates (conchostracans and unionid bivalves), offer limited stratigraphic value.^[1] Recent report of an ash bed and other potentially datable beds near fossil bearing horizons opens the possibility of a future age calibration.^[8]

Fossil content

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.

Bivalves

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Adrarunio[9]	A. deserticus	Teguidda-n-Adrar	Lower Member	Shells	A nakamuranaiadid freshwater bivalve; one of the earliest known trigonioidoids
Afrohyrioides[9]	A. jowikolensis	20 km E of Mount Bellal Mount Iguallala	Upper Member	Shells	A unionid freshwater bivalve
Asturianaia[9][10]	A. soudanensis	In-Tedreft KP-35, Zinder track Reg Tamesna	All Members	Shells	A margaritiferid freshwater bivalve
Coactunio[9]	C. iguallalensis	Mount Iguallala Mount Ebenenanoua	Upper Member	Shells	A unionid freshwater bivalve
Rostrunio[9]	R. lapparenti	KP-35, Zinder track	Upper Member	Shells	A unionid freshwater bivalve
Saharella[9]	S. tedreftensis	Reg Tamesna	Upper Member	Shells	A unionid freshwater bivalve
Tamesnella[9]	T. amatouensis	SE of In-Afer In-Amatou 20 km E of Mount Bellal SW of Oued Tessellamane	Upper Member	Shells	A tamesnelloid freshwater epifaunal substrate bivalve
Tamesnelloides[9]	T. lithoides	SE of In-Afer	Upper Member	Shells	A tamesnelloid freshwater epifaunal substrate bivalve
Tegulaedon[9]	T. humei	SE of In-Afer 35 km NE of Mount Bellal	Upper Member	Shells	A margaritiferid freshwater bivalve
Tuaregunio[9]	T. agadesensis	KP-35, Zinder track	Upper Member	Shells	A unionid freshwater bivalve
Unionelloides[9]	U. globulosus	Teguidda-n-Tessoumt SE of In-Afer In-Amatou 35 km NE of Mount Bellal 20 km E of Mount Bellal SW of Oued Tessellamane Erg Jadal	Upper Member	Shells	A unionid freshwater bivalve. U. giganteus represents an unusually large taxon.[11]
	U. (Phortunio) giganteus	10 km E of In-Abangarit
	U. bellalensis	35 km NE of Mount Bellal	Upper Member	Shells
Unionida[9]	Indet A	Reg Tamesna	All Members	Shells	Indeterminate A unionid freshwater bivalves	Example of extant Unionid
	Indet. B	Teguidda-n-Adrar

Fishes

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Asiatoceratodus[1][12]	A. tiguidensis	Irhazer Plain Falaise de Tiguidit	Upper Member	Isolated tooth plates & other remains	An asiatoceratodontid lungfish
Ceratodus[13]	C. sp.	Falaise de Tiguidit	Upper Member	Tooth plates	A ceratodontid lungfish	Reconstruction
Holostei[13]	Indeterminate	Falaise de Tiguidit	Upper Member	"scales of ganoid fishes"	Indeterminate fish remains
Hybodus?[1]	H.? spp.	Abaka, Agadez Tadibene Irhazer Plain	Upper Member	Teeth	A hybodontiform chondrichthyan	Hybodus model
Mawsoniidae[1][14]	Indeterminate		Upper Member	Teeth, isolated scales & partially articulated remains of the caudal fin	A coelacanth, previously referred to Mawsonia
Lepidotes?[1]	L. spp.		Upper Member	Isolated scales	A lepisosteiform bony fish

Testudinata

"Turtle Bones" where quoted in the OR description of the unit.^[5]

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Testudinata?[15]	Indeterminate	Irhazer Plain	Upper Member	Isolated egg	Based on the "small size, spherical shape, and small pores" was suggested it belonged to a turtle

Crocodylomorpha

"Crocodiles" where quoted in the OR description of the unit.^[5]

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Crocodylomorpha[13]	Indeterminate	Falaise de Tiguidit Tawachi[16]	Upper Member	Teeth, osteoderms	Indeterminate crocodylomorph remains
Goniopholididae[17]	Gen. et sp. nov A	Irhazer Plain	Upper Member	Complete skull	The first African goniopholidids, suggesting connections with Laurasia
	Gen. et sp. nov B	Irhazer Plain	Upper Member	Narrow cranium with elongated snout

Avemetarsalia

"Rare (in abundance) pterosaurs" where quoted in the OR description of the unit.^[5]

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Afrovenator[18][19]	A. abakensis	Abaka, Agadez	Upper Member	UC OBA 1, partial skull and associated postcranial remains	An afrovenatorine megalosauroidean
	A? sp.	NE of Tadibene	Upper Member	TP4-12, rostral part of left maxilla
	Cf. A sp.[20][16]	Tawachi	Upper Member	Premaxillae, dentaries and appendicular skeleton
Allosauridae[19]	Indeterminate	NE of Tadibene	Upper Member	TP4-6; TP4-7, isolated teeth	Teeth referred to allosaurids or basal allosauroids
Ceratosauria[19]	Indeterminate	NE of Tadibene	Upper Member	TP4-4, isolated teeth	An indeterminate ceratosaur
Eusauropoda[8]	Gen. et sp. nov 1	Irhazer Plain	Lower Member	Skull and multiple articulated postcranial skeletons	A notoriously complete taxon with stocky proportions, robust skull, and short neck
	Gen. et sp. nov 2	Agadez	Upper Member	Dorsal vertebrae, humerus, and femur	Differs from other local taxa on pleurocoels on posterior dorsal vertebrae and a longer humerus relative to the femur
Jobaria[21]	J. tiguidensis	Tamerát, Agadez Fako, Agadez Tawachi[16]	Upper Member	Skull and several skeletons	A sauropod, maybe a eusauropod; among the most abundant terrestrial vertebrates in the formation
Megalosauridae[19]	Indeterminate	NE of Tadibene	Upper Member	TP4-5, TP4-8, TP4-10, teeth	An indeterminate megalosaur
"Rebbachisaurus"[18][22]	"R." tamesnensis[18]	Tamerát, Agadez	Upper Member	Dorsal vertebrae and scapula	An indeterminate sauropod, also reported from younger Cretaceous beds, likely representing different taxa.
Sauropoda[13][23]	Indeterminate	Falaise de Tiguidit Soureya buttes	Upper Member	SMNB 1695-R, articulated caudal series, partial other postcrania Undescribed isolated & disarticulated bones	Indeterminate or unnamed sauropod remains
Spinosauridae?[19]	Indeterminate	NE of Tadibene	Upper Member	TP4-2, TP4-3, teeth	Referred to spinosaurs, may be of ceratosaur origin instead
Spinostropheus[24]	S. gautieri	Fako, Agadez Tawachi[16] Tedreft	Upper Member	Remains of many individuals including cervical, dorsal, and caudal vertebra, partial left humerus, ulna, distal pubis, distal femur, incomplete tibia, fibulae, metatarsals, pedal phalangeal fragments, and manual unguals[25]	Possibly a basal ceratosaurian, a basal abelisauroid, or a noasaurid
Thyreophora[26]	Gen. et sp. nov	Abaka, Agadez Tawachi[16]	Upper Member	"Associated, but disarticulated, bones, teeth, and abundant scutes from many individuals ranging in maturity from subadult to adult"	A basal thyreophoran, suggested to be related to Scutellosaurus. A relatively common taxon, with a bonebed of up to twenty individuals.[14]
Turiasauria[27]	Gen. et sp. nov	Agadez	Upper Member	Partial articulated skeletons	Differs from Jobaria in deflected humeral head, shorter to the ulna and radius

Plantae

Genus	Species	Stratigraphic position	Stratigraphic position	Material	Notes	Images
Taxodioideae[13]	Indeterminate	Falaise de Tiguidit	Upper Member	Fossil wood	Conifer wood referred the family Cupressaceae. Petrified wood is notoriously abundant, suggesting dense forested areas surrounding the local braided river systems	Taxodium distichum, extant example of conifer of the same family

See also

• List of dinosaur-bearing rock formations
• Lists of fossiliferous stratigraphic units in Africa
  • List of fossiliferous stratigraphic units in Niger
• Geology of Niger