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 in age. Other works suggested it reaches the Barremian. It is the uppermost unit of the Irhazer Group. Dinosaur remains & other vertebrates are among the fossils that have been recovered from the formation. 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.

Description

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. Other lithology includes green or grayish clays, marls, dolomite beds with chert, and phosphatic sandstone limestones. 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.
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. This latter feature is suggested by the widespread occurrence freshwater ostracod accumulations and rarer unionid bivalve shells. Local sedimenst were very affected and influenced by large scale faulting.
The Early Cretaceous dating for the Tiouaren Formation was based on vertebrate fossil evidence, specially Mawsoniidae coelacanths , while other taxa like Hybodus? sp. and Lepidotes? sp.'', are either dubious or have a suggested wide temporal distribution and invertebrates, offer limited stratigraphic value. Recent report of an ash bed and other potentially datable beds near fossil bearing horizons opens the possibility of a future age calibration.

Fossil content

Testudinata

"Turtle Bones" where quoted in the OR description of the unit.

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Pleurodira	Indeterminate	Abaka, Agadez	Upper Member	Isolated Remains	Indeterminate Turtle remains
Testudinata?	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.

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

Avemetarsalia

"Rare pterosaurs" where quoted in the OR description of the unit.

Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Afrovenator	A. abakensis	Abaka, Agadez	Upper Member	UC OBA 1, partial skull and associated postcranial remains	An afrovenatorine megalosauroidean
Afrovenator	A? sp.	NE of Tadibene	Upper Member	TP4-12, rostral part of left maxilla	An afrovenatorine megalosauroidean
Afrovenator	Cf. A sp.	Tawachi	Upper Member	Premaxillae, dentaries and appendicular skeleton	An afrovenatorine megalosauroidean
Allosauridae	Indeterminate	NE of Tadibene	Upper Member	TP4-6; TP4-7, isolated teeth	Teeth referred to allosaurids or basal allosauroids
Ceratosauria	Indeterminate	NE of Tadibene	Upper Member	TP4-4, isolated teeth	An indeterminate ceratosaur
Eusauropoda	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
Eusauropoda	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	J. tiguidensis	Tamerát, Agadez Fako, Agadez Tawachi	Upper Member	Skull and several skeletons	A sauropod, maybe a eusauropod; among the most abundant terrestrial vertebrates in the formation
Megalosauridae	Indeterminate	NE of Tadibene	Upper Member	TP4-5, TP4-8, TP4-10, teeth	An indeterminate megalosaur
"Rebbachisaurus"	"R." tamesnensis	Tamerát, Agadez	Upper Member	Dorsal vertebrae and scapula	An indeterminate sauropod, also reported from younger Cretaceous beds, likely representing different taxa.
Sauropoda	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?	Indeterminate	NE of Tadibene	Upper Member	TP4-2, TP4-3, teeth	Referred to spinosaurs, may be of ceratosaur origin instead
Spinostropheus	S. gautieri	Fako, Agadez Tawachi 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	Possibly a basal ceratosaurian, a basal abelisauroid, or a noasaurid
Thyreophora	Gen. et sp. nov	Abaka, Agadez Tawachi	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.
Thyreophora	Gen. et sp. nov	Abaka, Agadez Tawachi	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.
Turiasauria	Gen. et sp. nov	Agadez	Upper Member	Partial articulated skeletons	Differs from Jobaria in deflected humeral head, shorter to the ulna and radius