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.Tuiguidit foreland at Fossilworks.org 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.Weishampel, David B; et al. (2004). "Dinosaur distribution (Early Cretaceous, Africa)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 571-573. . 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 (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. 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
Bivalves Bivalves of the Tiourarén FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImageAdrarunioA. deserticusTeguidda-n-AdrarLower MemberShellsA nakamuranaiadid freshwater bivalve; one of the earliest known trigonioidoidsAfrohyrioidesA. jowikolensis 20 km E of Mount Bellal Mount IguallalaUpper MemberShellsA unionid freshwater bivalveAsturianaiaA. soudanensis In-Tedreft KP-35, Zinder track Reg TamesnaAll MembersShellsA margaritiferid freshwater bivalveCoactunioC. iguallalensis Mount Iguallala Mount EbenenanouaUpper MemberShellsA unionid freshwater bivalveRostrunioR. lapparentiKP-35, Zinder trackUpper MemberShellsA unionid freshwater bivalveSaharellaS. tedreftensisReg TamesnaUpper MemberShellsA unionid freshwater bivalveTamesnellaT. amatouensis SE of In-Afer In-Amatou 20 km E of Mount Bellal SW of Oued TessellamaneUpper MemberShellsA tamesnelloid freshwater epifaunal substrate bivalveTamesnelloidesT. lithoidesSE of In-AferUpper MemberShellsA tamesnelloid freshwater epifaunal substrate bivalveTegulaedonT. humei SE of In-Afer 35 km NE of Mount BellalUpper MemberShellsA margaritiferid freshwater bivalveTuaregunioT. agadesensisKP-35, Zinder trackUpper MemberShellsA unionid freshwater bivalveUnionelloidesU. 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 JadalUpper MemberShellsA unionid freshwater bivalve. U. giganteus represents an unusually large taxon.U. (Phortunio) giganteus10 km E of In-AbangaritU. bellalensis35 km NE of Mount BellalUpper MemberShellsUnionidaIndet AReg TamesnaAll MembersShellsIndeterminate A unionid freshwater bivalvesIndet. BTeguidda-n-Adrar
Fishes Fishes of the Tiourarén FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImageAsiatoceratodusA. tiguidensis Irhazer Plain Falaise de TiguiditUpper MemberIsolated tooth plates & other remainsAn asiatoceratodontid lungfishCeratodusC. sp.Falaise de TiguiditUpper MemberTooth platesA ceratodontid lungfishHolostei Indet.IndeterminateFalaise de TiguiditUpper Member"scales of ganoid fishes"Indeterminate fish remains Hybodus? H.? spp. Abaka, Agadez Tadibene Irhazer PlainUpper Member TeethA hybodontiform chondrichthyan Lepidotes?L. spp. Abaka, Agadez Tadibene Irhazer PlainUpper MemberIsolated scalesA lepisosteiform bony fish Mawsoniidae Indet.Indeterminate Abaka, Agadez Tadibene Irhazer PlainUpper MemberTeeth, isolated scales & partially articulated remains of the caudal finA coelacanth, previously referred to Mawsonia
Turtles "Turtle Bones" where quoted in the OR description of the unit.
Turtles of the Tiourarén FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImagePleurodira Indet.IndeterminateAbaka, AgadezUpper MemberIsolated RemainsIndeterminate Turtle remainsTestudinata? Indet.IndeterminateIrhazer PlainUpper MemberIsolated eggBased on the "small size, spherical shape, and small pores" was suggested it belonged to a turtle
Crocodylomorphs "Crocodiles" where quoted in the OR description of the unit.
Crocodylomorphs of the Tiourarén FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImageCrocodylomorpha Indet.Indeterminate Abaka, Agadez Falaise de Tiguidit TawachiUpper MemberTeeth, osteodermsIndeterminate crocodylomorph remainsGoniopholididae Indet.Gen. et sp. nov AIrhazer PlainUpper MemberComplete skullThe first African goniopholidids, suggesting connections with LaurasiaGen. et sp. nov BIrhazer PlainUpper MemberNarrow cranium with elongated snout
Dinosaurs "Rare (in abundance) pterosaurs" where quoted in the OR description of the unit.
Dinosaurs of the Tiourarén FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImage AfrovenatorA. abakensisAbaka, AgadezUpper MemberUC OBA 1, partial skull and associated postcranial remainsAn afrovenatorine megalosauroidean A? sp.NE of TadibeneUpper MemberTP4-12, rostral part of left maxillaCf. A sp.TawachiUpper MemberPremaxillae, dentaries and appendicular skeletonAllosauridae Indet.IndeterminateNE of TadibeneUpper MemberTP4-6; TP4-7, isolated teethTeeth referred to allosaurids or basal allosauroidsCeratosauria Indet.IndeterminateNE of TadibeneUpper MemberTP4-4, isolated teethAn indeterminate ceratosaurEusauropoda Indet.Gen. et sp. nov 1Irhazer PlainLower MemberSkull and multiple articulated postcranial skeletonsA notoriously complete taxon with stocky proportions, robust skull, and short neckGen. et sp. nov 2AgadezUpper MemberDorsal vertebrae, humerus, and femurDiffers 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 TawachiUpper Member Skull and several skeletons A sauropod, maybe a eusauropod; among the most abundant terrestrial vertebrates in the formation Megalosauridae Indet.IndeterminateNE of TadibeneUpper MemberTP4-5, TP4-8, TP4-10, teethAn indeterminate megalosaur"Rebbachisaurus""R." tamesnensisTamerát, AgadezUpper MemberDorsal vertebrae and scapulaAn indeterminate sauropod, also reported from younger Cretaceous beds, likely representing different taxa.Sauropoda Indet.Indeterminate Falaise de Tiguidit Soureya buttesUpper Member SMNB 1695-R, articulated caudal series, partial other postcrania Undescribed isolated & disarticulated bonesIndeterminate or unnamed sauropod remainsSpinosauridae? Indet.IndeterminateNE of TadibeneUpper MemberTP4-2, TP4-3, teethReferred 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 ungualsPossibly a basal ceratosaurian, a basal abelisauroid, or a noasaurid Thyreophora Indet. Gen. et sp. nov Abaka, Agadez TawachiUpper 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 Indet.Gen. et sp. nov AgadezUpper MemberPartial articulated skeletonsDiffers from Jobaria in deflected humeral head, shorter to the ulna and radius
Plants Plants of the Tiourarén FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImageTaxodioideae Indet.IndeterminateFalaise de TiguiditUpper MemberFossil woodConifer wood referred the family Cupressaceae. Petrified wood is notoriously abundant, suggesting dense forested areas surrounding the local braided river systems
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
References
Further reading A. F. d. Lapparent. 1960. Les Dinosauriens du "Continental intercalaire" du Saharal central [The dinosaurs of the "Continental Intercalaire" of the central Sahara]. Mémoires de la Société géologique de France, nouvelle série 39(88A):1-57 P. C. Sereno, A. L. Beck, D. B. Dutheil, H. C. E. Larsson, G. H. Lyon, B. Moussa, R. W. Sadleir, C. A. Sidor, D. J. Varricchio, G. P. Wilson, and J. A. Wilson. 1999. Cretaceous sauropods from the Sahara and the uneven rate of skeletal evolution among dinosaurs. Science 286:1342-1347 P. C. Sereno, J. A. Wilson, H. C. E. Larsson, D. B. Dutheil, and H.-D. Sues. 1994. Early Cretaceous dinosaurs from the Sahara. Science 266(5183):267-271 F. Witzmann, O. Hampe, B. M. Rothschild, U. Joger, R. Kosma, D. Schwarz, and P. Asbach. 2016. Subchondral cysts at synovial vertebral joints as analogies of Schmorl's Nodes in a sauropod dinosaur from Niger. Journal of Vertebrate Paleontology 36(2):e1080719:1-11