Irbzer Formation

Irbzer Formation
Stratigraphic range: Maastrichtian-Paleocene ~70–60  Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Area	Fes-Boulmane
Lithology
Primary	Gray mudstone
Location
Coordinates	33°1′N4°8′W / 33.017°N 4.133°W / 33.017; -4.133
Approximate paleocoordinates	24°5′N5°2′W / 24.083°N 5.033°W / 24.083; -5.033
Region	Fes-Boulmane
Country	Morocco
Irbzer Formation (Morocco)

The Irbzer Formation is a geological formation located in Morocco in the area of Fes-Boulmane of latest Cretaceous (Maastrichtian) to Paleocene age. The lower section of this formation consists of yellowish, cross-bedded calcareous sandstone containing shark teeth, while the layer above comprises phosphatic marls with vertebrate bone beds, including dinosaur remains. ^[1]

Paleoenvironment

Reconstructions of the "Phosphate sea" of Morocco. The Irbzer Formation area is seen at the NE

During the Maastrichtian the inner area was alocated^{[ check spelling ]} within a Anoxic marine setting, as revelated by bituminous, very oily and dolomitic black shells. ^[2] Palynology of the underliying and coeval El Koubbat Formation has revelated an microbiota composed of Dinoflagellates, Pterospermopsis , Scolecodonts and Tasmanaceae. ^[3]

The formation reflects a shallow marine to lagoonal setting, transitioning from fine sands to marls and limestones. The presence of marine organisms, including bivalves and gastropods, along with phosphatic layers containing fish remains, indicates periodic marine incursions, with intermittent lagoonal or nearshore conditions. ^[4] Oxidation and sedimentary discontinuities suggest episodes of exposure or subaerial erosion. The overall environment was likely a shallow, low-energy, marginal marine setting with occasional deeper marine influences. ^[4] No planktonic foraminifera are present, and the few benthic foraminifera offer limited ecological insights. However, ostracodes, though poorly preserved, are more abundant and provide significant information about the environment. The ostracode assemblage including indicates a shallow (0–20 m), oligohaline, moderately alkaline, and relatively warm limnic environment, likely permanent and near the shoreline, as suggested by the presence of isolated dinosaur teeth and eggshell fragments in these layers. ^{[4] [5]}

Marine Amniote fauna is known from coeval layers of the El Koubbat Formation, mostly Mosasaurs (Halisaurinae, Gavialimimus , Globidens , Mosasaurus , Prognathodontini) and Elasmosauridae plesiosaurs. ^[6]

Biota

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.

Charophytes

Genus	Species	Location	Material	Notes	Images
Feistiella [7]	F. sp.	Oudiksou syncline	Gyrogonites	A charophyte of the family Feistiellaceae
Lamprothamnium [7]	L. sp.	Oudiksou syncline	Gyrogonites	A charophyte of the family Characeae
Sphaerochara [7]	S. cf. edda	Oudiksou syncline	Gyrogonites	A charophyte of the family Characeae
Stephanochara [7]	S. sp.	Oudiksou syncline	Gyrogonites	A charophyte of the family Characeae

Ostracods

Genus	Species	Location	Material	Notes	Images
Brachycythere [4]	B. cf. gr. sapucariensis	El Koubbat	Valves	A marine Ostracod of the family Brachycytheridae
Clithrocytheridea [4]	C. senegali	El Koubbat	Valves	A marine Ostracod of the family Cytherideidae
Costa [4]	C. sp	El Koubbat	Valves	A marine Ostracod of the family Trachyleberididae
Cytheretta [4]	C.? koubbatensis	El Koubbat	Valves	A marine Ostracod of the family Cytherettidae
Cytherella [4]	C. sp	El Koubbat	Valves	A marine Ostracod of the family Cytherellidae
Gomphocythere [5]	G. achloujensis	Achlouj	Valves	A freshwater Ostracod of the family Limnocytheridae
Oertliella [4]	O. sp.	El Koubbat	Valves	A marine Ostracod of the family Trachyleberididae
Rehacythereis [4]	R. sp	El Koubbat	Valves	A marine Ostracod of the family Trachyleberididae
Paracandona [5]	P. occitanica	Achlouj	Valves	A freshwater Ostracod of the family Candonidae
Paracypris [4]	P. cf. mdaouerensis P. sp. P.? sp.	El Koubbat	Valves	A marine Ostracod of the family Paracyprididae

Echinoderms

Genus	Species	Location	Material	Notes	Images
Cretasterias [8]	C. reticulatus	Bakrit	Thousands of specimens	A sea star of the family Asteriidae

Fish

Genus	Species	Location	Material	Notes	Images
Cretalamna [1]	C. maroccana	Oukdiksou syncline	Teeth	A Shark of the family Otodontidae	Cretalmana reconstruction
Dalpiazia [1]	D. strollleri	Oukdiksou syncline	Teeth	A Chondrichthian of the family Sclerorhynchidae
Ganopristis [1]	G. leptodoll	Oukdiksou syncline	Teeth	A Chondrichthian of the family Sclerorhynchidae
Serratolamna [1]	S. serrata	Oukdiksou syncline	Teeth	A Shark of the family Serratolamnidae
Squalicorax [1]	S. pristodontus S. bassallii	Oukdiksou syncline	Teeth	A Shark of the family Anacoracidae	Squalicorax reconstruction

Crocodrylomorpha

Genus	Species	Location	Material	Notes	Images
Krokolithidae [1]	Indeterminate	Oukdiksou syncline	eggshells	Indeterminate Crocodrilian eggshells

Sauropoda

Genus	Species	Location	Material	Notes	Images
Pseudomegaloolithus [1]	P. atlasi	Oukdiksou syncline	eggshells	Indeterminate Sauropod eggshells
Megaloolithus [1]	M. maghrebiensis M. sp.	Oukdiksou syncline	eggshells	Eggshells referred to Titanosauridae sauropods	Example of Megaloolithus

Theropoda

Genus	Species	Location	Material	Notes	Images
Pseudogeckoolithus [1]	P. tirboulensis	Oukdiksou syncline	eggshells	Theropod eggs referred to Maniraptora
Rodolphoolithus [1]	R. arioul	Oukdiksou syncline	eggshells	Indeterminate eggs likely laid by small theropods
" Paronychodon " [1]	"P. sp."	Oukdiksou syncline	Teeth	A theropod, probably related with Troodontidae or Unenlagiinae
Tipoolithus [1]	T. achloujensis	Oukdiksou syncline	eggshells	Theropod eggs, referred to an enantiornithine bird or small theropod

References

1. Garcia, G.; Tabuce, R.; Cappetta, H.; Marandat, B.; Bentaleb, I.; Benabdallah, A.; Vianey-Liaud, M. (2003). "First record of dinosaur eggshells and teeth from the North-West African Maastrichtian (Morocco)". Palaeovertebrata. 32 (2–4): 59–69.
2. Jacobshagen, Volker H. (1988). "The Atlas System of Morocco Volume 15 || Synsedimentary tectonics in the Northern Middle Atlas (Morocco) during the late Cretaceous and Tertiary" . Studies on Its Geodynamic Evolution. 18: 321–337. doi:10.1007/BFb0011599.
3. Rauscher, R.; Schuler, M.; Benalioulhaj, N. (1986). "Les Conditions de Depôt des Schistes Bitumineux et des Phosphates Maastrichtiens au Maroc: une Approche Palynologique". Documents du Bureau de Recherches Géologiques et Minières. 110 (1): 127–139.
4. Andreu, Bernard; Tronchetti, Guy (1996). "Ostracodes et foraminifèresdu Crétacé supérieur du synclinal d'El Koubbat, Moyen Atlas, Maroc" . Geobios. 29 (1): 45–71. Bibcode:1996Geobi..29...45A. doi:10.1016/s0016-6995(96)80071-4. ISSN   0016-6995.
5. Colin, Jean-Paul; Tabuce, Rodolphe (2004). "Ostracodes limniques de la Formation d'Irbzer, Crétacé terminal du Moyen-Atlas, Maroc: taxonomie, biostratigraphie, paléoécologie, paléobiogéographie" . Revue de Micropaléontologie. 47 (2): 103–109. Bibcode:2004RvMic..47..103C. doi:10.1016/j.revmic.2004.04.001. ISSN   0035-1598.
6. Vinkeles Melchers, Alexander P. M.; Martens, Brennan P.; Rempert, Trevor H. "The marine reptile fauna of the Bekrit syncline (El Koubbat Formation, lower Maastrichtian), Middle Atlas Mountains, Morocco". 7th Triennial Mosasaur Meeting – A Global Perspective on Mesozoic Marine AmniotesAt: Maastricht, the Netherlands.
7. Schudack, Michael; Herbig, H.G. (1995). "Charophytes from the Cretaceous -Tertiary Boundary Beds of the Middle Atlas Mountains, Morocco" . Géologie Méditerranéenne. 22 (3): 125–139. doi:10.3406/geolm.1995.1574. ISSN   0397-2844.
8. GALE, ANDY; VILLIER, LOÏC (2013). "Mass mortality of an asteriid starfish (Forcipulatida, Asteroidea, Echinodermata) from the late Maastrichtian (Late Cretaceous) of Morocco". Palaeontology. 56 (3): 577–588. Bibcode:2013Palgy..56..577G. doi:10.1111/pala.12002. ISSN   0031-0239.