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
During the Maastrichtian the inner area was alocated 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
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Color key
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Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
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Charophytes
| Genus
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Species
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Location
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Material
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Notes
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Images
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| Feistiella[7]
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Oudiksou syncline
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Gyrogonites
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A charophyte of the family Feistiellaceae
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| Lamprothamnium[7]
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Oudiksou syncline
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Gyrogonites
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A charophyte of the family Characeae
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| Sphaerochara[7]
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Oudiksou syncline
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Gyrogonites
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A charophyte of the family Characeae
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| Stephanochara[7]
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Oudiksou syncline
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Gyrogonites
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A charophyte of the family Characeae
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Ostracods
| Genus
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Species
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Location
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Material
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Notes
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Images
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| Brachycythere[4]
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El Koubbat
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Valves
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A marine Ostracod of the family Brachycytheridae
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| Clithrocytheridea[4]
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El Koubbat
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Valves
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A marine Ostracod of the family Cytherideidae
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| Costa[4]
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El Koubbat
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Valves
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A marine Ostracod of the family Trachyleberididae
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| Cytheretta[4]
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El Koubbat
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Valves
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A marine Ostracod of the family Cytherettidae
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| Cytherella[4]
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El Koubbat
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Valves
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A marine Ostracod of the family Cytherellidae
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| Gomphocythere[5]
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Achlouj
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Valves
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A freshwater Ostracod of the family Limnocytheridae
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| Oertliella[4]
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El Koubbat
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Valves
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A marine Ostracod of the family Trachyleberididae
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| Rehacythereis[4]
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El Koubbat
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Valves
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A marine Ostracod of the family Trachyleberididae
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| Paracandona[5]
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Achlouj
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Valves
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A freshwater Ostracod of the family Candonidae
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| Paracypris[4]
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El Koubbat
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Valves
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A marine Ostracod of the family Paracyprididae
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Echinoderms
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Species
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Location
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Material
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Notes
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Images
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| Cretasterias[8]
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Bakrit
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Thousands of specimens
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A sea star of the family Asteriidae
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Fish
Crocodrylomorpha
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Species
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Location
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Material
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Notes
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Images
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| Krokolithidae[1]
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Oukdiksou syncline
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eggshells
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Indeterminate Crocodrilian eggshells
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Sauropoda
Theropoda
References
- ^ a b c d e f g h i j k l m 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.
- ^ 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.
- ^ 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.
- ^ a b c d e f g h i j k 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.
- ^ a b c 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.
- ^ 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.
- ^ a b c d 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.
- ^ 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.