Irbzer Formation

File:Palaeogeographic models Phosphate basins Morocco - Herbig 1991.png

During the Maastrichtian the inner area was alocated{{typo help inline|reason=similar to allocated|date=June 2025}} within a Anoxic marine setting, as revelated by bituminous, very oily and dolomitic black shells.{{Cite journal |last=Jacobshagen |first=Volker H. |date=1988 |title=The Atlas System of Morocco Volume 15 {{!}}{{!}} Synsedimentary tectonics in the Northern Middle Atlas (Morocco) during the late Cretaceous and Tertiary |url=https://link.springer.com/chapter/10.1007/BFb0011599 |journal=Studies on Its Geodynamic Evolution |volume=18 |pages=321–337|doi=10.1007/BFb0011599 |url-access=subscription }} Palynology of the underliying and coeval El Koubbat Formation has revelated an microbiota composed of Dinoflagellates, Pterospermopsis, Scolecodonts and Tasmanaceae.{{Cite journal |last1=Rauscher |first1=R. |last2=Schuler |first2=M. |last3=Benalioulhaj |first3=N. |date=1986 |title=Les Conditions de Depôt des Schistes Bitumineux et des Phosphates Maastrichtiens au Maroc: une Approche Palynologique. |url=https://paleobotany.ru/palynodata/publication/15643 |journal=Documents du Bureau de Recherches Géologiques et Minières |volume=110 |issue=1 |pages=127–139}}

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.{{Cite journal |last1=Andreu |first1=Bernard |last2=Tronchetti |first2=Guy |date=1996 |title=Ostracodes et foraminifèresdu Crétacé supérieur du synclinal d'El Koubbat, Moyen Atlas, Maroc |url=http://dx.doi.org/10.1016/s0016-6995(96)80071-4 |journal=Geobios |volume=29 |issue=1 |pages=45–71 |doi=10.1016/s0016-6995(96)80071-4 |bibcode=1996Geobi..29...45A |issn=0016-6995|url-access=subscription }} 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. 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.{{Cite journal |last1=Colin |first1=Jean-Paul |last2=Tabuce |first2=Rodolphe |date=2004 |title=Ostracodes limniques de la Formation d'Irbzer, Crétacé terminal du Moyen-Atlas, Maroc: taxonomie, biostratigraphie, paléoécologie, paléobiogéographie |url=http://dx.doi.org/10.1016/j.revmic.2004.04.001 |journal=Revue de Micropaléontologie |volume=47 |issue=2 |pages=103–109 |doi=10.1016/j.revmic.2004.04.001 |bibcode=2004RvMic..47..103C |issn=0035-1598|url-access=subscription }}

Marine Amniote fauna is known from coeval layers of the El Koubbat Formation, mostly Mosasaurs (Halisaurinae, Gavialimimus, Globidens, Mosasaurus, Prognathodontini) and Elasmosauridae plesiosaurs.{{Cite journal |last1=Vinkeles Melchers |first1=Alexander P. M. |last2=Martens |first2=Brennan P. |last3=Rempert |first3=Trevor H. |title=The marine reptile fauna of the Bekrit syncline (El Koubbat Formation, lower Maastrichtian), Middle Atlas Mountains, Morocco |url=https://www.researchgate.net/publication/385855276 |journal=7th Triennial Mosasaur Meeting – A Global Perspective on Mesozoic Marine AmniotesAt: Maastricht, the Netherlands}}

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{{Major African geological formations}}

Category:Geology of Morocco

Category:Cretaceous paleontological sites of Africa

Category:Cretaceous System of Africa

Category:Paleontological sites of Morocco