| Irbzer Formation | |
| Type: | Geological formation |
| Age: | Maastrichtian-Paleocene ~ |
| Period: | Maastrichtian |
| Prilithology: | Gray mudstone |
| Region: | Fes-Boulmane |
| Country: | Morocco |
| Coordinates: | 33.0167°N -12°W |
| Paleocoordinates: | 24.0833°N -7°W |
| Area: | Fes-Boulmane |
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]
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. 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.[5]
Marine Amniote fauna is know from coeval layers of the El Koubbat Formation, mostly Mosasaurs (Halisaurinae, Gavialimimus, Globidens, Mosasaurus, Prognathodontini) and Elasmosauridae plesiosaurs.[6]
| Genus | Species | Location | Material | Notes | Images | |
|---|---|---|---|---|---|---|
| Feistiella[7] |
| Oudiksou syncline | Gyrogonites | A charophyte of the family Feistiellaceae | ||
| Lamprothamnium |
| Oudiksou syncline | Gyrogonites | A charophyte of the family Characeae | ||
| Sphaerochara |
| Oudiksou syncline | Gyrogonites | A charophyte of the family Characeae | ||
| Stephanochara |
| Oudiksou syncline | Gyrogonites | A charophyte of the family Characeae |
| Genus | Species | Location | Material | Notes | Images | |
|---|---|---|---|---|---|---|
| Brachycythere |
| El Koubbat | Valves | A marine Ostracod of the family Brachycytheridae | ||
| Clithrocytheridea |
| El Koubbat | Valves | A marine Ostracod of the family Cytherideidae | ||
| Costa |
| El Koubbat | Valves | A marine Ostracod of the family Trachyleberididae | ||
| Cytheretta |
| El Koubbat | Valves | A marine Ostracod of the family Cytherettidae | ||
| Cytherella |
| El Koubbat | Valves | A marine Ostracod of the family Cytherellidae | ||
| Gomphocythere |
| Achlouj | Valves | A freshwater Ostracod of the family Limnocytheridae | ||
| Oertliella |
| El Koubbat | Valves | A marine Ostracod of the family Trachyleberididae | ||
| Rehacythereis |
| El Koubbat | Valves | A marine Ostracod of the family Trachyleberididae | ||
| Paracandona |
| Achlouj | Valves | |||
| Paracypris |
| El Koubbat | Valves | A marine Ostracod of the family Paracyprididae |
| Genus | Species | Location | Material | Notes | Images | |
|---|---|---|---|---|---|---|
| Cretalamna |
| Oukdiksou syncline | Teeth | A Shark of the family Otodontidae | ||
| Dalpiazia |
| Oukdiksou syncline | Teeth | A Chondrichthian of the family Sclerorhynchidae | ||
| Ganopristis |
| Oukdiksou syncline | Teeth | A Chondrichthian of the family Sclerorhynchidae | ||
| Serratolamna |
| Oukdiksou syncline | Teeth | A Shark of the family Serratolamnidae | ||
| Squalicorax |
| Oukdiksou syncline | Teeth | A Shark of the family Anacoracidae |
| Genus | Species | Location | Material | Notes | Images | |
|---|---|---|---|---|---|---|
| Pseudomegaloolithus |
| Oukdiksou syncline | eggshells | Indeterminate Sauropod eggshells | ||
| Megaloolithus |
| Oukdiksou syncline | eggshells | Eggshells referred to Titanosauridae sauropods |
| Genus | Species | Location | Material | Notes | Images | |
|---|---|---|---|---|---|---|
| Pseudogeckoolithus |
| Oukdiksou syncline | eggshells | Theropod eggs referred to Maniraptora | ||
| Rodolphoolithus |
| Oukdiksou syncline | eggshells | Indeterminate eggs likely laid by small theropods | ||
| "Paronychodon" |
| Oukdiksou syncline | Teeth | A theropod, probably related with Troodontidae or Unenlagiinae | ||
| Tipoolithus |
| Oukdiksou syncline | eggshells | Theropod eggs, referred to an enantiornithine bird or small theropod |