Irbzer Formation

Irbzer Formation
Stratigraphic range: Maastrichtian-Paleocene
~70–60 Ma
TypeGeological formation
AreaFes-Boulmane
Lithology
PrimaryGray mudstone
Location
Coordinates33°1′N 4°8′W / 33.017°N 4.133°W / 33.017; -4.133
Approximate paleocoordinates24°5′N 5°2′W / 24.083°N 5.033°W / 24.083; -5.033
RegionFes-Boulmane
CountryMorocco
Irbzer Formation is located in Morocco
Irbzer Formation
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][2]

Description

The Irbzer Formation is 100–440 m thick, that records the transition from marginal-marine to continental environments. It is divided into three members: Lower member (20–190 m): begins with marine-influenced phosphatic sandstones, sandy limestones and marly limestones rich in marine fossils (shark teeth, mosasaurs, bivalves), then passes upward into thick white-to-varicoloured marls, often gypsiferous, with charophytes, ostracods and dinosaur eggshell fragments.[2] Middle member (2–55 m): sharp-based terrigenous interval resting on an erosive disconformity; composed of red sandstones, channelized polymictic conglomerates and siltstones with cross-bedding, ripples and bioturbation, reflecting fluvial-alluvial deposition.[2] Finally, the Upper member (25–170 m): dominantly varicoloured or gray marls with basal gypsum in many sections, thin sandstones and occasional charophyte levels; deposited in restricted lacustrine–floodplain settings.[2]

Paleoenvironment

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

During the Maastrichtian the inner area was situated within an anoxic marine setting, as revelated by bituminous, very oily and dolomitic black shells.[3] Palynology of the underliying and coeval El Koubbat Formation has revelated an microbiota composed of Dinoflagellates, Pterospermopsis, Scolecodonts and Tasmanaceae.[4]

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.[5] 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.[5] 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][6]

Marine Amniote fauna is known from coeval layers of the El Koubbat Formation, mostly Mosasaurs (Halisaurinae, Gavialimimus, Globidens, Mosasaurus, Prognathodontini) and Elasmosauridae plesiosaurs.[7]


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[8]
  • F. sp.
 Oudiksou syncline Gyrogonites A charophyte of the family Feistiellaceae
Lagynophora[9]
  • L. liburnica
 Oudiksou syncline Gyrogonites A charophyte of the family Characeae
Lamprothamnium[8]
  • L. sp.
 Oudiksou syncline Gyrogonites A charophyte of the family Characeae
Porochara[9]
  • P. stacheana
 Oudiksou syncline Gyrogonites A charophyte of the family Characeae
Sphaerochara[8]
  • S. cf. edda
 Oudiksou syncline Gyrogonites A charophyte of the family Characeae
Stephanochara[8]
  • S. sp.
 Oudiksou syncline Gyrogonites A charophyte of the family Characeae

Ostracods

Genus Species Location Material Notes Images
Brachycythere[5]
  • B. cf. gr. sapucariensis
 El Koubbat Valves A marine Ostracod of the family Brachycytheridae
Clithrocytheridea[5]
  • C. senegali
 El Koubbat Valves A marine Ostracod of the family Cytherideidae
Costa[5]
  • C. sp
 El Koubbat Valves A marine Ostracod of the family Trachyleberididae
Cytheretta[5]
  • C.? koubbatensis
 El Koubbat Valves A marine Ostracod of the family Cytherettidae
Cytherella[5]
  • C. sp
 El Koubbat Valves A marine Ostracod of the family Cytherellidae
Gomphocythere[6]
  • G. achloujensis
 Achlouj Valves A freshwater Ostracod of the family Limnocytheridae
Oertliella[5]
  • O. sp.
 El Koubbat Valves A marine Ostracod of the family Trachyleberididae
Rehacythereis[5]
  • R. sp
 El Koubbat Valves A marine Ostracod of the family Trachyleberididae
Paracandona[6]
  • P. occitanica
 Achlouj Valves A freshwater Ostracod of the family Candonidae
Paracypris[5]
  • 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[10]
  • 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

Crocodylomorpha

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

Sauropoda

Genus Species Location Material Notes Images
Megaloolithus[1][11]
  • M. maghrebiensis
  • M. sp.
 Achlouj 2, levels 17 to 19, eggshells Eggshells referred to Titanosauridae sauropods
Example of Megaloolithus
Pseudomegaloolithus[1][11]
  • P. atlasi
 Achlouj 2, level 18-19 eggshells Indeterminate Sauropod eggshells

Theropoda

Genus Species Location Material Notes Images
Pseudogeckoolithus[1][11]
  • P. tirboulensis
 Achlouj 2, levels 17 to 19 eggshells Theropod eggs referred to Maniraptora
Rodolphoolithus[1][11]
  • R. arioul
 Achlouj 2, levels 18 to 19 eggshells Indeterminate eggs likely laid by non-avian or avian theropods
"Paronychodon"[1]
  • "P. sp."
 Oukdiksou syncline Teeth A theropod, probably related with Troodontidae or Unenlagiinae
Tipoolithus[1][11]
  • T. achloujensis
 Achlouj 2, levels 18 to 19 eggshells Theropod eggs, referred to an enantiornithine bird or small Coelurosaur

References

  1. ^ 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.
  2. ^ a b c d Amelieh, Abdessamad; Oukassou, Mostafa; Guinot, Guillaume; Zafaty, Omar; Mhamdi, Hicham Si; Yans, Johan; Charrière, André; Tabuce, Rodolphe (2025-11-28). "Biostratigraphy, palaeoenvironments and palaeogeography of the Cretaceous–Paleogene succession in the Oudiksou Basin, Central Middle Atlas of Morocco". Palaeogeography, Palaeoclimatology, Palaeoecology 113451. doi:10.1016/j.palaeo.2025.113451. ISSN 0031-0182.
  3. ^ 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.
  4. ^ 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.
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.
  8. ^ 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.
  9. ^ a b Enßlin, Rainer (1993). Die Kreide des zentralen Mittleren Atlas und der Haute Moulouya, Marokko: Stratigraphie, Mikrofazies, Paläogeographie und Paläotektonik. Selbstverlag Fachbereich Geowissenschaften, FU Berlin. ISBN 978-3-927541-72-6.
  10. ^ 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.
  11. ^ a b c d e Vianey-Liaud, Monique; Garcia, Géraldine (2003-12-15). "Diversity among north african dinosaur eggshells". PalaeoVertebrata. ISSN 2274-0333.

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