El Mers Group Explained

El Mers Group
Period:	Bathonian
Age:	Bajocian–Callovian ~
Type:	Group
Prilithology:	Marl, gypsum (only in unit 3)
Otherlithology:	Sandstone, limestone
Subunits:	El Mers Formations 1–3
Underlies:	Unconformity with Barremian or Plio-Pleistocene sediments
Overlies:	Ich Timellaline–Bou Akrabene Formation
Thickness:	Over 500m (1,600feet)
Coordinates:	33.5°N -4.3°W
Paleocoordinates:	28.3°N -2°W
Region:	Boulemane and Azilal Provinces
Country:	Morocco
Extent:	Middle Atlas

The El Mers Group is a geological group in the Middle Atlas of Morocco. It is subdivided into three formations named the El Mers I, II, and III Formations, respectively. It is a marine deposit primarily consisting of marl, with gypsum present in the upper part of unit 3. It is the lateral equivalent of the terrestrial Guettioua Sandstone. Dinosaur remains are among the fossils that have been recovered from the group, most notably those of sauropods and the unusual thyreophorans Adratiklit, Thyreosaurus, and Spicomellus.

Description and paleoenvironment

The El Mers formations are composed primarily of marls with intermittent layers of limestone and sandstone, characterized by abundant organic matter and benthic fauna.^[1] It is delineated into five distinct members, each exhibiting diverse lithological characteristics. The three members comprise a combination of layers of marls, sandstones, and limestones, marked by various unique fossils and organic materials. Sedimentary discontinuities reveal deltaic sequences that exhibit varying sedimentary structures and lithological compositions, reflecting dynamic depositional environments ranging from subtidal to continental. The facies associations within the El Mers Formation are organized into elementary and mesosequences, delineating the transition from prodelta to deltaic plain environments. These sequences capture the evolution of tidal regimes and depositional dynamics.^[2]

The shifts in facies and microfauna evolution in our study area reveal intriguing patterns, from the establishment of initial supratidal environments characterized by charophytic marls and ostracod limestones followed by a resurgence of marine conditions, evident from the reappearance of coastal facies and the diversification of ostracod faunas, indicating a significant transgressive phase during the Upper Bathonian–Lower Callovian period. While in the Central High Atlas marine influences ceased by the Upper Bajocian–Lower Bathonian giving way to continental red layers, in the Middle Atlas marine influences persisted until the Upper Bathonian–Lower Callovian boundary, indicating a diachronic filling of the Atlas gulfs towards the Tethyan domain from west to east.^[3]

Fossils

Dasycladales

Genus	Species	Stratigraphic position	Material	Notes	Images
Heteroporella	H. lusitanica	SW part of the Skoura syncline	Calcareous imprints	A dasycladacean algae of the family Dasycladaceae
Sarfiatella	S. dubari	SW part of the Skoura syncline	Calcareous imprints	A dasycladacean algae, associated in adjacent regions with Aalenian–Bajocian faunas

Foraminifera

Genus	Species	Stratigraphic position	Material	Notes	Images
Bullopora	B. tuberculata	SW part of the Skoura syncline	Calcareous imprints	A benthic foraminiferan of the family Polymorphinidae
Pfenderella	P. cf. arabica	SW part of the Skoura syncline	Calcareous imprints	A benthic foraminiferan of the family Pfenderininae
Praekurnubia	P. crusei	SW part of the Skoura syncline	Calcareous imprints	A benthic foraminiferan of the family Pfenderinidae; a genus found in the Tethys between Bajocian and Oxfordian-aged layers
Pseudocyclammina	P. maynci	SW part of the Skoura syncline	Calcareous imprints	A benthic foraminiferan of the family Hauraniidae

Ostracoda

Genus	Species	Stratigraphic position	Material	Notes	Images
Cytherella	C. index	Ait Hammou	Valves	A freshwater/brackish ostracod of the family Cytherellidae
Fastigatocythere	F. aff. brentonensis	Ait Hammou	Valves	A freshwater/brackish ostracod of the family Progonocytheridae
Kinkelinella	K. aff. triangula	Ait Hammou	Valves	A freshwater ostracod of the family Progonocytheridae
Metacypris	M. spp.	Ait Hammou	Valves	A freshwater ostracod of the family Limnocytheridae. Local members of the genus genus would not be confined to limnic environments, but would be euryhaline or brackish, since they disappear when faunal diversity is at its maximum.
Procytheridea	P. ihopyensis	Ait Hammou	Valves	A freshwater ostracod of the family Schulerideidae

Mollusca

Genus	Species	Stratigraphic position	Material	Notes	Images
Cadomites	C. cf. bremeri	East Skoura syncline	Isolated shells	An ammonite of the family Stephanoceratidae and indicator of the Bathonian age
Choffatia	C. cf. urinacensis	East Skoura syncline	Isolated shells	An ammonite of the family Perisphinctidae and indicator of the Callovian age
Clydoniceras	C. discus	Tamguert n'Tarit Tizi n'Juillerh	Isolated shells
Modiolus	M. imbricatus	El Mers Tamguert n'Tarit	Isolated shells	A marine mussel of the family Mytilidae
Morphoceras	M. macrescens	East Skoura syncline	Isolated shells	An ammonite of the family Morphoceratidae and indicator of the Bathonian age
Oraniceras	O. sp.	East Skoura syncline	Isolated shells	An ammonite of the family Parkinsoniidae and indicator of the Bathonian age
Ostrea	O. sandalina	El Mers Tamguert n'Tarit	Isolated shells	A marine oyster of the family Ostreidae
Parkinsonia	P. sp.	Skoura syncline	Isolated shells	An ammonite of the family Parkinsoniidae and indicator of the Bajocian age for the lower portions of the Group
Protocardia	P. tikechkachensis	El Mers Tamguert n'Tarit	Isolated shells	A marine cockle of the family Cardiidae

Fishes

Genus	Species	Stratigraphic position	Material	Notes	Images
Lepidotes^[5]	L. spp.	Ait Hammou Djmila Oued El Mers Tizi n'Juillerh	Cranial material, isolated teeth and scales	A marine/brackish bony fish of the family Lepidotidae
Scheenstia	S. cf. mantelli	Oued El Mers	Partial specimen wirth cranial material	A marine/brackish bony fish of the family Lepidotidae

Crocodylomorpha

Genus	Species	Stratigraphic position	Material	Notes	Images
Hatcherichnus^[8]	H. ispp.	Inzar O'Founass	Footprints	Indeterminate Crocodrylomorph Tracks
"Megalosaurus"	"M." mersensis	Botane Tizi n'Juillerh	Isolated teeth and vertebra	A marine crocodylomorph of the family Teleosauridae. Mistaken as Theropod remains in the past.^[9]
Steneosaurus?	S.? spp.	Bou Iferaoun Botane Darak Djmila Oued Tamemecht Tamguert r'Tane Tirardine Tissenfelt	Isolated teeth, cranial and postcranial material, both isolated and semi-articulated	A marine crocodylomorph of the family Teleosauridae. The referral to the genus Steneosaurus should be taken with caution, as this genus was overlumped.

Dinosauria

Theropoda

Genus	Species	Stratigraphic position	Material	Notes	Images
Carmelopodus	cf.C. isp.	Tassmante O'Moche	Footprints	Theropod tracks of uncertain affinity, suggested to come from Ceratosauria members
Grallator?	G.? isp.	Ifri N'Tfrane	Footprints	Theropod Tracks, referred usually to small-medium sized Genera
Hispanosauropus?	H.? isp.	Ifri N'Tfrane	Footprints	Theropod tracks of uncertain affinity, different from Megalosauripus in the larger metatarsophalangeal region
Megalosauripus^[10]	M. ispp. cf.M. ispp.	El Mers Tasra Tasra Westbank Tassmante O'Moche Oued Tamghilt	Footprints	Traces of theropods; members of the ichnofiber family Eubrontidae, incertae sedis within Theropoda
Theropoda	Indeterminate	El Mers	Teeth	Isolated teeth of unidentified or undescribed/studied theropods
Theropodipedia^[11]	Indeterminate	El Mers Inzar O'Founass Ifri N'Tfrane Laach O'Medda Oulad Ali Tasra Tasra Westbank Tassmante O'Moche	Footprints	Theropod tracks of uncertain affinity, suggested to come from "allosaurs or megalosaurs"

Sauropoda

Genus	Species	Stratigraphic position	Material	Notes	Images
Breviparopus	B. isp.	El Mers Oued Tamghilt	Footprints	Traces of sauropods typical of the ichnofamily Parabrontopodidae, incertae sedis within Sauropodomorpha. Includes traces with pes similar to Diplodocoidea.
Cetiosaurus^[12]	"C." mogrebiensis	Aîn ou N'Jourh Taghrout Tamguert r'Tane Tamguert n'Tarit Tich Niouine	Complete skeleton and referred co-types of partially complete and incomplete specimens	A eusauropod of the family Cetiosauridae, currently awaiting revision and likely not a member of the genus Cetiosaurus^[13]
Sauropoda^[14] ^[15]	Indeterminate	Aït Tamjout Boulahfa 1 km east of Taguelft	Isolated and articulated bones	Indeterminate or undescribed sauropod remains
Sauropodina^[16]	Indeterminate	El Mers Tasra Tasra Westbank Oulad Ali	Footprints	Sauropod tracks of uncertain affinity. There are both small and enormous sauropod tracks, including some among the largest known worldwide, with a pes track length of up to 130 cm.

Ornithischia

Genus	Species	Stratigraphic position	Material	Notes	Images
Adratiklit^[17]	A. boulahfa	Boulahfa	NHMUK PV R37366 (A dorsal vertebra), three cervical vertebrae (NHMUK PV R37367; R37368), a dorsal vertebra (NHMUK PV R37365), and a left humerus (NHMUK PV R37007)	A dacentrurine stegosaur
Ornithopodichnus?	O.? ispp.	Ifri N'Tfrane	Footprints	Ornithichian Tracks, referred to short-toed forms such as Gilmoreosaurus
Spicomellus^[18]	S. afer	Boulahfa	NHMUK PV R37412, a partial rib bearing four co-ossified spines	An early ankylosaurian
Thyreosaurus^[19]	T. atlasicus	Boulahfa North	HIIUC-BN00, a partial postcranial skeleton that includes nine dorsal vertebrae and 21 dorsal rib remains, a limb bone (fibula?), and six dermal elements	A dacentrurine stegosaur with unusual recumbent osteoderms

Plantae

See also

• Tafraout Group (Toarcian–Aalenian)
• Azilal Formation (Toarcian-Aalenian)
• Guettioua Formation (Bathonian–?Callovian)
• Anoual Formation (Bathonian)
• Ksar Metlili Formation (Tithonian–?Berrasian)

Notes and References

1. Oukassou. M.. Boumir. Kh.. Benshili. Kh.. Ouarhache. D.. Lagnaoui. A.. Charrière. A.. June 2019. The Tichoukt Massif: a Geotouristic Play in the Folded Middle Atlas (Morocco). Geoheritage. 11. 2. 371–379. 10.1007/s12371-018-0287-y. 2019Geohe..11..371O . 134800520 . 1867-2477.
2. Soufiani . N. . Fedan . B. . 2002 . Les dépôts bathoniens du synclinal d'El Mers (Moyen Atlas, Maroc): unités formationnelles, analyse et cadre géodynamique . Bulletin de l'Institut scientifique . 24 . 6 . 1–14.
3. Charrière . André . Dépêche . Françoise . Feist . Monique . Grambast-Fessard . Nicole . Jaffrezo . Michel . Peybernès . Bernard . Ramalho . Miguel . 1994 . Microfaunes, microflores et paléoenvironnements successifs dans la formation d'El Mers (Bathonien-?Callovien) du synclinal de Skoura (Moyen-Atlas, Maroc) . Geobios . 27 . 2 . 157–174 . 10.1016/s0016-6995(94)80002-2 . 1994Geobi..27..157C . 0016-6995.
4. Oukassou. Mostafa. Charrière. André. Lagnaoui. Abdelouahed. Gibb. Stacey. Michard. André. Saddiqi. Omar. April 2016. First occurrence of the Ichnogenus Selenichnites from the Middle Jurassic Strata of the Skoura Syncline (Middle Atlas, Morocco); Palaeoecological and palaeoenvironmental context. Comptes Rendus Palevol. 15. 5. 461–471. 10.1016/j.crpv.2015.09.013. 2016CRPal..15..461O . free.
5. Beltan . Laurence . 1957-01-01 . Etude d'un neurocrane de Lepidotes du Bathonien du Maroc . Bulletin de la Société Géologique de France . S6-VII . 8–9 . 1091–1106 . 10.2113/gssgfbull.s6-vii.8-9.1091 . 1777-5817.
6. Lapparent . A. F. d. . 1955 . Étude paléontologique des vertébrés du Jurassique d'El Mers (Moyen Atlas) [Paleontological study of the Jurassic veretebrates from El Mers (Middle Atlas)] ]. Notes et Mémoires du Service Géologique du Maroc . 124 . 1 . 1–36.
7. Termier . H. . Gubler . J. . Lapparent . A. F. . 1940 . Reptiles et Poissons du Bathonien d'El-Mers (Moyen-Atlas marocain) [Reptiles and fishes from the Bathonian of El Mers (Moroccan Middle Atlas)]. ]. Comptes Rendus de l'Académie des Sciences de Paris . 210 . 3 . 768–770.
8. Amzil . Mustapha . Oukassou . Mostafa . Lallensack . Jens N. . Klein . Hendrik . Zafaty . Omar . Saber . Hafid . Charrière . André . Meyer . Christian . Gierliński . Gerard D. . 2024 . New dinosaur tracks from the Middle Jurassic red beds of the Middle Atlas (Morocco): Application of photogrammetry to ichnology and conservation of geological heritage . Proceedings of the Geologists' Association . 22 . 3 . 12–31. 10.1016/j.pgeola.2024.06.004 .
9. Chabli . S. . 1986 . Données nouvelles sur un «Dinosaurien» jurassique moyen du Maroc: Megalosaurus mersensis Lapparent 1955, et sur les Megalasaurides en Sénégal . Les dinosaures de la Chine à la France . 1 . 2 . 65–72.
10. Hadri . M. . Lorente . F. P. . 2012 . Historia de yacimientos con huellas de dinosaurio, desde su descubrimiento hasta su primer estudio: alrededores de El Mers (Marruecos) . Zubia . 30 . 6 . 93–147.
11. Jenny . Jacques . Le Marrec . Alain . Monbaron . Michel . 1981 . Les empreintes de pas de Dinosauriens dans le Jurassique moyen du Haut Atlas central (Maroc): Nouveaux gisements et precisions stratigraphiques . Geobios . 14 . 3 . 427–431 . 10.1016/s0016-6995(81)80186-6 . 1981Geobi..14..427J . 0016-6995.
12. Allain. Ronan. Aquesbi. Najat. 2008. Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco . Geodiversitas . 30 . 2 . 345–424.
13. Läng . E. . 2008 . Les Cétiosaures (Dinosaura, sauropoda) et les sauropodes du Jurassique moyen: revision systématique, nouvelles découvertes et implications phylogénétiques . (Doctoral dissertation, Paris, Muséum national d'histoire naturelle) . 1–223. 160327994 .
14. Termier . Henri . 1942-01-01 . Donnees nouvelles sur le Jurassique rouge a dinosauriens du Grand et du Moyen-Atlas (Maroc) . Bulletin de la Société Géologique de France . S5-XII . 4–6 . 199–207 . 10.2113/gssgfbull.s5-xii.4-6.199 . 1777-5817.
15. Charroud . M. . Fedan . B. . 1992 . Données préliminaires sur la découverte du gisement de Boulahfa à dinosauriens (SW de Boulemane, Moyen Atlas central) . Notes et Mémoire du Service géologique du Maroc . 366 . 5 . 448–449.
16. Meyer . C. A. . Thüring . B. . 2005 . Mind the Middle Jurassicgap-bone versus track record in dinosaurs . Abstracts 3rd Swiss Geoscience Meeting Zurich . 3 . 1 . 59–60.
17. Maidment. Susannah C.R.. Raven. Thomas J.. Ouarhache. Driss. Barrett. Paul M.. January 2020. North Africa's first stegosaur: Implications for Gondwanan thyreophoran dinosaur diversity. Gondwana Research. 77. 82–97. 10.1016/j.gr.2019.07.007. 2020GondR..77...82M . free. 10141/622706. free.
18. Maidment. Susannah C. R.. Strachan. Sarah J.. Ouarhache. Driss. Scheyer. Torsten M.. Brown. Emily E.. Fernandez. Vincent. Johanson. Zerina. Raven. Thomas J.. Barrett. Paul M.. 2021-09-23. Bizarre dermal armour suggests the first African ankylosaur. Nature Ecology & Evolution. 5 . 12 . en. 1576–1581. 10.1038/s41559-021-01553-6. 34556830 . 2021NatEE...5.1576M . 237616095 . 2397-334X.
19. Zafaty . O. . Oukassou . M. . Riguetti . F. . Company . J. . Bendrioua . S. . Tabuce . R. . Charrière . A. . Pereda-Suberbiola . X. . 2024 . A new stegosaurian dinosaur (Ornithischia: Thyreophora) with a remarkable dermal armour from the Middle Jurassic of North Africa . . 131 . 344–362 . In press . 10.1016/j.gr.2024.03.009. 2024GondR.131..344Z .
20. Philippe . M. . Bamford . M. . McLoughlin . S. . Alves . L.S.R. . Falcon-Lang . H.J. . Gnaedinger . S. . Ottone . E.G. . Pole . M. . Rajanikanth . A. . Shoemaker . R.E. . Torres . T. . Zamuner . A. . 2004 . Biogeographic analysis of Jurassic–Early Cretaceous wood assemblages from Gondwana . Review of Palaeobotany and Palynology . 129 . 3 . 141–173 . 10.1016/j.revpalbo.2004.01.005 . 2004RPaPa.129..141P . 0034-6667.