El Mers Formation
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. 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.
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.
Fossils
Color key
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Notes Uncertain or tentative taxa are in small text; |
Dasycladales
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Heteroporella |
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Calcareous imprints | A dasycladacean algae of the family Dasycladaceae | |
| Sarfiatella |
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Calcareous imprints | A dasycladacean algae, associated in adjacent regions with Aalenian–Bajocian faunas |
Foraminifera
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Bullopora |
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Calcareous imprints | A benthic foraminiferan of the family Polymorphinidae | |
| Pfenderella |
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Calcareous imprints | A benthic foraminiferan of the family Pfenderininae | |
| Praekurnubia |
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Calcareous imprints | A benthic foraminiferan of the family Pfenderinidae; a genus found in the Tethys between Bajocian and Oxfordian-aged layers | |
| Pseudocyclammina |
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Calcareous imprints | A benthic foraminiferan of the family Hauraniidae |
Ostracoda
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Cytherella |
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Valves | A freshwater/brackish ostracod of the family Cytherellidae | |
| Fastigatocythere |
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Valves | A freshwater/brackish ostracod of the family Progonocytheridae | |
| Kinkelinella |
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Valves | A freshwater ostracod of the family Progonocytheridae | |
| Metacypris |
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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 |
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Valves | A freshwater ostracod of the family Schulerideidae |
Xiphosura
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Selenichnites |
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Isolated crescent-shaped trace fossils | Traces of xiphosurans, representing the second occurrence of this ichnogenus in Morocco |
Mollusca
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Cadomites |
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Isolated shells | An ammonite of the family Stephanoceratidae and indicator of the Bathonian age |  |
| Choffatia |
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Isolated shells | An ammonite of the family Perisphinctidae and indicator of the Callovian age | |
| Clydoniceras |
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Isolated shells | An ammonite of the family Clydoniceratidae | |
| Modiolus |
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Isolated shells | A marine mussel of the family Mytilidae | .jpg) |
| Morphoceras |
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Isolated shells | An ammonite of the family Morphoceratidae and indicator of the Bathonian age | |
| Oraniceras |
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Isolated shells | An ammonite of the family Parkinsoniidae and indicator of the Bathonian age | |
| Ostrea |
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Isolated shells | A marine oyster of the family Ostreidae |  |
| Parkinsonia |
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Isolated shells | An ammonite of the family Parkinsoniidae and indicator of the Bajocian age for the lower portions of the Group |  |
| Protocardia |
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Isolated shells | A marine cockle of the family Cardiidae |
Fishes
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Lepidotes |
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Cranial material, isolated teeth and scales | A marine/brackish bony fish of the family Lepidotidae |  |
| Scheenstia |
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Partial specimen wirth cranial material | A marine/brackish bony fish of the family Lepidotidae |  |
Testudinata
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Testudinata |
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Very numerous debris: escutcheons, plates, vertebrae, ribs, long bones | Turtle remains of uncertain affinity |
Crocodylomorpha
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Hatcherichnus |
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Footprints | Indeterminate Crocodrylomorph Tracks | |
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Isolated teeth and vertebra |
A marine crocodylomorph of the family Teleosauridae. Mistaken as Theropod remains in the past. |
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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 |
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Footprints | Theropod tracks of uncertain affinity, suggested to come from Ceratosauria members | |
| Grallator? |
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Footprints | Theropod Tracks, referred usually to small-medium sized Genera | |
| Hispanosauropus? |
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Footprints | Theropod tracks of uncertain affinity, different from Megalosauripus in the larger metatarsophalangeal region | |
| Megalosauripus |
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Footprints | Traces of theropods; members of the ichnofiber family Eubrontidae, incertae sedis within Theropoda | |
| Averostra |
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Isolated Teeth | Isolated teeth of unidentified or undescribed/studied theropods. Teeth associated with the Teleosaur "Megalosaurus" mersensis have recently been suggesting to come from indeterminate Averostrans. Other remains need revision. | |
| Theropodipedia |
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Footprints | Theropod tracks of uncertain affinity, suggested to come from "allosaurs or megalosaurs" |
Sauropoda
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Breviparopus |
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Footprints | Traces of sauropods typical of the ichnofamily Parabrontopodidae, incertae sedis within Sauropodomorpha. Includes traces with pes similar to Diplodocoidea. | |
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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 |
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| Sauropoda |
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Isolated and articulated bones | Indeterminate or undescribed sauropod remains | |
| Sauropodina |
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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 |
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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 | 
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| Ornithopodichnus? |
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Footprints | Ornithichian Tracks, referred to short-toed forms such as Gilmoreosaurus | |
| Spicomellus |
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NHMUK PV R37412, a partial rib bearing four co-ossified spines | An early ankylosaurian | 
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| Thyreosaurus |
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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 | 
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Charophyta
| Genus | Species | Stratigraphic position | Material | Notes | Images |
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| Porochara |
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Oogonia | A characean algae of the family Porocharaceae; charophytes are abundant in lower levels, associated with freshwater ostracods |  |
Plantae
| Genus | Species | Stratigraphic position | Material | Notes | Images |
|---|---|---|---|---|---|
| Protocupressinoxylon |
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Fossil wood | Conifer wood of the family Hirmeriellaceae, considered to be a potential synonym of the genus Brachyoxylon |  |
See also
- Tafraout Group (Toarcian–Aalenian)
- Azilal Formation (Toarcian-Aalenian)
- Guettioua Formation (Bathonian–?Callovian)
- Anoual Formation (Bathonian)
- Ksar Metlili Formation (Tithonian–?Berrasian)
References
- ^ 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. Bibcode:2019Geohe..11..371O. doi:10.1007/s12371-018-0287-y. ISSN 1867-2477. S2CID 134800520.
- ^ Soufiani, N.; Fedan, B. (2002). "Les dépôts bathoniens du synclinal d'El Mers (Moyen Atlas, Maroc): unités formationnelles, analyse et cadre géodynamique" (PDF). Bulletin de l'Institut scientifique. 24 (6): 1–14.
- ^ 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. Bibcode:1994Geobi..27..157C. doi:10.1016/s0016-6995(94)80002-2. ISSN 0016-6995.
- ^ 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. Bibcode:2016CRPal..15..461O. doi:10.1016/j.crpv.2015.09.013.
- ^ 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.
- ^ 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)]" (PDF). Comptes Rendus de l'Académie des Sciences de Paris. 210 (3): 768–770.
- ^ 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. doi:10.2113/gssgfbull.s6-vii.8-9.1091. ISSN 1777-5817.
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- ^ 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.
- ^ 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)" (PDF). Zubia. 30 (6): 93–147.
- ^ "Non-theropods". theropoddatabase.github.io. Retrieved 2024-10-05.
- ^ "Neotheropoda". theropoddatabase.github.io. Retrieved 2024-11-01.
- ^ 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. Bibcode:1981Geobi..14..427J. doi:10.1016/s0016-6995(81)80186-6. ISSN 0016-6995.
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- ^ 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. S2CID 160327994.
- ^ 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. doi:10.2113/gssgfbull.s5-xii.4-6.199. ISSN 1777-5817.
- ^ Charroud, M.; Fedan, B. (1992). "Données préliminaires sur la découverte du gisement de Boulahfa à dinosauriens (SW de Boulemane, Moyen Atlas central)" (PDF). Notes et Mémoire du Service géologique du Maroc. 366 (5): 448–449.
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