El Mers Group

Last updated
El Mers Group
Stratigraphic range: BajocianCallovian
~168–166  Ma
O
S
D
C
P
T
J
K
Pg
N
Type Group
Sub-unitsEl Mers Formations 1–3
UnderliesUnconformity with Barremian or Plio-Pleistocene sediments
Overlies Ich Timellaline–Bou Akrabene Formation
ThicknessOver 500 m (1,600 ft)
Lithology
Primary Marl, gypsum (only in unit 3)
Other Sandstone, limestone
Location
Coordinates 33°30′N4°18′W / 33.5°N 4.3°W / 33.5; -4.3
Approximate paleocoordinates 28°18′N2°00′W / 28.3°N 2.0°W / 28.3; -2.0
Region Boulemane and Azilal Provinces
CountryFlag of Morocco.svg  Morocco
Extent Middle Atlas
Morocco relief location map.jpg
Blue pog.svg
El Mers Group (Morocco)

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 .

Contents

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

Color key
Taxon Reclassified taxonTaxon falsely reported as presentDubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Dasycladales

GenusSpeciesStratigraphic positionMaterialNotesImages
Heteroporella [3]
  • H. lusitanica
  • SW part of the Skoura syncline
Calcareous imprintsA dasycladacean algae of the family Dasycladaceae
Sarfiatella [3]
  • S. dubari
  • SW part of the Skoura syncline
Calcareous imprintsA dasycladacean algae, associated in adjacent regions with Aalenian–Bajocian faunas

Foraminifera

GenusSpeciesStratigraphic positionMaterialNotesImages
Bullopora [3]
  • B. tuberculata
  • SW part of the Skoura syncline
Calcareous imprintsA benthic foraminiferan of the family Polymorphinidae
Pfenderella [3]
  • SW part of the Skoura syncline
Calcareous imprintsA benthic foraminiferan of the family Pfenderininae
Praekurnubia [3]
  • P. crusei
  • SW part of the Skoura syncline
Calcareous imprintsA benthic foraminiferan of the family Pfenderinidae; a genus found in the Tethys between Bajocian and Oxfordian-aged layers
Pseudocyclammina [3]
  • P. maynci
  • SW part of the Skoura syncline
Calcareous imprintsA benthic foraminiferan of the family Hauraniidae

Ostracoda

GenusSpeciesStratigraphic positionMaterialNotesImages
Cytherella [3]
  • C. index
  • Ait Hammou
ValvesA freshwater/brackish ostracod of the family Cytherellidae
Fastigatocythere [3]
  • F. aff. brentonensis
  • Ait Hammou
ValvesA freshwater/brackish ostracod of the family Progonocytheridae
Kinkelinella [3]
  • K. aff. triangula
  • Ait Hammou
ValvesA freshwater ostracod of the family Progonocytheridae
Metacypris [3]
  • M. spp.
  • Ait Hammou
ValvesA 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 [3]
  • P. ihopyensis
  • Ait Hammou
ValvesA freshwater ostracod of the family Schulerideidae

Xiphosura

GenusSpeciesStratigraphic positionMaterialNotesImages
Selenichnites [4]
  • S. tesiltus
  • S. isp.
  • Skoura Syncline
  • Taferdouste
Isolated crescent-shaped trace fossilsTraces of xiphosurans, representing the second occurrence of this ichnogenus in Morocco

Mollusca

GenusSpeciesStratigraphic positionMaterialNotesImages
Cadomites [3]
  • C. cf. bremeri
  • East Skoura syncline
Isolated shellsAn ammonite of the family Stephanoceratidae and indicator of the Bathonian age
Example of specimens 31 - Museum de Toulouse - Cadomites deslongchampsii - Bayeux Calvados France.jpg
Example of specimens
Choffatia [5]
  • C. cf. urinacensis
  • East Skoura syncline
Isolated shellsAn ammonite of the family Perisphinctidae and indicator of the Callovian age
Clydoniceras [5] [6]
  • C. discus
  • Tamguert n'Tarit
  • Tizi n'Juillerh
Isolated shellsAn ammonite of the family Clydoniceratidae
Modiolus [6]
  • M. imbricatus
  • El Mers
  • Tamguert n'Tarit
Isolated shellsA marine mussel of the family Mytilidae
Example of extant member of the genus Katwijk - Paardenmossel (Modiolus modiolus).jpg
Example of extant member of the genus
Morphoceras [5]
  • M. macrescens
  • East Skoura syncline
Isolated shellsAn ammonite of the family Morphoceratidae and indicator of the Bathonian age
Oraniceras [5]
  • O. sp.
  • East Skoura syncline
Isolated shellsAn ammonite of the family Parkinsoniidae and indicator of the Bathonian age
Ostrea [5] [6]
  • O. sandalina
  • El Mers
  • Tamguert n'Tarit
Isolated shellsA marine oyster of the family Ostreidae
Example of extant member of the genus Oyster.jpg
Example of extant member of the genus
Parkinsonia [3]
  • P. sp.
  • Skoura syncline
Isolated shellsAn ammonite of the family Parkinsoniidae and indicator of the Bajocian age for the lower portions of the Group
Example of specimen Parkinsonia parkinsoni NHM.jpg
Example of specimen
Protocardia [5] [6]
  • P. tikechkachensis
  • El Mers
  • Tamguert n'Tarit
Isolated shellsA marine cockle of the family Cardiidae

Fishes

GenusSpeciesStratigraphic positionMaterialNotesImages
Lepidotes [7]
  • L. spp.
  • Ait Hammou
  • Djmila
  • Oued El Mers
  • Tizi n'Juillerh
Cranial material, isolated teeth and scalesA marine/brackish bony fish of the family Lepidotidae
Example of specimen of the genus Lepidotes sp. - Naturhistorisches Museum, Braunschweig, Germany - DSC05183.JPG
Example of specimen of the genus
Scheenstia [7]
  • S. cf. mantelli
  • Oued El Mers
Partial specimen wirth cranial materialA marine/brackish bony fish of the family Lepidotidae
Reconstruction Scheenstia maximus.jpg
Reconstruction

Testudinata

GenusSpeciesStratigraphic positionMaterialNotesImages
Testudinata [5] [6]
  • Indeterminate
  • Tamguert n'Tarit
  • Tizi n'Juillerh
Very numerous debris: escutcheons, plates, vertebrae, ribs, long bonesTurtle remains of uncertain affinity

Crocodylomorpha

GenusSpeciesStratigraphic positionMaterialNotesImages
Hatcherichnus [8]
  • H. ispp.
  • Inzar O'Founass
FootprintsIndeterminate Crocodrylomorph Tracks

" Megalosaurus " [5] [6]

  • "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? [5]

  • 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

GenusSpeciesStratigraphic positionMaterialNotesImages
Carmelopodus [8]
  • cf.C. isp.
  • Tassmante O'Moche
FootprintsTheropod tracks of uncertain affinity, suggested to come from Ceratosauria members
Grallator ? [8]
  • G.? isp.
  • Ifri N'Tfrane
FootprintsTheropod Tracks, referred usually to small-medium sized Genera
Hispanosauropus ? [8]
  • H.? isp.
  • Ifri N'Tfrane
FootprintsTheropod tracks of uncertain affinity, different from Megalosauripus in the larger metatarsophalangeal region
Megalosauripus [10] [8]
  • M. ispp.
  • cf.M. ispp.
  • El Mers
  • Tasra
  • Tasra Westbank
  • Tassmante O'Moche
  • Oued Tamghilt
FootprintsTraces of theropods; members of the ichnofiber family Eubrontidae, incertae sedis within Theropoda
Theropoda [10]
  • Indeterminate
  • El Mers
TeethIsolated teeth of unidentified or undescribed/studied theropods
Theropodipedia [8] [11] [10]
  • Indeterminate
  • El Mers
  • Inzar O'Founass
  • Ifri N'Tfrane
  • Laach O'Medda
  • Oulad Ali
  • Tasra
  • Tasra Westbank
  • Tassmante O'Moche
FootprintsTheropod tracks of uncertain affinity, suggested to come from "allosaurs or megalosaurs" [11]

Sauropoda

GenusSpeciesStratigraphic positionMaterialNotesImages
Breviparopus [10] [8]
  • B. isp.
  • El Mers
  • Oued Tamghilt
FootprintsTraces of sauropods typical of the ichnofamily Parabrontopodidae, incertae sedis within Sauropodomorpha. Includes traces with pes similar to Diplodocoidea. [10]

Cetiosaurus [5] [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 bonesIndeterminate or undescribed sauropod remains
Sauropodina [8] [11] [16]
  • Indeterminate
  • El Mers
  • Tasra
  • Tasra Westbank
  • Oulad Ali
FootprintsSauropod 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. [8]

Ornithischia

GenusSpeciesStratigraphic positionMaterialNotesImages
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 Adratiklit boulahfa.png
Ornithopodichnus ? [8]
  • O.? ispp.
  • Ifri N'Tfrane
FootprintsOrnithichian Tracks, referred to short-toed forms such as Gilmoreosaurus
Spicomellus [18]
  • S. afer
  • Boulahfa
NHMUK PV R37412, a partial rib bearing four co-ossified spinesAn early ankylosaurian Spicomellus afer holotype illustration.png
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 elementsA dacentrurine stegosaur with unusual recumbent osteoderms Thyreosaurus Skeletal.svg

Charophyta

GenusSpeciesStratigraphic positionMaterialNotesImages
Porochara [3]
  • P. hians
  • Ait Hammou
Oogonia A characean algae of the family Porocharaceae; charophytes are abundant in lower levels, associated with freshwater ostracods
Example of modern characean algae CharaFragilis.jpg
Example of modern characean algae

Plantae

GenusSpeciesStratigraphic positionMaterialNotesImages
Protocupressinoxylon [20]
  • P. choubertii
  • Skoura syncline
Fossil wood Conifer wood of the family Hirmeriellaceae, considered to be a potential synonym of the genus Brachyoxylon
Example of wood trunk of the same genus Protocupressinoxylon.JPG
Example of wood trunk of the same genus

See also

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<i>Spicomellus</i> Extinct genus of dinosaurs

Spicomellus is an extinct genus of early ankylosaurian dinosaur from the El Mers III Formation (Bathonian-Callovian) of Morocco. The genus contains a single species, S. afer, known from a single rib with fused osteoderms. Spicomellus represents the oldest named ankylosaur.

<i>Thyreosaurus</i> Extinct genus of stegosaurian dinosaurs

Thyreosaurus is an extinct genus of stegosaurian dinosaur from the Middle Jurassic El Mers III Formation of Morocco. The genus contains a single species, Thyreosaurus atlasicus, known form a partial disarticulated partial skeleton consisting of several dorsal vertebrae, ribs, a limb bone, and dermal bones. Thyreosaurus is characterized by a unique dermal armor with an asymmetrical texture, indicating that it may have been recumbent. Alongside Adratiklit, Thyreosaurus increases the diversity of unique stegosaurs occurring in the Middle Jurassic of Africa.

<span class="mw-page-title-main">Tafraout Group</span> Geological formations in Morocco

The Tafraout Group is a geological group of formations of Toarcian-Aalenian age in the Azilal, Béni-Mellal, Imilchil, Zaouiat Ahansal, Ouarzazate, Tinerhir and Errachidia areas of the High Atlas of Morocco. The Group represents the remnants of a local massive Siliciclastic-Carbonate platform, best assigned to succession W-E of alluvial environment occasionally interrupted by shallow marine incursions and inner platform to open marine settings, and marks a dramatic decrease of the carbonate productivity under increasing terrigenous sedimentation. Fossils include large reef biotas with richness in "lithiotid" bivalves and coral mounts, but also by remains of vertebrates such as the sauropod Tazoudasaurus and the basal ceratosaur Berberosaurus, along with several undescribed genera. While there have been attributions of its lowermost layers to the Latest Pliensbachian, the current oldest properly measured are part of the Earliest Toarcian regression ("MRST10"), part of the Lower-Middle Palymorphum biozone. This group is composed of the following units, which extend from west to east: the Azilal Formation ; the Amezraï Formation ; the Aguerd-nˈTazoult Formation ; the Tagoudite Formation & the Trafraout Formation. They are connected with the offshore Ait Athmane Formation and the deeper shelf deposits of the Agoudim 1 Formation. Overall, this group represents a mixed carbonate-siliciclastic system of several hundred meters thick, dominated by deposits of shallow marine platforms linked to a nearby hinterland dominated by conglomerates. The strata of the group extend towards the central High Atlas, covering different anticlines and topographic features along the mountain range.

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