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Milieux de dépôts et foraminifères (Lituolidés) de la plate-forme carbonatée du Lias moyen au Maroc

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Michel Septfontaine at University of Lausanne
Michel Septfontaine
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Abstract

The Middle Liassic inner platform carbonate deposits of Morroco are characterized by a succesion of metric regressive cycles (as in Spain, Italy, Dinarids and Oman). An autochtonous microfauna (Orbitopsellids & Hauraniids) is associated with the lower part of the cycle (subtidal lagoon) whereas an allochtonous assemblage is displaced on top by tidal currents and hurricanes (tempestites). A recent equivalent is described by Davaud & Septfontaine (1995).
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ADDENDA 1. Carottes prises dans un lagon de Tunisie actuel (région de Zarzis),
avec séquence émersive identique à une « shallowing upward » séquence du
Lias moyen du Haut Atlas (- 180 Ma).
(Ci-dessous, page 2.)
Le fond du golfe de Gabès et ses dépôts de lagon et de sables côtiers à algues
et foraminifères (dépôts de tempêtes et de marée) est pratiquement identique
au fond du golfe atlasique et de son « tidal flat » de plusieurs dizaines de
kilomètres de large.
Voir aussi l’article de Davaud & Septfontaine (1995) : Post-mortem onshore
transportation of epiphytic foraminifera : recent example from the Tunisian
coastline . – Jour. Sediment. Research., 65/1A, 136-142
Réf : Davaud, Strasser & M’Rabet
(1991) : Livret guide excursion Tunisie : sédimentologie comparée des dépôts littoraux…
ADDENDA 2. Ciment stalactitique (« stalactic cement ») dans un grainstone
carbonaté du Lias moyen du Haut Atlas (Maroc), datant de – 180 millions
d’années. L’émersion du sédiment est ici prouvée, en sommet de séquence
métrique émersive (« shallowing upward sequence »).
Ci-dessous, page 4
Ce type de séquence (parfois allocycliques, mais le plus souvent autocycliques)
est connu dans tous le domaine néo-téthysien, du mésozoïque à l’actuel (du
Maroc à l’Oman), sur les plates-formes carbonatées des deux marges de
l’océan jurassique.
On notera la « fraîcheur » de cet échantillon qui pourrait tout aussi bien
provenir d’une plage carbonatée et cimentée actuelle des Bahamas…
Hauteur de la photo : env. 0,5 mm

Supplementary resources (24)

Mixed clastic-carbonate platforms in the W-Tethyan realm: High Atlas and Briançonnais domain - Importance of Jurassic paleotectonics and topography on cyclic sedimentation
Data
March 2016
Michel Septfontaine
Washover shells of Aulacoceras (Belemnoid ?) and algal film on the supratidal flat (Lias High Atlas Morocco)
Data
February 2016
Michel Septfontaine
Giant dino foot-prints on supratidal flat-Lias assif S'remt-Laghdar, High Atlas (courtesy J. Jenny)
Data
January 2016
Michel Septfontaine
Slumped stromatolithic carbonate beds (Lias, High Atlas, Morocco)
Data
January 2016
Michel Septfontaine
Séquences saisonnières de comblement, alternance de dépôts de haute (Gr) et basse (Mu) énergie (Lias, Maroc)
Data
January 2016
Michel Septfontaine
Disrupted dolomitic "teepee" structure, supratidal flat ( Early Liassic, High Atlas, Morocco)
Data
January 2016
Michel Septfontaine
Giant oysters (lithiotids) in the liassic lagoon and channels (Lias, Haut Atlas, Maroc)
Data
January 2016
Michel Septfontaine
Floated and storm transported ammonites and foraminifera on a "teepee" structure supratidal flat (Lias, High Atlas, Morocco)
Data
January 2016
Michel Septfontaine · J.-A. Jossen
Orbitopsella Lias (Domerien) Moyen Atlas, Maroc
Data
December 2015
Michel Septfontaine
Dinosaur tracks on top of a Haurania (foraminifera) bed, Middle Liassic High Atlas (Tabant)
Data
December 2015
Michel Septfontaine
Todhra Lias en séquences+
Data
December 2015
Michel Septfontaine
Brèche de tempête, sommet de séquence régressive métrique, R'nim, (Haut Atlas, Maroc)
Data
December 2015
Michel Septfontaine
Phylogeny of Orbitopsellids (from Lituosepta recoarensis to Orbitopsella) - a model
Data
December 2015
Michel Septfontaine
Brecciated dolomitic crusts by storm waves, "tempestite" (Lias, Haut Atlas, Maroc)
Data
December 2015
Michel Septfontaine
Lithiotidés déplacés dans un chenal de marée (Lias Haut Atlas)
Data
December 2015
Michel Septfontaine
Calcretes "open sheet craks", stalactitic cement on vadose pisolithes and birdseyes (Lias, High Atlas, Morocco)
Data
December 2015
Michel Septfontaine
Diagenetic vadose, microstalactitic cement; Lias, Haut Atlas (Maroc)
Data
December 2015
Michel Septfontaine
Cycle émersif Aganane Haut Atlas
Data
December 2015
Michel Septfontaine
Stromatolite en dôme sommet cycle Lias Adoumaz+
Data
December 2015
Michel Septfontaine
"Teepee" diagenetic dolomitic crust on supratidal flat, top of regressive sequence (Lias, High Atlas)
Data
December 2015
Michel Septfontaine
Cycle émersif carotte actuel chott tunisien
Data
December 2015
Michel Septfontaine
Dessication paleosurface, supratidal zone, top of regressive metric sequence; Middle Liassic, R'nim High Atlas (Morocco)
Data
December 2015
Michel Septfontaine
Keystone vugs meniscus
Data
December 2015
Michel Septfontaine
Cycle virtuel émersif ("shallowing upward sequence")
Data
December 2015
Michel Septfontaine
... The upper Pliensbachian is subdivided into four carbonatedominated formations: the Aganane Formation (paralic; Septfontaine, 1985), the Choucht Formation (upper shoreface; Septfontaine, 1985), the Aberdouz Formation (lower shoreface; Stüder and du Dresnay, 1980), and the Ouchbis Formation (lower shoreface and deeper; Stüder and du Dresnay, 1980). The Toarcian is a mixed siliciclastic-carbonate system subdivided into five formations: the Tagoudite Formation (lower shoreface to toe of slope; Stüder and du Dresnay, 1980), the Wazzant/Azilal Formation (continental to paralic ;Jossen, 1988;Ettaki et al., 2000), the Tafraout Formation (upper to lower shoreface; Bouchouata et al., 1995), the Ait Athmane Formation (lower shoreface to upper offshore; Wilmsen et al., 2002), and the Agoudim 1 Formation (deeper shelf to toe of slope; Stüder and du Dresnay, 1980). ...
... The upper Pliensbachian is subdivided into four carbonatedominated formations: the Aganane Formation (paralic; Septfontaine, 1985), the Choucht Formation (upper shoreface; Septfontaine, 1985), the Aberdouz Formation (lower shoreface; Stüder and du Dresnay, 1980), and the Ouchbis Formation (lower shoreface and deeper; Stüder and du Dresnay, 1980). The Toarcian is a mixed siliciclastic-carbonate system subdivided into five formations: the Tagoudite Formation (lower shoreface to toe of slope; Stüder and du Dresnay, 1980), the Wazzant/Azilal Formation (continental to paralic ;Jossen, 1988;Ettaki et al., 2000), the Tafraout Formation (upper to lower shoreface; Bouchouata et al., 1995), the Ait Athmane Formation (lower shoreface to upper offshore; Wilmsen et al., 2002), and the Agoudim 1 Formation (deeper shelf to toe of slope; Stüder and du Dresnay, 1980). ...
... In the central High Atlas, a similar pattern has been documented at the Pliensbachian/Toarcian boundary (see Krencker et al., 2020 and references herein) and we argue that the discontinuity corresponds to the Pliensbachian/Toarcian boundary in section S1. This interpretation is in agreement with the biostratigraphic findings from El Bchari and Souhel (2008) who reported the occurrence of foraminifera belonging to the Biozone E (Septfontaine, 1985) in the study area within the topmost part of the Aganane Formation indicative of a middle Domerian (Margaritatus Zone) to Toarcian age. ...
The effects of strong sediment-supply variability on the sequence stratigraphic architecture: Insights from early Toarcian carbonate factory collapses
Article
Full-text available
  • Nov 2021
  • MAR PETROL GEOL
Standard sequence stratigraphy interpretations are commonly built upon the premise of fairly constant sediment supply, leaving vast uncertainties about sequence architecture and sea-level change recorded during major paleoenvironmental disturbances, usually associated with carbonate productivity collapse and increased siliciclastic sediments supply. During relative sea-level rise, this process is referred to as drowning event. However, drastic collapse of carbonate productivity during relative sea-level drop remains poorly documented. The Pliensbachian/Toarcian boundary in Morocco provides an outstanding example of such a case, referred here to as poisoning event. Using bio-, chemo- and high-resolution sequence stratigraphic approaches on horizontal seismic-scale outcrop data, we characterize the architecture of vertically and laterally mixed siliciclastic/carbonate systems. During poisoning event, the standard sequence Lowstand-Transgressive-Highstand system tracts is altered into Highstand-Transgressive-Falling Stage system tracts with little or no evidence for Highstand deposits. Noteworthy, it is important to note that poisoning and drowning events can be confused together in sedimentary records where the shoreline trajectory cannot be clearly tracked, as it has often been the case in previous Pliensbachian/Toarcian studies. The outcome of this study calls thus for a closer re-examination of other carbonate factory collapse event attributed to drowning events without an unambiguous knowledge of their coeval shoreline trajectory.
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... 7a, for the large-scale depositional profile). The broadly time-equivalent deposits can be subdivided into three formations (generalized environments noted in parentheses) in the study area: the Choucht Formation ( platform margin ;Septfontaine 1985); the Aberdouz Formation (slope; Stüder and du Dresnay 1980); and the Ouchbis Formation (toe-of-slope; Stüder and du Dresnay 1980) (Fig. 3). ...
... During the latest Pliensbachian (Emaciatum Zone; step 0), paralic facies consisting of claystone alternating with microbial mats were deposited to the west of the study area (Aganane Formation; Septfontaine 1985;Krencker et al. 2022). Paralic environments graded eastwards to the marine platform margin (Choucht Formation), slope and, eventually, toe-of-slope settings (Ouchbis Formation; Fig. 15; see Fig. 6 for details about the facies). ...
Anatomy of a platform margin during a carbonate factory collapse: implications for the sedimentary record and sequence stratigraphy interpretation of poisoning events
Article
  • Aug 2022
Sequence stratigraphic interpretations face limitations in predicting the sedimentary architecture and sea-level change in systems characterized by marked fluctuations in sediment supply, particularly in carbonate-dominated environments. Scenario of pronounced variations in sediment supply occurred during the Pliensbachian/Toarcian transition, when significant perturbations of the carbon cycle and intense environmental disturbances led to a global shutdown of carbonate production. We have studied the impact of this event on sedimentation and stratal stacking patterns in the Moroccan central High-Atlas. We reconstruct the lateral variations of facies and sedimentary geometries along a carbonate platform margin and slope in the field by tracking six key discontinuity surfaces covering the Pliensbachian/Toarcian transition from the platform margin to the toe-of-slope. This work highlights,the difficulty of sequence stratigraphy interpretations in cases of neritic carbonate factory collapse without assessing the shoreline movement, as stacking patterns in open marine environments do not necessary reflect regional base level variation in disturbed carbonate systems. This study also emphasizes uncertainties associated with focusing solely on lower offshore strata for assessing the history and causes of paleoenvironmental perturbations, as decreases in the rates of carbonate production dampens neritic carbonate shedding and therefore favors the creation of hiatus in deepwater settings.
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... The Lower Lias facies are essentially marly-dolomitic, often karstified and rich in onchoids with occasional gypsum; these formations are surmounted by the calcaro-dolomites of the Jbel Rat Formation of Upper Sinemurian age (Souhel 1996, Ettaki et al. 2007). The Jbel Rat Formations are succeeded by the carbonate deposits of the Aganane formation of the Upper Sinemurian-Middle Domerian age (Septfontaine 1985, Souhel 1996, Ettaki et al. 2007). The transition from carbonate to terrigenous facies is marked by the marl-sandstone sediments of the Azilal Formation of Toarcian-Aalenian (Souhel 1996, Ettaki et al. 2011. ...
Inventory and Assessment of Geosites and Geodiversity Sites of the Ait Attab Syncline (M’goun Unesco Geopark, Morocco) to Stimulate Geoconservation, Geotourism and Sustainable Development
Article
Full-text available
  • Aug 2023
The Ait Attab syncline, in the southwestern part of the Moroccan Central High Atlas (CHA), is a vast basin characterised by an exceptional geodiversity illustrating the complete sedimentary series in the CHA. This series offers the opportunity to study regional palaeogeography, transgressive and regressive megasequences, Jurassic Cretaceous volcanism and Atlas tectonics, and various fossils, including dinosaur footprints. The study area also harbours considerable landscape and cultural wealth that can play a significant role in sustainable geotourism and geoeducation development. To promote and protect this geoheritage wealth, the present work provides the first quantitative and qualitative inventory of geosites of interest by adopting Brilha’s (2016) method. Thus, 3 geotrails covering 8 geosites and 11 geodiversity sites have been selected. The evaluation of these sites confirms their scientific and educational importance, which helps understand the geological, tectonic and palaeogeographical evolution of the Ait Attab syncline.The tourist value of these sites is also high, explained by the high interpretative potential of the geosites and their location as a gateway to the M’Goun Unesco geopark. The degradation risk assessment showed that most of these siteshave a medium risk, except for palaeontological and magmatic sites, which have a high degradation risk.
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... The sedimentation is heterogeneous in terms of lithology and thickness, indicating a littoral environment with briny deltaic and lagoonal sedimentation. This formation unconformably covers the Rhynchonella limestone bars of the third formation of the Bin El Ouidane Group (Rebouillat, 1983;Rolley, 1973) and is attributed to the upper Bajocian-Bathonian Löwner, 1997;Septfontaine, 1984Septfontaine, , 1986Souhel, 1996). It begins with a marly series showing intercalations of limestones and sandy silts. ...
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... The sedimentation is heterogeneous in terms of lithology and thickness, indicating a littoral environment with briny deltaic and lagoonal sedimentation. This formation unconformably covers the Rhynchonella limestone bars of the third formation of the Bin El Ouidane Group (Rebouillat, 1983;Rolley, 1973) and is attributed to the upper Bajocian-Bathonian Löwner, 1997;Septfontaine, 1984Septfontaine, , 1986Souhel, 1996). It begins with a marly series showing intercalations of limestones and sandy silts. ...
Geodynamic Evolution During the Mesozoic and Cenozoic in the Central High Atlas of Morocco from Anisotropy of Magnetic Susceptibility
Chapter
  • Jan 2023
The anisotropy of magnetic susceptibility provides valuable information on the imprint of the different tectonic processes occurred in the Central High Atlas (CHA), complementing the structural analysis and paleomagnetic information. Different types of magnetic ellipsoids, related with extensional, diapiric or intrusive processes occurred during the Mesozoic, or with the Cenozoic compression, can be recognized. The predominance of one or another type of fabric varies spatially, and a transition can be observed from bedding-related fabrics in Western and Eastern sectors, to more abundant, modified magnetic fabrics in the Central sectors and in the Southern border of the CHA. Extensional fabrics are characterized by the orientation of the kmin axes normal to bedding and the kmax axes clustered in a NW–SE direction within the bedding plane. This direction represents the regional (and local) extension, perpendicular to the main faults. Compressional magnetic fabrics show their kmin axes in NW–SE or N-S directions and/or kmax axes sub-horizontal and clustered in the NE-SW direction, consistently with the shortening direction inferred from the trend of compressional structures (folds and thrusts). Compressional tectonic fabrics are unequivocally interpreted in areas showing regional cleavage. Magnetic lineations vertical or close to the bedding dip direction are found near thrust planes or near the core of narrow and tight anticlines and are related to transport direction or re-tightening of structures, in many cases nucleated in relation to salt tectonics features.
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... The sedimentation is heterogeneous in terms of lithology and thickness, indicating a littoral environment with briny deltaic and lagoonal sedimentation. This formation unconformably covers the Rhynchonella limestone bars of the third formation of the Bin El Ouidane Group (Rebouillat, 1983;Rolley, 1973) and is attributed to the upper Bajocian-Bathonian Löwner, 1997;Septfontaine, 1984Septfontaine, , 1986Souhel, 1996). It begins with a marly series showing intercalations of limestones and sandy silts. ...
Magnetic Properties of the Jurassic Sedimentary Rocks of the Central High Atlas Affected by a Regional Chemical Remagnetization
Chapter
  • Jan 2023
This chapter presents the results of numerous rock experiments carried out on Jurassic marine carbonates and red beds from the Central High Atlas, which have been affected by a regional remagnetization related to burial. As in other sedimentary rocks affected by chemical remagnetizations, the analyzed samples show a characteristic magnetic fingerprint. The dominant magnetic mineralogy of carbonates is composed of non-interacting uniaxial magnetite, in the superparamagnetic (SP) and stable single domain (SSD) states. Besides, a variable contribution of pyrrhotite is present in most of the samples. The combined presence of neoformed magnetite and pyrrhotite seems to be indicative that these rocks have reached temperatures around 200–250 °C, compatible with previous studies of illite crystallinity. ARM and IRM unmixing curves define a very characteristic pattern for remagnetized carbonates differentiated from other rocks types bearing magnetite. On the other hand, the high temperature susceptibility curves used to characterize the magnetic anisotropy studies show different contribution of paramagnetic and ferromagnetic (s.l.) minerals. Among paramagnetic phases, it is expected the presence of phyllosilicates and pyrite that can be the precursors of the neoformation of magnetite and pyrrhotite both during burial in natural conditions and in the different performed experiments. With regard to the ferromagnetic (s.l.) fractions, magnetite is the dominant phase with a minor contribution of pyrrhotite. In red beds, rock magnetic experiments show a dominance of hematite with different contribution of magnetite. In general, the susceptibility curves show a dominance of paramagnetic signal to the bulk susceptibility.
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... The sedimentation is heterogeneous in terms of lithology and thickness, indicating a littoral environment with briny deltaic and lagoonal sedimentation. This formation unconformably covers the Rhynchonella limestone bars of the third formation of the Bin El Ouidane Group (Rebouillat, 1983;Rolley, 1973) and is attributed to the upper Bajocian-Bathonian (Jenny, 1988;Löwner, 1997;Septfontaine, 1984Septfontaine, , 1986Souhel, 1996). Fig. 19). ...
The Geological Setting of the Moroccan High Atlas and Its Plate Tectonics Context
Chapter
  • Jan 2023
In this introductory chapter we summarize the geological evolution of the atlasic domain, making reference to many (not all) of the significant previous works carried out in the area. The geological setting of the Moroccan Central High Atlas is characterized by a complex Mesozoic-Cenozoic evolution that included (i) an extensional to transtensional stage during the Mesozoic, in which episodes with intense magmatic activity (forming lava flows, dykes and intrusion) and salt-driven movements took place and (ii) a compressional stage that generated well developed fold-and-thrust systems in the northern and southern basin and upright folds and tightening of previously formed structures (both extensional and diapiric) in the central part of the basin. The sedimentary sequence characteristic of the Central High Atlas is the frame for the structural observations and the magnetic techniques applied elsewhere in this book. It consists of a thick (Permo)Triassic (red beds) and Jurassic (mainly limestones and marls) syn-rift sequences reaching thickness of more than 7 km in the basin center. Facies changes in the Jurassic sequence indicate deepening conditions towards the central part of the domain. Conversely, the Cretaceous and Cenozoic materials crop out discontinuously in the studied domain. Particularly significant from the structural and geophysical points of view are the incompetent levels (mainly Upper Triassic) and the igneous rocks of Triassic and Jurassic age.
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... The sedimentation is heterogeneous in terms of lithology and thickness, indicating a littoral environment with briny deltaic and lagoonal sedimentation. This formation unconformably covers the Rhynchonella limestone bars of the third formation of the Bin El Ouidane Group (Rebouillat, 1983;Rolley, 1973) and is attributed to the upper Bajocian-Bathonian Löwner, 1997;Septfontaine, 1984Septfontaine, , 1986Souhel, 1996). It begins with a marly series showing intercalations of limestones and sandy silts. ...
Paleomagnetism of the Central High Atlas. The Widespread Cretaceous Remagnetization and Structural Implications
Chapter
  • Jan 2023
Previous works developed by our research group have shown that the Jurassic rocks of the Central high Atlas (CHA) have recorded a Cretaceous widespread remagnetization. In this chapter, a high resolution paleomagnetic study on 424 new paleomagnetic sites in Mesozoic units of CHA is presented. This work provides new information about the Cretaceous magnetic overprint of the CHA, as well as contributes to the knowledge of the geodynamic evolution of the Atlas. The new results confirm the extent of remagnetization throughout the study area (10,000 km2) in both carbonates (carried by magnetite) and red beds (carried by hematite) showing systematically normal polarity and an inter-folding acquisition. By using small circle techniques, the remagnetization direction (n = 531, Dec = 335.4°, Inc = 42.7° for carbonates and n = 62, Dec = 344.4°, Inc = 41.7° for red beds) and the age of acquisition (100 Ma ± 5 Ma for limestones) have been determined. The remagnetization properties in the carbonates and their paleomagnetic direction are maintained throughout the studied area and the different stratigraphic units. The small but statistically significant difference between the directions of remagnetization in carbonates and red beds suggests a delay in the acquisition in red beds. Remagnetization directions have been restored using small circle techniques, allowing to generate a set of 593 paleo-dips of the beds at 100 Ma. This valuable information has been used in Chap. “Kinematics of Structures and Basin Evolution in the Central High Atlas. Constraints from AMS and Paleomagnetic Data” to elaborate palinspastic reconstructions and to study the evolution of the different structures of the CHA. For this purpose, a new diagram (paleo-dip evolution diagram, PED) is here proposed.
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... Dans la région d'Aït Athmane, la séquence du Toarcien, nommée Formation d'Aït Athmane (Lachkar, 2000), affleure sur le versant gauche de la vallée de l'Oued Ziz. Cette formation, souvent recouverte par les éboulis de pente, repose sur les calcaires bioclastiques à gros bivalves du Pliensbachien supérieur de la Formation d'Aganane (Septfontaine, 1986), équivalente latérale de la Formation d'Ouchbis (Stüder, 1980). Dans ce secteur, comme dans le secteur d'Amellago, les marnes du Toarcien sont surmontées par Pierre et al., 2005), complété par des données de Bodin et al. (2016) pour la séquence du Toarcian. ...
Brachiopodes toarciens de la coupe d’Aït Athmane
Article
  • Dec 2022
  • Ann Palaontol
La coupe d'Aït Athmane est située dans la partie sud-est du Haut Atlas central, à environ 20 km au nord d'Er-rachidia. Sa série toarcienne, formée de marnes silteuses et de marno-calcaires, est riche en Brachiopodes (rhyn-chonellidés et térébratulidés) dans sa partie inférieure, Toarcien inférieur (Zone à Levisoni ?) et moyen (Zones à Bifrons et Gradata ?) ; sa partie supérieure, d'âge Toarcien supérieur, est riche en térébratulidés. Parmi dix-huit taxons de brachiopodes répertoriés, six sont nouveaux pour le domaine du Haut Atlas central. Les associations de ces taxons et leur répartition stratigraphique sont semblables à celles des brachiopodes toarciens signalées dans plusieurs bassins des deux marges de la Téthys occidentale et du domaine subboréal, en particulier de l'ouest de la France. The Aït Athmane section is located in the eastern part of the central High Atlas, about 20 km north of Errachidia. Its Toarcian series consists of silty marl and silty marly limestone. Its lower part, of early (Levisoni Zone?) to middle Toarcian (Bifrons and Gradata? zones) age, is rich in brachiopods (rhynchonellides and terebratulides). Its upper part, of late Toarcian age, is rich in terebratulids. Among eighteen reported brachiopod taxa, six are new for the central High Atlas. Their specific assemblages and stratigraphic distributions are similar to those of the Toarcian brachiopods reported from several basins of northern and southern margins of the Tethys and the Sub-boreal domain, particularly of the western France.
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... Dans la région d'Aït Athmane, la séquence du Toarcien, nommée Formation d'Aït Athmane (Lachkar, 2000), affleure sur le versant gauche de la vallée de l'Oued Ziz. Cette formation, souvent recouverte par les éboulis de pente, repose sur les calcaires bioclastiques à gros bivalves du Pliensbachien supérieur de la Formation d'Aganane (Septfontaine, 1986), équivalente latérale de la Formation d'Ouchbis (Stüder, 1980). Dans ce secteur, comme dans le secteur d'Amellago, les marnes du Toarcien sont surmontées par la dalle des calcaires sablonneux néritiques de l'Aalénien-Bajocien basal de la Formation d'Amellago (Stüder, 1980). ...
Toarcian ammonites of the Polymorphum Zone, Amellago area (eastern central High Atlas), Morocco, with a discussion on ammonite turnover events
Article
Full-text available
  • Nov 2022
  • Palaeoworld
In the Amellago area (central High Atlas), the widely distributed Toarcian succession consists of marl and marly limestones of the Tagoudite and Agoudim formations. We here describe, for the first time, the ammonites of the Polymorphum Zone from the Tagoudite Formation, including Canavaria cf. rosenbergi Fucini, C. aff. zancleana (Fucini), Dactylioceras (Eodactylites) mirabile (Fucini), D. (E.) aff. mirabile (Fucini), D. (E.) pseudocommune Fucini, D. (E.) simplex (Fucini), D. (Orthodactylites) aff. crosbeyi (Simpson), Lytoceras gr. villae Meneghini, Neolioceratoides cf. hoffmanni (Gemmellaro) and Praepolyplectus sp. This ammonite assemblage is closely correlated with those reported from the Polymorphum Zone of several basins of the Tethyan margins and the Northwest European Subboreal Realm, indicating marine communications between the different Moroccan Jurassic basins and the central Atlantic trough. The overlying Agoudim Formation yields ammonites of the Levisoni Zone in its base and rare ammonites of the Bifrons Zone in the middle part. Four significant changes in the ammonite assemblages during the early-middle Toarcian and their probable causes are also discussed.
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