We report tetrapod traces from two stratigraphic intervals in Morocco, and discuss their palaeoecological implications. In the first interval, crocodylomorph footprints assigned to Crocodylopodus ...meijidei are described from Middle–?Upper Jurassic continental fluvial red beds of the Isli Formation in the Imilchil region, Central High Atlas, Morocco. These traces are associated with a diverse dinosaur-dominated ichnofauna, including the footprints of theropods, ornithischians, sauropods and pterosaurs, together with numerous invertebrate traces. In the second interval, we report crocodylomorph swim traces assigned to Hatcherichnus isp., turtle trackways assigned to Emydhipus isp. and isolated mammal footprints in the mid-Cretaceous Midelt Formation, in the High Moulouya region, Morocco. These traces are, also, associated with a diverse dinosaur-dominated ichnofauna including theropods and ornithopods as well as pterosaurs and abundant invertebrate traces. Together with plant remains, conchostracans and fishes, findings indicate a diverse community populating a fluvial-brackish environment.
•First report of a larger assemblage with crocodylomorph tracks from the Jurassic of Morocco.•First report of the Jurassic-Cretaceous turtle ichnogenus Emydhipus from the African continent.•First mammaliamorph footprints from Mesozoic strata of Morocco.
The Marmoucha syncline is located in the eastern part of the Middle Atlas. In this syncline, the “Gypsum marls” (Bathonian-?Callovian) are covered by red detrital deposits which outcrop in Aït Bazza ...locality. The upper limit of these detrital deposits is below the transgressional unconformity of the Albian?-Cenomanian marine series. The present work introduces a synthesis of stratigraphical, sedimentological and micropalaeontological studies, which has led to new dating and to the identification of different depositional environments. These results have allowed us to define a new chrono-lithostratigraphic unit, the "Aït Bazza Formation", which comprises three superimposed members AB1-3 separated by two sedimentary discontinuities. This formation, exceeding 300 m in thickness, is formed by conglomerate, sandstone, sand and varicoloured marls. Micropalaeontological bulk sampling in marly horizons revealed associations of charophytes and ostracods, particularly in Member AB2. The charophytes are represented by oogonia of small Porocharaceae, Clavatoraceae such as
Hemiglobator rectispirale
,
Dictyoclavator ramalhoi
, and
Nodosoclavator bradleyi
that characterise the Tithonian. The ostracod microfauna is diverse, consisting of non-marine and lagoonal- shallow marine species at several horizons, associated with sea urchin spines and rare foraminifera, which indicate fluvio-deltaic sedimentary environments subjected to marine influences. This new age constraints of AB2 Mb to the Late Jurassic, and the discovery of marine influences in this eastern part of the folded Middle Atlas, consequently indicates the existence of palaeogeographical connections with the Tethyan domain located to the NE in the Rif foreland.
Besides bones, fossil tracks and trackways are important sources of knowledge about dinosaur palaeobiology. Here, we report three new tracksites from two different synclines in the Imilchil area, ...Central High Atlas, Morocco. The tracks and trackways are preserved in fluvial deposits in different levels of the Isli Formation (Early Bathonian–?Upper Jurassic), and contain impressions made by sauropods, theropods and ornithopods, as well as tracks that might represent bird-like non-avian theropod dinosaurs. In addition to traditional field measurements, three-dimensional digital models of the track sites were created using photogrammetry. These new tracksites add to the rich faunal ichnoassemblage already recorded from the High Atlas Mountains and North Africa, which is considerably richer than the contemporaneous body fossil record, and also provide new data on dinosaurs–substrate interactions.
A new dinosaur tracksite is reported from continental red beds of the Jurassic (Late Bathonian-?Callovian) Isli Formation along the northern flank of the Aït Ali ou Ikkou Syncline of the Imilchil ...area, Central High Atlas, Morocco. The succession was deposited in a fluvio-lacustrine environment, and contains at least fourteen track-bearing levels. The diverse dinosaur-dominated ichnofauna includes the footprints of crocodylomorphs, pterosaurs, theropods, sauropods and ornithischians, together with numerous invertebrate traces. Here, we focus on a long sauropod trackway, which comprises nine consecutive manus-pes sets preserved as concave epireliefs. The low heteropody and asymmetry of manus prints with a large digit I (pollex) impression oriented medially, and a large triangular claw trace, which is posteriorly oriented, are characteristic of the ichnogenus Polyonyx. Different from typical Polyonyx is the narrow gauge pattern compared to the wide gauge observed in the type trackway from Portugal. Additional material from Morocco, similar to Polyonyx, comprises the trackway of a very small (?juvenile) individual found close to the main trackway, as well as a short trackway from a different locality in the Isli Formation. Our data from the Moroccan High Atlas indicates the presence of basal eusauropods in the Middle Jurassic-Early Cretaceous interval in the northwestern part of Gondwana for the first time, and suggests they inhabited a lacustrine paleoenvironment.
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•Diverse dinosaur-dominated ichnofauna are reported from Jurassic red beds at Imilchil, Morocco.•We describe, in detail, a long sauropod trackway of Polyonyx type.•Ichnotaxonomy of Middle Jurassic-Early Cretaceous sauropod tracks is reviewed.•Findings improve knowledge of sauropods along the southern margin of the Tethys.
The northern boundary of the Central High Atlas was affected by a transgression during the Aptian that reached the junction zone between the Middle and the High Atlas. In this sector (Naour-Aghbala) ...which corresponds to the presumed closure zone of this Aptian Atlantic marine trough, the sedimentary record reveals a strong dependence on the regional structural framework. The Barremian continental sedimentation is concentrated in an elongated W-E highly subsiding zone, limited to the south by the polyphase Aghbala-Afourer Fault Zone (AAFZ), which corresponds to the contact between the main Atlasic Belt and its northern boundary (Beni Mellal Atlas). The Aptian deposits preserve similar littoral marine characters from West to East without showing any confined facies, which could evoke the eastern limit of the gulf. On the other hand, towards the North, the Aptian layers rapidly change from marine to lagoonal then to continental facies. The paleogeographic boundary of the Aptian shoreline, oriented E-W, is locally controlled by the North El Ksiba Fault (NKF) in the North. The Aptian Atlantic transgression, closely linked to the narrow Barremian graben, shows a wide northward extension of the marine sedimentary area.
The Barremian graben highlighted in the Aghbala-Naour area represents only a segment of a major east-west intracontinental rift that continued eastward with the more recent frontal thrust of the eastern Moroccan High Atlas. This faulted structure was the penetration axis of a double transgression: from the Tethys to the East and from the Atlantic Ocean to the West on the emerged Atlasic domain.
•Identification of an E-W intracontinental Barremian graben in the Aghbala-Naour area.•Evidence of an Aptian paleogeographic S–N zoning from marine to continental deposits.•Geodynamic evolution from Barremian intracontinental rift to Aptian marine gulf.•Extensional faulting between Atlantic & Tethyan Oceans, across the High Atlas domain.
Tridactyl theropod and ornithischian dinosaur tracks and trackways from Imilchil and Isli formations (Middle-?Late Jurassic, Bajocian-?) of the central High Atlas region (Morocco) are described. The ...Imilchil Formationconsists of brackish marine-continental deposits, and the Isli Formation is a continental red-bed succession. Considering numerous new footprint discoveries, including recently described Polyonyx sauropod trackways, tridactyl dinosaur tracks from the Imilchil-Tounfite region are revised. Dominating are theropod footprints resembling the ichnogenus Changpeipus and known from Lower-Middle Jurassic deposits of China. Other theropod ichnotaxa are Trisauropodiscus isp., cf. Wildeichnus isp.,Carmelopodus isp., Megalosauripus isp., Kayentapus isp. and an indeterminate small grallatorid. Ornithischians are represented by small indeterminate ornithischian tracks, large ornithischian footprints cf. Stegopodus isp. and a large indeterminate ornithopod form. Makers of the small theropod trackswere small coelurosaurs or basal tetanurans, larger forms belong toceratosaurs, megalosauroids, allosauroids or tyrannosauroids. Ornithischian tracks suggest dryomorphs, iguanodontians and thyreophorans as producers. Together with crocodylomorph and pterosaur tracks, invertebrate traces and plants, the Imilchil and Isli formations document a flourishing ecosystem and dinosaur habitat. Remarkable is the presence of Changpeipus theropod tracks known from abundant occurrences in East Asia. This suggests an exchange of dinosaur faunas between this region and northern Africa during the Middle Jurassic.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Stratigraphic, sedimentologic, and micropaleontologic studies have been undertaken on the “Infra-Cenomanian” continental red beds (= Dekkar Group) located on the northern side of the Moroccan eastern ...High Atlas. Rich charophyte assemblages containing Sphaerochara magna, Ascidiella stellata, Hemiclavator sp. A, Globator trochiliscoides, Atopochara trivolvis, At. triquetra, and Flabellochara harrisii indicate a late Barremian age for the lower part of the series. Within the continental deposits we have discovered in the Middle Member of the Dekkar 2 Formation limestones and marls containing echinoderms, dasycladacean algae and foraminifera (miliolids, Ammobaculites sp., Choffatella decipiens). The existence of two littoral to lagoonal-marine intercalations within the continental sedimentation reveals marine transgressive events during the late Barremian–?early Aptian. The lateral extension of these marine sediments allows the erection of paleogeographic boundaries that define a « Marginal Folds Gulf » characterized mainly by restricted marine paleoenvironments. This E-W directed gulf is a relatively long depression, a few tens of kilometers wide and one hundred kilometers long, developed in an area which is now at the foot of the eastern High Atlas. The infilling deposits is dominantly controlled by the distance from the North High Atlas Fault. The gulf terminated westward and probably opened northeastward into the Tethyan domain. This narrow gulf was separated from both the Tethyan Gulf known in the Central Middle Atlas during the Aptian and the coeval Atlantic Gulf located on the northern side of the Marrakech and Central High Atlas. Thus, the « Marginal Folds Gulf » is a new paleogeographic feature that documents marine incursions within the Jurassic–Early Cretaceous continental areas of the NW Africa.
Since the discovery of shatter cones (SCs) near the village of Agoudal (Morocco, Central High Atlas Mountains) in 2013, the absence of one or several associated circular structures led to speculation ...about the age of the impact event, the number, and the size of the impact crater or craters. Additional constraints on the crater size, age, and erosion rates are obtained here from geological, structural, and geophysical mapping and from cosmogenic nuclide data. Our geological maps of the Agoudal impact site at the scales of 1:30,000 (6 km2) and 1:15,000 (2.25 km2) include all known occurrences of SCs in target rocks, breccias, and vertical to overturned strata. Considering that strata surrounding the impact site are subhorizontal, we argue that disturbed strata are related to the impact event. Three types of breccias have been observed. Two of them (br1‐2 and br2) could be produced by erosion–sedimentation–consolidation processes, with no evidence for impact breccias, while breccia (br1) might be impact related. The most probable center of the structure is estimated at 31°59′13.73ʺN, 5°30′55.14ʺW using the concentric deviation method applied to the orientation of strata over the disturbed area. Despite the absence of a morphological expression, the ground magnetic and electromagnetic surveys reveal anomalies spatially associated with disturbed strata and SC occurrences. The geophysical data, the structural observations, and the area of occurrence of SCs in target rocks are all consistent with an original size of 1.4–4.2 km in diameter. Cosmogenic nuclide data (36Cl) constrain the local erosion rates between 220 ± 22 m Ma−1 and 430 ± 43 m Ma−1. These erosion rates may remove the topographic expression of such a crater and its ejecta in a time period of about 0.3–1.9 Ma. This age is older than the Agoudal iron meteorite age (105 ± 40 kyr). This new age constraint excludes the possibility of a genetic relationship between the Agoudal iron meteorite fall and the formation of the Agoudal impact site. A chronolgy chart including the Atlas orogeny, the alternation of sedimentation and erosion periods, and the meteoritic impacts is presented based on all obtained and combined data.
Mesozoic strata of North Africa yield the first occurrence of the ichnogenus Selenichnites. The trace fossils occur on the top surface of a sandy carbonate deposit in the axis of a Middle Atlas ...syncline (Skoura Syncline, NE Morocco). The ichnofossil-bearing horizon belongs to the Late Bajocian–Early Bathonian Ich Timellaline/Bou Akrabene Formation. The trace fossils are crescent-shaped and the best preserved exhibits a posterior central axial impression (possible telson tail impression). They are interpreted as feeding burrows (fodinichnia) or hiding depressions of Xiphosurids or Limulids (horseshoe crabs) on a sandy carbonate substrate beneath a veneer of muddy deposits. The sedimentological character suggests a relatively protected shallow water subtidal palaeoenvironment preceding the Bathonian regression of the Atlas domain. This discovery provides the first evidence of xiphosurans or xiphosuran-like organisms inhabiting the southern shores of the Tethys in the Middle Jurassic.
Des traces d’invertébrés, attribuées à l’ichnogenre Selenichnites, ont été découvertes dans les couches d’âge Bajocien supérieur–Bathonien inférieur (formation d’Ich Timellaline/Bou Akrabène) du synclinal de Skoura, dans le Moyen Atlas marocain. Conservées sur une dalle gréso-calcaire subhorizontale, ces traces montrent des formes en croissant ou fer à cheval avec, dans le spécimen le mieux conservé, une empreinte arrière selon l’axe médian (trace du telson caudal). Elles sont interprétées comme des traces d’enfouissement (fodinichnia) de Xiphosures (=Limules) cherchant leur nourriture sur le fond sablo-carbonaté ou sous un voile de vase le recouvrant. Les caractères sédimentologiques indiquent des dépôts subtidaux dans une zone peu profonde relativement abritée. Ces paléoenvironnements littoraux précèdent la régression bathonienne du domaine atlasique. Cette découverte permet d’établir la présence de Xiphosuridés sur les rivages sud de la Téthys dès le Jurassique moyen.
Neoproterozoic glacial and post-glacial sediments from the Volta Basin (West Africa) form a stratigraphic Triad of tillites, carbonates and cherts. The carbonates that cap the tillites were studied ...in detail at Bwipe (Ghana), in the western part of the basin. They are made of finely-laminated dolostones with well-preserved sedimentary features, suggesting that dolomite formation was penecontemporaneous of deposition in a warm, arid peritidal environment, with microbial activity. Rare-earth element distribution display seawater-like patterns. Redox-sensitive trace elements indicate suboxic conditions. High Ba/Al ratios can be related to high organic productivity. a13C values are nearly constant at 6e. super(87)Sr/ super(86)Sr ratios range between 0.7061 and 0.7073. The delta super(13)C signatures are nearly similar to those of coeval cap dolostones from the northern part of the Basin. The dolostones change upwards to limestones with secondary textures, as well as more negative delta super(13)C and higher super(87)Sr/ super(86)Sr ratio. Therefore, only the dolostones witness the post-glacial conditions in seawater. It is proposed that, due to a bloom of microbial productivity following ice thaw, organic matter likely accumulated at the water-sediment interface and was consumed by sulphate-reducing bacteria, leading to the precipitation of delta super(13)C-negative dolomite. This microbially mediated model is supported by present-day field evidence from hypersaline lagoons in Brazil and by previously published culture experiments. It is consistent with the sedimentological and geochemical data from the Ghana cap dolostones and can be applied to other Neoproterozoic cap dolostones worldwide.Original Abstract: Les sediments glaciaires et post-glaciaires du bassin des Volta (Afrique occidentale) constituent une Triade formee de tillites, carbonates et silexites. Les cap carbonates qui surmontent directement les tillites ont ete etudies en detail a Bwipe (Ghana), dans l'Ouest du bassin. Ce sont des dolomies finement laminees ayant conserve des caracteres sedimentaires primaires, indiquant que la formation de la dolomie est penecontemporaine du depot et s'est produite en conditions peritidales, sous un climat chaud et aride et en presence d'activite microbienne. Les spectres de terres rares sont de type eau de mer. Les teneurs en elements traces sensibles aux conditions redox indiquent des conditions suboxiques. La valeur elevee de Ba/Al suggere une productivite elevee. delta super(13)C reste a peu pres constant a -3.7e. delta super(18)OPDB est voisin de -6e. super(87)Sr/ super(86)Sr varie entre 0,7061 et 0,7073. La signature isotopique en carbone est tres voisine de celle des cap dolomies du Nord du bassin. Vers le haut de la serie, les dolomies sont remplacees par des calcaires presentant des recristallisations secondaires, des valeurs plus negatives de delta super(13)C et une augmentation de super(87)Sr/ super(86)Sr. Ces signatures isotopiques sont donc considerees comme secondaires. Seules les dolomies de base, non modifiees, sont representatives des conditions marines post-glaciaires. On propose que, consecutivement a une explosion de productivite microbienne a la fonte des glaces, la matiere organique se soit accumulee a l'interface eau-sediment. La degradation de la matiere organique par des bacteries sulfato-reductrices en conditions anoxiques conduit alors a la precipitation de dolomite appauvrie en super(13)C. Ce modele organogenetique s'appuie sur un analogue actuel observe dans des lagunes hypersalees du Bresil et sur des resultats experimentaux deja publies. Il rend compte des donnees sedimentologiques et geochimiques observees dans les cap dolomies du Ghana et peut s'appliquer a d'autres cap dolomies neoproterozoiques ailleurs dans le monde.
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