Lithostratigraphic, paleoenvironmental and sequential evolution of the Cenomanian-Lower Turonian in the Guir area (western Algeria)

La lithostratigraphie, les paléoenvironnements et la stratigraphie séquentielle des terrains crétacés affleurant au pied méridional de l'Atlas saharien (Sud-Ouest de l'Algérie), sont discutés dans le présent article. Les études s'appuient sur l'analyse de quinze coupes réparties le long des limites méridionale et septentrionale du bassin du Guir, entre Ben-Zireg, à l'Est et l'axe Meridja-Boukais à l'Ouest. Dans cette région, trois formations ont été identifiées et interprétées sur le plan environnemental et séquentiel : 1- La Formation des "Grès rouges", attribuée au Cénomanien inférieur, est dominée par des dépôts gréseux fins, fluviatiles ou littoraux ; 2- La Formation des "Marnes à gypse inférieures", rapportée au Cénomanien inférieur-moyen, est caractérisée par des assises à caractères littoraux, soumises à l'influence des tempêtes, notamment vers la base ; 3- La Formation des "Calcaires de Sidi Mohamed Ben Bouziane", d'âge Cénomanien supérieur-Turonien inférieur, correspond à une sédimentation carbonatée franchement marine de plate-forme peu profonde très généralisée. Les dépôts de ces entités lithostratigraphiques s'agencent en mégaséquence d'ouverture, composée de méso-séquences "transgression-régression". L'ouverture des milieux de dépôts en direction du Nord est confirmée par l'organisation des unités lithostratigraphiques et par l'affinité paléobiogéographique nettement téthysienne de l'échinofaune, des bivalves et en particulier de l'ammonite Neolobites vibrayeanus.The lithostratigraphy, paleoenvironment and sequence stratigraphy of the Cretaceous succession outcropping at the southern foot of the Saharan Atlas (south-western Algeria) are discussed in this work. Our current study focuses on the analysis of fifteen sections distributed along to the northern and southern limits of the Guir Basin, between the Ben-Zireg to the East and the Meridja-Boukais axis to the West. In this area, three lithostratigraphic formations were identified and interpreted from an environmental and a sequential points of view: 1 - The lower "Grès rouges" Formation attributed to the Lower Cenomanian, is dominated by fluvial or coastal detrital deposits; 2 - The middle "Marnes à gypse inférieures" Formation assigned to the Lower-Middle Cenomanian is characterized by littoral setting with some storm influences, especially towards the base; 3 - The upper "Calcaires de Sidi Mohamed Ben Bouziane" Formation of upper Cenomanian-early Turonian in age, is represents a laterally extensive, shallow carbonate platform environment. The three formations constitute an overall transgressive megasequence built of a number of transgressive-regressive minor sequences. The opening of the deposits towards the North is confirmed by the organization of the lithostratigraphic units and by the Tethyan paleobiogeographic affinity of the echinoids and bivalves, and especially the occurrence of Neolobites vibrayeanus ammonite

The hyaenodontidans from the Gour Lazib area (?Early Eocene, Algeria): implications concerning the systematics and the origin of the Hyainailourinae and Teratodontinae

International audienceThe Algerian localities of the Gour Lazib area (Early or early Middle Eocene) have yielded an important mammalian fauna. The Hyaenodontida are well represented in this fauna: three species-two are new- are reported. The genus Glibzegdouia, which has been previously described as a possible Carnivora, is now clearly referred to the Hyaenodontida. It appears morphologically close to Masrasector and Dissopsalis. A new genus, Furodon, is described. It appears morphologically close to the oldest Pterodon species. This discovery supports an African origin for the hyainailourine genus Pterodon and related genera (e.g. Hyainailouros, Akhnatenavus). Two very small lower molars are referred to a new genus Parvavorodon, which is also referred to Hyainailourinae. The localities of the Gour Lazib area therefore show important hyaenodontid diversity for the Early or early Middle Eocene. We performed a new phylogenetic analysis to question the relationships between the African, Asian, North American and European hyaenodontidans. Our study supports the endemism and originality of the Asian proviverrines' Indohyaenodon, Paratritemnodon, Kyawdawia and Yarshea; we propose a new subfamily: Indohyaenodontinae. The African proviverrines' (e.g. Masrasector, Anasinopa, Dissopsalis and Glibzegdouia), which are notably characterized by large premolars and the presence of a wide talonid on the molars, are close to the enigmatic African Teratodon. We therefore propose to refer them to Teratodontinae. The Hyainailourinae, which include the new genus Furodon, are characterized by the presence of secant dentition related to a hypercarnivorous diet. They appear phylogenetically close to the African Koholiinae. The genus Metapterodon is referred to Koholiinae based on the phylogenetic analysis. The African origin of the Teratodontinae and Hyainailourinae is supported by Glibzegdouia and Furodon. The origination of several subfamilies in Africa supports the hypothesis of an African origin for the Hyaenodontida. The origination of the Teratodontinae in Africa contradicts the previous hypotheses of Afro-Asian proviverrines'

A Phororhacoid bird from the Eocene of Africa

International audienceThe bird fossil record is globally scarce in Africa. The early Tertiary evolution of terrestrial birds is virtually unknown in that continent. Here, we report on a femur of a large terrestrial new genus discovered from the early or early middle Eocene (between similar to 52 and 46 Ma) of south-western Algeria. This femur shows all the morphological features of the Phororhacoidea, the so-called Terror Birds. Most of the phororhacoids were indeed large, or even gigantic, flightless predators or scavengers with no close modern analogs. It is likely that this extinct group originated in South America, where they are known from the late Paleocene to the late Pleistocene (similar to 59 to 0.01 Ma). The presence of a phororhacoid bird in Africa cannot be explained by a vicariant mechanism because these birds first appeared in South America well after the onset of the mid-Cretaceous Gondwana break up (similar to 100 million years old). Here, we propose two hypotheses to account for this occurrence, either an early dispersal of small members of this group, which were still able of a limited flight, or a transoceanic migration of flightless birds from South America to Africa during the Paleocene or earliest Eocene. Paleogeographic reconstructions of the South Atlantic Ocean suggest the existence of several islands of considerable size between South America and Africa during the early Tertiary, which could have helped a transatlantic dispersal of phororhacoid

New material of Seggeurius amourensis (Paenungulata, Hyracoidea), including a partial skull with intact basicranium

International audienceSeggeurius is the basal-most hyracoid known to date, and one of the earliest known fossil afrotherians. This taxon has a dramatic importance in mammalian phylogeny, but until now it was known from dental remains only. Here we describe previously unpublished material of Seggeurius, including some mandibular and maxillary fragments, and a braincase. This study is the first to thoroughly describe and discuss the morphology of the ear region and osseous inner ear of a Paleogene hyracoid. It allows a reappraisal of some important characters that are often used in cladistic analyses of Paenungulata. In particular, it seems that in stem hyracoids the orbit is located caudally, the eustachian sac is absent or reduced, the course of the internal carotid artery is intrabullar and medial, and a deep epitympanic sinus, a basisphenoid contribution to the bulla, and the stapedial artery are present. The cochlear canal is rather flattened, and the secondary common crus was rapidly lost. A cladistic analysis of stem placental mammals highlights three derived traits shared by Seggeurius and stem sirenians (the tuber-shaped postglenoid process, the squared and massive mastoid apophysis of the petrosal, and the presence of a swelling on the septum metacochleare) and supports molecular analysis that hypothesizes a Hyracoidea-Sirenia sister-group relationship. This study demonstrates how useful the petrosal and labyrinthine characters of fossils can be for mammalian phylogenetic inference

Impact of the Anoxic Oceanic Event II on the evolution of ostracods in the Cenomanian-Turonian deposits of the Tinrhert Basin (SE Algeria).

Dans le bassin du Tinrhert, au passage Cénomanien/Turonien, les ostracodes sont rares dans la plupart des niveaux échantillonnés ; ils ne présentent aucune variabilité, leur fréquence ne dépassant pas 4% de toute la microfaune. Leur présence optimale, tant qualitative que quantitative, s'observe à la base du Turonien inférieur où leurs cortèges sont dominés par les genres Cythereis, Paracypris et Cytherella. Afin de comprendre ces observations, nous avons mené une étude paléoécologique sur cinq coupes géologiques et reconstitué l'impact des conditions sédimentologiques (quartz, gypse et pyrite) et celui des variations eustatiques.Around the Cenomanian/Turonian boundary in the Tinrhert Basin, ostracods are seldom found in most of the sampled levels. The assemblages show no specific diversity, their frequency not exceeding 4% of the whole microfauna. Their 'climactic' presence, both qualitatively and quantitatively, is observed at the base of the lower Turonian, where ostracod assemblages are dominated by the genera Cythereis, Paracypris, and Cytherella. In order to interpret this data, we document a paleoecological study supported by evidence compiled from five geological sections, dealing with the respective impact of sedimentological conditions (quartz, gypsum and pyrite), and sea-level fluctuations

Latest Early-early Middle Eocene deposits of Algeria (Glib Zegdou, HGL50), yield the richest and most diverse fauna of amphibians and squamate reptiles from the Palaeogene of Africa

International audienceHGL50 is a latest Early-early Middle Eocene vertebrate-bearing locality located in Western Algeria. It has produced the richest and most diverse fauna of amphibians and squamate reptiles reported from the Palaeogene of Africa. Moreover, it is one of the rare faunas including amphibians and squamates known from the period of isolation of Africa. The assemblage comprises 17 to 20 taxa (one gymnophionan, one probable caudate, three to six anurans, seven 'lizards', and five snakes). Two new taxa were recovered: the anuran Rocekophryne ornata gen. et sp. nov. and the snake Afrotortrix draaensis gen. et sp. nov. The locality has also yielded the first confirmed anilioid snake, the first Palaeogene gymnophionan, and probably the first caudate from the Palaeogene (and possibly from the Tertiary) of Africa. The presence of a caudate at that time in Africa would be of particular interest; unfortunately, the available material does not permit a definitive identification. The fauna comprises Gondwanan and more specifically West Gondwanan vicariants, probably autochthonous groups and a Eurasian immigrant (assuming that the identification of the caudate is accurate). The fauna from HGL50 is clearly distinguished from the few other Eocene assemblages of Africa. However, if this results largely from differences in geological ages, geographic positions of the localities and mainly differences in environments took a part in the composition of the faunas

Earliest occurrence of Hydrocynus (Characiformes, Alestidae) from Eocene continental deposits of Méridja Hamada (northwestern Sahara, Algeria)

We here report the oldest remains (teeth) of the African tigerfish (Hydrocynus) from the Oued MĂŠridja and Garet Dermchane sections, Hamada of MĂŠridja deposits, in southwestern Algeria. The tigerfish, a large carnivorous fish today represented by several species in the freshwaters of Africa, was previously found in upper middle to upper Eocene deposits in Egypt and Libya. The remains described here are several million years older, being early to middle Eocene in age, and are associated with other fish elements including lungfish, polypterid, amiiform, possible cichlid, and Alestes/Brycinus material, along with several fish elements that cannot be associated with a specific taxon and some fragmentary amphibian bones. This represents the first description of a freshwater fish assemblage from the Eocene of Algeria, although a short list of fish taxa from Eocene Algerian deposits was previously reported. Furthermore, these new Algerian fossils allow us to assess the hypothesized existence of an east-west or west-east permanent hydrological connection between eastern and western parts of northern Africa. We suggest that the shared presence of tigerfish in the Eocene deposits of Algeria, Libya and Egypt does not necessarily indicate a permanent (i.e., non-seasonal) connection east-west or west-east among these areas. Rather, the observed faunal similarities could have been the result of seasonal flooding that caused the dispersal of Hydrocynus and associated taxa across coastal flood plains.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Talar morphology of azibiids, strepsirhine-related primates from the Eocene of Algeria: Phylogenetic affinities and locomotor adaptation

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Taxonomic review of the “Bulimes”, terrestrial gastropods from the continental Eocene of the Hamada de Méridja (northwestern Sahara, Algeria) (Mollusca: Stylommatophora: Strophocheilidae?), with a discussion of the genera of the family Vidaliellidae

International audienceTerrestrial gastropods occur in many North African localities in Eocene continental deposits. Here we analyse the faunal assemblage from the Hamada de Méridja Formation in southwestern Algeria, dated as Early to Middle Eocene on the basis of charophytes. The assemblage consists of three closely related species that to date have been classified either in the extant Madagascan genus Leucotaenius v. Martens, 1860, or in the SW European Eocene genera Romanella Jodot, 1957 and Vicentinia Jodot, 1957. This is rejected for shell morphological and phylogeographical reasons, and a new classification as Maghrebiola gen. nov. is proposed. Maghrebiola is tentatively placed in the South American family Strophocheilidae, as species from the Early Eocene Itaboraí Basin of Brazil, currently placed in the genus Eoborus Klappenbach and Olazarri, 1970 in the family Strophocheilidae, superfamily Acavoidea, have a very similar shell habitus. This record possibly extends the known geographical range of the Strophocheilidae into the African continent during the Eocene. Immigration of this stock into North Africa during the Cretaceous via a still existing plate connection is assumed. An attribution of Maghrebiola to the African family Achatinidae is unlikely for shell morphological reasons despite certain habitus similarities, although the Priabonian genera Arabicolaria and Pacaudiella from Oman most likely belong into this family, and not to the Vidaliellidae as originally proposed. Possible causes for the very low diversity of the assemblage are mainly unfavourable living conditions, i.e. a relatively dry climate resulting in sparse vegetation and only occasional presence of water bodies, which may have had increased salinities, accounting for the lack of freshwater mollusks. The absence of any competing large gastropods may possibly have facilitated high intraspecific variability leading to sympatric occurrence of three closely related species, due to the animals occupying a wide range of available ecological niches. As the species discussed here have also been attributed to the genera Romanella and Vicentinia in the Vidaliellidae, we provide an appendix with annotated characterisations of most genera of the Vidaliellidae and list the nominal species assigned to them. This family is tentatively placed in the South American superfamily Orthalicoidea; its stock would have similarly immigrated from South America, but have successfully colonized mainly SW Europe, with only one Eocene species [Romanella kantarensis (Jodot, 1936)] recognized in Algeria

L’Eocène continental du complexe de Gour Lazib (Sahara nord-occidental, Algérie)

International audienceLe Complexe des Gour Lazib compte trois localités : Glib Zegdou, Gour Lazib et Gour Idergane, qui constituent un ensemble de buttes-témoins d’âge éocène localisée à environ 400 km au Sud-Ouest de Béchar. Ce complexe offre une série sédimentaire continentale riche en restes de vertèbres fossiles, notamment en mammifères, et en microflore. Les récentes missions annuelles de prospections géologiques et paléontologiques, réalisées dans ces terrains, ont permis de compléter la lithostratigraphie de la formation du Glib Zegdou vers sa base, d’affiner la connaissance de sa stratigraphie et sa sédimentologie. L’étude des faunes (poissons, mammifères) et de la flore (charophytes) récoltée a sensiblement amélioré la connaissance du registre fossile des taxons concernés et a permis de préciser le paléoenvironnement et l’âge de la formation. Les affleurements prospectés s’étendent sur plus de 50 km, du Glib Zegdou à l’Est jusqu’au Gour Idergane à l’Ouest. L’étude de huit coupes lithologiques a permis de faire des corrélations lithostratigraphiques et de subdiviser la formation du Glib Zegdou en trois membres sédimentaires. A savoir, un membre inférieur argilo-marno-gypseux reposant sur un substratum paléozoïque et surmonté par un membre intermédiaire argilo-silto-gréseux, l’ensemble est coiffé par un membre supérieur gréso-carbonaté souvent silicifié. L’étude sédimentologique réalisée sur trois coupes de références, à l’affleurement et sur les lames minces, met en évidence deux importantes phases d’épigénie (calcitisation et silicification) des sédiments détritiques originels. Cette double épigénèse, qui affecte essentiellement le membre supérieur, est marquée sur le terrain par diverses structures : structures à débits en boules, en desquamations et en glaebules roses non stratifiées, concrétions silicifiées trahis parfois par des reliques du sédiment originel. En lames minces, le quartz est abondant, souvent corrodé et entouré par une pellicule microsparitique à sparitique. Dans l’ensemble des Gour, le membre intermédiaire de la formation a livré, un nombre impressionnant de gyrogonites de charophytes. Deux familles sont reconnues : les Characeae et Raskyellaceae. La première est documentée par une douzaine d’espèces, tandis que la deuxième est représentée par deux espèces appartenant au même genre Raskyella. Sur le plan biostratigraphique, et compte tenu de l’extension stratigraphique de certains taxons communs aux gisements européens, l’ensemble des espèces de charophytes permettent de proposer un âge Yprésien supérieur à Lutétien basal pour le membre intermédiaire de la formation du Glib Zegdou. Les analyses magnétostratigraphiques réalisées sur la coupe type de Glib Zegdou suggèrent que le membre inférieur et le membre intermédiaire de cette formation pourraient avoir un âge autour de 49 Ma, correspondant dès lors à la limite Yprésien-Lutétien ou au Lutétien inférieur. Le contenu fossilifère du membre inférieur se limite à des restes de poissons actinoptérygiens (écailles de polyptères et os brisés de siluriformes) et de chélonien podocnémididé (crâne et dossière). Avant 2004, le registre mammalien du membre intermédiaire de cette formation ne comptait qu’une dizaine d’espèces. Depuis, les nouvelles prospections paléontologiques menées annuellement dans ces régions, nous ont conduits à la découverte d’une quinzaine de sites fossilifères remarquables à mammifères associés à des poissons d’eau douce, chéloniens, oiseaux, et à un nombre impressionnant de charophytes. Aujourd’hui, plus de 30 espèces de mammifères sont recensées, incluant de nouvelles espèces en cours de description, et documentent plusieurs ordres modernes de placentaires connus en Afrique au cours du Paléogène ancien : rongeurs, primates, insectivores, hyracoïdes, chauve-souris, condylarthres, macroscélidés, carnivores créodontes. Seule l’absence des proboscidiens est à signaler. La faune du Complexe des Gour Lazib, en cours d’étude, éclaire d’un jour nouveau notre connaissance de l’évolution et de la radiation initiale des mammifères en Afrique