La Formation des Argiles de Saïda (Jurassique supérieur) dans le domaine tlemcenien oriental (Takhemaret, Algérie) : données biostratigraphiques,ichnologiques et sédimentologiques

International audienceThe study area is located in the outskirt to the Takhemaretvillage, constituting part of the Saïda Mountains, eastern segment of the tlemcenian domain (northwest Algeria). In thisarea, the “Argiles de Saïda” Formation is subdivided into three lithostratigraphic units : the lower clay-sandstone unit,the clay-carbonate unit and the upper clay-sandstone unit. They were previously assigned to the Callovian-Oxfordian.However, the newly discovered ammonites assign the “Argiles de Saïda” Formation to the Middle (TransversariumBiozone)-Upper (Bifurcatus Biozone) Oxfordian. Ichnofacies and sedimentary facies analyses indicate a shallow detritalor carbonate platform depositional environment, with combined hydrodynamic influence (tides, swells, strong waves) andexceptional strong currents (gravity currents and storms).La région d’étude se localise aux environs du village de Takhemaret, dans les Monts de Saïda, segment oriental dudomaine tlemcenien (nord-ouest algérien). Dans cette région, la Formation des Argiles de Saïda a été subdivisée en troisunités lithostratigraphiques, respectivement argilo-gréseuse inférieure, argilo-carbonatée et argilo-gréseuse supérieure.Ces unités ont été attribuées au Callovo-Oxfordien. Cependant, de nouvelles récoltes d’ammonites permettent à présentde les attribuer à l’Oxfordien moyen (Zone à Transversarium) et supérieur (Zone à Bifurcatus). L’analyse des ichnofacièset des faciès sédimentaires témoigne d’un milieu de plateforme peu profonde, détritique ou carbonatée, à influencehydrodynamique (marées, houles, vagues fortes) combinée à des courants forts exceptionnels (courants gravitaires,tempêtes)

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

New stratigraphic data from the Cretaceous Basin of Guir (Bechar, South-Western Algeria)

Benyoucef Madani, Malti Fatima Zohra, Bensalah Mustapha, Bendella Mohamed. New stratigraphic data from the Cretaceous Basin of Guir (Bechar, South-Western Algeria). In: Documents des Laboratoires de Géologie, Lyon, n°164, 2008. Mid-Mesozoic life and environments. Cognac (France), June 24th-28th 2008. pp. 19-22

Les crinoïdes du massif de l’Ouarsenis (Algérie) comblent la lacune du Crétacé inférieur (Berriasien et Valanginien) de l’Afrique du Nord

The Ouarsenis Massif belongs to the Algerian Tell domain which is considered as the eastern part of the Maghrebian Tethys former margin. The Berriasian-Valanginian Oued Fodda Formation outcropping in the Kef Aïn El Hadjela section, at the foot of the great peak of the Ouarsenis Massif, is composed of marls and laminated and bioturbated limestone alternations. The marl facies reveals diverse microfauna, including crinoids. These latter are represented by: Isocrinida [isocrinids (Balanocrinus cf. gillieroni (de Loriol), Percevalicrinus aldingeri Klikushin, Isocrinus? lissajouxi (de Loriol)], Cyrtocrinida [cyrtocrinids (Phyllocrinus sp., Hemibrachiocrinus sp.)], and Roveacrinida [roveacrinids (Gen. indet. sp. indet.)]. All these, with exception of roveacrinids and phyllocrinids, are noted for the first time from Algeria and African continent (southern margin of Tethys in the Maghreb). Knowledge on Cretaceous crinoids formerly described from Algeria is presented. It is also shown that crinoid assemblage and associated invertebrates are typical for relatively shallow, distal depositional setting situated below storm wave base

Callovo-Oxfordian ichnofacies of Takhmaret Area (Saida Mounts, Western-North Algeria)

Bendella Mohamed, Benhamou Miloud, Benyoucef Madani, Malti Fatima Zohra, El Habib Hadj. Callovo-Oxfordian ichnofacies of Takhmaret Area (Saida Mounts, Western-North Algeria). In: Documents des Laboratoires de Géologie, Lyon, n°164, 2008. Mid-Mesozoic life and environments. Cognac (France), June 24th-28th 2008. pp. 15-18

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

The “mid”-Cretaceous (Lower Cenomanian) Continental Vertebrates of Gara Samani, Algeria. Sedimentological Framework and Palaeodiversity

International audienceExcellent outcrops of the upper part of the “Continental Intercalaire” deposits occur in the Gara Samani area, southern Algeria. These strata are recognised herein as belonging to the Gara Samani Formation, which is composed of the Samani Vertebrate-rich Sand Member, the Samani Sandstone Member and the Méguidène Stratified Sand Member. The first two members are from a fluvial system and the last member corresponds to an aeolian (dune and interdune) system. They have preserved one of the most diverse continental vertebrate faunas of latest Albian–early Cenomanian age yet known from northern Africa. Most of the taxa identified there, cited for the first time for the “mid”-Cretaceous of Algeria, have not been analysed in detail so far; and many of them have never been figured. The faunal list of vertebrates from this locality was supplemented thanks to detailed analysis of new and relatively abundant finds. As a consequence, the Gara Samani vertebrate assemblage is recognised as composed of elasmobranchs (two Hybodontiformes, i.e., Tribodus sp. and Distobatidae indet.; and a Batoidea, Onchopristis numida ), actinopterygians ( Bawitius sp., Adrianaichthys sp., Obaichthys africanus , and Calamopleurus africanus ), sarcopterygians (Mawsoniidae indet. and the Dipnoi, cf. Lavocatodus humei and Neoceratodus africanus ), testudines (at least two Pelomedusoides, one of them being a representative of Araripemydidae), crocodyliforms (all remains being compatible with Neosuchia, represented at least by Elosuchus broinae ), ornithocheirid pterosaurs, and non-avian dinosaurs (titanosauriform sauropods and at least two theropods, Spinosaurus aegyptiacus and Carcharodontosaurus saharicus ). This fauna association displays close similarities to contemporaneous ones from North Africa, especially with that from the Kem Kem beds

Famennian rhynchonellides (Brachiopoda) from deep-water facies of the Ougarta Basin (Saoura Valley, Algeria)

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