La stratigraphie isotopique du Strontium est-elle une méthode fiable pour dater les plates-formes carbonatées à la transition du Barrémien à l'Aptien ? Révision de cas d'études en Téthys occidentale.

Strontium-isotope measurements on Lower Cretaceous marine rocks derive from belemnite material sampled in ammonite-constrained basinal successions. A group of values with a narrow range across the Barremian/Aptian boundary does not allow the separation of the uppermost Barremian (Martelites sarasini ammonite zone) from the lower Aptian pro parte (Deshayesites oglanlensis-D. forbesi ammonite zones). Growing numbers of studies applied Sr-Isotope Stratigraphy (SIS) on Barremian-Aptian shallow-marine sequences (Urgonian facies) in order to solve controversial results obtained by using different shallow-water biological time markers. Based on re-examination of case studies, we conclude that Sr-isotope values can neither be used to prove nor to disprove the location of the putative Barremian/Aptian boundary based on biostratigraphy. Pending more data available, SIS should be used with caution for dating ammonite-free carbonate sediments in the corresponding time interval.Les mesures de l'isotope du Strontium dans des roches carbonatées marines du Crétacé inférieur proviennent de restes de bélemnites récoltés dans des séries de bassins datées directement par ammonites. Autour de la limite Barrémien/Aptien, une gamme étroite de valeurs du Strontium ne permet pas de distinguer le Barrémien supérieur (Zone d'ammonite à Martelites sarasini) de l'Aptien inférieur pro parte (zones d'ammonite à Deshayesites oglanlensis et D. forbesi). Pourtant, l’application de la Stratigraphie Isotopique du Strontium (SIS) sur des séquences marines carbonatées barrémo–aptiennes (à faciès urgonien) apparaît dans un nombre croissant d’études, essentiellement afin de résoudre les datations souvent controversées des marqueurs biologiques d’environnements peu profonds. La révision de ces cas d'étude montre que l’utilisation des valeurs de l'isotope du Strontium n’est pas un outil fiable pour prouver ou réfuter la localisation de la limite Barrémien/Aptien telle que déduite par la biostratigraphie. Dans l'attente de données complémentaires, la SIS doit être utilisée avec précaution pour dater des séries carbonatées non datées directement par ammonites dans l'intervalle de temps concerné

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Quantitative characters used for statistical approach

Data from: Evolution of the rudist bivalve Agriopleura Kühn (Radiolitidae, Hippuritida) from the Mediterranean region

The genus Agriopleura (Radiolitidae) is restricted to the Lower Cretaceous of the Mediterranean region, including the Middle East, and this rudist is apparently absent from the New World. Agriopleura underwent a size increase from late Hauterivian to mid-late Barremian, matching Cope's rule, followed by a Lilliput phase in the early Aptian. The relative development of radial bands increased through time and represents a key evolutionary index. During its evolution, Agriopleura increased in species diversity and expanded geographically onto the European Mediterranean Tethyan margin from the late Hauterivian to Barremian, after which it disappeared from the region (pseudotermination). In the lower Aptian, after a Lazarus gap, the genus reappears in the southern Mediterranean Tethyan margin. Assuming that Archaeoradiolites is the direct descendant of Agriopleura, the disappearance of the genus in the mid-Aptian was a pseudoextinction and this coincided with a major crisis of shallow carbonate settings and their associated biota. The definition of Agriopleura species is based on a set of qualitative and quantitative external and internal characters. Five species are recognized: three Barremian species, Agriopleura blumenbachi, the type species, A. marticensis and A. carinata; one lower Aptian species A. libanica; and a new species A. sequana restricted to the upper Hauterivian. Principal component analysis is used to test the distinctiveness of the species and the pattern of relationships of some of their key quantitative characters

Archaeoradiolites, a new genus from the Upper Aptian of the Mediterranean Region and the origin of the Rudist Family Radiolitidae

Archaeoradiolites gen. nov. (Radiolitidae), mainly characterized by radially arranged branching walls structuring the outer shell layer, includes two species, Archaeoradiolites primitivus gen. et sp. nov. and Archaeoradiolites hispanicus gen. et sp. nov. (type species), the distinction of which is based on size, shell habit and development of the radially branching microstructure. Their geographical distribution is restricted to south-east Spain and south-west France, i.e. the Western European Tethyan margin, whereas data from the Black Sea coast of Turkey suggest a possible extension to the Eastern European Tethyan margin. Each species has a distinct biostratigraphic distribution within the Upper Aptian (mainly the Gargasian). Agriopleura is suggested to be the direct ancestor of Archaeoradiolites, which in turn is considered as the progenitor of Eoradiolites. The onset of the Radiolitidae is associated with global oceanic changes that favoured calcite as opposed to aragonite biomineralization. The acquisition of a porous shell microstructure appears, in many respects, biologically advantageous and may account for gaining a rapid (< 1 myr) ecological ability for efficient colonization and occupation of space of the family in the earlier phase of its radiation

Stratigraphic organisation, spatial distribution, palaeoenvironmental reconstruction, and demise of Lower Cretaceous (Barremian-lower Aptian) carbonate platforms of the Western Pontides (Black Sea region, Turkey)

Barremian-Lower Aptian platform carbonates ("Urgonian limestones") of the northern margin of the Istanbul zone extend from Zonguldak to the Kurucasile area along the Black Sea coast. New stratigraphic data on the "Inpiri" Formation of the Inpiri-Kurucasile area are based on the identification of calcareous algae, foraminifera, and rudists. They show that this lithostratigraphic unit is stratigraphically and lithologically equivalent to the Okusmedere Formation from Zonguldak. Some of the biostratigraphic markers are reported for the first time in Anatolia. Foraminifera are represented by several forms with a significant biostratigraphic potential used to distinguish the Barremian from the lower Aptian. Lower Aptian beds also yield relatively advanced caprinid rudists

Caprinidae (Bivalvia, Hippuritida) de l'Aptien basal du Liban

International audienceThe presence in Lebanon of Offneria murgensis and Offneria nicolinae, two characteristic components of the Early Aptian Arabo-African rudist faunas, fills a distributional gap of the corresponding assemblage between the Arabic and African occurrences, on the one hand, and the Apulian occurrences, on the other hand. This fauna bears out the palaeogeographic placement of Lebanon on the southern Mediterranean Tethys margin established by palaeostructural reconstructions. The associated micropaleontological elements suggest an earliest Aptian age (early Bedoulian) for the Offneria murgensis-O. nicolinae assemblage found in the "Falaise de BLANCHE" stratigraphic interval, instead of a late Early Aptian age as proposed for most of the peri-Adriatic and Middle East occurrences recognized so far. These caprinid specimens are characterized by relatively modest sizes, moreover other rudists commonly part of the assemblage are lacking. The dominance of caprinids in the study area suggests a distal platform setting, i.e., close proximity to the platform edge. Résumé : Caprinidae (Bivalvia, Hippuritida) de l'Aptien basal du Liban.-La présence au Liban d'Offneria murgensis et d'Offneria nicolinae, deux membres clés des faunes de rudistes de l'Aptien inférieur africain ou arabe, comble un vide dans la répartition de ces associations entre sites africains ou arabes d'une part et sites apuliens d'autre part. Cette faune confirme la position paléogéographique du Liban sur la marge méditerranéenne téthysienne méridionale telle que présentée dans les reconsti-tutions de la tectonique des plaques. Les éléments micropaléontologiques associés suggèrent un âge Aptien basal (Bédoulien inférieur) pour l'association Offneria murgensis-O. nicolinae provenant de l'intervalle stratigraphique de la "Falaise de BLANCHE", au lieu d'un âge Aptien inférieur non basal com-me ce qui est proposé pour la plupart des sites périadriatiques et moyen-orientaux connus jusqu'à pré-sent. Les exemplaires de ces caprinidés sont caractérisés par des tailles relativement modestes ; de plus les autres rudistes faisant couramment partie de ces associations sont ici absents. La prédomi-nance des caprinidés dans la région étudiée suggère un environnement distal sur la plate-forme, voire une proximité immédiate de sa bordure.La présence au Liban d'Offneria murgensis et d'Offneria nicolinae, deux membres clés des faunes de rudistes de l'Aptien inférieur africain ou arabe, comble un vide dans la répartition de ces associations entre sites africains ou arabes d'une part et sites apuliens d'autre part. Cette faune confirme la position paléogéographique du Liban sur la marge méditerranéenne téthysienne méridionale telle que présentée dans les reconstitutions de la tectonique des plaques. Les éléments micropaléontologiques associés suggèrent un âge Aptien basal (Bédoulien inférieur) pour l'association Offneria murgensis - O. nicolinae provenant de l'intervalle stratigraphique de la "Falaise de Blanche", au lieu d'un âge Aptien inférieur non basal comme ce qui est proposé pour la plupart des sites périadriatiques et moyen-orientaux connus jusqu'à présent. Les exemplaires de ces caprinidés sont caractérisés par des tailles relativement modestes ; de plus les autres rudistes faisant couramment partie de ces associations sont ici absents. La prédominance des caprinidés dans la région étudiée suggère un environnement distal sur la plate-forme, voire une proximité immédiate de sa bordure

Berriasian rudist faunas and micropalaeontology of Stramberk type carbonate exotics from the Lycian nappes, Bodrum Peninsula, southwest Turkey

Megablocks of coral-rudist bearing platform limestone, of Stramberk type, are present as exotics in upper Santonian-Campanian flysch-like deposits of the Karabortlen formation, near Bodrum. These beds belong to the Lycian nappes and the palaeogeographic origin of the megablocks is unclear. The micro-paleontological assemblage of benthic foraminifera, calcareous green algae and problematica of the blocks indicates a Berriasian age, and has a Mediterranean character. Rudists are essentially represented by Heterodiceras luci (Epidiceratidae) and Hypelasma salevensis (Requieniidae), commonly found in the Upper Tithonian-Berriasian of the European margin of the Mediterranean Tethys. The Lycian specimens of Hypelasma represent the first record of this taxon on the southern Tethyan margin whereas Heterodiceras has been reported from the pen-Adriatic regions but is identified for the first time in Turkey. (C) 2015 Elsevier Ltd. All rights reserved

Is Strontium-isotope stratigraphy a reliable tool for dating shallow-marine platform carbonates at the Barremian-Aptian transition? Review of western Tethyan case studies

Strontium-isotope measurements on Lower Cretaceous marine rocks derive from belemnite material sampled in ammonite-constrained basinal successions. A group of values with a narrow range across the Barremian/Aptian boundary does not allow the separation of the uppermost Barremian (Martelites sarasini ammonite zone) from the lower Aptian pro parte (Deshayesites oglanlensis-D. forbesi ammonite zones). Growing numbers of studies applied Sr-Isotope Stratigraphy (SIS) on Barremian-Aptian shallow-marine sequences (Urgonian facies) in order to solve controversial results obtained by using different shallow-water biological time markers. Based on re-examination of case studies, we conclude that Sr-isotope values can neither be used to prove nor to disprove the location of the putative Barremian/Aptian boundary based on biostratigraphy. Pending more data available, SIS should be used with caution for dating ammonite-free carbonate sediments in the corresponding time interval