Lower Aptian Rudist Faunas (Bivalvia, Hippuritoidea) from Croatia

Lower Aptian rudist faunas from Croatia consist of Requienia? zlatarskii PAQUIER, Toucasia sp., Agriopleura sp., Glossomyophorus costatus MASSE, SKELTON & SLISKOVIC, Himeraelites sp. and Offneria sp. This assemblage has a clear Southern Tethyan (Arabo–African) significance and typifies the Early Aptian. Faunas from the interior of the Adriatic Carbonate Platform in Istria are dominated by Requieniidae while those from the northeastern area in the vicinity of Tounj–Ogulin, close to the platform margin, exhibit a higher diversity and include, beside requieniids, Caprinidae, Caprotinidae and Monopleuridae, in conjunction with evidence of open marine conditions

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

Les communautés à rudistes du crétacé inférieur de la marge ouest européenne de la Téthys

AIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

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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