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This computer-generated column selects for you the four latest titles published by "our" e-journals.

 

Carnets Geol., vol. 20, nº 09

Mon, 11 May 2020 17:04:45 GMT

Jean-Jacques Fleury & Recep Özkan.- Metacuvillierinella sireli n. sp., a Campanian Rhapydioninidae (Foraminifera), from southeast Turkey. New considerations on the endoskeleton and particularities of the family, with a specialized lexicon.- The family Rhapydioninidae is a part of the superfamily Alveolinacea. The main characteristic of this superfamily is its endoskeleton with each chamber divided into tubular chamberlets, fundamentally parallel to the coiling direction, and only connected in an undivided space located in the anterior part of the chamber: The preseptal space. The family Rhapydioninidae is distinguished by the coexistence of two sets of chamberlets: Primary chamberlets, which are isolated by partitions ("cloisonnettes"), forming a unique layer at the chamber periphery, and secondary chamberlets pierced in a more or less compact mass, the central endoskeleton (by no way homologous of the "couche basale", sometimes called flosculinisation or columella in some Alveolinidae). Two particular modes of organization of the secondary chamberlets occur, the Basal Secondary Chamberlets-Scattered Secondary Chamberlets structure (BSC-SSC) and the Confluent structure; they constitute supplementary features that distinguish this family from other groups. The BSC-SSC structure (a new name for a previously well-known organization of chamberlets in the genus Pseudochubbina and Cuvillierinella salentina) is the object of a large inventory undertaken among the known taxa of the Rhapydioninidae. It leads to the observation that this particular endoskeleton is found in the various subfamilies on both sides of the Atlantic and cannot be used as a feature of taxonomic significance within the group. However, it is not observed in apparently "primitive" taxa equipped with chamberlets of large isodiametric diameter which display a "fishnet" appearance. The confluent structure is a new name for the helicoidal structure, which is also widespread within the family. Metacuvillierinella sireli n. sp., of Campanian age, is described from outcrop and subsurface limestones in southeast Anatolia, Turkey. The new taxon is a Rhapydioninidae based on its test architecture and endoskeleton. As a species, it is clearly distinct because of its initial planispiral coiling of A generation tests, its both pseudoplanispiral generations with an advolute final stage and its thin chamberlets showing an obvious BSC-SSC structure. The generic attribution appears more uncertain: The faint dimorphism between generations and the persisting pseudoplanispiral-advolute final stage are only known in the genus Metacuvillierinella. But M. decastroi, the type species, displays a small proloculus in the A forms, a miliolid juvenile stage, and an endoskeleton of "fishnet" appearance (cryptic BSC-SSC structure), which give it a particular character, appearing as being "primitive". This contrasts with the relatively large proloculus in the A forms, pseudoplanispiral coiling and the obvious BSC-SSC structure of the new taxon. Thus, all these features being subjected to evolution, the faint generational differences and the pseudoplanispiral-advolute coiling seem sufficient to suggest the affinities between the two taxa. The new taxon is, nevertheless, clearly more "advanced", which could be interpreted as a clue for a higher standing, possibly compatible with a new genus. This is not undertaken here, in consideration of the unknown "radiance" (small variations in several well-disseminated populations and/or other species of the same kind) of the new taxon with the present state of knowledge. Additionally, with a review of the BSC-SSC structure, the various genera of the family Rhapydioninidae are revisited, namely Pseudochubbina, Cuvillierinella, Murciella, Sigalveolina, Cyclopseudedomia, Sellialveolina, Rhapydionina, Fanrhapydionina, Chubbina, Praechubbina, Raadshoovenia, Neomurciella, Twaraina; special attention is reserved to the Euro-Asiatic genus Pseudedomia, of which the original material and, consequently, the consecutive interpretative identifications, appear doubtful. New sections of Subalveolina dordonica and Fleuryana adriatica are figured. The conclusion deals mainly with the criteria used for distinguishing various systematic levels within the family. The classical differentiation between "specific" and "generic" characters, if eventually convenient for simple or inadequately known groups, seems unsuited for a complex and well known family like this one. A more pragmatic mode of working is proposed, using any character as a simple element without any meaning by itself, but to be understood and interpreted among the others, that is to say in the evolutionary perspective of the whole group. A lexicon of the used terms in Rhapydioninidae and closely related taxa in given in an appendix.- Handle-ID: http://hdl.handle.net/2042/70793

 

Carnets Geol., vol. 20, nº 08

Mon, 11 May 2020 17:31:26 GMT

Soumia Tchenar, Bruno Ferré, Mohammed Adaci, Djamila Zaoui, Madani Benyoucef, Mustapha Bensalah & Touria Kentri.- Incidences de l'Évènement Anoxique Océanique II sur l'évolution des ostracodes des dépôts cénomano-turoniens du bassin du Tinrhert (SE Algérie) - 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.- Handle-ID: http://hdl.handle.net/2042/70792

 

Carnets Geol., vol. 20, nº 07

Tue, 17 Mar 2020 12:14:52 GMT

Pierre Lozouet, Bruno Cahuzac & Laurent Charles.- New occurrences of Modulidae (Mollusca: Gastropoda) from European Eocene, Oligocene and Miocene deposits: Data from 19th century collections.- A re-examination of the historical collections deposited at the Bordeaux Museum of Natural History and the Faculty of Sciences of the University of Bordeaux made it possible to identify new taxa of Modulidae in the Oligocene and Miocene of the Aquitaine Basin. These Modulidae belong to the American groups Modulus modulus and Trochomodulus. In addition, three new species are described: Modulus benoisti sp. nov. (Serravallian), Trochomodulus stampinicus sp. nov. (Rupelian), which is close to Trochomodulus sublaevigatus (Orbigny, 1852), a Chattian species, and Incisilabium trochiformis sp. nov. (Priabonian). The latter is the oldest known Modulidae, together with Incisilabium parisiensis (Deshayes, 1832) (Middle Eocene) that was previously classified in the Trochidae. These results show that the paleobiogeography and origin of the family Modulidae need to be reconsidered.- Handle-ID: http://hdl.handle.net/2042/70761

 

Carnets Geol., vol. 20, nº 06

Tue, 17 Mar 2020 12:12:40 GMT

Francesco Sciuto & Angela Baldanza.- Full restoration of marine conditions after the late Messinian Mediterranean Lago-Mare phase in Licodia Eubea and Villafranca Tirrena areas (east Sicily).- After the Upper Messinian Mediterranean Lago-Mare phase, at the end of the Messinian salinity crisis, the Mediterranean basin was characterized by a return to normal marine conditions starting with the Lower Pliocene (Zanclean). In this period, remarkably thick layers of calcareous pelitic sediments, very rich in planktonic foraminifers and nannofossils, were widely deposited in the Mediterranean basin. The calcareous pelitic deposits of Sicily (Trubi Formation), as well as in other Mediterranean regions, were deposited conformably on the pre-Pliocene substrate, which is mainly represented by Messinian evaporites or by the post-evaporitic Lago-Mare facies. We have analysed samples taken from the lower portion of the Trubi Formation (Zanclean), just above the Messinian facies, collected from Licodia Eubea and Villafranca Tirrena areas (eastern Sicily). Micropalaentological assemblages consist of benthic and planktonic foraminifers and a typical deep-water ostracod fauna. The microfossil association and the stratigraphy of the Messinian-Pliocene transitional layers, supported by calcareous nannoplankton data, demonstrate not only rapid sea-level rise in this sector of the Mediterranean region, but also that this event, occurred without producing erosional features, unlike at other sites (e.g., Strait of Gibraltar).- Handle-ID: http://hdl.handle.net/2042/70760

 

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