Ammonoid taphonomy, palaeoenvironments and sequence stratigraphy at the Bajocian/Bathonian boundary on the Bas Auran area (Subalpine Basin, south-eastern France)

Bas Auran, in south‐eastern France, is the candidate area for Global Boundary Stratotype Section and Point (GSSP) of the base of the Bathonian Stage (Middle Jurassic). In the Bas Auran area, upper Bajocian and lower Bathonian deposits are made up of limestone beds alternating with marls that correspond to the ‘Marno‐calcaires àCancellophycus’, below the ‘Terres Noires’ Formation. Taphonomic analyses of the successive ammonoid fossil assemblages provide new and complementary data for biostratigraphic completeness, palaeoenvironmental setting and sequence stratigraphy. Lithologic differentiation between limestone and marl intervals resulted from alternating episodes of carbonate input and starvation. Both lithologic phases may contain evidence for sedimentary and taphonomic reworking, associated with scours, that reflects low rates of sedimentation and stratigraphic condensation. Three successive types of elementary cycles resulted from increasing rates of stratigraphic condensation, sedimentary condensation and substrate stabilization during early Bathonian. The occurrence of reelaborated ammonoids (i.e. exhumed and displaced before their final burial) implies that tractive current flows or winnowing affected the burial of concretionary internal moulds. In the lower Bathonian strata, the dominance of homogeneous concretionary internal moulds of phragmocones, completely filled with sediment, is indicative of low rates of sedimentation and sediment accumulation, respectively associated with low degrees of stratigraphic and sedimentary condensation. However, at the Bajocian/Bathonian transition, hemipelagic, bed‐scale limestone–marl alternations show a maximum value of biostratigraphic completeness and there is no evidence for taphonomic condensation in the ammonoid fossil assemblages. Taphonomic analyses of the successive ammonoid fossil assemblages and taphofacies confirm the development of a deepening phase associated with sedimentary starvation, which characterizes the last episode within the deepening half‐cycle of third and second order cycles, in the Bas Auran area of French Subalpine Basin during early Bathonian.     

Calcareous nannofossil biostratigraphy of the Cenomanian/Turonian boundary interval of ODP Leg 207 at the Demerara Rise

During Ocean Drilling Program Leg 207 at Demerara Rise (western tropical Atlantic) expanded sections of organic-rich laminated shales of late Cretaceous age, including the Cenomanian/Turonian boundary interval (CTBI) were recovered. These sediments yield rich assemblages of calcareous nannofossils, offering a unique possibility to calibrate the stable carbon isotope curve (δ¹³C_org). The calcareous nannofossils of Sites 1258, 1259, 1260 and 1261 have been investigated in order to gain a detailed biostratigraphic framework for the CTBI in the tropical latitudes. The bioevents observed have been correlated with the characteristic δ¹³C_org excursion of the CTBI. The events occurring during the excursion, and slightly below and above it, include the first occurrences of the calcareous nannofossil species Cylindralithus biarcus, Quadrum gartneri, Quadrum intermedium, Eprolithus octopetalus, Eprolithus eptapetalus, Eiffellithus eximius and the last occurrences of Corollithion kennedyi and Axopodorhabdus albianus. These bioevents have been correlated with those of other biostratigraphically and chemostratigraphically studied CTBI sections.     

Leaf essential oil composition of 10 species of Ocotea (Lauraceae) from Monteverde,Costa Rica

The leaf essential oils of 10 species of Ocotea (Lauraceae) from Monteverde, Costa Rica (Ocotea floribunda, Ocotea holdridgeana, Ocotea meziana, Ocotea sinuata, Ocotea tonduzii, Ocotea valeriana, Ocotea veraguensis, Ocotea whitei, and two undescribed species, Ocotea new species “los llanos”, and Ocotea new species “small leaf”) have been obtained by hydrodistillation and analyzed by GC–MS in order to discern the differences and similarities between the volatile chemical compositions of these species. The principal common constituents of the 10 species of Ocotea were α-pinene, β-pinene, β-caryophyllene, and germacrene-D.     

Cristatopecten nov. gen. benoisti (Pectinidae, Bivalvia) du Chattien d'Aquitaine (France). Révision systématique et réflexions sur l'origine et l'évolution des Cristatopecten

The detailed study of a sample of “Pecten (Amussiopecten) benoisti” Cossmann and Peyrot (1914) from the Chattian outcrops of the Adour Basin, allowed to improve our knowledge of this species poorly known till now and to show its important ornamental variability. It follows that some nomenclatural points have been clarified at the generic level: we refute the attribution of this species to the genus Amussiopecten Sacco (1897) as used by authors—genus which was besides emended several times subsequently— and we propose its allocation to Cristatopecten nov. gen. Furthermore, this study allowed to remove the ambiguity existing originally as for the attribution of the species benoisti and burdigalensis to a same genus: our comparison of the latter two taxa shows that if benoisti has to be henceforth included in the new genus Cristatopecten (as its type species), burdigalensis (which is the type species of Amussiopecten) must be incorporated in the genus Flabellipecten Sacco (1897). The two genera Amussiopecten and Flabellipecten are therefore synonymous, as Depéret and Roman had already stated in 1910. The Cristatopecten from the Old World seem to be derived from a group of “Aequipecten” notably known in the Italian Rupelian, the group of “Aequipecten deletus” (Michelotti, 1861), of which we study here a sample from the Aquitaine Chattian. In the Aquitaine Basin, the Cristatopecten are represented, in the Chattian, by Cristatopecten benoisti (Cossmann and Peyrot, 1914); in the Lower Aquitanian, by C. praehaueri (Bongrain, Cahuzac and Freneix, 1994); in the Burdigalian-Langhian of the Saubrigues paleocanyon, by C. haueri (Michelotti, 1847) and C. miogallicus (Cossmann and Peyrot, 1914). During the whole Neogene, they spread and evolved in the Tethys and the Paratethys areas, and seem to have become extinct in the Pliocene with the disappearance of C. cristatus (Bronn, 1827), a species that we consider not as an Amusium s.s., but as the last representative of the Cristatopecten phylum.     

Les Megacricetodon du gisement karstique miocène moyen de Blanquatère 1 (Pyrénées-Orientales, Sud de la France) : nouvelles espèces, implications biochronologique et phylogénique

Three Megacricetodon species are recognized in the Middle Miocene locality of Blanquatère 1 (Languedoc-Roussillon province, France). Two are new, the small-sized M. tautavelensis nov. sp. the medium to large-sized M. aunayi nov. sp., the third one being the already known M. “collongensis-gersii”, a medium-sized species found in other Miocene localities of the area. Size and morphology differentiate these species. Such a high number of contemporaneous species of the genus Megacricetodon is found for the first time in a Miocene locality in the region and indicate that the evolution of this genus in western Europe is likely more complicated. It may testify both of a biogeographical differentiation and of migration events. According to our calibration charts, the deposit is dated ca. 16 Ma ago. The position of Vieux-Collonges (MN 5) and Sansan (MN 6) on the biochronological scale is also discussed, as well as the estimated age of the biozonal boundaries MN 3/MN 4, MN 4/MN 5 and MN 5/MN 6.