Organic-walled dinoflagellate cysts from the Upper Cretaceous–lower Paleocene succession in the western External Rif,Morocco: New species and new biostratigraphic results

Palynological investigation of the Upper Cretaceous–lower Paleocene succession from the Tahar section near Arba Ayacha in northwestern Morocco (westernmost External Rif Chain) reveals the presence of rich, diverse and well-preserved dinoflagellate cyst assemblages. For the first time in the study region, biostratigraphic interpretations based on the dinoflagellate cyst assemblages from the studied interval allow the recognition of the upper Maastrichtian and Danian. Relevant upper Maastrichtian–Danian global dinoflagellate cyst events include: the First Appearance Datum of the upper Maastrichtian species Disphaerogena carposphaeropsis, Glaphyrocysta perforata, and Manumiella seelandica; the Last Appearance Datum of the Cretaceous taxa Dinogymnium spp., Isabelidinium cooksoniae, and Pterodinium cretaceum; and the First Appearance Datum of the earliest Danian markers Carpatella cornuta, Damassadinium californicum, Membranilarnacia? tenella, and Senoniasphaera inornata. We formally describe the biostratigraphical range and potential of two new dinoflagellate cyst species, namely Nematosphaeropsis silsila Guédé and Slimani nov. sp., and Pterodinium ayachensis Guédé and Slimani nov. sp. Both species are found in the westernmost External Rif Chain and are restricted to the upper Maastrichtian.     

Strontium isotope stratigraphy of the Gabbs Formation (Nevada): implications for global Norian–Rhaetian correlations and faunal turnover

The Luning and Gabbs formations in west‐central Nevada, USA represent a Late Triassic shallow marine sedimentary succession with global significance (the Gabbs Formation was a candidate for the basal Jurassic GSSP). Typically, the Norian–Rhaetian stage boundary is placed at the contact between the formations, and the Rhaetian–Hettangian boundary (the Triassic–Jurassic boundary) is within the Müller Canyon Member of the Gabbs Formation. However, the use of different biostratigraphical index‐species schemes in Norian–Rhaetian successions between Tethys and Panthalassa, the two largest ocean basins at the time, makes precise correlation problematic. Here, we compare ⁸⁷Sr/⁸⁶Sr measurements of well‐preserved carbonate shell material from Nevada to the well‐known and biostratigraphically constrained ⁸⁷Sr/⁸⁶Sr record from Tethys, where a negative excursion in ⁸⁷Sr/⁸⁶Sr is noted across the Norian–Rhaetian boundary. Our new ⁸⁷Sr/⁸⁶Sr data from the Luning and Gabbs formations reveal a comparable trend, with a sharp drop in ⁸⁷Sr/⁸⁶Sr within the Nun Mine Member of the Gabbs Formation, suggesting the position of the Norian–Rhaetian boundary is higher in the succession, and not between the Luning and Gabbs formations as previously defined. Relating the stage boundary using global isotopic signals is a useful tool for biostratigraphical correlation of successions between Tethys and Panthalassa, and for estimating the rate of faunal turnover at the Norian–Rhaetian stage boundary in comparison with the succeeding Late Triassic mass extinction. If correct, this biostratigraphical–chemostratigraphical correlation suggests that the current index groups for the Panthalassic stage boundary should be changed.     

“Earliest Zanclean age for the Colombacci and uppermost Di Tetto formations of the « latest Messinian » northern Apennines: New palaeoenvironmental data from the Maccarone section (Marche Province, Italy)” by Popescu et al. (2007) Geobios 40 (359-373)

Two possible alternative interpretations of the claimed Zanclean age (Popescu et al., 2007) of two historical lithostratigraphic units of the Northern Apennines, usually referred to as Late Messinian in age and recording the so called Lagomare final event of the Messinian salinity crisis (MSC), are here discussed. The wrong age attribution of the Colombacci and “tetto” Fms. is ruled out based on data from the Maccarone and other sections showing that the Colombacci-Argille Azzurre Fm. boundary is basin wide synchronous and coincident with the Miocene-Pliocene boundary as far as it has been formally defined in the Eraclea Minoa GSSP. Alternatively, the opportunity of emending the Zanclean GSSP to a stratigraphically lower horizon recording the first evidence of marine influences in the Mediterranean following the MSC peak, seems not suitable, as (1) the marine signature of uppermost Messinian deposits is weak and still controversial and (2) no significant bio- and magnetostratigraphic events, well chronologically defined and recognizable at a global scale appear to be available to such a purpose.     

Albian calcareous nannofossils from ODP Site 1258, Demerara Rise

Site 1258, drilled during Ocean Drilling Program (ODP) Leg 207 on Demerara Rise off the northern coast of South America, recovered organic-rich Albian sediments that yield abundant, moderately to well preserved calcareous nannofossils. Biostratigraphic analysis shows the section primarily spans Roth’s (Initial Reports DSDP 44. US Government Printing Office, Washington (1978) 731) middle to late Albian Zone NC9. A disconformity separates these sediments from overlying uppermost Albian laminated shales from Zone NC10. The presence of Seribiscutum primitivum within the Albian section represents the first known occurrences of this species at such low latitudes, as Demerara Rise was located within 15° of the equator during the mid-Cretaceous. This species exhibits a bipolar distribution and is considered a cool-water, high-latitude species. Its presence on Demerara Rise indicates cooler water incursions either through changes in surface circulation or upwelling conditions during the opening of the Equatorial Atlantic.     

Maastrichtian calcareous nannofossil biostratigraphy and paleoecology in the Equatorial Atlantic (Demerara Rise, ODP Leg 207 Hole 1258A)

Species richness, absolute and relative abundances of Maastrichtian calcareous nannofossils were analyzed in Hole 1258A. Absolute abundances of taxa were used for the biozonation of this hole and the record of successive bio-events. Distribution patterns of cool water taxa such as Ahmuellerella octoradiata, Gartnerago segmentatum and Kamptnerius magnificus underscore two major cooling events. These events occurred during Chron C31r and during undifferentiated Chrons C31n to C30n. The latter event appears to be accompanied by lowered productivity, as expressed by the lower abundances of fertility index taxa Biscutum constans and Zeugrhabdotus spp. An end-Maastrichtian warming event is recorded in Chron C29r by the sudden drop in abundance of cool water taxa and acme of tropical taxon Micula murus. The disappearance of B. constans just before this event and the significant increase of Micula decussata, respectively, suggest lowered productivity and high-stress environmental conditions prior to the K/P boundary (Cretaceous-Paleogene). These results correlate very well with the climatic scenario proposed by Li and Keller (1998a) in South Atlantic Hole 525A as suggested by stable isotopes and distribution patterns of planktic foraminifera.     

山东省青州地区寒武-奥陶系界线研究的新进展

首次报道了山东省青州地区尧王山剖面的寒武 奥陶系界线地层的牙形石生物地层学的最新研究成果,在该剖面的炒米店组灰岩建立了 9个牙形石带,其中下奥陶统为 3个带,上寒武统凤山阶为 6个带;并与国内外研究较详细的寒武 奥陶系界线地层进行了对比。在该剖面首次发现了界线牙形石分子Iapetognathusfluctivagus,这也是在整个华北地区的首次报道,这一发现为山东地区乃至整个华北地区的寒武 奥陶系的界线划分提供了新的标尺。     

Répartition stratigraphique et biozones des kystes de dinoflagellés au passage Jurassique moyen–Jurassique supérieur (Bathonien supérieur–Oxfordien inférieur) dans le Bassin de Guercif,Maroc nord-oriental

Despite the stratigraphical significance of dinoflagellate cysts as reliable markers for correlating and dating Jurassic–Cretaceous strata, investigations into this palynomorph group in the southern Tethyan Realm, specifically northwest Africa, are sparse and somewhat parochial. Most research on Jurassic dinoflagellate cysts is focussed on European depocentres in the Boreal and Sub-Boreal realms. This study is on biostratigraphical data from two petroleum boreholes (MSD1 and KDH1) drilled during 1985 in the Guercif Basin, northeast Morocco by ONAREP (Office National de Recherche et d’Exploitation Pétrolier), now ONHYM (Office National des Hydrocarbures et des Mines). These boreholes penetrated a thick siliciclastic succession, attributed to the Middle and Upper Jurassic, below Miocene marls. Over sixty dinoflagellate cyst taxa were identified. Four dinoflagellate cyst biozones, named GI to GIV, are established for the late Bathonian to early Oxfordian interval. These biozones are defined on the basis of the first appearance datum (FAD) and/or the last appearance datum (LAD) of some biomarker taxa which have wide geographical distributions. These are: Ctenidodinium combazii and Ctenidodinium sellwoodii for the GI Biozone (late Bathonian–early Callovian); Ctenidodinium continuum and Meiourogonyaulax caytonensis for the GII Biozone (middle Callovian); Gonyaulacysta centriconnata and Wanaea thysanota for the GIII Biozone (late Callovian–earliest Oxfordian); and Liesbergia liesbergensis and Systematophora penicillata for the GIV Biozone (early Oxfordian). These biozones are correlated to those already established for the respective intervals in other palaeogeographic regions, such as the Boreal, Sub-boreal and Tethyan realms.     

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A new Reynesocoeloceras, R. praeincertum, hasbeen found in the Portuguese Middle Carixian (Luridum sub-zone); it is very primitive for the genus. This species keeps some strong affinities with the latest Metaderoceras (gr. venarense and gr. evolutum).R. praeincertum displays a progressive transition between Metaderoceras and Reynesocoeloceras.     

Conodonts of the genus Lochriea near the Visean–Serpukhovian boundary (Mississippian) at the Naqing section,Guizhou Province,South China

The First Appearance Datum (FAD) of the conodont Lochriea ziegleri in the lineage Lochriea nodosa–L. ziegleri has been considered the most suitable definition and global correlation-level for a revised base of the Serpukhovian Stage. Abundant specimens of Lochriea are recorded throughout the Late Visean–early Serpukhovian interval in the Naqing section, South China. Among them, the P1 elements, with wide morphological variability, enable confirmation and refinement of main lineages within the genus. Two lineages are proposed: 1) noded Lochriea species, such as L. mononodosa–L. nodosa–L. ziegleri, L. senckenbergica and L. multinodosa, and 2) ridged Lochriea species such as L. monocostata–L. costata–L. cruciformis. The possibility for their phylogenetic relationships is evaluated in this paper.     

Sur quelques flores du Carbonifère des Pyrénées béarnaises

The fossil Carboniferous flora of various localitiesof the «zone primaire axiale in Pyrénées Mountains, which was mainly known only by lists of determinations, is described and figured for the first time, due to the recent discovery of a very nice fossiliferous locality. The plant association comprises Lepidophyta, Arthrophyta, Filicophyta, Pteridospermaphyta and Cordaitophyta, with the following dominant species: Neuralethopteris schelehanii (Stur), Karinopteris acuta (Brongniart), Eusphenopteris hollandica (Gothan & Jongmans), Paripteris gigantea (Sternberg), Calamites cf. cistiiformis (Stur) and Corynepteris sp.Such an association is typical for an Upper Namurian B-Lower Namurian C age in Western Europe. The biostratigraphic results are compared with the data obtained by Goniatites found also in these localities.The identity of such plant-assemblages from WesternEurope as well as South and North-East China is in favour of a continental continuity between these provinces during the Namurian.