Search results for "stratigraphy"
showing 10 items of 904 documents
The Mid-Cenomanian Event in southeastern France: evidence from palaeontological and clay mineralogical data.
2013
16 pages; International audience; Reconstruction of main palaeoenvironmental conditions across the Mid-Cenomanian Event (MCE I) in the hemipelagic Tethyan section of Blieux (Southeast France, Vocontian Basin) is proposed. Quantitative analyses of calcareous nannofossil, ammonoid and clay mineral assemblages have been made and compared with respect to sea level changes and the carbon cycle perturbations. The nannofossil primary productivity, as recorded by nannofossil fluxes and relative abundances of meso-eutrophic taxa, is low just below and during the MCE Ia, then slightly increases in the interval including the MCE Ib. The clay assemblages mainly consist of illite/smectite mixed-layers w…
Late Jurassic palaeoclimatic change from clay mineralogy and gamma-ray spectrometry of the Kimmeridge Clay, Dorset, UK
2009
Abstract: The Late Jurassic was a time of increasing aridity in NW Europe. Here, a new clay mineral dataset is presented from a 600 m thick composite core through the Kimmeridge Clay Formation, southern England. Clay mineral assemblages comprise mainly illite and kaolinite, with minor randomly interstratified illite–smectite mixed-layer clays. SEM observations indicate that clay minerals are mainly detrital, except in silty strata of late Tithonian age, which contain abundant pore-filling kaolinite aggregates. Th/K ratios determined from gamma-ray spectrometry mirror palaeoclimatically significant variations in kaolinite/illite ratios, with notable exception where diagenetic kaolinite occur…
Paleobiogeography of Early Cretaceous Ammonoids
2015
International audience
Les Gregoryceras (Ammonitina) de l'Oxfordien moyen terminal et supérieur téthysien : révision systématique, biostratigraphie et évolution.
2009
43 pages; Les Gregoryceras Spath, 1924 (Ammonitina, Peltoceratina) de la fin de l'Oxfordien moyen (sous-zone à Rotoides) et de la base de l'Oxfordien supérieur (zone à Bifurcatus) sont révisés. Les coupes ayant fourni la plupart des spécimens de ce travail (Espagne et Maghreb) sont décrites et datées sur la base de comparaisons fauniques entre les domaines téthysien et subtéthysien. Le meilleur outil pour ces corrélations est la présence du genre Gregoryceras. La succession des espèces de Gregoryceras est identique pour les deux domaines suscités, ce qui permet de compléter l'échelle biostratigraphique proposée antérieurement et parallèle à la zonation standard. Les espèces reconnues et red…
Biostratigraphy and isotope stratigraphy of upper Maastrichtian–Danian marine deposits of the Kopet-Dagh Basin, northeast Iran
2018
Abstract Biostratigraphy, using foraminifera and echinoids, plus high-resolution carbon isotope stratigraphy of the upper Maastrichtian–Danian interval in the western part of the Kopet-Dagh Basin in northeast Iran are outlined. Our study of shallow-marine carbonate platform deposits of the Kalat Formation, rich in larger benthic foraminifera (predominantly Clypeorbis mammillatus Schlumberger, Lepidorbitoides sp. and Siderolites calcitrapoides Lamarck), has allowed the definition of a C. mammillatus-S. calcitrapoides Assemblage Zone, of late Maastrichtian age. Clypeorbis mammillatus is here recorded for the first time from the Maastrichtian Kalat Formation and represents the most easterly fi…
Distribution of late Maastrichtian pachydiscid and scaphitid ammonites in the Maastricht and Kunrade formations of the southeast Netherlands
2018
Abstract The pachydiscid Pachydiscus ( Pachydiscus ) gollevillensis (d'Orbigny, 1850), long held to be confined to the ‘Kunrade Limestone’ (nowadays Kunrade Formation) in the eastern part of southern Limburg (Kunrade–Benzenrade area, the Netherlands), is now recorded from the basal Nekum Member (Maastricht Formation) at the ENCI-HeidelbergCement Group quarry, Sint-Pietersberg (Maastricht). Here we review the stratigraphic distribution of pachydiscid and scaphitid ammonites in outcrops west of the River Maas (Maastricht Formation) and in the Kunrade–Benzenrade area (Kunrade Formation). The latter unit has been correlated with part of the Lanaye Member (Gulpen Formation) up to the basal Emael…
The lower Ovetian Stage (lower Cambrian Stage 3) trilobite zonation in Spain and correlation with West Gondwana
2020
New trilobites from the upper part of the Pusa Formation (base of Cambrian Stage 3) in Central Spain are studied for their systematic and biostratigraphic significance. The trilobites Proabadiella ...
Emsian (Lower Devonian) conodonts from the Daliantang Formation at Daliantang, southeastern Yunnan, China
2021
Abstract The lower/upper Emsian boundary witnessed prominent diversification of biostratigraphically important genera Polygnathus Hinde, Caudicriodus Bultynck, and Latericriodus Muller. In contrast, conodonts previously reported around this boundary from the South China Block were characterized by relatively low species or subspecies diversity, and only a few widely distributed and extensively studied zone-defining taxa were recorded. In this paper, conodonts from the Daliantang Formation at the Daliantang section (Guangnan, southeastern Yunnan), one of the representative sections of the transitional facies between the benthic Xiangzhou facies and the pelagic Nandan facies, are investigated…
Upper Ovetian trilobites from Spain and their implications for the palaeobiogeography and correlation of the Cambrian Stage 3 in Gondwana
2016
Abstract The upper part of the La Herreria Formation in Los Barrios de Luna (Leon Province, N Spain) has been revised from a palaeontological and biostratigraphical point of view. Two stratigraphic sections have been studied including their trilobite and ichnofossils contents. The ichnofossil assemblages have a high diversity of species characterising the Cruziana ichnofacies, suggesting a shallow sublittoral environment for the upper part of the La Herreria Formation. The trilobites species recognised are Lunagraulos antiquus , Dolerolenus formosus , Dolerolenus longioculatus , Lunolenus lunae , Metadoxides richterorum , Metadoxides armatus and Sardaspis ? sp. from the upper Ovetian (lower…
Givetian (Middle Devonian) historical bio- and chronostratigraphical subdivision based on conodonts
2017
The conodont record supports the intended threefold subdivision of the Givetian as envisaged by the International Subcommision on Devonian Stratigraphy into Lower, Middle and Upper Givetian substages. The lower boundary of the Lower Givetian Stage coincides with the lower boundary of the Givetian and it is recognized with the entry of Polygnathus hemiansatus. The lower boundary of the Middle Givetian is identified with the entry of either P. varcus or P. rhenanus. The base of the Upper Givetian is defined with the entry of Schmidtognathus hermanni. The historical review shows the conceptual evolution from a stage with just one and a half zones to one with ten zones that are the basis for th…