Search results for "Ammonite"
showing 10 items of 96 documents
La lumachelle à Cardinia (Bivalves) et Alsatites (Ammonites) du " Revers de Côte Dure " dans l'Hettangien de la couverture sédimentaire du Massif du …
2011
29 pages; International audience; Ce travail est consacré à l'étude d'une faune de l'Hettangien moyen (Chronozone à Liassicus, Sous-Chronozone à Laqueus) qui, relativement peu diversifiée, mais très abondante et bien préservée, caractérise un niveau lumachellique spectaculaire dans la série du Jurassique inférieur, globalement peu fossilifère, de la couverture sédimentaire, du massif du Rochail (Bassin subalpin, zone dauphinoise). Cette faune, qui provient du Revers de Côte Dure (Villard-Notre-Dame, Isère, France), est essentiellement composée de bivalves (e.g., Cardinia, " Astarte ") et d'ammonites (e.g., Alsatites, Saxoceras), mais elle livre aussi, surtout au sommet du banc lumachellique…
Les ammonites de la limite Albien - Cénomanien dans la région de Sumbe (Bassin de la Kwanza, Angola).
2011
97 pages; International audience; Une faune originale, pour l’essentiel constituée d’ammonites de grande taille, est décrite pour le Crétacé angolais (Albien supérieur etCénomanien inférieur) de la région de Sumbe. La limite de ces étages est précisée et est caractérisée par la présence de Mortoniceras(Subschloenbachia) aff. perinflatum (Spath), Arestoceras goliath (Haas), Mariella (Mariella) gr. bergeri (Brongniart) pour l’Albienterminal et de Mariella (Mariella) gr. oehlerti (Pervinquière), Mariella (Mariella) aff. gallienii (Boule, Lemoine & Thévenin)et des Sharpeiceras du groupe de S. florencae Spath et de Sharpeiceras aff. schlueteri Hyatt pour le Cénomanien basal. L’espèceA. goliath (…
Early Jurassic (Sinemurian to basal Toarcian) ammonites of the Brescian Prealps (Southern Alps, Italy).
2017
This work provides a more precise up-to-date biostratigraphical framework of the Early Jurassic ammonite succession of the Brescian Prealps with more than seventy taxa for the Sinemurian, Pliensbachian and basal Toarcian corresponding to a about 30 horizons or faunal assemblages rather well correlable with the NW European standard zonation. These results are supported with already published data, new data from recent field investigations, revised contributions of different authors and with the study of the historical collection of the Museum of Natural Sciences of Brescia (Northern Italy). The biohorizons are referred to the Lower Jurassic carbonate series of the Brescian Prealps, cropping …
Deep-Time Phylogenetic Clustering of Extinctions in an Evolutionarily Dynamic Clade (Early Jurassic Ammonites)
2012
7 pages; International audience; Conservation biologists and palaeontologists are increasingly investigating the phylogenetic distribution of extinctions and its evolutionary consequences. However, the dearth of palaeontological studies on that subject and the lack of methodological consensus hamper our understanding of that major evolutionary phenomenon. Here we address this issue by (i) reviewing the approaches used to quantify the phylogenetic selectivity of extinctions and extinction risks; (ii) investigating with a high-resolution dataset whether extinctions and survivals were phylogenetically clustered among early Pliensbachian (Early Jurassic) ammonites; (iii) exploring the phylogene…
Ammonite Faunal Dynamics Across Bio-Events During the Mid-and Late Cretaceous Along the Russian Pacific Coast
2012
The present paper focuses on the evolutionary dynamics of ammonites from sections along the Russian Pacific coast during the mid-and Late Cretaceous. Changes in ammonite diversity (i.e., disappearance [extinction or emigration], appearance [origination or immigration], and total number of species present) constitute the basis for the identification of the main bio-events. The regional diversity curve reflects all global mass extinctions, faunal turnovers, and radiations. In the case of the Pacific coastal regions, such bio-events (which are comparatively easily recognised and have been described in detail), rather than first or last appearance datums of index species, should be used for glo…
High-resolution dynamics of Early Jurassic marine extinctions: the case of Pliensbachian–Toarcian ammonites (Cephalopoda).
2010
Abstract: The Pliensbachian–Toarcian interval was marked by major environmental disturbances and by a second-order mass extinction. Here, we reappraise the taxonomic, spatiotemporal and selective dynamics of extinctions over the whole interval, by analysing a high-resolution dataset of 772 ammonite species from NW Tethyan and Arctic domains. On average, 40–65% of ammonite species disappeared during each subchronozone, but higher extinction pulses (reaching 70–90%) prevailed from the Margaritatus to the Dispansum Chronozone. The main extinctions, corresponding to the Gibbosus, Pliensbachian–Toarcian boundary, Semicelatum, Bifrons–Variabilis, and Dispansum events, differed in their dynamics, …
Ammonite faunas from condensed Cenomanian-Turonian sections (‘Tourtias’) in southern Belgium and northern France
2011
AbstractIn southern Belgium (Mons Basin and Tournai region) and northern France (area between Lille, Valenciennes and Maubeuge), condensed sequences have been referred to as ‘tourtias’ since the start of the nineteenth century. These levels correspond to a succession of trangressive systems tracts and generally appear as dark green, glauconitic and microconglomeratic facies. They are distributed all along the base of the more important transgressive systems tracts of the Cenomanian and basal Turonian from the Boulonnais (northwest France) to the Mons Basin (southern Belgium), through the Artois and Douaisis. Their age can now be determined more accurately by identification of their ammonite…
Testing a portable laser-induced breakdown spectroscopy system on geological samples.
2012
9 pages; International audience; This paper illustrates the potentialities of a home-made portable LIBS (laser-induced breakdown spectroscopy) instrument in Earth sciences, more particularly in geochemically recognizing (i) tephra layers in lacustrine sediments and (ii) fossilization processes in ammonites. Abundances for selected lines of Al, Ca, Fe, Ti, Ba and Na were determined in lacustrine chalk sediments of the Jura, where the Laacher See Tephra (LST) layer is recorded. A statistical treatment of elemental maps produced from the section of a sedimentary column containing the LST event allows instrumental conditions to be optimized. Accumulating spectra from close shot positions gives …
Ammonite extinction and nautilid survival at the end of the Cretaceous
2014
One of the puzzles about the end-Cretaceous extinctions is why some organisms disappeared and others survived. A notable example is the differential extinction of ammonites and survival of nautilids, the two groups of co-occurring, externally shelled cephalopods at the end of the Cretaceous. To investigate the role of geographic distribution in explaining this outcome, we compiled a database of all the occurrences of ammonites and the nautilid genus Eutrephoceras in the last 0.5 m.y. of the Maastrichtian. We also included recently published data on ammonite genera that appear to have briefly survived into the Paleocene. Using two metrics to evaluate the geographic range of each genus (first…
An orbital floating time scale of the Hauterivian/Barremian GSSP from a magnetic susceptibility signal (Río Argos, Spain).
2012
10 pages; International audience; An orbital floating time scale of the HauterivianeBarremian transition (Early Cretaceous) is proposed using high-resolution magnetic susceptibility measurements. Orbital tuning was performed on the Río Argos section (southeast Spain), the candidate for a Global boundary Stratotype Section and Point (GSSP) for the HauterivianeBarremian transition. Spectral analyses of MS variations, coupled with the frequency ratio method, allow the recognition of precession, obliquity and eccentricity frequency bands. Orbitallytuned magnetic susceptibility provides minimum durations for ammonite biozones. The durations of well-constrained ammonite zones are assessed at 0.78…