Search results for "IOS"
showing 10 items of 8115 documents
Thuoux and Saint-Pierre d’Argençon Sections (Subalpine Basin, Southeastern France): Case Studies of Ammonite Biostratigraphy for the Potential Candid…
2014
The Thuoux and Saint-Pierre d’Argencon sections (Subalpine Basin, southeastern France) display a thick silty–clayey sedimentation with abundant and diversified ammonite faunas, free of detectable hiatuses. The Callovian–Oxfordian boundary is biostratigraphically located between the Lamberti and the Mariae zones or, more precisely, between the Lamberti Subzone (paucicostatum horizon) and the Scarburgense Subzone (thuouxensis horizon). The mixing of Boreal–Sub-Boreal Cardioceratinae and Sub-Mediterranean–Tethyan Hecticoceratinae, Peltoceratinae, and Perisphinctinae in this basin allows reliable worldwide correlations that enhance the choice of the Thuoux and Saint-Pierre d’Argencon sections a…
A record of the Jurassic/Cretaceous boundary climatic variation on the southern margin of the Tethys : clay minerals and palynofacies of the early Cr…
2005
Abstract In order to precise the paleogeographic extension of the climatic variation known at the Jurassic/Cretaceous boundary, the sedimentary organic matter (palynofacies and Rock-Eval) and the clay minerals content of Berriasian sediments of the Sidi Kralif Formation are studied on the Jebel Meloussi section, central Tunisia. Standard sedimentological and palynofacies analysis allow to reconstruct the bathymetric curve and the sequence stratigraphic scheme. Using existing biostratigraphy based on calpionellids and ammonite zonation, the sequence stratigraphic interpretation can be correlated with the established eustatic chart. Clay mineral assemblages are characterized by a shift in the…
Integrated stratigraphy of the potential candidate Oxfordian GSSP at Thuoux and Saint-Pierre d'Argençon (France).
2013
5 pages; International audience; The Thuoux and Saint-Pierre d'Argençon sections (Subalpine Basin, southeastern France) are proposed as a potential GSSP candidate for the Callovian-Oxfordian boundary. Several aspects of stratigraphy that have recently been applied in the two selected sections are discussed, including ammonite and nannofossil biostratigraphy, palynology, physical stratigraphy, and cyclostratigraphy.
Nouvelles données biostratigraphiques sur les dépots cénomanoturoniens du Nord-Est du fosse de ia Bénoué (Nigéria)
1993
Abstract The Upper Cretaceous deposits of the Upper Benue (North-East Nigeria) record regional and local events (sea-level changes, biological successions and tectonic movements) which throw light on the Upper Cenomanian transgression. Evidence of discontinuities and sedimentary assemblages well dated by micropalaeontological data, allows the sedimentary sequence to be interpreted in the context of sequence stratigraphy. The discovery of new ammonite faunas has enabled a more precise definition of the local biostratigraphy and a correlation of this with the standard zonal scheme. In the near future, when they are better known, the ammonite successions recognized in the Upper Benue could ena…
Un exemple de spéciation lié à l'eustatisme: l'apparition précoce de Schackoina cabri (foraminifère planctonique mésogéen)
1997
Investigation of planktic foraminifers from the Lower Aptian of the Vocontian Basin (SE France) reveals that Schackoina cabri makes a very discrete first appearance in the Weissi ammonite zone and not in the Deshayesi zone, i.e. before the global anoxic event OAE 1a and not after as was accepted in the literature. This discovery seems to support the recent model whereby speciation of planktic foraminifers occurred in marine lowstands and their real expansion during the ensuing sea-level rise.
Variations in Jurassic echinoid biodiversity at ammonite zone levels: Stratigraphical and palaeoecological significance
2020
After a relatively low but stable phase of taxonomic diversity during the Lias (Lower Jurassic), echinoids diversity strongly increases from Aalenian (Dogger-Middle Jurassic) to Kimmeridgian (Malm-Late Jurassic) and a conspicuous crisis takes place in Tithonian times, before the end of the Jurassic. During these major phases, minor decreases in diversity correspond with regressions (sea-level falls), mainly in the Middle Bathonian (Middle Jurassic). From the Aalenian to Callovian, the average duration of irregular echinoid species is about 3.8 m.y. whereas it is about 5.5 m.y. for the regular ones; the later value corresponding to the average duration of a Jurassic. From Callovian to Tithon…
Ammonites on the Brink of Extinction: Diversity, Abundance, and Ecology of the Order Ammonoidea at the Cretaceous/Paleogene (K/Pg) Boundary
2015
We examined the stratigraphic distribution of ammonites at a total of 29 sites around the world in the last 0.5 myr of the Maastrichtian. We demarcated this interval using biostratigraphy, magnetostratigraphy, cyclostratigraphy, and data on fossil occurrences in relation to the K/Pg boundary in sections without any facies change between the highest ammonites and the K/Pg boundary. The ammonites at this time represent all four Mesozoic suborders comprising six superfamilies, 31 (sub)genera, and 57 species. The distribution of ammonites is dependent on the environmental setting. Recent data suggest that ammonites persisted to the boundary and some species may have survived for several tens of…
Albian ammonites of the Benguela Basin (Angola): a biostratigraphic framework.
2007
20 pages; The study of the Albian ammonite fauna of the sedimentary series in the Benguela Basin (Angola) allows a major revision of the biostratigraphy of the south Atlantic area. The new biostratigraphic approach allows the recognition of 17 horizons distributed in 8 subzones correlated with the ammonite zonation of the Tethyan Province. The Lower Albian is characterized by the Douvilleiceras inaequinodum Subzone (including the D. mammillatum aequinodum Horizon). The Middle Albian is represented by the Oxytropidoceras (Mirapelia) buarquianum Subzone (subdivided into O. (M.) buarquianum and O. (M.) sergipense horizons). The Upper Albian is characterized by the Dipoloceras sp. Subzone (defi…
Spines and behaviour as defences against fish predators in an invasive freshwater amphipod.
2006
7 pages; International audience; Selective predation may be an important proximate cause of the success or failure of invader species. Gammarus roeseli is an invasive amphipod, for which the causes of establishment in rivers where the native species, Gammarus pulex, predominates remain unstudied. Freshwater amphipods are important prey for numerous fish predators, but empirical evidence of lower predation rates on exotic prey is scarce. In laboratory experiments, we compared the susceptibility of G. pulex and G. roeseli to fish predation, determined the mechanisms influencing prey selection, and studied the interaction between behavioural and morphological defences. Fish predators (brown tr…
Comparison of the functional responses of invasive and native amphipods
2008
While we can usually understand the impacts of invasive species on recipient communities, invasion biology lacks methodologies that are potentially more predictive. Such tools should ideally be straightforward and widely applicable. Here, we explore an approach that compares the functional responses (FRs) of invader and native amphipod crustaceans. Dikerogammarus villosus is a Ponto-Caspian amphipod currently invading Europe and poised to invade North America. Compared with other amphipods that it actively replaces in freshwaters, D. villosus exhibited significantly greater predation, consuming significantly more prey with a higher type II FR. This corroborates the known dramatic field imp…