Search results for "CEO"
showing 10 items of 398 documents
Late Cretaceous continental weathering evolution on the southern Atlantic margins of Africa and South America : contributions of a new geochemical tr…
2022
The late Cretaceous records a pronounced decrease in temperatures on a global scale between 90 and 65 million years that marks the first step of the progressive climatic decline ultimately leading to our modern climate mode. This first cooling step is concomitant to a major tectonic uplift of the east South American and west African margins. Relief formation on the African ans South American continent, enhancing continental weathering, can have induced a climatic cooling at a global scale through atmospheric CO2 consumption linked to silicate weathering reactions. The main objective of this project is to explore the potentially determinant impact of this tectonic uplift on the long-term coo…
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…
First record of the enigmatic coleoid genus Longibelus from Sakhalin (Far East Russia): a contribution to our understanding of Cretaceous coleoid hab…
2021
AbstractA newly collected specimen of the enigmatic coleoid genus Longibelus is recorded from lower Turonian strata along the River Shadrinka in Sakhalin (Russian Far East). To date, this is the first record of Late Cretaceous coleoid cephalopods from the island and, in fact, from the entire Pacific coast of the Russian Federation. Lithological characteristics, coupled with published geochemical analyses (δ13C and Corg content), suggest the habitat of this coleoid taxon to have been the middle to outer (i.e. distal) shelf. Its provenance from the stratigraphical level that is known as the Scaphites Event, characterised by a mass occurrence of Scaphites and Yesoites, may be indicative of occ…
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.
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…
Apparition d'une morphologie scaphitomorphe par miniaturisation chez une ammonite oxfordienne : Scaphitodites scaphitoides ()
1997
The pyritized fossil-bearing marls of the Jura (Lower Oxfordian) contain an ammonite that is remarkable because of its tiny adult size (less than 16 mm) and of the scaphitoidal coiling of its body chamber, which is similar to that of certain Cretaceous Scaphitaceae. Anatomical and ontogenetic analysis demonstrates that these individuals, which are ascribed to Scaphitodites scaphitoides (Coquand, 1853), formed a single species. We argue that the genus Scaphitodites derived from Taramelliceras by a complex process of progenesis (sensu Landman et al., 1991).
Microcrinoids from the lower and middle Albian of the Anglo-Paris Basin (southern England, UK, Seine Maritime, Pas de Calais and Aube, France).
2021
16 pages; International audience; Microcrinoids of the family Roveacrinidae Peck, 1943 are described from lower and middle Albian clays of the Anglo-Paris Basin (Seine Maritime, Pas de Calais and Aube, France; Kent and Bedfordshire, UK). They are referred to two subfamilies - the Orthogonocrininae Gale, 2019 and the Plotocrininae Gale, 2020. Orthogonocrinines include the long-ranging (middle Albian-lower Cenomanian) species Orthogonocrinus apertus Peck, 1943, and Styracocrinus peracutus (Peck, 1955), known from Texas, USA, Morocco, the UK and France, and two stratigraphically successive species of the genus Hyalocrinus, H. magniezii Destombes, 1984 and H. bulliensis Destombes, 1984, known o…
THE DIASCIA FLOWER AND ITS BEE - AN OIL-BASED SYMBIOSIS IN SOUTHERN AFRICA
1984
As has been formerly shown, the double-spurred flowers of the South African genus Diascia (Scrophulariaceae) produce fatty oil as a primary attractant. Their oil-collecting pollinators have so far remained unknown. It is concluded from the morphology and from direct evidence of flower visitation that the recently established Melittid genus Rediviva represents the co-evolved pollinator group of these plants, at the same time demonstrating the presence of “manual” oil collectors in Southern Africa. The bees must introduce their especially equipped forelegs into the paired spurs of Diascia for harvesting the oil, thereby pollinating the flower. In the described case, a new species, Rediviva em…
Influence of enzyme-aided extraction and ultrasonication on the phenolics content and antioxidant activity of Paeonia officinalis L. petals
2020
Peony is a less utilized herbaceous plant of ornamental and medicinal relevance. The petals are rich in bioactive phenolics and hence, the development of efficient extraction is required for maximum recovery and bioactivity. In this study, the optimal conditions for the ultrasound-assisted extraction of peony phenolics were first investigated by comparing to conventional extraction and testing the data fit by mathematical models (linear, two factor interactions, quadratic) followed by investigation of cellulase pre-treatment combined with ultrasonication. High amounts of flavonoids, phenolics and tannins were extracted in 30 min under ultrasound conditions of 150 W, 40 kHz, 50 % amplitude, …