Search results for "STRATIGRAPHY"
showing 10 items of 904 documents
Comparison of rainfall structures between NCEP/NCAR reanalyses and observed data over tropical Africa
2000
A comparison is made between modelled (NCEP/NCAR reanalysis) and observed (CRC and CRU dataset) annual and monthly precipitation over tropical Africa during the period 1958–1997. The split moving-windows dissimilarity analysis (SMWDA) is used to locate abrupt changes in rainfall time series. In the NCEP reanalysis data, we identify a main abrupt shift, which occurs in 1967 and concerns more than 50% of grid points. In the observation, this shift is only found over parts of tropical North Africa. Three other NCEP abrupt shifts (1975, 1983 and 1987) in the reanalysis shown by the SMWDA, each concerning about 20% of tropical Africa, are not identified in the observation. One hypothesis concern…
Application of daily rainfall principal component analysis to the assessment of the rainy season characteristics in Senegal
2003
The interannual variability of the onset and cessation dates of the rainy season (RS) in Senegal is analyzed over the 43 yr period 1950-1992, using daily rainfall data for 34 stations. The use of principal component analysis, based on rainfall only, is explored to identify aggregate, regional indexes for the onset and cessation of the rains. The minimum and maximum values of the cumula- tive scores of principal component 1, for each year, are used to locate the onset and cessation dates, respectively. Very distinct spatial rainfall patterns are found before and after the onset/cessation dates. Mean dates compare favorably with those based on other definitions, though our method is not meant…
Middle Triassic conodont apparatus architecture revealed by synchrotron X-ray microtomography
2018
Abstract The composition of conodont apparatuses is crucial for understanding the feeding mechanisms of these early vertebrates. However, the multielement apparatus reconstructions of most species remain equivocal because they have been inferred from loose element collections, guided by knowledge from rare articulated ‘bedding plane assemblages’ and fused clusters, often from distantly related taxa. Even these natural assemblages can be difficult to interpret because the component elements can be closely juxtaposed or embedded in matrix, making it hard to discern the morphology of each element and their relative positions within the architecture of the feeding apparatus. Here we report five…
Typologie du zircon des bentonites du Frasnien (carrière du Lion, Belgique) : utilité avant la datation U-Pb.
2006
5 pages; National audience
Étude du paléoclimat ordovicien (440 millions d'années) à travers l'enregistrement de la dynamique des glaciers au Niger.
2008
6 pages; National audience
Palaeozoic Reefs and Bioaccumulations: Climatic and Evolutionary Controls.
2007
291 pages
Le Dogger supérieur calcaire de la Côte dijonnaise et nuitonne et des plateaux du Chatillonnais - Stratigraphie, sédimentologie, paléoenvironnements,…
2009
22 pages; National audience
The significance of dropstones in a tropical lacustrine setting, eastern Cameros Basin (Late Jurassic–Early Cretaceous, Spain)
2004
International audience; Outsized clasts (mainly white quartzite pebbles) are found in carbonate deposits of the Enciso Group exposed on the northern border of the Cameros rift basin (Late Jurassic – Early Cretaceous, northern Spain). In the Arnedillo section, all the stones are enclosed in micrite, which was assumed deposited in littoral to open lacustrine environments, with minor inputs of deltaic sandstones. The clasts are found in fine-grained lacustrine sediments either as isolated stones or as loosely packed elongated clusters occasionally associated with quartz sands and gravels. The mean size of the clasts is 40 mm (range: 3 – 100 mm); they are polished, well-rounded, and lack any fa…
On the use of geophysical methods to characterize heterogeneities of quaternary alluvial deposits. Application to stormwater infiltration.
2007
Colloque avec actes et comité de lecture. International.; International audience; Stormwater infiltration basins are generally built on geological formations with large values of hydraulic conductivity. Such is the case for quaternary alluvial formations, among which are glaciofluvial deposits. Two geophysical investigation methods, namely ground-penetrating radar and electrical tomography, were tested on an infiltration basin built on a glaciofluvial deposit. Geophysical profiles were calibrated on a trench wall dug in the glaciofluvial formation. A sedimentological study coupled to geophysical measurements behind the trench wall highlights the three-dimensional architecture of the deposit…
Paléoclimats : l'enregistrement des variations climatiques.
2014
240 pages; National audience; Ce livre traite de la reconstitution des climats anciens aux échelles de temps utilisées en géosciences : de la centaine de millions d’années à l’échelle des générations humaines. Après une présentation des principaux acteurs du système climatique et des supports de l’enregistrement géologique des variations climatiques, l’auteur présente les principales étapes de l’évolution du climat de la Terre.Ce nouveau manuel, outre la présence d’exercices intégralement corrigés, intègre les résultats les plus récents en matière de recherches sur les paléoclimats et porte notamment sur les récents développements de la théorie de la terre « Boule de neige », les premiers r…