Search results for "milieu"
showing 10 items of 19813 documents
L'enquête sur les archives de la recherche en sciences humaines et sociales (ARSHS). Premier bilan
2009
Le reperage, la collecte et la conservation des archives produites par la recherche en sciences humaines et sociales sont une preoccupation recente en France. Cet article presente une experience originale menee par le reseau des Maisons des sciences de l’homme en collaboration avec les Archives nationales et le ministere de l’Enseignement superieur aupres des archives et des centres de recherche (universites, CNRS) pour faire un inventaire des archives de la recherche. Outre le sauvetage de fonds en perdition, l’enquete vise a sensibiliser les chercheurs a la conservation des donnees qu’ils produisent et a rendre possible une histoire des pratiques de recherche et une histoire sociale des s…
After the emergence of the Acheulean at Melka Kunture (Upper Awash, Ethiopia): From Gombore IB (1.6 Ma) to Gombore Iγ (1.4 Ma), Gombore Iδ (1.3 Ma) a…
2021
International audience; While the emergence of the Acheulean is well documented in East Africa at ~1.7 Ma, subsequent developments are less well understood and to some extent controversial. Here, we provide robust evidence regarding the time period between 1.6 Ma and 1.2 Ma, based on an interdisciplinary approach to the stratigraphic sequences exposed in the Gombore gully of Melka Kunture, in the upper Awash Valley of Ethiopia. Throughout the Pleistocene, the environment differed significantly from elsewhere in Africa because of the elevation at 2000 m asl, the cooler and rainy climate, the Afromontane vegetation, the development of endemic animal species, and the recurrent impact of volcan…
The Last Deglaciation of the Southeastern Sector of Scandinavian Ice Sheet
2006
The Scandinavian Ice Sheet (SIS) was an important component of the global ice sheet system during the last glaciation, but the timing of its growth to or retreat from its maximum extent remains poorly known. We used 115 cosmogenic beryllium-10 ages and 70 radiocarbon ages to constrain the timing of three substantial ice-margin fluctuations of the SIS between 25,000 and 12,000 years before the present. The age of initial deglaciation indicates that the SIS may have contributed to an abrupt rise in global sea level. Subsequent ice-margin fluctuations identify opposite mass-balance responses to North Atlantic climate change, indicating differing ice-sheet sensitivities to mean climate state.
Evidence of tephra reworking in loess based on 2D magnetic susceptibility mapping: A case study from Rocourt, Belgium
2016
Abstract In this article, a new and original approach to characterize tephra layers based on high resolution magnetic susceptibility (MS) mapping is applied to the tephra deposits of Rocourt (Belgium). A series of MS maps of selected sections show the 3D morphology of tephra horizons, including local dip and reworked structures of the Rocourt and Eltville tephras, proven by chemical analyses of phenocrysts. At Rocourt, tephras are observed in loess which is an excellent material for testing the efficiency of the magnetic susceptibility mapping of tephra deposits. We also attempted to locate the volcanic source of the Eltville tephra based on the spatial analysis of the thickness of deposits…
Carbon-isotope records of the Early Jurassic (Toarcian) Oceanix Anixic Event from the Valdorbia (Umbria-Marche Apennines) and Monte Mangart (Julian A…
2009
The Toarcian oceanic anoxic event (ca 183 Ma) coincides with a global perturbation marked by enhanced organic carbon burial and a general decrease in calcium carbonate production, probably triggered by changes in the composition of marine plankton and elevated carbon dioxide levels in the atmosphere. This study is based on high-resolution sampling of two stratigraphic successions, located in Valdorbia (Umbria-Marche Apennines) and Monte Mangart (Julian Alps), Italy, which represent expressions of the Toarcian oceanic anoxic event in deep-water pelagic sediments. These successions are characterized by the occurrence of black shales showing relatively low total organic carbon concentrations (…
Isotopic seawater temperatures in the Albian Gault Clay of the Boulonnais (Paris Basin): Palaeoenvironmental implications
2016
13 pages; International audience; Oxygen isotopes were measured on several types of fossil hardparts from the Gault Clay Formation including benthic and planktonic foraminifera, belemnite guards, and fish small-teeth. Belemnites δ18O values indicate low temperatures (13.5–19.3 °C) with an increase from the Middle to Late Albian. Foraminifera provide variable δ18O values, some too low to be relevant in terms of temperature (until 42 °C). These low values probably result from a diagenetic alteration of the foraminiferal tests even though SEM observations revealed well-preserved microstructures. However, higher foraminiferal δ18O values recorded in some levels indicate temperatures in the rang…
Accuracy of IKONOS for mapping benthic coral-reef habitats: a case study from the Puerto Morelos Reef National Park, Mexico
2012
International audience; Reefs are being threatened by global warming, natural disasters, and the increased pressure of the global population. These habitats are in urgent need of mapping at high resolution so that these threats can be quantified. Remote sensing can potentially provide such quantitative data. In this article, we attempt to map benthic coral-reef habitats at the Puerto Morelos Reef National Park in Yucatan Peninsula (Mexico) and to assess the accuracy of the technique in providing a baseline data for future monitoring of changes and evolution of the reef system. An IKONOS image was used in combination with checkpoint ground sampling and classified using a supervised maximum l…
Oxygen respiration rates of benthic foraminifera as measured with oxygen microsensors
2011
Abstract Oxygen respiration rates of benthic foraminifera are still badly known, mainly because they are difficult to measure. Oxygen respiration rates of seventeen species of benthic foraminifera were measured using microelectrodes and calculated on the basis of the oxygen fluxes measured in the vicinity of the foraminiferal specimens. The results show a wide range of oxygen respiration rates for the different species (from 0.09 to 5.27 nl cell−1 h−1) and a clear correlation with foraminiferal biovolume showed by the power law relationship: R = 3.98 10−3 BioVol0.88 where the oxygen respiration rate (R) is expressed in nl O2 h−1 and in μm3 biovolume (BioVol) (n = 44, R2 = 0.72, F = 114, p
Comment on the letter of the Society of Vertebrate Paleontology (SVP) dated April 21, 2020 regarding “Fossils from conflict zones and reproducibility…
2020
International audience
Evolutionary trends within Jurassic ammonoids.
2015
An evolutionary trend is a pattern of traits shifting in a given direction over a sufficiently long period of time to be detected. In this study, we examine trends among Jurassic ammonoids. First, a compilation of selected literature on evolutionary patterns and trends leads to the conclusion that such trends have rarely been studied among Jurassic ammonoids and even more rarely are they formally studied using statistical tests. Second, a preliminary survey of trends for the entire Jurassic at the family level (based on four published articles) suggests two sustained trends occurred each lasting nearly 10 myr: the Early Jurassic and Middle Jurassic radiations, which were related to the firs…