Search results for "OCR"
showing 10 items of 13223 documents
Understanding volcanoes in the Vanuatu arc
2016
We report the first helium isotope survey of volcanic gases, hot springs and some olivine phenocrysts along the Vanuatu island arc, from Tanna in the south to Vanua Lava in the north. Low CO2 content and low He-3/He-4 ratios in thermal fluids of Epi (4.0 +/- 0.1 R-a), Efate (4.5 +/- 0.1 R-a) and Pentecost (5.3 +/- 0.5 R-a) islands coherently indicate reduced mantle gas leakage and crustal contamination by radiogenic helium on these extinct volcanic systems of the former (Pliocene) arc. Instead, presently active Vanuatu volcanoes display He-3/He-4 and C/He-3 ratios typical of subduction-related volcanic arcs: He-3/He-4 ratios range from 6.4 +/- 0.5 Ra in southernmost Tanna and 7.23 +/- 0.09 …
Antisana volcano: A representative andesitic volcano of the eastern cordillera of Ecuador: Petrography, chemistry, tephra and glacial stratigraphy
2017
Antisana volcano is representative of many active andesitic strato-volcanoes of Pleistocene age in Ecuador's Eastern Cordillera. This study represents the first modern geological and volcanological investigation of Antisana since the late 1890's; it also summarizes the present geochemical understanding of its genesis. The volcano's development includes the formation and destruction of two older edifices (Antisana I and II) during some 400 + ka. Antisana II suffered a sector collapse about 15,000 years ago which was followed by the birth and growth of Antisana III. During its short life Antisana III has generated >= 50 eruptions of small to medium intensity, often associated with andesitic t…
Effects of climate change and land use intensification on regional biological soil crust cover and composition in southern Africa
2022
Biological soil crusts (biocrusts) form a regular and relevant feature in drylands, as they stabilize the soil, fix nutrients, and influence water cycling. However, biocrust forming organisms have been shown to be dramatically vulnerable to climate and land use change occurring in these regions. In this study, we used Normalized Difference Vegetation Index (NDVI) data of biocrust-dominated pixels (NDVIbiocrust) obtained from hyperspectral and LANDSAT-7 data to analyse biocrust development over time and to forecast future NDVIbiocrust development under different climate change and livestock density scenarios in southern Africa. We validated these results by analysing the occurrence and compo…
High-resolution 40Ar/39Ar chronostratigraphy of the post-caldera (<20 ka) volcanic activity at Pantelleria, Sicily Strait
2011
Abstract The island of Pantelleria (Sicily Strait), the type locality for pantellerite, has been the locus of major caldera-forming eruptions that culminated, ca. 50 ka ago, in the formation of the Cinque Denti caldera produced by the Green Tuff eruption. The post-caldera silicic activity since that time has been mostly confined inside the caldera and consists of smaller-energy eruptions represented by more than twenty coalescing pantelleritic centers structurally controlled by resurgence and trapdoor faulting of the caldera floor. A high-resolution 40Ar/39Ar study was conducted on key units spanning the recent (post-20 ka) intracaldera activity to better characterize the present-day status…
Charcoal-painted images from the French Neolithic Villevenard hypogea: an experimental protocol for radiocarbon dating of conserved and in situ carbo…
2020
A conserved painting removed from a Neolithic collective grave in Marne, France, provided an opportunity for radiocarbon dating to place Les Ronces Hypogeum 21 (Villevenard) into the chronology of that region. Chemical analysis with direct analysis in real time (DART) mass spectrometry, Fourier transform infrared (FTIR) spectroscopy and gas chromatography-mass spectrometry (GC-MS) of samples from the painting revealed the presence of two kinds of wax (beeswax and paraffin or microcrystalline wax) that likely were added during the conservation, a drying oil like linseed oil, as well as markers of pine resin that may arise from turpentine or colophony. A new pretreatment protocol of chlorofor…
Ocre, hematites y óxido de hierro: el problema terminológico = Ochre, Hematite and Iron Oxid: The Terminological Issue
2016
Los óxidos de hierro son prácticamente omnipresentes al analizar contextos, no solo referentes al arte rupestre, sino también en relación con toda una serie de actividades que podríamos considerar cotidianas en ambientes prehistóricos. Sin embargo, su estudio sistemático no ha comenzado hasta tiempos muy recientes. Fruto de ello, podría decirse que una parte de la literatura arqueológica no especializada en el campo de la pigmentología muestra, en ocasiones, cierta inexactitud terminológica. Con este documento pretendemos, a través de un análisis tanto de su funcionamiento, como de las propiedades geoquímicas y mineralógicas del ocre, la hematites y los propios óxidos de hierro, exponer la …
First report of Gogia (Eocrinoidea, Echinodermata) from the Early-Middle Cambrian of Sonora (Mexico), with biostratigraphical and palaeoecological co…
2009
10 pages; International audience; The blastozoan echinoderm genus Gogia is reported for the first time in the Early and the Middle Cambrian of Mexico. Reports in different members of the section of San José de Gracia (Sonora State, northwestern Mexico) extend the palaeogeographical range of the genus to the South Laurentia, and the stratigraphic range of Gogia granulosa to the whole first half of middle Middle Cambrian. Isolated plates occur in rocks deposited in detrital inner platform and complete specimens, in carbonate outer platform, confirming their ability to live in diverse environments. Their presence in these different environments through the Early-Middle Cambrian on Laurentia ag…
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…
Condition-dependent effects of corticosterone on a carotenoid-based begging signal in house sparrows
2008
International audience; Begging is a complex display involving a variety of different visual and auditory signals. Parents are thought to use these signals to adjust their investment in food provisioning. The mechanisms that ensure the honesty of begging displays as indicators of need have been recently investigated. It has been shown that levels of corticosterone (Cort), the hormone released during the stress response, increase during food shortage and are associated with an increased begging rate. In a recent study in house sparrows, although exogenous Cort increased begging rate, parents did not accordingly adjust their provisioning rate. Here, we tested the hypothesis that Cort might af…
The cranium of Proviverra typica (Mammalia, Hyaenodonta) and its impact on hyaenodont phylogeny and endocranial evolution.
2019
19 pages; International audience; We describe the first endocast reconstruction of a hyaenodont mammal based on X‐ray microtomography. The endocast belongs to the type material of the European hyaenodont Proviverra typica. We performed phylogenetic analysis to contextualize the evolution of endocranial size and complexity in Hyaenodonta. We added several European hyaenodonts and modified several codings of the most recent character–taxon matrix established to question the relationships within Hyaenodonta. Including these new species in a phylogenetic analysis reveals a new clade: Hyaenodontoidea. Comparisons with several previously described endocasts show that there was an increase in comp…