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171.
Dominique Schwartz Michel Thinon Stéphanie Goepp Christian Schmitt Julien Casner Thierry Rosique Patrice Wuscher Anne Alexandre Étienne Dambrine Charly Martin Bernard Guillet 《Comptes Rendus Geoscience》2005,337(14):1250-1256
The age of the upland grasslands of the Vosges Mountains is still not well known. On the basis of the study of historical archives, it was assumed that the forest clearings, which led to grasslands establishment, were done by the monks who colonized the Vosges valleys between the 7th and the 8th centuries. Our pedo-anthracological study raises questions about this hypothesis, based on the discovery of Juniperus communis charcoal in soils from the 2nd or 1st century BC. This plant specie is characteristic of grasslands developing into fallows. The occurrence of Juniperus communis charcoals indicates that upland grasslands did exist at least 800 years earlier than it was expected before our study, i.e. at least since the late Iron Age. To cite this article: D. Schwartz et al., C. R. Geoscience 337 (2005). 相似文献
172.
River networks in mountain ranges owe their existence to the competing effects of tectonic uplift and climate-controlled erosion. However, paradoxically, the universal geometric properties of river networks are independent of both tectonics and climate. Currently, this paradox has still not been resolved. Here we propose a solution that consists in considering that the geometry of river networks is established on the lowland margins of incipient uplifts, and is quenched into the erosion zone as the mountain belts widen with time. In our model, the geometry of river networks simply reflects the downward coalescence of alluvial rivers on un-dissected surfaces outside of mountain belts, and is therefore independent of erosion processes. To cite this article: S. Castelltort, G. Simpson, C. R. Geoscience 338 (2006). 相似文献
173.
Gilles Grandjean Céline Pennetier Adnan Bitri Ombeline Meric Jean-Philippe Malet 《Comptes Rendus Geoscience》2006,338(9):587-595
Geophysical methods such as seismic surveying and electrical resistivity imaging appear to be well-adapted to investigate and understand landslide mechanisms. They allow direct and non-intrusive measurement of acoustic velocity and electrical resistivity, two fundamental parameters used to define the physical properties of the reworked moving materials. Both methods were applied at the Super-Sauze site in the French South Alps, where a typical example of an intra-material earthflow-mudslide can be observed. Measurements were taken simultaneously along two orthogonal profiles: one 325 m in length is perpendicular to the axis of the earthflow; the other 235 m in length is located along the axis of the earthflow. The results show a correlation between the seismic and electrical resistivity data, confirming that the simultaneous use of both methods gives complementary information about landslide mechanisms. The seismic data provide information on fracture density variations, whereas the electrical resistivity data provide information on water content variations. To cite this article: G. Grandjean et al., C. R. Geoscience 338 (2006). 相似文献
174.
Mahendra P. Verma 《Geostandards and Geoanalytical Research》2008,32(3):317-330
A statistical evaluation of the results of geochemical analyses of geothermal waters during interlaboratory comparison programmes of the International Association of Geochemistry and Cosmochemistry (IAGC) and International Atomic Energy Agency (IAEA) was performed to estimate the uncertainty of measurement of pH, electrical conductivity, Na+, K+, Ca2+, Mg2+, Li+, Cl?, HCO3?, SO42?, SiO2 and B. The uncertainty of measurement was found to increase exponentially with decrease in value (concentration) for all the parameters except for pH, electrical conductivity and SiO2 and was of the same order of magnitude as the concentrations for values of less than 1 μ ml?1. There was an overall uncertainty of ± 2.5% in the measurement of pH and ± 30% in SiO2. For all the other chemical species the uncertainty data were modelled by exponential curves. The sample IAEA14 was prepared by dissolving commercial reagents (i.e., represents a solution of known composition). Thus, the calculated values are considered to be the conventional true values for each chemical parameter. The difference between the measured mean of the data submitted by participating laboratories and the conventional true value for each parameter (i.e., bias of submitted measurements) for the species Na+, K+, Ca2+, Mg2+, Cl? and SO42? was ‐3.5, ‐1.1, ‐13.3, ‐53.6, ‐12.6 and ‐86.6%, respectively. The observed bias was of the same order of magnitude as statistical fluctuations (1s) for Na+ and K+, but significantly higher for Ca2+, Mg2+, Cl? and SO42?. Two methods, uncertainty interval and GUM (“guide to the expression of uncertainty of measurement”) were used to propagate uncertainty in the pH calculation of geothermal reservoir fluid. The application of the methods is illustrated by considering the IAEA10 and IAEA11 samples analysed in the interlaboratory comparisons as separated geothermal waters at atmospheric pressure. 相似文献
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176.
Pulok K. Mukherjee Param P. Khanna Naresh K. Saini 《Geostandards and Geoanalytical Research》2014,38(3):363-379
A simple, single sample preparation involving pressed rock powder pellets was utilised to determine the trace and ultra trace abundances of petrogenetically important elements including high field‐strength elements and REEs by laser ablation‐ICP‐MS. One of the elements predetermined by XRF spectrometry served as an internal standard. The influence of sample preparation parameters (grain size, pellet compactness and amount of binding media) on analytical performance was also investigated, including sample homogeneity issues at the laser sampling scale. Line scanning with a high repetition frequency (20 Hz) and large beam diameter (200 μm) ensured ablation from a larger sample surface area, eliminating issues related to sample heterogeneity. A median grain size of about 10 μm for silicate rock powders was found to be sufficiently representative at this scale of laser sampling. Granitic rocks or samples containing resistant minerals such as zircon needed extra grinding to achieve grain sizes down to < 5 μm for better precision for elements that are concentrated in these phases. Using 137Ba as an internal standard, reasonable accuracies within 15–20% for most of the high mass trace elements were achieved; in the case of low mass elements, it may deviate up to 40%. Precision of measurements rarely exceeded 15% RSD. 相似文献