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21.
Sarah-Jane Barnes Dany Savard L. Paul Bédard Wolfgang D. Maier 《Mineralium Deposita》2009,44(6):647-663
We have determined the S, Se, Cu and La contents through a complete stratigraphic section of the Bushveld Complex. The principle
aim was to determine which phases controlled these elements. S, Se and Cu show positive correlations, but these elements do
not correlate with La. In most cases, the concentration of S, Se and Cu in rocks containing greater than 800 ppm S can be
modeled by segregation of a Fe–Ni–Cu sulfide liquid from a fractionating magma. As the magma evolved, Se and Cu were depleted
by the continual segregation of sulfide liquid and the S/Se and S/Cu of the rocks increased. The Se/Cu ratio is higher in
the more evolved rocks, which suggests that Se has a slightly lower partition coefficient than Cu into sulfide liquid (1,200
versus 1,700). The Lower and lower Critical Zone of the complex contains on average only 99 ppm S. The low S content of these
rocks has led some authors to suggest that these rocks do not contain cumulate sulfides, despite the fact that they are moderately
enriched in PGE. These samples fall along the same trend as the S-rich samples on the S-versus-Se plot and the S/La and Se/La
ratios are greater than the initial magmas suggesting that despite the low S contents cumulate sulfides are present. Three
models may be suggested in order to explain the low S content in the Lower and Critical Zone rocks: (a) the sulfides that
were present have migrated away from the cumulate pile into the footwall or center of the intrusion; (b) the magma was saturated
in sulfides at depth and during transport some sulfides lagged in embayments; (c) the rocks have lost both S and Se at high
temperature. The first two models have important implications for exploration. 相似文献
22.
We use field measurements and airborne LiDAR data to quantify the potential effects of valley geometry and large wood on channel erosional and depositional response to a large flood (estimated 150-year recurrence interval) in 2011 along a mountain stream. Topographic data along 3 km of Biscuit Brook in the Catskill Mountains, New York, USA reveal repeated downstream alternations between steep, narrow bedrock reaches and alluvial reaches that retain large wood, with wood loads as high as 1261 m3 ha−1. We hypothesized that, within alluvial reaches, geomorphic response to the flood, in the form of changes in bed elevation, net volume of sediment eroded or aggraded, and grain size, correlates with wood load. We hypothesized that greater wood load corresponds to lower modelled average velocity and less channel-bed erosion during the flood, and finer median bed grain size and a lower gradation coefficient of bed sediment. The results partly support this hypothesis. Wood results in lower reach-average modelled velocity for the 2011 flood, but the magnitude of change in channel-bed elevation after the 2011 flood among alluvial and bedrock reaches does not correlate with wood load. Wood load does correlate with changes in sediment volume and bed substrate, with finer grain size and smaller sediment gradation in reaches with more wood. The proportion of wood in jams is a stronger predictor of bed grain-size characteristics than is total wood load. We also see evidence of a threshold: greater wood load correlates with channel aggradation at wood loads exceeding approximately 200 m3 ha−1. In this mountain stream, abundant large wood in channel reaches with alluvial substrate creates lower velocity that results in finer bed material and, when wood load exceeds a threshold, reach scale increases in aggradation. This suggests that reintroducing small amounts of wood or one logjam for river restoration will have limited geomorphic effects. © 2020 John Wiley & Sons, Ltd. 相似文献
23.
Triploporella ? edgelli n. sp., a new Dasycladalean alga from the Lower Cretaceous of Lebanon 
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下载免费PDF全文 The Dasycladalean assemblage of the Jezzinian strata (uppermost Barremian–lowermost Aptian) of Lebanon consists of two organo‐genera and eight genera with eleven species, including eight Triploporellaceae. Although Triploporella marsicana (Praturlon, 1964) was reported by Saint‐Marc from the same interval, it is not found in our material. However, a lookalike, which is herein described as Triploporella ? edgelli n. sp., is identified. This new species has cyst‐containers within the primary segments of its laterals but, because it lacks calcified secondary segments, it is left in open nomenclature. 相似文献
24.
A hemipteran nymph of the sternorrhynchan lineage,placed in the family Protopsyllidiidae is the first found in the fossil record,based on an inclusion in amber from the Lower Cretaceous of Hammana / Mdeyrij,Abeih Formation,Central Lebanon.Based on distinctive features such as a median dorsal elevation and the presence of a large,conical,exposed,setiferous anal tube,the fossil is placed in Talaya batraba gen.et sp.nov.and the newly erected taxon is compared to known nymphs of extinct Protopsyllidiidae.The evolutionary traits of the family and its relatives are considered. 相似文献
25.
Dany Savard L. Paul Bédard Sarah-Jane Barnes 《Geostandards and Geoanalytical Research》2009,33(2):249-259
The interest in selenium concentrations in whole rocks is growing, in part because it is a useful tool for base and precious metal exploration. Selenium is often neglected in whole rock geochemistry because of the inability of most laboratories to make reliable determinations of this element. A consequence of these difficulties is a paucity of assigned or certified values for Se in international geological reference materials, so that the "best practice" proposed by Kane and Potts (2007) to obtain robust values for such reference materials cannot be followed. In order to address this problem, we have determined Se by pre-concentration on thiol-cotton fibre followed by INAA (Se/TCF-INAA technique) in twenty-six international geological reference materials, and one quality control material (KPT-1). These values were used, in conjunction with a set of published values, to estimate Se concentrations for these twenty-seven reference samples. Robust statistics were developed for seven of the RMs, with standard deviations equal to or less than precisions calculated using the Horwitz function and so that consensus values could be proposed. For three of the RMs, the presence of outliers gave less robust results, and suggested values are proposed. For seventeen of the RMs, only information values are provided, because either insufficient determinations were available or because large standard deviations of the data were derived. 相似文献
26.
Dany Savard Sarah-Jane Barnes Thomas Meisel 《Geostandards and Geoanalytical Research》2010,34(3):281-291
The accurate determination of platinum-group elements (PGE), rhenium and gold is important in both fundamental research and ore deposit studies. Questions have been raised by some authors as to whether the nickel-sulfur fire assay technique (NiS-FA) efficiently collects all the PGE. On the other hand, most isotope dilution (ID) techniques can only treat small test portion masses (2 g was used for high-pressure asher digestion; HPA) and this makes them more vulnerable to nugget effects. We determined PGE concentrations in ten reference materials with the aim of comparing the performance characteristics of the two methods. Both methods determine Ru, Pd, Os, Ir and Pt and we found that there were no significant systematic differences in the recovery. The advantages of NiS-FA were that: (a) it is capable of determining Rh and Au; (b) the relatively large test portion mass (15 g) reduces the nugget effect and (c) it is faster and less expensive than HPA-ID. The advantages of HPA-ID were that: (a) it determined Re and (b) it had low level blanks, lower detection limits and hence better precision in low-level homogeneous samples. Each technique had advantages and limitations; they should be considered as complementary rather than competing techniques. 相似文献
27.
28.
RX J1856.5-3754 has been proposed as a strange star candidate due to its very small apparent radius measured from its X-ray
thermal spectrum. However, its optical emission requires a much larger radius and thus most of the stellar surface must be
cold and undetectable in X-rays. In the case the star is a neutron star such a surface temperature distribution can be explained
by the presence of a strong toroidal field in the crust (Pérez-Azorín et al.: Astron. Astrophys. 451, 1009 (2006); Geppert
et al.: Astron. Astrophys. 457, 937 (2006)) We consider a similar scenario for a strange star with a thin baryonic crust to
determine if such a magnetic field induced effect is still possible.
This work was partially supported by PAPIIT, UNAM, grant IN119306. J.A.H. studies at UNAM and travel to London are covered
by fellowships from UNAM’s Dirección General de Estudios de Posgrado. 相似文献
29.
Quantification of Metals and Semimetals in Carbon‐Rich Rocks: A New Sequential Protocol Including Extraction from Humic Substances 下载免费PDF全文
下载免费PDF全文 Renato Henrique‐Pinto Sarah‐Jane Barnes Dany Savard Sadia Mehdi 《Geostandards and Geoanalytical Research》2017,41(1):41-62
We have developed a new sequential extraction technique that does not require complex procedures and is efficient in determining metal and semimetal contents of carbon‐rich rocks. Six geological reference materials (SBC‐1, SCHS‐1, SCo‐1, SDO‐1, SGR‐1b and SLg‐1) and an in‐house black shale (SH‐1) were selected to test the method, which consists of four main digestion steps involving: (a) dilute HCl acid; (b) NaOH; (c) aqua regia; and (d) hydrofluoric acid. Compared with traditional aqua regia + hydrofluoric acid attack, this new protocol recovers more of the moderately volatile elements during early extraction of humic substances. In addition when compared with reference values, those for most elements are in agreement within uncertainty. Furthermore, this new protocol reveals important information on the partitioning of elements; for instance, steps one and two indicate which elements are associated with carbonates and organic phases from fulvic and humic acid extractions, whereas step three provides results for which elements are associated with sulfide minerals and step four indicates which elements remained in the silicate and oxide phases. 相似文献
30.
Raymond Gèze Isabelle Veltz Jean-Claude Paicheler Bruno Granier Roland Habchi Dany Azar Sibelle Maksoud 《Arabian Journal of Geosciences》2016,9(19):730
A dinosaur tracksite was discovered in Batha on the side of the road from Harissa to Ghosta (Keserwan, Lebanon). About ten trackways are exposed at the top of two beds of Lower Cretaceous limestones over an area of approximately 1000 m2. These footprints were probably made by at least two dinosaur species, Sauropoda and either Theropoda or Ornithopoda. The site, which is the first record from Lebanon, should be protected to allow further scientific investigations. 相似文献