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21.
Pierre Le Hir Andre Ficht Ricardo Silva Jacinto Patrick Lesueur Jean-Paul Dupont Robert Lafite Isabelle Brenon Benedicte Thouvenin Philippe Cugier 《Estuaries and Coasts》2001,24(6):950-963
A comprehensive study of fine sediment transport in the macrotidal Seine estuary has been conducted, including observations of suspended particulate matter (SPM), surficial sediment, and bathymetric data, as well as use of a three dimensional mathematical model. Tide, river regime, wind, and wave forcings are accounted. The simulated turbidity maximum (TM) is described in terms of concentration and location according to tidal amplitude and the discharge of the Seine River. The TM is mainly generated by tidal pumping, but can be concentrated or stretched by the salinity front. The computed deposition patterns depend on the TM location and are seasonally dependent. The agreement with observations is reasonable, although resuspension by waves may be overestimated. Although wave resuspension is likely to increase the TM mass, it generally occurs simultaneously with westerly winds that induce a transverse circulation at the mouth of the estuary and then disperse the suspended material. The resulting effect is an output of material related to wind and wave events, more than to high river discharge. The mass of the computed TM remains stable over 6 months and independent of the river regime, depending mainly on the spring tide amplitude. Computed fluxes at different cross-sections of the lower estuary show the shift to the TM according to the river flow and point out the rapidity of the TM adjustment to any change of river discharge. The time for renewing the TM by riverine particles has been estimated to be one year. 相似文献
22.
Jean-François Chiffoleau Dominique Auger Emmanuelle Chartier Pierre Michel Isabelle Truquet André Ficht Jean-Louis Gonzalez Louis-Alexandre Romana 《Estuaries and Coasts》2001,24(6):1029-1040
Cadmium (Cd) is among the major contaminants in the Seine estuary. In the biota, the RNO (Réseau National d’Observation, the French Mussel-Watch) has shown that Cd concentrations in mussels living at the mouth of the estuary are related to changes in inputs to this area of phosphogypsum, a calcium sulphate that is a by-product of the phosphoric acid naturally enriched with Cd. In the water column, Cd concentrations at several key estuary sites show a very marked trend toward decreased contamination in the particles as well as in the dissolved phase. The behavior of Cd in the estuary has been studied between 1991 and 1998 in the framework of the scientific program Seine-Aval. This program has highlighted punctual Cd inputs in the estuarine water column. The partition of Cd between the dissolved and the particulate phase, previously described in various estuaries, is characterized by an intense phenomenon of solubilization in the mixing zone freshwater-seawater, but the colloidal Cd fraction remains low along the whole salinity gradient, about 5% to 10% of the apparent dissolved fraction. Although the decrease of inputs induced a fall of Cd concentrations in the water column, laboratory experiments show that the estuarine particles are far from being exhausted in Cd. Despite continuous efforts to reduce the urban and industrial inputs into the estuarine and coastal waters, the Seine estuary still remains very contaminated by Cd. 相似文献
23.
Christian Bigler Evastina Grahn Isabelle Larocque Adam Jeziorski Roland Hall 《Journal of Paleolimnology》2003,29(4):509-510
Volume Contents
Volume contents 相似文献24.
The Chelopech deposit is one of the largest European gold deposits and is located 60 km east of Sofia, within the northern
part of the Panagyurishte mineral district. It lies within the Banat–Srednegorie metallogenic belt, which extends from Romania
through Serbia to Bulgaria. The magmatic rocks define a typical calc-alkaline suite. The magmatic rocks surrounding the Chelopech
deposit have been affected by propylitic, quartz–sericite, and advanced argillic alteration, but the igneous textures have
been preserved. Alteration processes have resulted in leaching of Na2O, CaO, P2O5, and Sr and enrichment in K2O and Rb. Trace element variation diagrams are typical of subduction-related volcanism, with negative anomalies in high field
strength elements (HFSE) and light element, lithophile elements. HFSE and rare earth elements were relatively immobile during
the hydrothermal alteration related to ore formation. Based on immobile element classification diagrams, the magmatic rocks
are andesitic to dacitic in compositions. Single zircon grains, from three different magmatic rocks spanning the time of the
Chelopech magmatism, were dated by high-precision U–Pb geochronology. Zircons of an altered andesitic body, which has been
thrust over the deposit, yield a concordant 206Pb/238U age of 92.21 ± 0.21 Ma. This age is interpreted as the crystallization age and the maximum age for magmatism at Chelopech.
Zircon analyses of a dacitic dome-like body, which crops out to the north of the Chelopech deposit, give a mean 206Pb/238U age of 91.95 ± 0.28 Ma. Zircons of the andesitic hypabyssal body hosting the high-sulfidation mineralization and overprinted
by hydrothermal alteration give a concordant 206Pb/238U age of 91.45 ± 0.15 Ma. This age is interpreted as the intrusion age of the andesite and as the maximum age of the Chelopech
epithermal high-sulfidation deposit. 176Hf/177Hf isotope ratios of zircons from the Chelopech magmatic rocks, together with published data on the Chelopech area and the
about 92-Ma-old Elatsite porphyry–Cu deposit, suggest two different magma sources in the Chelopech–Elatsite magmatic area.
Magmatic rocks associated with the Elatsite porphyry–Cu deposit and the dacitic dome-like body north of Chelopech are characterized
by zircons with ɛHfT90 values of ∼5, which suggest an important input of mantle-derived magma. Some zircons display lower ɛHfT90 values, as low as −6, and correlate with increasing 206Pb/238U ages up to about 350 Ma, suggesting assimilation of basement rocks during magmatism. In contrast, zircon grains in andesitic
rocks from Chelopech are characterized by homogeneous 176Hf/177Hf isotope ratios with ɛHfT90 values of ∼1 and suggest a homogeneous mixed crust–mantle magma source. We conclude that the Elatsite porphyry–Cu and the
Chelopech high-sulfidation epithermal deposits were formed within a very short time span and could be partly contemporaneous.
However, they are related to two distinct upper crustal magmatic reservoirs, and they cannot be considered as a genetically
paired porphyry–Cu and high-sulfidation epithermal related to a single magmatic–hydrothermal system centered on the same intrusion. 相似文献
25.
Ryder Allen Burton Ashley & Storey 《Monthly notices of the Royal Astronomical Society》1998,294(2):338-346
The newly commissioned University of New South Wales Infrared Fabry–Perot (UNSWIRF) has been used to image molecular hydrogen emission at 2.12 and 2.25 μm in the reflection nebula Parsamyan 18. P 18 is known to exhibit low values of the (1–0)/(2–1) S(1) ratio, suggestive of UV-pumped fluorescence rather than thermal excitation by shocks. Our line ratio mapping reveals the full extent of this fluorescent emission from extended arc-like features, as well as a more concentrated thermal component in regions closer to the central exciting star. We show that the emission morphology, line fluxes and gas density are consistent with the predictions of photodissociation region (PDR) theory. Those regions with the highest intrinsic 1–0 S(1) intensities also tend to show the highest (1–0)/(2–1) S(1) line ratios. Furthermore, variations in the line ratio can be attributed to intrinsic fluctuations in the incident radiation field and/or the gas density, through the self-shielding action of H2 . An isolated knot of emission discovered just outside P 18, and having both an unusually high (1–0)/(2–1) S(1) ratio and relative velocity, provides additional evidence for an outflow source associated with P 18. 相似文献
26.
Graham Ryder 《Earth and Planetary Science Letters》1976,29(2):255-268
Large, coarse-grained fragments of granite, containing plagioclase, a silica polymorph, potash feldspar, and exsolved pyroxene, with minor ilmenite, a phosphate, Fe-metal, and troilite, occur in sample 15405. A similar coarse-grained clast type (KREEP-rich quartz-monzodiorite) has a similar mineralogy but contains more ilmenite, large phosphates, less silica, and lacks troilite. One unusual KREEPy olivine vitrophyre fragment is also present. All the other fragments in 15405 are of Apollo 15-type KREEP basalt; ANT-suite and breccia fragments are conspicuously absent. The groundmass of 15405, of a KREEP basalt composition, is vesicular with a variolitic texture and is interpreted as an impact melt. Except for the olivine vitrophyre, the fragments are believed to be the remnants of a shallow-level KREEP basalt-granite differentiated pluton, in which granite was produced as the residual liquid without involvement of immiscibility effects.The large amount of melt required to produce the pluton, and the retention of the pluton's integrity from crystallization until the formation of the source boulder of 15405 suggest that KREEP basalt magma is not ancient (~4.3 b.y.), but was produced by the partial melting of the interior of the moon at around 3.90–3.95 b.y.; this conclusion is supported by the presence of KREEP basalt in soil breccia 15205, to the exclusion of other highland rock types. If this interpretation is correct, the source of Apollo 15-type KREEP basalt had a Rb/Sr ratio higher than anorthositic norite, commonly proposed as the source rock. 相似文献
27.
Graham Ryder 《Lithos》1974,7(3):139-146
The origin of massif anorthosites cannot be simply explained by a single magma type. Two of the commonly proposed parents for anorthosites are andesites (quartz-diorites) and high-alumina basalts. It is proposed here that these two magmas are the parents for two groups of anorthosites which include all anorthosite massifs, and that the parents for any given anorthosite massif can be determined by the rock sequence associated with the massif.Evidence from experiments and from phenocrysts in volcanics, suggests that andesites crystallizing in the granulite facies would produce plagioclase cumulates (anorthosites) at the base, followed by dioritic and acidic material, whereas high-alumina basalts would produce gabbros followed by anorthosite with very little succeeding acidic material. All massif anorthosites for which relevant data is available have one or the other of these stratigraphic sequences. Grouped according to these sequences, they coincide with two previously proposed groups, i.e. Andesine-type and Labradorite-type, whose characteristics are shown to be compatible with derivation from andesite and high-alumina basalt, respectively. 相似文献
28.
The second and third recorded births of southern elephant seals Mirounga leonina on the mainland of New Zealand occurred at Kaikoura in mid‐October 1976. One female pup died within 14 d of birth and the other (sex unknown) disappeared from the region with its mother on 19 November 1976. 相似文献
29.
Galateia Terti Isabelle Ruin Sandrine Anquetin Jonathan J. Gourley 《Natural Hazards》2015,79(3):1481-1497