Les monchiquites de Tchircotché, vallée de la haute Bénoué (Nord du Cameroun)     

Ismaı̈la Ngounouno  Bernard Déruelle  Daniel Demaiffe  Raymond Montigny 《Comptes Rendus Geoscience》2003,335(3):289-296

Dykes of monchiquites of Cainozoic age (37.5±2.3 Ma) are intrusive in Cretaceous sandstones in the Tchircotché area, Upper Benue valley (northern Cameroon). The differentiation of the monchiquites is explained by crystal fractionation of olivine, clinopyroxene, magnetite, ilmenite and apatite. A studied rock has low Sr-isotope ratio $\text{(0.703}\text{69±10)}$, which is similar to those of the alkali basalts of the Cameroon Line. Therefore the continental crust appears to have no significant role in the genesis of the monchiquites.  相似文献   

Organochlorine contaminants in sea turtles from the Eastern Pacific     

Gardner SC  Pier MD  Wesselman R  Juárez JA 《Marine pollution bulletin》2003,46(9):1082-1089

We measured organochlorine residues in three species of sea turtles from the Baja California peninsula, Mexico. Seventeen of 21 organochlorine pesticides analyzed were detected, with heptachlor epoxide and gamma-hexachlorocyclohexane the most prevalent (14 (40%) and 11 (31%) of the 35 tissue samples, respectively). PCBs were detected in all but one of the 9 turtles studied, with congener 18 the most commonly detected (8 (23%) of the samples). The dioxin-like congeners 118 and 180 were detected in 4 (11%) and 3 (9%) of the samples, respectively. Percent contribution of congeners was negatively correlated to their octanol-water partition coefficients, with kidney and muscle containing more lower-chlorinated congeners than liver or adipose samples. Levels of organochlorines detected in the present study were low, potentially attributable to the feeding habits of the predominant species collected in this study (herbivorous) and/or the samples obtained in an unindustrialized region.  相似文献   

Marine debris accumulation in the nearshore marine habitat of the endangered Hawaiian monk seal, Monachus schauinslandi 1999-2001     

Boland RC  Donohue MJ 《Marine pollution bulletin》2003,46(11):1385-1394

Large amounts of marine debris are present in shallow reefs adjacent to beach haulouts of the critically endangered Hawaiian monk seal, Monachus schauinslandi. These areas serve as seal pup nurseries, and injury and death caused by entanglement in marine debris are undermining population recovery efforts. We investigated the extent of this threat by measuring the accumulation of potentially entangling derelict fishing gear in nursery zones, 1999-2001. Plots of reef 1.0-1.3 km2 at three Northwestern Hawaiian Islands were initially cleaned of derelict fishing gear in 1999 then resurveyed in 2000 and 2001. Submerged debris densities across sites ranged from 16 to 165 debris items/km2. Resurveyed sites yielded annual marine debris accumulation rates from 0 to 141 debris items/km2. This large range was attributed to the physiography of reef areas surveyed. Trawl net webbing was significantly more common than other types of debris recovered and represented 84% of all debris encountered, suggesting that much of the debris originated from distant North Pacific Ocean fisheries. The likely source of most debris is the multinational trawl fisheries of the North Pacific Ocean. An international solution to this problem is needed. Targeted marine debris removal is a short-term, successful, entanglement mitigation strategy.  相似文献   

Carbon dioxide concentration and atmospheric flux in the Hudson River     

Peter A. Raymond  Nina F. Caraco  Jonathan J. Cole 《Estuaries and Coasts》1997,20(2):381-390

We made direct measurements of the partial pressure of CO₂ (P_{CO 2}) in the tidal-freshwater portion of the Hudson River Estuary over a 3.5-yr period. At all times the Hudson was supersaturated in CO₂ with respect to the atmosphere. P_{CO 2} in surface water averaged 1125±403 (SD) μatm while the atmosphere averaged 416±68 μatm. Weekly samples at a single, mid-river station showed a pronounced and reproducible seasonal cycle with highest values (～2000 μatm) in mid-to-late summer, and lowest values (～500 μatm) generally in late winter. Samples taken along the length of the 190-km section of river showed a general decline in CO₂ from north to south. This decline was most pronounced in summer and very slight in spring. Diel and vertical variation were small relative to the standing stock of CO₂. Over six diel cycles, all taken during the algal growing season, the mean range was 300±114 μatm. CO₂ tended to increase slightly with depth, but the gradient was small, about 0.5 μmol m^?1, or an increase of 190 μatm from top to within 1 m of the bottom. For a large subset of the samples (n=452) we also calculated CO₂ from measurements of pH and total DIC. Calculated and measured values of CO₂ were in reasonably good agreement and a regression of calculated versus measured values had a slope of 0.85±0.04 and an r₂ of 0.60. Combining our measurements with recent experimental studies of gas exchange in the Hudson, we estimate that the Hudson releases CO₂ at a rate of 70–162 g C m^?2 yr^?1 from the river to the atmosphere.  相似文献   

Potential magnetic field and potential vorticity in magnetohydrodynamics     

Raymond Hide 《Geophysical Journal International》1996,125(1):F1-F3

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Dispersion into pisolitic laterite from the greenbushes mineralized Sn-Ta pegmatite system, Western Australia     

Raymond E. Smith  J.L. Perdrix  J.M. Davis 《Journal of Geochemical Exploration》1987,28(1-3)

A study of dispersion into pisolitic laterite duricrust in the Archaean Greeenbushes mineralized pegmatite district reveals a geochemical anomaly that measures some 20 km by 12 km centred on the ore deposits that, prior to commencement of mining operations, were concealed. The anomaly is broadest for As, Sn, Be and Sb, all of which show well-defined centres over the swarm of mineralized pegmatites. Coincident highs of Nb, Ta and B also define the 5 km by 1 km anomaly centre. Over the strongest part of the multi-element anomaly, the following levels in ppm are reached in the pisolitic laterite: As 1150, Sb 75, Sn 4200, Nb 75, Ta 75, W 30, Li 100, B 500 and Be 60.The immediate source for the dispersion anomaly is the swarm of soft, weathered pegmatites and their wall rocks, most of which occur within a 5 km by 1 km area, elongated along strike. The source, as judged from past production plus soft pegmatite reserves, was a mass of some 30–40 million tonnes with an approximate average grade of 220 ppm Sn, 25 ppm Nb and 30 ppm Ta.The geochemical expression of the multi-element anomaly can conveniently be expressed in a map of pegmatite-associated elements. For example, the index PEG-4*X which uses an empirically derived weighted linear combination 0.09As + 1.33Sb + Sn + 0.6Nb + Ta (where values for each element are in ppm) gives a broad consistent anomaly.Investigation of dispersion processes shows that mechanical dispersion of cassiterite and columbo-tantalite took place for distances of at least 5 km during laterite formation along gradients ranging from 5 m to 20 m per km. The occurrence of anomalous As in the skins of pisolites indicates hydromorphic dispersion during laterite formation, but mechanical dispersion of goethitic material with scavenged As has also taken place.The size of the geochemical dispersion anomaly, together with its contrast and consistency, shows that it is feasible in the Australian environment to explore for concealed mineral deposits using low-density surface sampling. Sample spacings of 3 km are being tested in an extension of this approach to exploration.  相似文献   

The effect of leaching on the integrity of a natural clay     

Raymond N. Yong  Diaa S. Elmonayeri  T.S. Chong 《Engineering Geology》1985,21(3-4):279-299

Leaching effects on the strength of a natural clay substrate can lead to loss of integrity of pond containment situation — especially if the clay material constitutes the liner system for the containment pond. In this study, the integrity of the clay in the face of five different types of leachates is studied via the creep characteristics of the clay. The resultant effects are evaluated in terms of (a) soil fabric/structure reinforcement or degradation, and/or (b) changes in the relationships established between soil particles and chemical pore fluid. The integrity of the clay is seen to be severely conditioned by (a) factors producing the initial soil structural state, (b) the chemistry of the leachate, (c) local boundary conditions, and (d) time.  相似文献   

Crustal make-up of the northern Andes: evidence based on deep crustal xenolith suites, Mercaderes, SW Colombia   总被引：2，自引：0，他引：2  

Marion B. I. Weber  John Tarney  Pamela D. Kempton  Raymond W. Kent   《Tectonophysics》2002,345(1-4)

Samples of the deep crust and upper mantle in the Northern Andes occur as abundant xenoliths in the Granatífera Tuff, a late Cenozoic vent in the Mercaderes area of SW Colombia. The lower crustal assemblage includes granulites, hornblendites, pyribolites, pyroxenites and gneisses; mafic rocks predominate, but felsic material is also common. P–T conditions for the pyribolite assemblages (i.e. Hbl+Fs/Scp+Grt+Cpx+Qtz±Bt), which are the best constrained, are 720–850 °C and 10–14 kbar, consistent with a deep-to-lower crustal origin. A notable feature of this xenolith suite is that it is dominated by hornblende. However, mineral reactions within the suite show that there is a transition from amphibolite to granulite facies, and there is a probable restite–melt relationship represented within the suite. However, the latter appears to be dominated by hornblende and garnet.The mafic rocks mostly lack the high Cr and Ni that would be expected of cumulates. Neither do they possess the positive Sr and Eu anomalies that would be consistent with resite or cumulate models for the lower crust. They bear greatest similarity to oceanic basalts (s.l.). The Rb contents of the xenoliths, whether mafic or silicic, are very low, and the more silicic members of the suite tend to have small positive Sr and Eu anomalies, which are transitional to adakitic compositions. The Sr isotopic compositions of the xenoliths lie between 0.704 and 0.705; however, the Nd isotopic compositions are much more variable, indicating considerable long-term heterogeneity. Few of the xenoliths can be compositionally recognised as metasedimentary; however, a sedimentary component is evident in the Pb isotopic compositions. Within these constraints, our favoured model is a deep crust formed by basaltic components (subduction–accretion?), and minor sediment, which is subject to an increase in thermal gradient to produce the granulites, any melting being dominated by hornblende-out reactions involving garnet. However, there is no evidence of any pervasive crustal melting, leading to the conclusion that the voluminous Andean magmatism arises from the mantle wedge.  相似文献   

Liquefaction-induced ground deformations at Hotel Sapanca during Kocaeli (Izmit),Turkey earthquake     

K. Onder Cetin  T. Leslie Youd  Raymond B. Seed  Jonathan D. Bray  Rodolfo Sancio  W. Lettis  M. Tolga Yilmaz  H. Turan Durgunoglu 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):1083-1092

This paper presents a study of liquefaction-induced ground deformations at the Hotel Sapanca site during the 1999 Kocaeli (Izmit)—Turkey earthquake. The paper discusses: (1) observed ground deformations and displacements after the earthquake, (2) the results of field investigations by means of borings and in situ index tests including standard penetration tests (SPT), static cone penetration tests (CPT) and piezocone (CPTU) tests, (3) analyses of observed ground settlements and lateral deformations by a suite of methods, and (4) comparisons of observed and calculated ground movements.  相似文献   

Photogrammetric application of viking orbital photography     

Sherman S.C Wu  A.A Elassal  Raymond Jordan  F.J Schafer 《Planetary and Space Science》1982,30(1):45-55

Special techniques are described for the photogrammetric compilation of topographic maps and profiles from stereoscopic photographs taken by the two Viking Orbiter spacecraft. These techniques were developed because the extremely narrow field of view of the Viking cameras precludes compilation by conventional photogrammetric methods. The techniques adjust for internal consistency the Supplementary Experiment Data Record (SEDR—the record of spacecraft orientation when photographs were taken) and the computation of geometric orientation parameters of the stereo models. A series of contour maps of Mars is being compiled by these new methods using a wide variety of Viking Orbiter photographs, to provide the planetary research community with topographic information.  相似文献