On solitary waves generated by a moving pressure field     

J. N. Hunt  D. A. Tanner 《Pure and Applied Geophysics》1971,85(1):309-323

Summary The waves generated by a steadily moving two-dimensional pressure distribution are examined using non-linear shallow water theory. The applied pressure is zero ahead of the disturbance, that is in the downstream direction, and is a constantP ₀ in the upstream direction, these regions being joined smoothly by a cubic function.We consider here only the case of supercritical flow in both regions, the solution representing an asymmetric solitary wave travelling with the disturbance. The wave profiles are determined by an iterative method previously employed for non-linear waves. Wave amplitudes and profiles, and the wave drag, associated with each system are computed for various values ofP ₀/Q g h, whereh is the undisturbed depth of water ahead of the wave.The solution obtained reduces to the classical solitary wave of finite amplitude when the applied pressure is everywhere zero.

---

Résumé Nous avons calculé les expressions des profils d'ondes solitaires produites par une pression, qui se propagent sur la surface d'une couche d'eau peu profonde avec une vitesseU plus grande que (g h)^1/2. La pression appliquée est nulle en avant de l'onde, elle est une constanteP ₀ en arrière, et entre ces deux régions elle est representée par une fonction cubique. Les profils sont calculés par une methode iterative déjà employée pour des ondes non-linéaires. L'amplitude, le profil et la force ont été evalués pour diverses valeurs deP ₀/Q g h, ouh est la profondeur en avant de l'onde.

---

---

Division of Numerical and Applied Mathematics, National Physical Laboratory.  相似文献   

Pole-ward drift of North America     

William F. Tanner 《International Journal of Earth Sciences》1971,60(3):848-867

Thirty-one lines of evidence — structural, seismic, paleomagnetic, and others — are listed to show that North America has been migrating toward the Arctic Ocean area, since the end of Paleozoic time, at about two cm/yr. The North American plate has been pulling away from South America, during that time interval, at about one cm/yr; the Gulf of Mexico is the major tensional feature which has developed in Middle America as a result of that separation. Any eastward or westward drift that has been involved must have been either negligible or of such a nature that both Americas had essentially the same rate of displacement. The northern continent has been reshaped by its migration, becoming narrower (east-west) and longer (north-south). This reshaping has been accompanied by second-order grabens and other sag features in the eastern and western parts.During the northward movement, in Mesozoic and Cenozoic times, the Appalachian Mountains have been subjected to a combination of tension and right lateral dislocation. In Paleozoic time, when the Appalachians were closer to, and more nearly parallel with, the equator, the primary deformation was left lateral offset. In mid-Paleozoic time, what is now New York state appears to have been reasonably close to what is now northwestern Venezuela. Since then, North America has undergone counter-clockwise rotation, and South America has undergone clockwise rotation.The Gulf of Mexico, as a major tensional feature, has developed as a large, tectonically quiet, sediment trap. It can be considered a type of the geosyncline which forms along the trailing edge of a moving continental plate. The Paleozoic Appalachian geosyncline, however, was of a different type: the main deformation was strike slip rather than tensional, and sedimentation was more-or-less contemporaneous with deformation.Northward drift of the North American continent, along with poleward motions of at least two other continents, has been responible for Tertiary cooling of the globe and the onset of late Cenozoic glaciation. Inasmuch as North America is still approaching the Arctic, fully developed glaciation, either with or without freeze-thaw cycles, should continue for a geologically-long interval.

---

Zusammenfassung Es werden 31 Hinweise struktureller, seismischer, paleomagnetischer und anderer Art gebracht, um zu zeigen, da\ Nordamerika zum Arktischen Ozean hin abgewandert ist, und zwar seit dem PalÄozoikum ungefÄhr 2 cm pro Jahr. Die Nordamerikanische Platte hat sich in diesem Zeitintervall von Südamerika ungefÄhr 1 cm pro Jahr entfernt; der Golf von Mexiko ist in Mittelamerika der hauptsÄchliche Ausdruck tensioneller Art dieser Trennung. Jede Trift nach Osten oder Westen, die dabei teilgenommen hat, mu\ daher untergeordnet gewesen sein oder war von solcher Art, da\ die beiden Amerikas im wesentlichen gleichartige Versetzung erfuhren. Der nördliche Kontinent wurde indessen durch seine Wanderung in seinem Umri\ verÄndert, und zwar wurde er schmÄler (Ost-West) und lÄnger (Nord-Süd). Diese VerÄnderung war von GrÄben zweiter Ordnung und von anderen Verschleppungserscheinungen in den östlichen und westlichen Teilen des Kontinents begleitet.WÄhrend der Nordwanderung im Mesozoikum und KÄnozoikum wurden die Appalachian Mountains einer Kombination von Spannung und rechts-lateraler Dislokation unterworfen. Im PalÄozoikum, als die Appalachians nÄher und mehr parallel zum Äquator lagen, bestand die hauptsÄchliche Deformation aus linkslateraler Versetzung. Im MittelpalÄozoikum war die Gegend, die heute den Staat von New York darstellt, anscheinend ziemlich nahe der Gegend des heutigen nordwestlichen Venezuelas. Seitdem hat Nordamerika eine Rotation nach links und Südamerika eine Rotation im Uhrzeigersinn durchgeführt.Der Golf von Mexiko, ein Ausdruck gro\rÄumiger Spannung entwickelte sich als ein gro\es, tektonisch ruhiges Sedimentationsbecken. Man kann es als Typ einer Geosynklinale betrachten, die sich am Rückrand einer wandernden Kontinentalplatte bildet, Als andere Beispiele mögen das Schwarze Meer und die Kaspi-See dienen. Die palÄozoische Appalachian Geosynklinale stellte indessen einen anderen Typ dar: Die Hauptdeformation war Lateralversetzung und nicht tensional, und die Sedimentation verlief mehr oder weniger gleichzeitig mit der Deformation.Nordwanderung des nordamerikanischen Kontinents, zusammen mit polwÄrtiger Bewegung wenigstens noch zwei weiterer Kontinente war für die tertiÄre Klimaverkühlung der Erde und für den Beginn der spÄtkÄnozoischen Vergletscherung verantwortlich. Da sich Nordamerika immer noch der Arktis nÄhert, sollten vollentwickelte Vergletscherungen, entweder mit oder ohne Frost-Tau-Zyklen, noch für ein geologisch langes Zeitintervall andauern.

---

Resumen Son presentadas treinta y una pruebas — estructurales, sísmicas y paleomagnéticas entre otras — para demostrar que desde el final del Paleozoico el continente norteamericano ha ido girando en dirección al área del Océano árctico aproximadamente dos centímetros por año. El bloque norteamericano se ha alejado de América del Sur, durante este intervalo de tiempo, un centímetro por año aproximadamente; el Golfo de México es el mayor rasgo tensional que se ha formado como resultado de esta separación. La deriva que ha debido ocurrir, bien en direcciÔn este u oeste, debió de ser o insignificante o de tal naturaleza que ambas américas tuvieron que tener esencialmente la misma razón de traslación. Sin embargo el continente norteño ha sido reformado a causa de su deriva, estrechándose del este al oeste y alargándose del norte al sur. Esta reforma ha sido acompañada de grábenes de segundo orden y de otros fenómenos de disgregación en las partes este y oeste.Durante el movimiento hacia el norte, en tiempos mesozoicos y cenozoicos, las Montañas Apalachas han estado sujetas a una combinación de tensión y dislocación dextral-lateral. En el Paleozoico, cuando las Apalachas estaban más cercanas al ecuador y más paralelas al mismo, la deformación primaria fue un movimiento sinestral-lateral. En el Paleozoico medio la región que ahora ocupa el estado de Nueva York parece haber estado razonablemente más cercana a la parte noroeste de Venezuela. Desde entonces Norteamérica ha girado en dirección contraria al sentido de las agujas del reloj mientras Sudamérica ha rotado en sentido contrario.El Golfo de México, como mayor fenómeno tensional, se ha desarrollado como una cuenca enorme, tectonicamente tranquila, donde se acumulan sedimentos. Puede considerarse como el tipo de geosinclinal que se forma paralelamente a la parte posterior de un bloque en movimiento. Ejemplos como éste se encuentran en las cuencas del Mar Negro y del Mar Caspio. Sin embargo el geosinclinal de las Apalachas en el Paleozoico era diferente: la deformación más importante y mayor fué mas bien lateral (strike slip) y no tensional; la sedimentación fue más o menos contemporánea a la deformación.La traslación del continente norteamericano hacia el norte, en unión con movimientos hacia el polo de, por lo menos, dos continentes más ha sido la causa de la deterioración climatológica durante el Terciario y de la glaciación durante el Cenozoico superior. En vista de que Norteamérica sigue acercándose al árctico, las glaciaciones — con o sin ciclos de máximas y mínimas — probablemente continuarán durante un intervalo geologicamente largo.

---

-, , , 2 . . 1 . . , , , , . : ( -) (-). . . , , . , - , - , . , — . — — . , , . . : , , , . , , , . . . , , .

  相似文献   

The growth of the continent through geological time studied by Nd isotope analysis of shales   总被引：2，自引：0，他引：2  

Claude J. Allègre  Dominique Rousseau 《Earth and Planetary Science Letters》1984,67(1):19-34

We determined the Nd isotopic composition and the Sm/Nd ratios in a series of Australian shales ranging from 0.2 Gy to 3.3 Gy. The first result of this study is the constancy of the Sm/Nd ratio in these shales, as in granitoids. Secondly, the initial (¹⁴³Nd/¹⁴⁴Nd) ratio gives a regular curve decreasing through geological time. Both results confirm that shales are representative samples of the continental crust, when insoluble elements, like REE, are studied.We calculated their Nd model ages of crustal differentiation. The model ages regularly decrease with the stratigraphic ages and after 2 Gy, the curve flattens and tends to an asymptotic value at around 1.8 Gy. The significance of the shales is that they represent a mixture of continental materials and we consider the model age of such a mixture directly linked with the mean age of the continental portion feeding the sedimentary basin.From these results, we deduce a quantitative model of the growth curve of the continental source of the shales taking into account the effects of erosion which selectively sample recent mountains relative to shield areas. We propose that the results obtained here are representative of the whole Gondwana continent.Having studied the case of the Australian shales, we try to extend our study. First we applied our quantitative approach to the recent results obtained by O'Nions et al. on North Atlantic provinces. The continental growth curves obtained by our inversion procedure are quite distinct from the Australian shales showing the regional character of shales.With these two cases studied we try to compare our results with the already developed model for continental growth. The consideration of the surface conservative versus surface non-conservative models clearly show the non-uniqueness of the geological interpretation of the growth curve. On the other hand, we have calculated for each case the recycling rate versus geological time by comparing the growth curve with the Hurley-Rand province age curve. Such recycling increases with time in agreement with the data obtained on Nd and Sr initial ratios on granitoids.  相似文献   

Experimental study of the coastal thermocline height variations caused by an impulsively applied wind of limited along-shore extent     

Dal S. Lee  Dominique P. Renouard 《Dynamics of Atmospheres and Oceans》1983,7(3):129-145

On the large rotating platform of Grenoble's University, a channel (8×2×0.6 m) has been built, equipped with a wind entrainment simulation effects mechanism. With a local wind, acting over a two-layered ocean, upwelling or downwelling patterns are induced, which are Kelvin-type height variations of the interface; propagating so that, in the northern hemisphere, they leave the coastline to the right of their direction of propagation, and having a profile exponentially decreasing from the coastline towards the open sea. The agreement between these observations and the recently proposed model of Crepon and Richez (1982) is very good at some distance from the excitation zone.However, this model, for its application, is limited to the situation in which the Ekman layer is of the same order of magnitude as the upper layer. Otherwise the oceanographic observations, as well as our observations, show a cross-shore current in the intermediate layer. Near the boundaries of the excitation zone (i.e., the wind zone), such a current is responsible for vortices which cause local upwelling. The model does not account for such local upwelling which is superimposed on the Kelvin-type height variation of the thermocline. These vortices may be explained by consideration of variations of relative vorticity. The experiments also show that a wind perpendicular to the coast may also induce upwelling or downwelling.  相似文献   

Benthic primary production, respiration and remineralisation: in situ measurements in the soft-bottom Abra alba community of the western English Channel (North Brittany)     

Aline Mign  Dominique Davoult  Jean-Jacques Bourrand  Guy Boucher 《Journal of Sea Research》2005,53(4):223

In situ measurements of ammonium and carbon dioxide fluxes were performed using benthic chambers at the end of spring and the end of summer in two soft-bottom Abra alba communities of the western English Channel (North Brittany): the muddy sand community (5 m, about 10% of surface irradiance) and the fine-sand community (19 m, about 1% of surface irradiance). High rates of ammonium regeneration were measured in the two communities at the end of summer (296.03±40.07 and 201.7±62.74 μmolN m⁻² h⁻¹, respectively) as well as high respiration rates (2.60±0.94 and 2.23±0.59 mmolC m⁻² h⁻¹, respectively). Significant benthic gross primary production (up to 6.11 mmolC m⁻² h⁻¹) was measured in the muddy sand community but no benthic primary production was measured in the fine-sand community. It suggests that microphytobenthic production values used in simulations previously published for these two communities were overestimated while values of community respiration were underestimated. The study confirms that this benthic system is heterotrophic and strengthens the idea that an important pelagic-benthic coupling is required for the functioning in such coastal ecosystems.  相似文献   

A new approach to detecting vegetation and land-use change using high-resolution lipid biomarker records in stalagmites   总被引：2，自引：0，他引：2  

Alison J. Blyth  Asfawossen Asrat  Andy Baker  Pauline Gulliver  Melanie J. Leng  Dominique Genty 《Quaternary Research》2007,68(3):314-324

A hundred-year stalagmite lipid biomarker record from Mechara, southeastern Ethiopia, is presented. The record has been recovered at a 10-yr temporal resolution, marking the first time this has been achieved in stalagmite biomarker work and providing the first opportunity to investigate the relationship between stalagmite lipid records and hydrological transport lags, a vital issue in interpreting palaeoenvironmental signals. Preserved plant-derived n-alkanes and n-alkanols show clear changes in composition over time, relating to known land-use changes in the area, particularly the expansion of agriculture in the early twentieth century. The level of environmental detail provided by this technique, combined with the long-term chronological framework offered by stalagmites, holds significant promise for the investigation of early human environments and their associated climatic and anthropogenic controls.  相似文献   

Utilisation de dépôts d'argile sur lame de verre pour leur étude en spectroscopie infrarouge     

Sabine Petit  Alain Decarreau  Dominique Righi 《Comptes Rendus Geoscience》2003,335(9):737-741

IR spectra of clay samples can be collected in transmission through oriented deposits onto glass slide and are similar to the IR spectra of the same samples obtained by traditional way (KBr pellets). As examples, it is shown that it is possible to differentiate dickite from kaolinite and smectites of various chemistries, as easily by both ways. It is thus possible to use oriented clay deposits onto glass slide for both XRD and IR studies and to easily take benefit of the complementarity of both techniques. To cite this article: S. Petit et al., C. R. Geoscience 335 (2003).  相似文献   

Characterization and correlation of Upper Jurassic (Oxfordian) bentonite deposits in the Paris Basin and the Subalpine Basin, France   总被引：1，自引：0，他引：1  

Pierre Pellenard  Jean-Francois Deconinck  Warren D. Huff†  Jacques Thierry‡  Didier Marchand‡  Dominique Fortwengler§  Alain Trouiller¶ 《Sedimentology》2003,50(6):1035-1060

Abstract Explosive volcanic activity is recorded in the Upper Jurassic of the Paris Basin and the Subalpine Basin of France by the identification of five bentonite horizons. These layers occur in Lower Oxfordian (cordatum ammonite zone) to Middle Oxfordian (plicatilis zone) clays and silty clays deposited in outer platform environments. In the Paris Basin, a thick bentonite (10–15 cm), identified in boreholes and in outcrop, is dominated by dioctahedral smectite (95%) with trace amounts of kaolinite, illite and chlorite. In contrast, five bentonites identified in the Subalpine Basin, where burial diagenesis and fluid circulation were more important, are composed of a mixture of kaolinite and regular or random illite/smectite mixed-layer clays in variable proportions, indicating a K-bentonite. In the Subalpine Basin, a 2–15 cm thick bentonite underlain by a layer affected by sulphate–carbonate mineralization can be correlated over 2000 km². Euhedral zircon, apatite and biotite crystals have been identified in all the bentonites. The geochemical composition of the bentonites in both basins is characterized by high concentrations of Hf, Nb, Pb, Ta, Th, Ti, U, Y, Zr and low concentrations of Cr, Cs and Rb. Biostratigraphical and geochemical data suggest that the thick bentonite in the Paris Basin correlates with the thickest bentonite in the Subalpine Basin, located 400 km to the south. These horizons indicate that significant explosive volcanic events occurred during the Middle Oxfordian and provide potential long-distance isochronous marker beds. Immobile element discrimination diagrams and rare-earth element characteristics indicate that the original ash compositions of the thickest bentonites correspond to a trachyandesitic source from a within-plate alkaline series that was probably related to North Atlantic rifting.  相似文献   

Debris-avalanche deposits of the Milo Lahar sequence and the opening of the Valle del Bove on Etna volcano (Italy)     

Sonia Calvari  Lawrence H. Tanner  Gianluca Groppelli   《Journal of Volcanology and Geothermal Research》1998,87(1-4)

Previously undescribed debris-avalanche deposits occur in two locations downslope from the open end of the Valle del Bove. These outcrops comprise unstratified, ungraded deposits of metre-scale lava blocks in a matrix of weathered and fractured lava clasts. The avalanche deposits are unconformably overlain by matrix- to clast-supported conglomerates, representing debris-flow and interbedded fluvial deposits, that constitute most of the Milo Lahar sequence. We present evidence that the Milo Lahar sequence, which crops out just at the exit of the Valle del Bove, formed during the opening and enlargement of this depression. The presence of the avalanche deposits at the base of the Milo Lahar sequence indicates that catastrophic landslides were involved in the formation of the Valle del Bove. The composition of lavas in the debris avalanche deposits is similar to that of most of the Ellittico volcanic sequence exposed along the northern wall of the Valle del Bove. Radiocarbon dates of 8400 and 5300 years BP from the base and top, respectively, of the debris-flow sequence indicate that the Milo Lahars are correlative with the exposed part of the Chiancone deposit. The basal lahars of the Chiancone, which contain lava blocks whose compositions partially overlap that of blocks in the avalanche deposits, may have formed by water concentration in the distal end of the avalanche causing transformation to debris, or alternatively by reworking of the avalanche deposit.  相似文献   

In Situ Vertical Circulation Column: Containment System for Small-Scale DNAPL Field Experiments     

Dominique Sorel  John A. Cherry  Suzanne Lesage 《Ground Water Monitoring & Remediation》1998,18(1):114-125

The in situ vertical circulation column (ISVCC) is a cylindrical containment system consisting of an instrumented steel cylinder used for experimental ground water studies in sandy aquifers. Vertical flow is imposed inside the ISVCC. Although vertical wells are an option, the ISVCC installed in the Borden Aquifer is instrumented with horizontal wells and monitoring ports to avoid creating vertical preferential flow paths. The cylinder was driven downward into the aquifer using a small backhoe equipped with a vibrating plate. The ISVCC penetrates the 2.3-m-thic sand aquifer and is keyed 20 cm into the underlying clay aquitard. The cylinder was installed inside a 2 m X 2 m steel sheet pile enclosure so that the enclosed segment of aquifer could be conveniently dewatered and then excavated to allow installation of the horizontal wells. The dispersivity of the column was comparable to literature values for long sand-packed laboratory columns.
Pure phase DNAPL (tetrachloroethene and 1,1,1-trichloroethane) was slowly pumped into two ports in the center of the column. Following this DNAPL injection, an aqueous solution of vitamin B₁₂ and reduced titanium was circulated through the column to promote degradation of the solvents. Processes observed in the ISVCC included DNAPL distribution, dissolution, and degradation, and geochemical evolution of the aquifer.
The ISVCC provides a convenient means for testing in situ technologies in the experimental stage or for selection of proven technologies to find the most effective at a specific site. It is inexpensive, easy to install, and maximizes control over flow distribution in a heterogeneous aquifer. Its application will be restricted where low hydraulic conductivity beds are present in the aquifer.  相似文献