Petrology of the Skien basaltic rocks,southwestern Oslo Region,Norway     

Tom Victor Segalstad 《Lithos》1979,12(3):221-239

The pile of Permian continental basaltic rocks near Skien has a minimum thickness of 1 500 m, dipping 40^g towards NE, consisting of several thin lava flows. Most flows are porphyric, though both tuffs and aphyric flows occur to a lesser extent. Amygdules are abundant and a characteristic feature. The flows in the lower 2/3 of the basalt pile are mainly classified as melanite-ankaramite; some in the middle part as melanite-nephelinite; and the upper 1/3 of the flows as basanite. The basaltic rocks evolved from an assumed olivine-nephelinitic magma at great depths principally by clinopyroxene crystal fractionation accompanied by later olivine and maybe melilite reactions at moderate pressure in minor shallower magma chambers.  相似文献   

Experimental study of silica diffusion during metasomatic reactions in the presence of water at 550°C and 1000 bars     

Jean-Pierre Ildefonse  Victor Gabis 《Geochimica et cosmochimica acta》1976,40(3):297-303

Metasomatic reactions between quartz and incompatible oxides or hydroxides were experimentally studied at 550°C and 1000 bars water pressure. Two porous pellets of the initial reagents pressed one against the other were used. Reaction rims in the millimeter range develop at the initial boundary in the oxide pellet. All the experiments show that an important transfer of silica occurs by diffusion in the stationary intergranular solution.The chemical transfer of silica through the intergranular fluid is quantitatively determined by studying the kinetics of growth of the forsterite rim in the system quartz-brucite. The kinetics limiting stage being silica transfer, the experiments allow the determination of the diffusion coefficient of silica through the solution. At 550°C and 1000 bars, a value of 2.4 × 10^?1cm² s¹ is found.This high value shows the importance of chemical diffusion in the intergranular fluid of rocks during metamorphic processes.  相似文献   

The role of horizontal impulses of the faulting continental slope in generating the 26 December 2004 tsunami     

Y. Tony Song  L.-L. Fu  Victor Zlotnicki  Chen Ji  Vala Hjorleifsdottir  C.K. Shum  Yuchan Yi 《Ocean Modelling》2008,20(4):362-379

For a long time, people have believed that the vertical displacement of seafloor due to undersea earthquakes is the primary cause of tsunami genesis. However, seismically-inverted seafloor deformation of the 2004 Sumatra–Andaman earthquake shows that the total vertical displacement is not enough to have generated the powerful Indian Ocean tsunami. Based on the seismically-inverted data and a three-dimensional ocean general circulation model (OGCM), we show that the momentum force, transferred by the horizontal impulses of the faulting continental slope in that earthquake, has accounted for two thirds of the satellite-observed tsunami height and generated kinetic energy 5 times larger than the potential energy due to the vertical displacement. The asymmetric tsunami pattern, recorded by tide-gauges showing leading-elevation waves toward Sri Lanka and leading-depression waves toward Thailand, is best explained by the horizontally-forced mechanism. The same mechanism has also explained the March 2005 Nias earthquake and tsunami data, suggesting that the horizontal motions of faulting have played more important roles in tsunami genesis than previously thought.  相似文献   

Gradients in coral reef communities exposed to muddy river discharge in Pohnpei,Micronesia     

Yimnang Golbuu  Katharina Fabricius  Steven Victor  Robert H. Richmond 《Estuarine, Coastal and Shelf Science》2008

This study analyzed how coral communities change along a gradient of increasing exposure to a mud-discharging river in the Enipein Catchment, Pohnpei, Micronesia. Using video transects, we quantified benthic communities at five sites along a gradient moving away from the river mouth towards the barrier reef. The most river-impacted site was characterized by a high accumulation of mud, low coral cover and low coral diversity. Although coral cover leveled off at ∼400 m from the river mouth to values found at the outer-most sites, coral diversity continued to increase with increasing distance, suggesting that the most distant site was still impacted by the river discharges. Fungiidae, Pavona, Acropora, Pachyseris and Porites rus all significantly increased in cover with distance from the river, while Turbinaria decreased. The combined presence and abundance of these six species groups, together with coral species richness, may help to indicate the effects of terrestrial runoff in similar runoff-exposed settings around Micronesia, whereas coral cover is not a sensitive indicator for river impact. Coral reefs are important resources for the people of Pohnpei. To prevent further degradation of this important resource, an integrated watershed approach is needed to control terrestrial activities.  相似文献   

Continuous spatially distributed simulation of surface and subsurface hydrological processes in a small semiarid catchment     

Marco Maneta  Susanne Schnabel  Victor Jetten 《水文研究》2008,22(13):2196-2214

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Experimental investigation of water impact on axisymmetric bodies     

G. De Backer  M. Vantorre  C. Beels  J. De Pré  S. Victor  J. De Rouck  C. Blommaert  W. Van Paepegem 《Applied Ocean Research》2009,31(3):143-156

The results of an elaborate experimental investigation on bottom slamming of axisymmetric objects are presented. Drop tests have been performed on a hemisphere and two conical shapes with different deadrise angles. The test setup is designed so as to prevent small rotations of the test objects which cause scatter in the measurement data. The pressure distribution and evolution as well as the body motion parameters are measured during impact. By means of a high speed camera the water uprise is visualized and the wetting factor is determined for the cones. The results are compared with a three-dimensional asymptotic theory for axisymmetric rigid bodies with constant entry velocity. The ratio between the registered peak pressures and the asymptotic theory are in accordance with comparable experiments in the literature. The asymptotic theory, however, is found to be quite conservative, since the measured peak pressure levels appear to be approximately 50% to 75% of the theoretical levels.  相似文献   

Late Quaternary moisture export across Central America and to Greenland: evidence for tropical rainfall variability from Costa Rican stalagmites     

Matthew S. Lachniet  Leah Johnson  Yemane Asmerom  Stephen J. Burns  Victor Polyak  William P. Patterson  Lindsay Burt  April Azouz 《Quaternary Science Reviews》2009,28(27-28):3348-3360

We present a high-resolution terrestrial archive of Central American rainfall over the period 100–24 and 8.1–6.5 ka, based on δ¹⁸O time series from U-series dated stalagmites collected from a cave on the Pacific Coast of Costa Rica. Our results indicate substantial δ¹⁸O variability on millennial to orbital time scales that is interpreted to reflect rainfall variations over the cave site. Correlations with other paleoclimate proxy records suggest that the rainfall variations are forced by sea surface temperatures (SST) in the Atlantic and Pacific Oceans in a fashion analogous to the modern climate cycle. Higher rainfall is associated with periods of a warm tropical North Atlantic Ocean and large SST gradients between the Atlantic and Pacific Oceans. Rainfall variability is likely linked to the intensity and/or latitudinal position of the intertropical convergence zone (ITCZ). Periods of higher rainfall in Costa Rica are also associated with an enhanced sea surface salinity gradient on either side of the isthmus, suggesting greater freshwater export from the Atlantic Basin when the ITCZ is stronger and/or in a more northerly position. Further, wet periods in Central America coincide with high deuterium excess values in Greenland ice, suggesting a direct link between low latitude SSTs, tropical rainfall, and moisture delivery to Greenland. Our results indicate that a stronger tropical hydrological cycle during warm periods and large inter-ocean SST gradients enhanced the delivery of low latitude moisture to Greenland.  相似文献   

Meteorites at Meridiani Planum provide evidence for significant amounts of surface and near‐surface water on early Mars     

Alberto G. FAIRÉN  James M. DOHM  Victor R. BAKER  Shane D. THOMPSON  William C. MAHANEY  Kenneth E. HERKENHOFF  J. Alexis P. RODRÍGUEZ  Alfonso F. DAVILA  Dirk SCHULZE‐MAKUCH  M. Ramy EL MAARRY  Esther R. UCEDA  Ricardo AMILS  Hirdy MIYAMOTO  Kyeong J. KIM  Robert C. ANDERSON  Christopher P. McKAY 《Meteoritics & planetary science》2011,46(12):1832-1841

Abstract– Six large iron meteorites have been discovered in the Meridiani Planum region of Mars by the Mars Exploration Rover Opportunity in a nearly 25 km‐long traverse. Herein, we review and synthesize the available data to propose that the discovery and characteristics of the six meteorites could be explained as the result of their impact into a soft and wet surface, sometime during the Noachian or the Hesperian, subsequently to be exposed at the Martian surface through differential erosion. As recorded by its sediments and chemical deposits, Meridiani has been interpreted to have undergone a watery past, including a shallow sea, a playa, an environment of fluctuating ground water, and/or an icy landscape. Meteorites could have been encased upon impact and/or subsequently buried, and kept underground for a long time, shielded from the atmosphere. The meteorites apparently underwent significant chemical weathering due to aqueous alteration, as indicated by cavernous features that suggest differential acidic corrosion removing less resistant material and softer inclusions. During the Amazonian, the almost complete disappearance of surface water and desiccation of the landscape, followed by induration of the sediments and subsequent differential erosion and degradation of Meridiani sediments, including at least 10–80 m of deflation in the last 3–3.5 Gy, would have exposed the buried meteorites. We conclude that the iron meteorites support the hypothesis that Mars once had a denser atmosphere and considerable amounts of water and/or water ice at and/or near the surface.  相似文献   

Measuring and managing changes in estuaries and lagoons: morphological and eco-toxicological aspects   总被引：1，自引：0，他引：1  

Zonta R  Guerzoni S  Pérez-Ruzafa A  de Jonge VN 《Marine pollution bulletin》2007,55(10-12):403-406

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Distribution of arsenic and mercury in subtropical coastal beachrock,Gulf of Mannar,India   总被引：1，自引：0，他引：1  

J Dajkumar Sahayam  N Chandrasekar  S Krishna Kumar  G Victor Rajamanickam 《Journal of Earth System Science》2010,119(1):129-135

An assessment of coastal pollution was made on the basis of trace element concentrations (arsenic — As, mercury — Hg) in the Gulf of Mannar. The beachrock samples were collected along the coastal tracts between Rameswaram and Kanyakumari. The samples were dried and digested to determine the As and Hg using atomic absorption spectrophotometer (AAS-air-acetylene and nitrous oxide method). The As and Hg accumulation status of the beachrock was assessed using geo-accumulation index values (I _geo). The accumulation of As and Hg in the beachrock ranges from 2.75 to 20.72 μg g⁻¹ and from 0.06 to 0.31 μg g⁻¹, respectively. The As and Hg concentrations in the beachrocks are compared with crustal average values and average of other region sediments. The possible source of the contamination is from atmospheric deposition and anthropogenic activities.  相似文献