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101.
The supertankerUrquiola grounded, exploded, and burned at the entrance to La Coruña harbor (Spain) on May 12, 1976. A total of 100,000 tons of Persian Gulf crude oil was lost, of which about 30,000 tons washed onto shoreline environments. From May 17 to June 10, 1976, the impact and interaction of oil on fine-sand, coarse-sand, and gravel beaches and on sheltered and exposed rocky coasts was monitored in detail. At 32 localities, the beach was profiled, trenched, extensively sampled, and photographed. Another 67 stations were examined for surficial oil coverage and distribution. The surficial distribution of oil on the beaches was influenced primarily by wave activity, tidal stage, and oil quantity. Heaviest accumulations formed along the high-tide swash line. Within beach sediments, oil was present at distinct oiled sediment layers, which were often deeply buried. The depth of burial was related to wave energy and sediment type. Deepest burial (1 m) was on a high-energy, coarse-sand beach (Mz=0.82φ). Burial on fine-sand beaches was less than 30 cm. The thickness of oiled sediment depended on sedimentary characteristics, the quantity of oil present, wave action, and capillary forces. Oil-soaked sediment, as much as 65-cm thick, occurred on coarse-grained beaches. On fine-sand beaches, oiled sediment was limited to thicknesses of 10 cm or less. On rocky shores, oil distribution was determined primarily by wave energy. Along high-energy, cliffed, or steeply dipping rocky areas, wave reflection kept the oil approximately 5 m offshore and contamination was minimal. In low-energy, sheltered areas, oil readily accumulated, causing apparent environmental damage.  相似文献   
102.
Hg contents ranging from 0.026 to 0.19 and 0.1 to 344 ppm were measured by activation analysis in a number of pyrite and sphalerite samples, respectively. The release of Hg based on stepwise heating shows a correlation with metamorphic grade of the pyrite samples and with Fe content of the sphalerite samples. Experiments were undertaken to study the equilibration of Hg at different temperatures in Hg-doped laboratory prepared ZnS and FeS2. On subsequent volatilization, trends in the Hg release were observed which paralleled those in the sulfide minerals.  相似文献   
103.
The distribution of selected hydrocarbons within ten dated sediment cores taken from the Mississippi River Bight off coastal Louisiana suggests a chronic contaminant loading from several sources including the river itself, oil and gas exploration in the central Gulf of Mexico (GOM) shelf area, and natural geologic hydrocarbon seeps. Data were grouped as either total polycyclic aromatic hydrocarbons (PAH's), which were indicative of pyrogenic PAH's; or estimated total hopanes (indicative of petrogenic hydrocarbons). The total PAH concentrations and estimated total hopanes begin increasing above background levels (approximately 200 ng g(-1)) after the 1950s. The distribution of these hydrocarbons and hopanes within the dated sediment cores suggests that the Mississippi River is a regional source of pyrogenic PAH's, and that the hopanes are from natural geologic hydrocarbon seeps, oil and gas exploration in the GOM, or both.  相似文献   
104.
105.
Lacustrine and alluvial stratigraphic sequences in the southern Animas Valley of New Mexico allow reconstruction of late Quaternary climates. Four separate stands of late Quaternary Lake Cloverdale in the southern Animas Valley are recorded by lacustrine shoreline deposits. Soils and stratigraphic evidence show that three young lake highstands occurred during the Holocene and that a higher lake stand occurred 18,000 to 20,00014C yr B.P. Fluvial systems aggraded the southern Animas Valley during the middle to late Holocene. The late Quaternary stratigraphy shows that several periods during the late Holocene were characterized by higher effective precipitation than at any time since the last glacial maximum.  相似文献   
106.
Structure and early evolution of the Arabian Sea and East Somali Basin   总被引:5,自引:0,他引:5  
The Laxmi Ridge is a large-scale basement high buried beneath the sediments of the Indus Fan. The location of the ocean–continent transition (OCT) on this margin has previously been proposed at either the southern edge of the Laxmi Ridge or beyond it towards the India–Pakistan shelf. The former explains the margin-parallel Laxmi Basin as thinned continental crust, the latter as a failed rift of earlier seafloor spreading. To examine the structure of this margin, a reassessment of marine magnetic data has detailed seafloor-spreading magnetic anomalies prior to anomaly 24 in both the Arabian and East Somali basins. The previously identified anomaly 28 is not interpreted as a seafloor-spreading anomaly but as a magnetized basement feature adjacent to, and merging with, the ridge—the Laxmi Spur. New gravity models across the Laxmi Ridge and adjacent margin using ship and satellite data corroborate the existence of underplated crust beneath the Laxmi Ridge and Basin and the location of the OCT at the southern edge of the Ridge. The results are not compatible with the existence of a pre-anomaly 28 phase of seafloor spreading, although large-scale intrusions may be the origin of some of the basement features in the Laxmi Basin. The models also identify the Laxmi Spur as a low-density feature with a natural remanent magnetization (NRM) compatible with serpentinization. The Laxmi Ridge is mapped to the southeast, where it appears to terminate at a point coinciding with the appearance of E–W magnetic lineations and gravity anomalies at 15.5°N. Thereafter it becomes indistinct. This is interpreted as necessary in the reconstruction to the Mascarene Plateau to avoid continental overlap.  相似文献   
107.
High rates of coastal land loss in Louisiana have prompted efforts to maintain or restore coastal wetland habitats, and structural management of marsh hydrology is one of a number of approaches that has been adopted. The aim of this study was to determine the effect of hydrologic management measures on marsh-surface sediment deposition in the Mississippi deltaic plain. Four impoundments, ranging in size from 50 ha to 177 ha and similarly sized control sites were included in the study. At each site, marsh-surface sediment traps were collected approximately biweekly for 3.5 yr to measure changes in sediment deposition. There was no significant difference in sediment deposition between any of the impoundment and control sites during the premanagement period. The results show no significant difference in marsh-surface sediment deposition between management year 1992–1993 and management year 1994–1995, but management year 1993–1994 had significantly lower sediment deposition than either the first or the last year of the study. Management year 1992–1993 showed the highest sediment deposition when it was assessed across all basins, areas, and sites, and this high rate of deposition is accounted for by the impact of Hurricane Andrew. For all management years there were significant differences between impoundment and control sites, with control sites showing higher rates of marsh surface sediment deposition than impoundments. No clear pattern was identified concerning the influence of various types of hydrologic management on rates of sediment deposition. This reduction in sediment deposition indicated that the areas under management in this study are receiving insufficient inorganic sediment deposition to keep pace with sea-level rise.  相似文献   
108.
The Bodie mining district in Mono County, California, is zoned with a core polymetallic-quartz vein system and silver- and gold-bearing quartz-adularia veins north and south of the core. The veins formed as a result of repeated normal faulting during doming shortly after extrusion of felsic flows and tuffs, and the magmatic-hydrothermal event seems to span at least 2 Ma.Epithermal mineralization accompanied repeated movement of the normal faults, resulting in vein development in the planes of the faults. The veins occur in a very large area of argillic alteration. Individual mineralized structures commonly formed new fracture planes during separate fault movements, with resulting broad zones of veinlets growing in the walls of the major vein-faults. The veinlet swarms have been found to constitute a target estimated at 75,000,000 tons, averaging 0.037 ounce gold per ton. The target is amenable to bulkmining exploitation.The epithermal mineralogy is simple, with electrum being the most important precious metal mineral. The host veins are typical low-sulfide banded epithermal quartz and adularia structures that filled voids created by the faulting. Historical data show that beneficiation of the simple vein mineralogy is very efficient. On the cover: Southeast view of Bodie mining district in Mono County, California, one of the more famous pioneer epithermal gold producers in the western U.S. Recent exploration drilling suggests an additional resource of 2 million ounces of gold. The townsite is at the intersection of roads near the center of the photo. The foreground is mainly tuff breccia of the Bodie Hills volcanic field. Arcuate lines in the valley beyond the hills are old Mono Lake shorelines. The White Mountains form the ridge on the skyline. Photo by Frank Kleinhampl, about 1970.  相似文献   
109.
110.
Nimbus 7 LIMS geopotential height data are utilized to infer the rotational wind distribution in the Northern Hemisphere stratosphere and lower mesosphere during a period of substantial wave-mean flow interaction in January, 1979. Rotational winds are derived from the application of a successive relaxation numerical procedure which incorporates the spherical polar coordinate iterative algorithm ofPaegle andTomlinson (1975) for the nondivergent nonlinear balance equation. Optimum convergence of the numerical solutions is found to occur when under-relaxation is utilized. The LIMS height analyses were also latitudinally smoothed and constrained to obey the ellipticity criterion for spherical coordinates. The balanced winds are compared with geostrophically derived values and within situ radiosonde reports for 100 mb to 10 mb over Berlin.From a localized perspective, the Berlin-LIMS comparison indicates that radiosonde and balanced wind vectors exhibit somewhat closer agreement in direction than is associated with the geostrophic estimates. However, substantial quantitative differences between radiosonde, balanced, and geostrophic wind speeds are also evident, suggesting that caution should be exercised in the local application of derived winds, as for example in the quantitative interpretation of trajectories derived from satellite height analyses during periods of enhanced stratospheric wave activity.On a longitudinally averaged basis, balanced zonal-mean wind speeds are typically 20% weaker than geostrophic values in polar latitudes, and as much as 50% weaker in tropical and midlatitude regions. Meridional balanced wind velocities, at a given longitude, are generally within ±10% of geostrophic values. Although these alterations in horizontal wind components result in only modest differences between balanced and geostrophic meridional eddy heat fluxes, a more substantial change appears in the meridional eddy momentum flux analysis. The corresponding patterns of Eliassen-Palm flux divergence are found to be somewhat more (less) intense for the balanced wind case in the stratosphere (lower mesosphere) in polar latitudes.  相似文献   
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