Uranium in the silicate inclusions of stony-iron and iron meteorites     

Ghislaine Crozaz  Scott F. Sibley  Douglas R. Tasker 《Geochimica et cosmochimica acta》1982,46(5):749-754

The microdistribution of U has been studied, using fission track techniques, in eleven mesosiderites, seven pallasites and four iron meteorites with silicate inclusions. When concentrated, U is usually found in phosphates: merrillite and/or chlorapatite. As in stony meteorites, the U concentrations in a given phosphate phase are highly variable from meteorite to meteorite and sometimes also exhibit variations in the same meteorite. Uranium is found to be concentrated in merrillite (0.25 to 1.43 ppm) in all the mesosiderites except Bondoc where none was observed. No U-rich phase was identified in six of the seven pallasites. In the seventh, Marjalahti, there are merrillite grains with concentrations ranging from 0.06 to 0.14 ppm. Where observed, the phosphates from silicate inclusions in the irons appear to have U concentrations similar to the mesosiderites.  相似文献   

Spatial Mapping of Conductive Ground Water Contamination With Electromagnetic Induction     

Dennis D. Weber  James F. Scholl  Douglas J. LaBrecque  Eric G. Walther  Roy B. Evans 《Ground Water Monitoring & Remediation》1984,4(4):70-77

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The Application of Combined Seismic and Electrical Measurements to the Determination of the Hydraulic Conductivity of a Lake Bed     

Robert W. Taylor  Douglas S. Cherkauer 《Ground Water Monitoring & Remediation》1984,4(4):78-85

The hydraulic properties of lake beds control the interactions between lakes and ground water systems, but these properties are normally difficult to measure directly. The authors'method combines seismic reflection and electrical measurements to map the relative hydraulic conductivity of lake bed sediments. A shipboard seismic profiling system provides sediment thickness, while a towed electrical array yields longitudinal conductance and electrical chargeability. The sediment's leakance (hydraulic conductivity/thickness) can be calculated from the longitudinal conductance data. Leakance may then be converted to relative hydraulic conductivity through the seismically derived sediment thicknesses. Simultaneously acquired electrical chargeability provides an independent measure of clay content. The seismic and electrical systems are computer automated and yield production rates of approximately five line-kilometers/hour or 300 electrical soundings/hour. The systems provide continuous hydraulic information along the ship track rather than the point information derived from coring.
The procedure and systems have been used to map the bed of Lake Michigan offshore from an area of heavy pumpage. This location has been chosen to test the method because lake water has intruded the aquifer in plumes largely controlled by lake bed hydraulics. Mapping these plumes onshore permits the inference of the spatial distribution of offshore hydraulic conductivities. Offshore seepage measurements and numerical, chemical transport modeling of this site have confirmed the reliability of the geophysically derived hydraulic conductivities and have also demonstrated the improvement in numerical results achieved through the availability of spatially determined hydraulic conductivities.  相似文献   

Historical seismicity near Chagos: a complex deformation zone in the equatorial Indian Ocean     

Douglas A. Wiens 《Earth and Planetary Science Letters》1986,76(3-4)

Over the last twenty years, Chagos Bank has a seismicity rate disproportionate to its supposed intraplate location. Earthquake relocation also shows a high seismicity rate in pre-WWSSN time (1912–1963), with seven events located off of the Central Indian Ridge, including large events in 1912 (M = 6.8) and 1944 (M = 7.2). This study uses the moment variance technique, a systematic search for the mechanism which best fits P, PP, SH, Love and Rayleigh amplitudes, to determine the focal mechanisms of two pre-WWSSN earthquakes. A test with a recent event of known mechanism demonstrates that accurate focal parameter determination is possible even when only a few good records are available. Moment variance analysis shows a thrust faulting mechanism for the 1944 event, northeast of Chagos Bank near the Chagos-Laccadive ridge, and a strike-slip focal mechanism for a smaller 1957 event west of Chagos Bank. The 1944 event, one of the largest oceanic “intraplate” earthquakes known (moment 1.4 × 10²⁷ dyne-cm), indicates that the Chagos seismicity reflects not an isolated occurrence of normal faulting as previously thought, but rather regional tectonic deformation extending northeast of Chagos Bank and including thrust, normal and strike-slip events. This seismicity and previously studied seismicity near the Ninetyeast Ridge and Central Indian Basin suggest a broad zone of deformation stretching across the equatorial Indian Ocean. This zone contains all known magnitude seven oceanic “intraplate” earthquakes not associated with subduction zones or continental margins, suggesting that elsewhere such extensive deformation occurs only along plate boundaries. This study proposes that a slow, diffuse plate boundary extends east from the Central Indian Ridge to the Ninetyeast Ridge and north to the Sumatra Trench. A recent plate motion study confirms this boundary and suggests that it separates the Australian plate from a single Indo-Arabian plate.  相似文献   

Tephrochronology of the western Gulf of Mexico for the last 185,000 years     

Karen Rabek  Michael T. Ledbetter  Douglas F. Williams 《Quaternary Research》1985,23(3):403-416

Tephra in 31 piston cores from the western Gulf of Mexico and 7 piston cores from the equatorial Pacific were analyzed by electron microprobe. Six ash layers in the western Gulf of Mexico were easily distinguished by TiO₂, FeO, and CaO contents and correlated by geochemistry in order to determine the distribution pattern for each ash layer. Correlation by geochemistry is an easier, more accurate method than biostratigraphic correlation; some of the tephras were miscorrelated by biostratigraphy. The six tephras were dated by geochemical identification in a piston core with oxygen-isotope stratigraphy and the ages are Y5 (30,000 yr B.P.), Y6 (65,000 yr B.P.), Y8 (84,000 yr B.P.), X2 (110,000 yr B.P.), W1 (136,000 yr B.P.), and W2 (185,000 yr B.P.). Data from this study corroborated correlations of the Y8 tephra in the western Gulf of Mexico with the D layer in the eastern equatorial Pacific Ocean. None of the other five layers in the Gulf of Mexico, however, were found in the Pacific Ocean. The limited distribution of the Y5, Y6, X2, and W2 ash layers close to Mexico indicates possible sources in Mexico. Tephra from the late Pleistocene La Primavera pumice in Mexico, however, does not correlate with the marine tephra.  相似文献   

The spatial structure of tourist accommodation and hotel demand in Spain     

Douglas G. Pearce  Jean-Pierre Grimmeau 《Geoforum》1985,16(1):37-50

Tourism in Spain has developed dramatically in recent decades but the growth of the tourist industry has not been experienced evenly throughout the country. Tourism is largely concentrated in a small number of essentially coastal and insular provinces. Analysis by principal components shows that significant regional variations occur in the demand for hotels from different national groups but, with the exception of the French, the spatial preferences of each nationality have remained remarkably constant in the period 1965–1980. However, as growth rates have differed from market to market, so the demand for hotels has developed at different rates from one province to another. Regional variations in the seasonality of demand also occur. These findings highlight the need for further geographical studies such as this to provide more spatial detail than is to be found in most national studies and at the same time to supply the synthesis which unrelated regional or local case studies lack.  相似文献   

A 10,000 yr B.P. extensive ice shelf over Viscount Melville Sound,Arctic Canada     

Douglas A. Hodgson  Jean-Serge Vincent 《Quaternary Research》1984,22(1):18-30

Late Wisconsinan age glacial landforms and deposits indicate that an ice shelf of at least 60,000 km² flowed northwestward into Viscount Melville Sound, probably from the M'Clintock Dome of the Laurentide Ice Sheet. The ice shelf overlapped coastal areas and laid Winter Harbour Till up to 125 m above present sea level on the southern coast of Melville Island, to 135 m on Byam Martin Island, to possibly 90 m on the northeast tip of Banks Island, and to 150 m on the north coast of Victoria Island. The contemporary sea level was 50 to 100 m higher than present (it now rises eastward). A maximum age of 10,340 ± 150 yr B.P. for the till, and thus the ice-shelf advance, is provided by shells in marine sediments which underlie it, whereas a minimum age of 9880 ± 150 yr B.P. is provided by overlying shells that postdate the ice advance. The major advance of shelf ice into Viscount Melville Sound may be the result of the rapid disintegration of the M'Clintock Dome while the climate ameliorated in the western Arctic.  相似文献   

Review     

Douglas M. Hawkins 《Mathematical Geosciences》1979,11(4):441-442

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The Amoco Cadiz oil spill. A summary of observations made by U.S. scientists 23 March–10 May, 1978     

Douglas A. Wolfe 《Marine pollution bulletin》1978,9(11):288-292

This paper summarizes briefly the observations made by a team of United States scientists during the two months immediately after the grounding of the Amoco Cadiz. Most of the information has been abstracted from the NOAA/EPA preliminary scientific report (Hess, 1978) which provides a more complete account of objectives and results to date. It is hoped that maximum use may be derived from a study of the effects of the spill.  相似文献   

Comparison of radiolarian/planktonic foraminiferal paleoceanography of the subantarctic Indian Ocean     

Douglas F. Williams  John Keany 《Quaternary Research》1978,9(1):71-86

A detailed paleoceanographic history of the Subantarctic region for the last million years was determined using paleomagnetic stratigraphy, radiolarian and planktonic foraminiferal biostratigraphy, and the oxygen isotope record from stages 1 to 13 (0.5 MY) in a deep-sea core (E45-74) from the southern Indian Ocean. Changes in the abundances of Antarctissa strelkovi and Neogloboquadrina pachyderma record 12 glacial/interglacial cycles. The paleoceanographic events based on the combined results of these siliceous and calcareous indexes agree with changes in the global ice-volume record. Calcium carbonate dissolution selectively alters the planktonic foraminiferal fauna and causes test fragmentation and increased numbers of benthic foraminifera and radiolarians. Intense periods of calcium carbonate dissolution are associated principally with glacial episodes and are probably related to increased Antarctic bottom-water activity as well as changes in surface-water mass positions.  相似文献