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971.
972.
Submarine landslides are described on very low angle slopes (0.5°–1.7°) in the Mississippi prodelta area and are evaluated using infinite slope analysis. For instability to occur, pore water pressure ratios in excess of hydrostatic (u/γwz) and approaching geostatic (u/γ′z) are needed. These calculated values, based on three sets of effective strength parameters and for two sediment depths to failure, are in close agreement with measured pore water pressure data from in situ piezometers. Ratios of (u/γ′z) as large as 0.986 have been monitored. Mud vents are also indicative of large internal pressures within the sediments, generated by rapid sedimentation, wave perturbation, and biogenic methane. The analysis suggests that the reduction in effective stress may be sufficient to cause failure by gravitational stresses alone. 相似文献
973.
The effect of pyrolysis at increasing temperature on sporopollenin, lignite and sporopollenin oxidized at 200°C has been investigated using measured infrared band absorption coefficients.Oxidation of sporopollenin in air at 200°C is marked by a decrease in the content of saturated hydrocarbon chains and a strong increase in the concentration of carboxylic acid groups.Pyrolysis of a thick bed of sporopollenin at increasing temperatures leads to the removal of a large proportion of oxygenated functions, before the removal of hydrocarbons. For lignite and oxidized sporopollenin, the loss of both types of functional groups extends over a broader temperature range. Reorganization of the carbonaceous residue at high temperature is hindered if a sufficiently low content of oxygenated functions, carbonyl and carboxyl as well as hydroxyl and ether groups, is not reached before the elimination of hydrocarbons. 相似文献
974.
Keith A. Kvenvolden David J. Blunt H.Edward Clifton 《Geochimica et cosmochimica acta》1979,43(9):1505-1520
Extents of racemization ( ratios) of amino acids in fossil Saxidomus giganteus (Deshayes) and Ostrea lurida Carpenter were measured on shell deposits exposed at 21 sites on the east side of Willapa Bay, Washington. Amino acids from Saxidomus show less variability in ratios and, therefore, are of greater use in correlation and age estimation than are amino acids from Ostrea. Shells of two different ages, about 120,000 ± 40,000 yr old and about 190,000 ± 40,000 yr old, are present. These ages correspond to Stages 5 and 7 of the marine isotope record defined by Shackleton and Opdyke in 1973 and hence the shell deposits likely formed during two different high stands of sea level. The stratigraphic record at Willapa Bay is consistent with this interpretation. 相似文献
975.
David M. Smith 《Geoforum》1979,10(3):297-310
The problems of the inner city are a subject of growing concern in the advanced capitalist world. The level of social deprivation may be identified on a territorial basis, by mapping numerical indicators relating to various relevant conditions. However, the application of conventional geographical methodology with its emphasis on pattern identification and ecological analysis provides an inadequate foundation for the explanation of localized deprivation and for the design of remedial policy. Inner-city deprivation arises from the operation of the contemporary capitalist system, the understanding of which requires a holistic social-science perspective. 相似文献
976.
David F. Reid Willard S. Moore William M. Sackett 《Earth and Planetary Science Letters》1979,43(2):227-236
The Mn-fiber technique for extracting radium from seawater has proved useful for studying the marine geochemistry of228Ra. In the Gulf of Mexico, this technique was used to measure the surface and near-surface distribution of226Ra and228Ra. The observed surface distribution of228Ra, and particularly the radium activity ratio (228/226) can be explained by known circulation patterns, or, when local surface currents are not well understood, may provide insight into their general characteristics.The radium activity ratio has increased from 0.5 in 1968 to 0.7 in 1973 in the surface Gulf of Mexico. This observed increase cannot be attributed to known anthropogenic or natural source perturbations within the Caribbean Sea-Gulf of Mexico system. Possible causes include a change in the residence time for near-surface water, or variations in the relative dominance of the two sources for water entering the eastern Caribbean; the North Equatorial Current and the Guiana Current.The temporal distribution of228Ra is unstable and naturally variable over a time period less than or equal to five years in the Gulf of Mexico and by extrapolation, the Caribbean Sea. Therefore, its usefulness in calculations of eddy diffusion coefficients for these regions is greatly diminished. 相似文献
977.
Jeffrey L. Bada E. Hoopes D. Darling Graham Dungworth Henk J. Kessels Keith A. Kvenvolden David J. Blunt 《Earth and Planetary Science Letters》1979,43(2):265-268
Enantiomeric measurements for aspartic acid, glutamic acid, and alanine in twenty-one different fossil bone samples have been carried out by three different laboratories using different analytical methods. These inter-laboratory comparisons demonstrate that D/L aspartic acid measurements are highly reproducible, whereas the enantiomeric measurements for the other amino acids show a wide variation between the three laboratories. At present, aspartic acid measurements are the most suitable for racemization dating of bone because of their superior analytical precision. 相似文献
978.
Surf Scoters and Greater Scaup and samples of species which comprise the major part of their diets, from Iona Island and Roberts Bank tidal flats, near Vancouver, British Columbia, were analysed for metal residues. Significantly higher silver, copper, lead and zinc levels were found in Greater Scaup than Surf Scoters. The latter species had higher mercury levels. Differences in residue levels between the species reflect interspecific variation in prey as well as feeding habitat. Significantly higher silver, mercury, lead and zinc in Surf Scoters and silver and lead in Greater Scaup observed at Iona Island than at Roberts Bank can be explained by higher levels of those metals occurring in a more metal-contaminated prey and sediment near the Iona Island sewer outfall. Ducks feeding on organisms in different intertidal zones show different accumulation of metal residues and constitute valuable indicators of pathways of toxic chemicals in specific estuarine regions. 相似文献
979.
Plagioclase preferred orientation, Foreshore Group metasediments, Bluff, New Zealand 总被引:1,自引:0,他引:1
David Shelley 《Tectonophysics》1979,58(3-4)
Recrystallised plagioclase in volcanic metasediments of the Foreshore Group (hornblende-hornfels facies) has a strong preferred orientation with crystal a-axes [100] lying parallel to bedding and with a maximum parallel to a lineation (= maximum principal strain axis or axis of greatest elongation); composition varies widely from bed to bed from oligoclase to anorthite. The preferred orientation is interpreted to result from the mechanical rotation of elongate plagioclase ejecta in the original unconsolidated tuff during strain caused by intrusion of the adjacent Bluff igneous complex. Evidence for such an orienting mechanism is found in the preferred orientation of large unrecrystallised plagioclase ejecta. Matrix plagioclase is generally recrystallised to form granoblastic mosaics; this texture represents a mimetic recrystallisation which reduced grainboundary energy in the fine-grained matrix during the thermal event immediately succeeding deformation. 相似文献
980.