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311.
Internal structure of mixed-sand-and-gravel beach deposits revealed using ground-penetrating radar 总被引:4,自引:1,他引:4
ABSTRACT Mixed‐sand‐and‐gravel beaches are a distinctive type of coarse‐clastic beach. Ground‐penetrating radar (GPR) and photographic records of previous excavations are used to investigate the stratigraphy and internal sedimentary structure of mixed‐beach deposits at Aldeburgh in Suffolk, south‐east England. The principles of radar stratigraphy are used to describe and interpret migrated radar reflection profiles obtained from the study site. The application of radar stratigraphy allows the delineation of both bounding surfaces (radar surfaces) and the intervening beds or bed sets (radar facies). The deposits of the main backshore berm ridge consist of seaward‐dipping bounding surfaces that are gently onlapped by seaward‐dipping bed sets. Good correspondence is observed between a sequence of beach profiles, which record development of the berm ridge on the backshore, and the berm ridge's internal structure. The beach‐profile data also indicate that backshore berm ridges at Aldeburgh owe their origin to discrete depositional episodes related to storm‐wave activity. Beach‐ridge plain deposits at the study site consist of a complex, progradational sequence of foreshore, berm‐ridge, overtop and overwash deposits. Relict berm‐ridge deposits, separated by seaward‐dipping bounding surfaces, form the main depositional element beneath the beach‐ridge plain. However, the beach ridges themselves are formed predominantly of vertically stacked overtop/overwash units, which lie above the berm‐ridge deposits. Consequently, beach‐ridge development in this progradational, mixed‐beach setting must have occurred when conditions favoured overtopping and overwashing of the upper beachface. Interannual to decadal variations in wave climate, antecedent beach morphology, shoreline progradation rate and sea level are identified as the likely controlling factors in the development of such suitable conditions. 相似文献
312.
Dr. Ken R. McClay 《International Journal of Earth Sciences》1983,72(2):469-491
Determination of preferred orientations in sulphide ores is an important facet in the analysis of the deformation and metamorphism in ore deposits. The methodology and problems of texture determinations in deformed sulphides are briefly reviewed. Deformation mechanisms and texture development in the common sulphide minerals are summarised. Axi-symmetric experimental deformation of galena, sphalerite and chalcopyrite produces similar pole figures with the (110) planes aligned normal to the compression axis. Deformation textures in naturally deformed sulphides however are best preserved in monomineralic ores which have undergone simple shear deformation. These textures can be correlated with the microstructures found in the sulphides. Computer simulations of deformation textures arising from dislocation mechanisms can be used to interpret the textures but the results to date are preliminary. These theoretical models emphasize the importance of the symmetry of the kinematic axes of the deformation, the operative glide systems and the strain history and the deformation path. Little is known, however, of the influence of static and dynamic recrystallisation on sulphide preferred orientations. 相似文献
313.
Initial 87Sr/86Sr rations were determined for more than 80 plutonic rocks in Japan. The 87Sr/86Sr ratios of gabbroic and granitic rocks show no significant difference in plutonic terranes where both rocks occur closely associated, implying a genetic relationship between them (e.g., Green Tuff belt) or reequilibration at deep level (e.g., Ryoke belt). Wherever granitic rocks occur independently from gabbroic rocks, the granites have higher ratios than the gabbros.Initial 87Sr/86Sr ratios of the granitic rocks are low (<0.706) in Northeast Japan but high (<0.706) in Southwest Japan, the boundary being the Tanakura Tectonic Line. Within Southwest Japan, the ratios are low along the Japan Sea side of the southernmost area. This regional variation is generally correlated with thickness of the continental crust as deduced from the Bouguer anomaly.Initial 87Sr/86Sr ratios of the granitic rocks vary from 0.7037 to 0.7124. The low group (<0.706) is considered to consist of essentially mantle-derived magmas contaminated by crustal material in lesser but varying degree, because of its geological setting and initial 87Sr/86Sr values. The high group may have been formed by contamination of a deep-seated magmas by crustal material or by generation of the main part of the magmas within the continental crust. The ratios of individual belts reflect their own history depending upon age and Rb/Sr ratio of the crustal material.Initial 87Sr/86Sr ratios of granitic rocks are generally low for the magnetite-series but high for the ilmenite-series. Thus, a negative correlation is observed between initial ratios and 34S for most Cretaceous-Paleogene granites. However, Neogene ilmenite-series granites are low in both initial 87Sr/86Sr and 34S indicating interaction of the granitic magma with young sedimentary rocks enriched in 32S. 相似文献
314.
Asger Ken Pedersen 《Contributions to Mineralogy and Petrology》1979,69(4):397-407
Immiscible sulphide bodies show eutectic quench textures in a basaltic glass rock (mg=66) from a native iron-bearing dyke chilled at T=1,200° C and P=250 bars. The sulphide bodies are composed of troilite (90–91%), iron (9–10%) and very scarce vanadium-rich chromite and approach a ternary cotectic in the Ni-poor part of the system Fe-Ni-S. Transition element partition between olivine (mg=83), silicate glass (mg=59) and sulphide blebs indicate that the phases were equilibrated at 1,200° C. D
vanadium(olivine/glass) is close to unity and reflect the reducing nature of the rock, for which estimates of f
O210–12 to –13 and f
S210–5 have been made. D
nickel, cobalt, copper (sulphide/glass)=4,300, 230 and 380 respectively, are much higher than reported experimentally determined D's onmonosulphide/basalt glass at the same temperature and show increasing positive deviation (Ni>Co>Cu) with the increasingly siderophile character of the elements. K
Dnickel-iron (sulphide/olivine)=63 is much higher than an experimentally reported value (33) and comparison with published thermodynamic data on Ni-partition between olivine and iron metal suggests that the positive deviation is roughly proportional to the excess metal component in the sulphide melt. The occurrence of strongly Ni-depleted reduced basalts on Disko shows that fractionation of metal and sulphides was a common and geologically important process. 相似文献
315.
316.
317.
Ken Suda M. Sc. 《Pure and Applied Geophysics》1955,32(1):159-169
Summary A synoptic study is made based primarily on 10-day and 5-day mean maps on an unusually cold spell which appeared all over the Far East in the end of January, 1954, following an abnormal warmth. It is found that while it is warm in Japan, cold air is accumulated in Siberia to the north of the climatological jet stream and is confined in the northern latitudes by the latter as long as the high index pattern prevails. But once the index drops, with the southward displacement of the jet stream, the permanent trough of the Far East deepens and the cold air so far accumulated is allowed to penetrate into southern latitudes. Some characteristic features of contour pattern and frontal activity preceding and following the cold air outbreak are described. Further, it is shown that the blocking wave directly related to the cold air outbreak in the Far East can be traced from as far east as North America or possibly the eastern Atlantic. 相似文献
318.
Urbanization and agricultural intensification in the Lower Fraser River valley,: Impacts on water use and quality 总被引:2,自引:0,他引:2
The Fraser River drains a quarter of the province of British Columbia and is renown as one of the greatest salmon rivers in the world. The Fraser watershed is under threat from rapid urbanization in its lower reaches as pollutants generated from domestic and industrial wastes, and stormwater runoff threaten the health of the aquatic ecosystem. Plans for secondary sewage treatment in the metropolitan area will reduce waste loadings of some contaminants, but rapid growth will soon offset these benefits. Intensive urbanization, spreading up the Lower Fraser valley, with a network of impervious roads and increased traffic volumes contribute pollutants in surface runoff that are difficult to control. Rapid growth in agrobusiness to provide fresh produce to the nearby markets has resulted in very high densities of farm animals and excessive use of fertilizers and pesticides on the land. These pollutants threaten the groundwater and many of the remaining salmonid streams in the lower valley. The Fraser Basin Management Program, the Fraser River Estuary Management Program, and a variety of government agencies are coordinating studies and analyzing issues and conflicts to develop a strategy for sustainable development in the region. 相似文献
319.
Samples of raw water were collected at regular intevals at two transects in the St. Lawremce River and four of its tributaries
from March to November 1991 and from April to June 1992. Water samples were analyzed for both the dissolved and the particulate
phase for cadmium (Cd), organic carbon, iron and manganese. Mean dissolved Cd concentration was 10±5 ng/L and no spatial variability
was observed. Higher concentrations were found during high flow periods, suggesting an uptake of cadmium by phytoplankton
during summer. In addition, dissolved cadmium did not appear to be associated with either DOC, dissolved Fe or dissolved Mn.
The mean particulate Cd concentration was 1.3±1.1 μg/g, with almost all stations presenting the same concentration except
the Yamaska River, which had a concentration of 0.5±0.2 μg/g. Particulate Cd showed a negative correlation with suspended
particulate matter and a positive correlation with particulate organic carbon and particulare manganese. Fifty-nine percent
of the cadmium was found to be in the particulate phase. Partition coefficients for cadmium (Kd), organic carbon (Kc), iron
(KdFe) and manganese (KdMn) were calculated for each sample. Log Kd varied from 3.9 to 5.9, with an average of 5.0±0.4. Log
Kd decreased with increasing particulate, matter as did Log Kc and Log KdMn. No significant correlation was found between
Log Kd and Log Kc, suggesting that the distribution of cadmium between the dissolved and the particulate phase is not influenced
by the distribution of organic carbon. In contrast, positive correlations were observed between Log Kd, Log KdFe and Log KdMn.
Cadmium distribution appears to be influenced by Fe and Mn distribution. 相似文献
320.
David J. Clifford Patrick G. Hatcher Robert E. Botto John V. Muntean Beverly Michels Ken B. Anderson 《Organic Geochemistry》1997,27(7-8)
Soluble polylabdanoids isolated by sequential solvent extraction have been characterized by liquid-state 13C- and 1H NMR and 13C-1H HMQC (heteronuclear correlation) NMR spectroscopy in addition to solid-state NMR and Py-GC-MS techniques. Two Holocene resins originating from Santander, Colombia and Mombasa, Kenya were analyzed. Soluble polymers were isolated by extraction with a 1:1 (v/v) methylene chloride-methanol mixture following sequential extractions with methylene chloride and methanol. The molecular weight of polymer extracts was shown by GPC analyses to exceed that of non-polymeric occluded terpenoids. Py-GC-MS, solid-state 13C CP/MAS and 13C cross-polarization/depolarization NMR spectroscopy results indicated that chemical compositions of soluble polymers isolated from immature resins are highly representative of the structure of corresponding insoluble polymers, i.e. polylabdatrienes. These data provide evidence for cross-linking or cyclization of side-chain olefinic carbons during or shortly after polymerization. Generally, the characterization of soluble resin polymers by liquid-state NMR spectroscopy has proven to be an excellent means for investigating the maturation mechanism of polylabdanoid resinites, and has potential for furthering the application of Class I resinites as geothermal indicators. 相似文献