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21.
Tsunami deposits in the geological record 总被引:2,自引:0,他引:2
A review is presented here of tsunami deposits in the geological record. It begins with a discussion of the relationships between the processes of tsunami generation and propagation and the sedimentary responses. This is followed by a consideration of the sedimentary processes associated with the passage of tsunami waves across coastlines. Attention is also given to the sedimentary processes associated with tsunami-triggered gravity backwash flows and comparisons are made with turbidity current action. We observe that despite sedimentary evidence for recent tsunamiites, geological research on ancient tsunamis has not identified stratigraphic units associated with onshore tsunami sedimentation. Equally, it is noted that nearly all published studies of sedimentary processes associated with modern tsunamis have not considered patterns of sediment transport and deposition in the offshore zone. 相似文献
22.
There have been many studies of the retail industry in recent years, and of the impact that retailing has had on the spatial arrangement of urban areas and on consumer behaviour. Little attention has been paid, however, to employment in retailing, which is disturbing in view of its growing importance and its rapidly changing nature and composition. This paper examines the nature of the broad structural changes within the industry, and investigates their spatial consequences through a case study of employment generation within a system of suburban retail centres in Canberra, Australia. It is shown that the evolution of suburban centres, particularly those of a regional variety, has had an important and enriching impact on the suburban labour market. The regional centres are also seen to be the focus of the major structural employment changes currently affecting the retail industry. This has some important implications for urban planning. 相似文献
23.
R.L. Hervig J.V. Smith I.M. Steele J.B. Dawson 《Earth and Planetary Science Letters》1980,50(1):41-58
Ion and electron microprobe analyses of twenty-one CrAl-spinel harzburgite xenoliths from southern African kimberlites show two chemical groups. Orthopyroxenes from “fertile” harzburgites have higher CaO (mean of 11, 0.95 wt.%), Al2O3 (3.05 wt.%), Cr2O3 (0.85 wt.%) and Li (0.8 ppmw) than those from “barren” harzburgites (mean of 10, CaO 0.24 wt.%, Al2O3 1.10 wt.%, Cr2O3 0.35 wt.%, Li 0.3 ppmw). Olivines from all harzburgites have similar chemistry except that mean values of Li and Na are higher for barren than fertile harzburgites (Li 0.9 vs. 0.4 ppmw; Na2O 16 vs. 7 ppmw). Orthopyroxenes from fertile harzburgites are chemically distinct from those in garne lherzolites from southern Africa and spinel lherzolites from southwest U.S.A., but orthopyroxenes from barren harzburgites are indistinguishable from those in many coarse garnet lherzolites.Chromium, Ca, Ni, Na and Li in coexisting olivines and orthopyroxenes from the above rock types show complex patterns, which for Ca, Cr and Ni can be related to pressure and temperature. Temperatures from an empirically calibrated thermometer based on Ni-Mg exchange between olivine and orthopyroxene, measured modes of harzburgites (fertile, mean of 10: ol 68, opx 31, spinel-silicate intergrowth <0.5; barren, mean of 8: ol 76, opx 23, spinel and spinel-silicate intergrowth 1), and high-pressure experimental studies suggest (a) that harzburgites are residues of partial melting, (b) that barren harzburgites were melted to a greater extent at a higher temperature (though probably at a similar depth) than fertile harzburgites, and (c) that incomplete reequilibration during retrograde metamorphism has led to development of complex inter- and intragranular textures, probably in the range ~700–900°C. 相似文献
24.
J.S. Delaney J.V. Smith D.A. Carswell J.B. Dawson 《Geochimica et cosmochimica acta》1980,44(6):857-872
Micas from coarse granular Iherzolites in S. African kimberlites may be separated into two groups; those showing primary textural relationships with coexisting silicates and those with secondary, alteration relationships with other silicates. Primary-textured micas form a tight cluster with a mean composition from 10 coarse garnet lherzolites of: SiO2 41.0, TiO2 0.18, Al2O3 13.5, Cr2O3 0.82, total Fe as FeO 2.60, MnO 0.02, MgO 26.0, NiO 0.22, CaO 0.01, BaO 0.29, Na2O 0.31, K2O 10.0, Rb2O 0.028, Cl 0.08, F 0.43 wt%. Primary-textured micas in aggregates with clinopyroxene have higher TiO2 and four specimens which look similar to the primary group but have textural ambiguities have still higher TiO2Micas with secondary textures have wide ranges of composition which may be correlated with details of the textural parageneses. Micas from kelyphitic rims around garnets tend to be Cr-rich while those from veinlets are Cr-poor. Both groups tend to have higher FeO and TiO2 than the primary group. Micas produced by alteration of, or filling veinlets through, orthopyroxene have a wide compositional range which overlaps that of the primary-textured micas, especially for harzburgite specimens.The primary-textured micas show a positive correlation with coexisting pyroxenes for MgO/(MgO + FeO) and TiO2, but not for Cr2O3. Secondary-textured micas do not show correlations with coexisting pyroxenes for any elements.The ‘primary-metasomatic’ micas described by Harte and Gurney (1975) and metasomatic and other micas described by Boettcher et al. (1979) and Boettcher and O'neil (1979) are richer in FeO and TiO2 than the present primary-textured micas, and are attributed to crystallization from fractionated fluids. 相似文献
25.
26.
Piles are frequently used to transfer the heavy compressive loads to strong soil layers located in the depth of bed. In addition, such piles may be subjected to combination of repeated compressive and tensile loads due to earthquake, wind, etc. This paper describes a series of laboratory model tests, at unit gravity, performed on belled pile, embedded in unreinforced and geocell-reinforced beds. The tests were performed to evaluate the beneficial effect of geocell in decreasing the downward and upward displacements and performance improvement of the uplift response of belled pile under repeated compressive and tensile loads. Pile displacements due to fifty load repetitions were recorded. The influence of the height of geocell above the bell of pile, an additional geocell layer at the base of belled pile, and the number of load cycles on pile displacements were investigated. The test results show that the geocell reinforcement reduces the magnitude of the final upward displacement. It also acts as a displacement retardant, and changes the behaviour of belled pile from unstable response condition due to excessive upward pile displacement in unreinforced bed to approximately steady response condition. Therefore, the geocell reinforcement permits higher tensile loads or increased cycling. The efficiency of reinforcement in reducing the maximum upward displacement of the pile (i.e. pull-out resistance) was increased by increasing the height of geocell above the bell of the pile. Furthermore, the comparison showed that a specific improvement in upward and downward displacement and the stability against uplift can be achieved using an additional geocell layer at the base. The geocell reinforcement may reduce the required length of pile shaft, consequently reducing required excavation, backfill, and pile’s material. Simple dimensional analysis showed the need for an increased stiffness of the geosynthetic components in order to match prototype-scale performance similitude. 相似文献
27.
Geochemically based hydrograph separation techniques were used in a preliminary assessment to infer how runoff processes change with landscape characteristics and spatial scale (1–233 km2) within a mesoscale catchment in upland Scotland. A two‐component end‐member mixing analysis (EMMA) used Gran alkalinity as an assumed conservative tracer. Analysis indicated that, at all scales investigated, acidic overland flow and shallow subsurface storm flows from the peaty soils covering the catchment headwaters dominated storm runoff generation. The estimated groundwater contribution to annual runoff varied from 30% in the smallest (ca 1 km2) peat‐dominated headwater catchment with limited groundwater storage, to >60% in larger catchments (>30 km2) with greater coverage of more freely draining soils and more extensive aquifers in alluvium and other drift. This simple approach offers a useful, integrated conceptualization of the hydrological functioning in a mesoscale catchment, which can be tested and further refined by focused modelling and process‐based research. However, even as it stands, the simple conceptualization of system behaviour will have significant utility as a tool for communicating hydrological issues in a range of planning and management decisions. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
28.
Evidence is presented for the observation of UHE gamma-rays from the direction of the active galaxy Centaurus A (NGC 5128). An excess of events from this direction is detected only for energies below the expected cosmic microwave background induced cut-off at around 150 TeV. 相似文献
29.
30.
Spatial and seasonal variations in CO2 and CH4 concentrations in streamwater and adjacent soils were studied at three sites on Brocky Burn, a headwater stream draining a peatland catchment in upland Britain. Concentrations of both gases in the soil atmosphere were significantly higher in peat and riparian soils than in mineral soils. Peat and riparian soil CO2 concentrations varied seasonally, showing a positive correlation with air and soil temperature. Streamwater CO2 concentrations at the upper sampling site, which mostly drained deep peats, varied from 2·8 to 9·8 mg l?1 (2·5 to 11·9 times atmospheric saturation) and decreased markedly downstream. Temperature‐related seasonal variations in peat and riparian soil CO2 were reflected in the stream at the upper site, where 77% of biweekly variation was explained by an autoregressive model based on: (i) a negative log‐linear relationship with stream flow; (ii) a positive linear relationship with soil CO2 concentrations in the shallow riparian wells; and (iii) a negative linear relationship with soil CO2 concentrations in the shallow peat wells, with a significant 2‐week lag term. These relationships changed markedly downstream, with an apparent decrease in the soil–stream linkage and a switch to a positive relationship between stream flow and stream CO2. Streamwater CH4 concentrations also declined sharply downstream, but were much lower (<0·01 to 0·12 mg l?1) than those of CO2 and showed no seasonal variation, nor any relationship with soil atmospheric CH4 concentrations. However, stream CH4 was significantly correlated with stream flow at the upper site, which explained 57% of biweekly variations in dissolved concentrations. We conclude that stream CO2 can be a useful integrative measure of whole catchment respiration, but only at sites where the soil–stream linkage is strong. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献