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111.
Overpressure generation is a function of the rates of sedimentation, compaction, fluid generation from kerogen and dehydration of minerals, and most importantly the lateral distribution of permeability within a basin as this controls lateral drainage. Sedimentary basins, however, are typically highly heterogeneous with respect to primary sedimentary facies, diagenesis and tectonic development. While fluid flow models based on idealised homogeneous basins may further our understanding of the processes that influence overpressure development, the results are very sensitive to the distribution of rock properties, particularly permeability. The absolute permeability of sedimentary rocks varies from more than 1 Darcy to less than 0.01 nanodarcy (nD) (10−11 Darcy). 相似文献
112.
Magnetic susceptibility was used to test the representativity of the lithostratigraphy of a master sediment sequence from Lake Ådran, eastern Sweden. Five further sediment cores from the same lake were correlated and compared with the master sequence using magnetic susceptibility records. Mineral magnetic correlations are generally based on matching prominent susceptibility features but may be significantly improved by using slot sequence analyses. The result of these analyses show that the sediment in the Lake Ådran master sequence can be considered representative for the basin. The variations in the magnetic susceptibility in relation to pollen and diatom analyses also seem to reflect water level changes and shore displacement in the Baltic between 9900 14C years B.P. and the isolation at 5900 14C years B.P. The first emergence of scattered non-vegetated islands is characterised by high susceptibility values. Along with a continuous water lowering and the development of the vegetation during the Ancylus fresh water stage, susceptibility values gradually decrease. A rapid phase of the Ancylus regression between 9200 and 9000 14C years B.P. is seen as an increase in magnetic susceptibility. During the following Baltic brackish water stage, the Litorina stage, susceptibility values are at their lowest, followed by higher values at the isolation from the Baltic with a maximum around 5000 14C years B.P.Shore displacement between 9900 and 5900 14C years B.P. is discussed based on the magnetic susceptibility measurements and their relationship to the pollen and diatom analyses. 相似文献
113.
Stephen Serjeant Steve Rawlings Stephen J. Maddox Joanne C. Baker Dave Clements Mark Lacy & Per B. Lilje 《Monthly notices of the Royal Astronomical Society》1998,294(3):494-504
Using complete samples of steep-spectrum quasars, we present evidence for a correlation between radio and optical luminosity which is not caused by selection effects, nor caused by an orientation dependence (such as relativistic beaming), nor a by-product of cosmic evolution. We argue that this rules out models of jet formation in which there are no parameters in common with the production of the optical continuum. This is arguably the most direct evidence to date for a close link between accretion on to a black hole and the fuelling of relativistic jets. The correlation also provides a natural explanation for the presence of aligned optical/radio structures in only the most radio-luminous high-redshift galaxies. 相似文献
114.
Per Knudsen 《Journal of Geodesy》1992,66(1):27-40
An analysis of the quasi-stationary sea surface topography (QSST) is carried out in the Norwegian Sea region (54°<ø<72°, -25°<<20°) using marine gravimetry and one year of Geosat ERM altimetry. As reference models the geopotential model OSU91A and the QSST model OSU89D were used. Two procedures to extract the QSST from mean sea surface heights and gravity anomalies were tested. Spherical FFT techniques were applied in both procedures. The results show that QSST associated with wavelength shorter than 4000 km exists. Relative to the OSU89D model the QSST was found to have a variance of (0.219 m)2 and a correlation length of 1.105°. The circulation pattern recovered in this paper agree with results of oceanographic analysis. 相似文献
115.
116.
A reversible method is presented to transform waterlogged sediment cores into dry and stable specimens which can go on exhibition or into permanent storage, needing no special precautions. Wet sediment core segments are bath-impregnated with polyethylene glycol of molecular weight 3,350 (PEG 3,350) dissolved in water. The samples are then subjected to a freeze-drying process, during which the PEG forms a stabilising and bonding porous network structure in the capillary system of the sediment. Standard sediment cores at least 1 m long become strong enough to stand upright. Sediment types ranging from muddy deep-sea sediments to very coarse littoral Halimeda sand were successfully stabilised. For standard cores of 10-cm diameters split length-wise, impregnation times vary from 2 weeks for coarse sand to 6–10 weeks for more compacted sediments. With regard to the stability of the samples and the visual clarity of detail, best results were obtained by impregnation with 25 to 60% solutions of PEG 3,350, coarse sediments needing more PEG than finer ones. Colour changes are systematic – the processed samples are lighter in appearance and the contrasts are enhanced, but there is no serious shift in colour tones. The PEG can easily be re-dissolved and washed out of the sediments. Display specimens can thus be made available for research again. 相似文献
117.
118.
All major ocean tide constituents are aliased into signals with periods less than 90 days from TOPEX/POSEIDON altimetry, except the K1 constituent. The aliased K1 has a period of 173 days. Consequently, it might be confounded with height variations caused by the semiannual cycle having a period of 183 days.The correlation between K1 and the semiannual signal has been investigated both locally and globally using combinations of T/P, ERS-1 and GEOSAT observations. Subsequently, two empirical methods have been investigated to improve the mapping of K1 from multiple satellites.At high latitudes, where the presence of crossing tracks cannot separate K1 from the semiannual signal from TOPEX/POSEIDON, the importance of including ERS-1 and GEOSAT observations was demonstrated. A comparison with 29 pelagic and coastal tide gauges in the Southern Ocean south of 50°S gave 5.59 (M2), 2.27 (S2) and 5.04 (K1) cm RMS agreement for FES95.1 ocean tide model. The same comparison for the best empirical estimated constituents based on TOPEX/POSEIDON + ERS-1 + GEOSAT gave 4.32, 2.21, and 4.29 cm for M2, S2 and K1, respectively. 相似文献
119.
A Boussinesq model for waves breaking in shallow water 总被引:2,自引:0,他引:2
120.
Triggered by urbanization and changing land use, coastal transformation is a rapidly increasing phenomenon in the global south, driving dramatic livelihoods impacts. However, the existing literature on small-scale fisheries (SSF) has paid little attention to the way coastal transformations shape conditions for SSF livelihoods communities. This study proposes a new orientation in SSF studies by exploring the assemblage of entangled sociomaterial processes that account for coastal transformations by investigating waterfront transformation in a fishing community in Karnataka, India. Drawing on ethnographic fieldwork, we conclude that an entanglement of sociomaterial processes produces unequal outcomes among stakeholders that subsequently reinforce the political and economic marginalization of certain groups of waterfront users. Moreover, the investigated context-specific waterfront assemblage intimately connects to the broader context of national fishery policy, urbanization, and tourism, directing the way coastal space can and should be transformed. Such an analysis contributes to the understanding of changing livelihoods in SSF communities. 相似文献