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排序方式: 共有155条查询结果,搜索用时 31 毫秒
101.
Ingrid Anell Valentin Zuchuat Anna Daniela Rhnert Aleksandra Smyrak‐Sikora Simon Buckley Gareth Lord Harmon Maher Ivar Midtkandal Kei Ogata Snorre Olaussen Per T. Osmundsen Alvar Braathen 《Basin Research》2021,33(1):478-512
The study describes the depositional development and sediment partitioning in a prograding paralic Triassic succession. The deposits are associated with the advance of large prism‐scale clinoforms across a shallower platform area. Approaching the platform, the limited accommodation and associated relative higher rates of deposition generated straighter clinoforms with lower foreset angles. The vertical restriction across the platform is interpreted to have amplified the tidal signature. Sediment was redistributed from the coast into increasingly sandy delta‐front deposits, compared to offshore equivalents. The deposits comprise extensive compound dune fields of amalgamated and increasingly clean sandbodies up‐section. Rapid deposition of significant amounts of sand led to differential subsidence and growth‐faulting in the delta front, with downthrown fault blocks further amplifying the tidal energy through funnelling. A mixed‐energy environment created along‐strike variability along the delta front with sedimentation governing process‐regime. Areas of lower sedimentation were reworked by wave and storm‐action, whereas high sedimentation rates preserved fluvially dominated mouth bars. A major transgression, however, favoured tidally dominated deposits also in these areas, attributed to increasing rugosity of the coastline. Formation of an extensive subaqueous platform between the coast and delta front dampened incoming wave energy, and tidally dominated deposits dominate the near‐shore successions. Meanwhile formation of wave‐built sand‐bars atop the platform attest to continued wave influence. The strong tidal regime led to the development of a heterolithic near‐shore tidally dominated channel system, and sandier fluvial channels up‐river. The highly meandering tidal channels incising the subaqueous platform form kilometre wide successions of inclined heterolithic stratification. The fluvially dominated channels which govern deposition on the delta plain are narrower and slightly less deep, straighter, generally symmetric and filled with cleaner sands. This study provides important insight into tidal amplification and sand redistribution during shallowing on a wide shelf, along with along‐strike process‐regime variability resulting from variations in sediment influx. 相似文献
102.
Yoshiro Watanabe Yutaka Kurita Masayuki Noto Yoshioki Oozeki Daiji Kitagawa 《Journal of Oceanography》2003,59(4):403-414
Growth and mortality rates of larval and early juvenile Pacific saury Cololabis saira were estimated for spring and autumn spawning seasons in the Kuroshio-Oyashio transitional waters and for winter spawning
season in the Kuroshio waters in 9 years from 1990–1998, based on quantitative fish sampling and otolith daily ring readings.
Growth and mortality rates were more variable in the Kuroshio-Oyashio transitional waters than in the Kuroshio waters. The
estimated production of 40-mm preschooling juveniles was a positive function of larval production in the hatching length class
(5.9–9.9 mm) in the Kuroshio waters. In the Kuroshio-Oyashio transitional waters, rather than larval production in the hatching
length class, cumulative survival through the larval and early juvenile stages determined the juvenile production. Variable
growth and survival rates of saury observed in the transitional waters seem to be associated with large environmental variability
in the waters, including shifts of the Kuroshio and Oyashio fronts and development of streamers and eddies between the fronts.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
103.
Tuneto Kurita 《Physics of the Earth and Planetary Interiors》1976,12(1):65-86
Regional variations of the velocity structure down to a depth of about two hundred kilometers in the central United States are investigated by a combined use of body-wave spectra, surface-wave dispersion, travel-time residuals and synthetic seismograms. With minor adjustments to models obtained in a preceding study of body-wave transfer ratios the revised models FLO74, OXF74 and SHA74 are proposed which reasonably satisfy all data in the above four kinds of methods. These models retain the same characteristic feature of the deepening of the low-velocity zone from the Gulf of Mexico to the Interior Plain nearly along 89°N longitude while decreasing its thickness and increasing its velocities as in the preceding models. The low-velocity zone is about 50 km thick ranging in depth from about 150 to 200 km around a junction of the Interior Plain with the Interior Highlands, about 80 km thick from about 120 to 200 km in the Coastal Plain, and about 90 km thick from about 90 to 180 km in the continental shelf of the Gulf of Mexico. Although it is not clear what relation, if any, exists between the above characteristic feature of the low-velocity zone and the recurrent relief of intra-plate stress along the central Mississippi Valley, an intricate crustal structure found along the valley northwest of the confluence of the Mississippi and Ohio rivers is apparently related to the occurrence of historical earthquakes. Comparisons of synthetic seismograms of the above models with teleseismic records of deep earthquakes reveal that the undulations in a time interval of over 100 sec between the onsets of the P and pP phases on long-period records are good surface expression of the underlying layered structure below the station and are not associated with the source. Relevant future high-quality data promise a comprehensive elucidation of the fine configuration of structure in the crust and upper mantle. 相似文献
104.
105.
Tadahide Ui Keiko Suzuki-Kamata Rumi Matsusue Kei Fujita Hideya Metsugi Mami Araki 《Bulletin of Volcanology》1989,51(2):115-122
The grain orientations within the matrix of two large-scale welded, two small-scale nonwelded and two nonwelded low-aspect ratio pyroclastic flow deposits are measured to analyze flow behavior. Preferred grain alignments are especially apparent in the middle part of layer 2 of each deposit. Preferred grain alignments do not vary laterally within a 10 m interval. The grain alignments obtained are radial from the source caldera, especially in proximal to medial and plateau-forming facies of pyroclastic flow deposits. Grain alignments are controlled by valley-channel directions for the valley-ponded facies of pyroclastic flow deposits, especially at medial to distal locations. Such local topographic factors strongly affect the data for high-aspect ratio and smallscale deposits, and weakly affect the data for widespread low-aspect ratio pyroclastic flow deposits. This work suggests that grain alignment analysis should be used with care when attempting to determine the location of an unknown source. 相似文献
106.
A simple expression is presented on the capability of storage-treatment systems to reduce non-point pollutant runoff load to natural waters. Their efficiency depends on the capacities of the facilities and probabilistic properties of runoff, such as interval, duration, volume, and concentration of runoff events. Assuming the compound Poisson process for runoff time series, the exact expressions of the ratio of treated load in terms of storage and treatment capacities are theoretically derived on the neighbourhoods of all boundaries of the domain on which the problem is defined. Then, an approximate expression over the whole domain is presented, of which the value and the first-order derivative coincide with those of the exact derived expressions near the boundaries. Accuracy is checked by Monte Carlo simulations. 相似文献
107.
108.
Abstract. Simulation experiments with a one-dimensional static model for formation of methane hydrate are used to demonstrate models of hydrate occurrence and its generation mechanism for two end-member cases. The simulation results compare well with experimental data for two natural examples (the Nankai Trough and the Blake Ridge).
At the MITI Nankai Trough wells, the hydrate occurrence is characterized by strongly hydrated sediments developing just above the BGHS. Such occurrence can be reproduced well by simulation in which the end-member case of upward advective fluid flow from below the BGHS is set. The strongly hydrated sediments is formed by oversaturated solution with free gas which directly enters the BGHS by the upward advective fluid flow. The recycling of dissociated methane of preexisting hydrate also contributes to the increase of hydrate saturation.
At the Site 997 in the Blake Ridge area, the hydrate occurrence is characterized by thick zone with poorly hydrated sediments and no hydrate zone developing above the hydrate zone. Such occurrence can be reproduced well by simulation in which the end-member case of in-situ biogenic production of methane in the sediment of methane hydrate zone is set. The distribution pattern of hydrate saturation is basically controlled by that of TOC. However, the hydrate concentration near the bottom of the hydrate zone is increased by the effect of recycling of dissociated methane of pre-existing hydrate. No hydrate zone expresses the geologic time needed until the local concentration of methane exceeds the solubility by gradual accumulation of in-situ biogenic methane with burial. 相似文献
At the MITI Nankai Trough wells, the hydrate occurrence is characterized by strongly hydrated sediments developing just above the BGHS. Such occurrence can be reproduced well by simulation in which the end-member case of upward advective fluid flow from below the BGHS is set. The strongly hydrated sediments is formed by oversaturated solution with free gas which directly enters the BGHS by the upward advective fluid flow. The recycling of dissociated methane of preexisting hydrate also contributes to the increase of hydrate saturation.
At the Site 997 in the Blake Ridge area, the hydrate occurrence is characterized by thick zone with poorly hydrated sediments and no hydrate zone developing above the hydrate zone. Such occurrence can be reproduced well by simulation in which the end-member case of in-situ biogenic production of methane in the sediment of methane hydrate zone is set. The distribution pattern of hydrate saturation is basically controlled by that of TOC. However, the hydrate concentration near the bottom of the hydrate zone is increased by the effect of recycling of dissociated methane of pre-existing hydrate. No hydrate zone expresses the geologic time needed until the local concentration of methane exceeds the solubility by gradual accumulation of in-situ biogenic methane with burial. 相似文献
109.
Solubility experiments for nitrogen and noble gases (Ar and Ne) in silicate melts were conducted using two experimental configurations: one was conducted at 1 atmospheric pressure, T =1300°C and oxygen fugacity (fO2) of IW + 0.9 (i.e., 0.9 log units higher than the iron-wüstite buffer) and the other at high pressures (Ptotal ∼ 2 × 108 Pa), 1500°C and fO2 ∼ IW + 6. For the former experiment, isotopically labeled-nitrogen (15N15N-enriched) was used to distinguish dissolved nitrogen from contaminating atmospheric or organic nitrogen and to examine dissolution mechanisms of nitrogen in silicate melts. The results obtained for the two series of experiments are consistent with each other, suggesting that Henry's law is satisfied for fN2 of up to ∼250 atm (2.5 × 107 Pa). The results are also consistent with our earlier results (Miyazaki et al., 1995) obtained at highly oxidizing conditions (fO2 ∼ IW + 10). All these results support physical dissolution of nitrogen as N2 molecules in silicate melts for fO2 from ∼IW + 10 down to ∼IW. The observed solubility (Henry's constant) of nitrogen (3-5 × 10−9 mol/g/atm) is comparable to that of Ar (2-4 × 10−9 mol/g/atm), and much lower than that of Ne (11-14 × 10−9 mol/g/atm) at 1300°C. A preliminary experiment was also performed for partitioning of nitrogen and noble gases between clinopyroxene (cpx) and basaltic melt using a piston cylinder-type apparatus at 1.5 GPa and at 1270 to 1350°C. The obtained cpx/melt partition coefficient of nitrogen is 0.06, slightly lower than those of noble gases (∼0.1 for Ne to Xe), suggesting that nitrogen is as incompatible as or even slightly more incompatible than noble gases. The present results imply that a large nitrogen/Ar fractionation would not be produced by magmatic processes. Therefore, the two orders of magnitude difference between the N2/36Ar ratios in the Earth's atmosphere (∼104) and that in the mantle (∼106) must be explained by some other processes, such as incomplete segregation of metal blobs into the core and their later oxidation. 相似文献
110.
Michael P. Eddy Mauricio Ibaez‐Mejia Seth D. Burgess Matthew A. Coble Umberto G. Cordani Joel DesOrmeau George E. Gehrels Xianhua Li Scott MacLennan Mark Pecha Kei Sato Blair Schoene Victor A. Valencia Jeffrey D. Vervoort Tiantian Wang 《Geostandards and Geoanalytical Research》2019,43(1):113-132
We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected 206Pb/238U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam 206Pb/238U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within < 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean 176Hf/177Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf0 of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of 206Pb/238U and 176Hf/177Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic 176Hf/177Hf. 相似文献