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有关长江下游中生代晚期火山岩系中铁矿的若干问题 总被引：2，自引：0，他引：2
引言长江下游南京-芜湖(宁芜)和庐江-枞阳(庐枞)两个中生代晚期火山岩盆地中的铁矿,经过近年来各部门的地质队伍、科研单位及院校的详细工作,基本上查明了矿床的赋有状态、蚀变特征、矿石特点和成矿的主要控制因素,并在宁芜地区根据各种类型铁矿床之间的成因联系,建立了“玢岩铁矿”模式。虽然对“玢岩模式”的名称还有不同意 相似文献
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天山乌鲁木齐河流域山区气候特征分析 总被引：12，自引：6，他引：12
乌鲁木齐河流域山区的地理特点使其气候特征与平原区不同；气温年变幅小，降水年内分配极不均匀。每年１１月至来年３月在海拔１０００－２４００ｍ处形逆温层。根据不同台站同期年平均降水量分析，天致在海拔１９００ｍ和３５００ｍ左右有两个较大降水带。气温与湿度随海拔的变化在不同高度带内并一不致。６０年代以来，其气温变化较平原地区要不得多，而降水量在减少的同时其变率增加。 相似文献
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INTRODUCTION The term 'Sinian', in its restricted sense, is used to designate asequence of old, sub-metamorphosed or normal sediments, lying unconfor-mably upon the deeply metamorphosed and schistose series of the Wutai,and below the fossiliferous beds of the Lower Cambrian. In the YangtzeValley, it generally comprises a sub-metamorphosed sequence including 相似文献
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在山地建筑设计过程中,基础设计是制约建筑形式的主要因素,解决好基础与地形之间的关系,成为房屋设计的重要任务,也是结构设计的难点。通过几种基础形式方案的比较,达到结构设计与建筑设计的和谐性,统一性,实现了房屋在复杂的山地地形中的可建设性。 相似文献
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《International Geology Review》2012,54(9):836-844
Previously undescribed, microscopic textures in partially serpentinized peridotite shed light on the process of serpentinization. Fracturing and fragmentation of the peridotite protolith produced a modest increase in volume and opened channels to reactive aqueous fluids. Prior to, or in conjunction with, the first appearance of serpentine, micrometer-scale grains of magnetite crystallized on the surfaces of fractures. This decoration of fracture surfaces faithfully preserved the original, angular outlines of fragments of forsterite and pyroxene through all stages of serpentinization. Simple geometric considerations indicate that the volume of a given fragment did not change during replacement. Partially serpentinized forsterite shows a penetrative, micrometer-scale, sieve or sponge texture. Fifty percent or more of the volume of optically continuous forsterite can consist of micrometer-scale perforations, filled with serpentine. This sponge texture has not been described elsewhere. The delicate connections between different parts of the same forsterite grain further support strict constant-volume replacement of the fragments. Serpentinization stopped before completion (mid-reaction) when the otherwise open, magnetite-decorated channels themselves filled with serpentine, effectively sealing the rock from further access by aqueous fluids. 相似文献
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Field, petrographical and geochemical studies of a group of late Pleistocene, alkaline and mildly peralkaline trachytic and trachyphonolitic lavas from the northern Kenya Rift have been undertaken. A large number of flows were erupted from widely dispersed centres to form an extensive volcanic shield within the floor of the rift. The major element composition of most rocks was substantially modified during crystallisation, but other data show that differentiation within the suite was the result of protracted feldspar fractionation of a trachytic magma with intially very low abundances of residual trace elements. 相似文献
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Numerical modeling of the Rideau Valley Watershed 总被引：1，自引：0，他引：1
Ferdous Ahmed 《Natural Hazards》2010,55(1):63-84
Using the Mike11 modeling system by the Danish Hydraulic Institute, a detailed model of the Rideau Valley Watershed was constructed.
It includes 532 km of rivers and lakes, 106 basins, 122 bridges and culverts, and 20 water control structures. The model was
calibrated using measured streamflow data for a time period of 5 years; additional 5 years of data was used for validation.
Various methods, both qualitative and quantitative, were used to evaluate the model performance. It was found that the model
can simulate the hydrological response with a reasonable to high degree of accuracy. This model is now being used for various
watershed management purposes, including flood forecasting, dam safety assessment, quantification of wetland functions, and
derivation of design flows. 相似文献
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A. V. Mokhov A. P. Rybchuk P. M. Kartashov T. A. Gornostaeva O. A. Bogatikov 《Doklady Earth Sciences》2017,475(2):923-925
Eskolaite crystals were discovered in the course of Scanning Electron Microscopy (SEM) studies of the regolith sample, which was delivered from the continental area between Serenitatis and Tranquilitatis Maria during the Apollo 17 mission. The finding was compared with an analogue sampled from Mare Crisium (Luna 24 mission). A condensate-impact origin of eskolaite is assumed for both findings. It was demonstrated that the eskolaite of the Apollo 17 probe is genetically and morphologically identical to the eskolaite from the Luna 24 probes. 相似文献
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E.M. Rutledge M.J. Guccione H.W. Markewich D.A. Wysocki L.B. Ward 《Engineering Geology》1996,45(1-4):167-183
Loesses of the Lower Mississippi Valley (LMV) are world-famous. Sir Charles Lyell (1847), Hilgard (1860), Stafford (1869), Call (1891) and Mabry (1898), thought the LMV loess was a single water deposit although “double submergence” was noted by Call (1891) and Salisbury (1891). Shimek (1902) and Emerson (1918) recognized LMV loess as a wind deposit which came from the valley. Although wind-deposited loess gained wide acceptance, Russell (1944a) published his controversial theory of “loessification” which entailed weathering of backswamp deposits, downslope movement and recharge by carbonates to form loess. Wascher et al. (1947) identified three LMV loesses, mapped distributions and strongly supported eolian deposition. Leighton and Willman (1950), identified four loesses and supported eolian deposition as did Krinitzsky and Turnbull (1967) and Snowden and Priddy (1968), but Krinitzky and Turnbull questioned the deepest loess. Daniels and Young (1968) and Touchet and Daniels (1970) studied the distribution of loesses in south-central Louisiana. West et al. (1980) and Rutledge et al. (1985) studied the source areas and wind directions which deposited the loesses on and adjoining Crowley's Ridge. B.J. Miller and co-workers (Miller et al., 1985, 1986, Miller and Alford, 1985) proposed that the Loveland Silt was Early Wisconsin rather than Illinoian age and advanced the name Sicily Island loess. They proposed the underlying loess was Illinoian and advanced the name Crowley's Ridge. We termed the loesses, from the surface downward, Peoria Loess, Roxana Silt, Loveland/Sicily Island loess, Crowley's Ridge Loess and Marianna loess. Researchers agree that the surfical Peoria Loess is Late Wisconsin and the Roxana Silt is Late to Middle Wisconsin, but little agreement exists on the age of the older loesses. Pye and Johnson (1988) proposed Early Wisconsin for the Loveland/Sicily Island. McKay and Follmer (1985) suggested this loess correlated with a loess under Illinoian till. Clark et al. (1989) agreed on Crowley's Ridge, but suggested the Loveland/Sicily Island loess on Sicily Island was older. Mirecki and Miller (1994) and Millard and Maat (1994) suggested an Illinoian age for the Loveland/Sicily Island loess. Miller and co-workers suggested, as did Pye and Johnson (1988), an Illinoian age for the Crowley's Ridge loess. McKay and Follmer (1985) suggested it correlated with a loess under “Kansan” till. Stratigraphy indicates the Marianna is the older of the five loesses.
Researchers identified loess on both the east and west side of the LMV as well as on higher terraces within the valley. Many researchers assumed unaltered loesses were commonly yellowish brown, and silts or silt loams (West et al., 1980; Miller et al., 1986). The nonclay fraction of unweathered LMV loesses was dominated by quartz followed * Corresponding author. by carbonates, mainly dolomites, followed by feldspars, and micas. Clays were dominated by montmorillonite followed by micaceous minerals, kaolinite and vermiculite (Miller et al., 1986). Soils in the Crowley's Ridge loess are most developed, followed by the soils in the Loveland/Sicily Island which are more developed than the modern soils in the Peoria Loess. Soils in the Roxana and Marianna loesses are least developed and the Farmdale Soil of the Roxana is the weaker of the two (Miller et al., 1986). There is certainly overlapping range in the degree of soil development in the various loesses. 相似文献
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In 1938, Clair A. Brown published his classic paleobotanical discoveries from the Tunica Hills of southeastern Louisiana, indicating ice-age plant migrations of more than 1100 km. Brown collected fossils of both boreal trees such as white spruce (Picea glauca) and southern coastal plain plants from deposits mapped as the Port Hickey (Prairie) river terrace by Harold N. Fisk. Subsequent revisions of terrace mapping, radiocarbon dating, and paleoecological analysis reconciled Brown's conceptual and stratigraphic “mixing” of these two ecologically incompatible fossil plant groups. An older Terrace 2 (of Sangamonian to Altonian age) contains the warm-temperate assemblage. A younger Terrace 1 (of Farmdalian, Woodfordian, and Holocene age) includes full-glacial and late-glacial remains of both boreal and cool-temperate plants; and a warm-temperate suite of plants dates from the Holocene interglacial. New plant fossil localities with radiocarbon chronologies are now available from within the Lower Mississippi Valley of Missouri and Arkansas as well as from the adjacent Ozark Plateaus, the Interior Low Plateaus of Kentucky and Tennessee, and the bordering Blufflands of Tennessee, Mississippi, and Louisiana. These studies demonstrate that glacial and interglacial patterns of vegetation have been influenced by regional changes in climate, glacial runoff, and regime of the Mississippi River. 相似文献
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Tony Waltham 《Geology Today》2012,28(1):31-38
Cut deep into the heart of California's Sierra Nevada, the Yosemite Valley has been dubbed the Incomparable Valley, because it is so seriously spectacular. And it is. It has also been called the finest example of a deep glaciated trough. But it's not. Yosemite is more than that, and the glaciation is only part of its splendid geological story. 相似文献
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The Upper Middle Rhine Valley, granted the status of a World Heritage site, is well known for its unique inner narrow valley
of Quaternary age with its historical legacy of numerous medieval castles and old towns. Less known is that this has always
been a risk area of floods and gravitative mass movements. Up to the recent past, mainly ice floods caused enormous damage.
The inhabitants of the valley were well aware that they lived in a risk area, but they had learned to handle the flood hazard.
With the demise of ice floods over the last 40 years, due to climate change and because of the additional heating of the river
water by power plants, the awareness of flood hazards has been much diminished, in contrast to that of potential damage by
rockfalls and landslides which were also much feared in the past, though at the local level only. Still in the people’s memory
is the Kaub catastrophe of March 10, 1876, when 28 persons were killed by a landslide. Nowadays, even minor rockfalls are
a major threat, as they will affect the much-used traffic lines on both banks of the river, in particular the railroads. Therefore,
since 2002, on behalf of German Rail (Deutsche Bahn, DB), all problematic slopes have been protected by costly steel-ring nets, although they are an aesthetic problem by UNESCO
standards. The feeling of absolute safety created among the public is only subjective, though, as planners are well aware
of. Moreover, the impact of modern climate change on slope stability is nearly unknown. Therefore, it is still necessary to
develop a risk map for the narrow valley, with emphasis on gravitational hazards. 相似文献
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Kenneth L. Cole 《Quaternary Research》1986,25(3)
A chronological sequence of plant macrofossil assemblages from twenty-five pack rat middens provides a record of desert scrub vegetation for most of the last 13,380 yr B.P. from a hyperarid portion of the lower Colorado River Valley. At the end of the late Wisconsin, and probably during much of the Quaternary, the Picacho Peak area, Imperial County, California, supported a typical Mohave Desert association of Larrea divaricata (creosote bush), Coleogyne ramosissima (blackbrush), Yucca brevifolia (Joshua tree), and Y. whipplei (Whipple yucca). Recent arrivals of Sonoran Desert plants such as Olneya tesota (ironwood) and Fouquieria splendens (ocotillo) suggest that the area supported relatively modern Sonoran desert scrub species for relatively short periods during interglaciations. 相似文献
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在岩性构成复杂的岷江龙门山河段,河谷两侧龙门山山顶面主要坡折点与岩性界线基本对应,但河床剖面上没有表现出明显的与岩石抗蚀界限相对应的阶梯状变化。研究结果表明,龙门山地区线状剥蚀速率是面状剥蚀速率的2.1倍,河床表面因岩性差异形成的原始地貌陡坎被水流剥蚀殆尽,从而导致该区域河床剖面样式与山顶面剖面样式存在显著差异。 相似文献