共查询到20条相似文献，搜索用时 31 毫秒
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MICHAEL J. SIMMS 《Geology Today》1990,6(1):24-27
Caves represent underground drainage routes formed by the passage of water through soluble rocks. Caves and the deposits they contain preserve evidence of landscape evolution and climatic change together with sediments and fossils that elsewhere have been destroyed by erosion. 相似文献
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M. M. Aksirov 《GeoJournal》1995,37(4):391-403
In studying the problem of the origin and history of rotation of the Sun and the planets, the author has concluded that the present speed of the Earth's rotation has increased during geological history. Therefore, material (physical) evidence of this phenomenon should exist in the planet's interior. This conclusion is fully confirmed by the vast amount of information contained in the Earth's sedimentary cover.On this basis of the overall geological data and changes in rotation of the Earth in the Proterozoic, we should assume that at the end of the Archean the planet had an opposite rotation relative to the present.In the Late Proterozoic the speed of direct rotation of the Earth, which by this time already transformed from retrograde to direct, was growing steadily by almost one rotation per year, for which there is ample evidence in the sedimentary cover. Correspondingly, the duration of the day during that period was lengthening as well. In the Cambrian, the planet's period of rotation equalled its orbital circulation. Therefore, duration of the solar day at that time reacted its maximum, and the day and night interchange reversed the succession. In the Late Proterozoic and Post-Cambrian Palaeozoic, palaeodays were long enough so that the climate was subjected to cycle variations of a large scale and for very different latitudes. At that time, the transition to the shadow side was accompanied by low latitude phases of glaciation, while on the insolated side, high temperature indicators were formed and an intense process of dolomite formation was in progress. During a long palaeoday the flux density of solar radiation changed very slowly. As a result, a period of one day consisted of several epochs, in each of which the climate and the thermal and physical conditions of sedimentation did not undergo considerable changes. Within each such period, highly specific types of sedimentary rocks were formed, depending on the individual features of the sedimentation region. Thus, different radiation flux densities, corresponding to different stages of the day, transformed through climate and thermal conditions, are reflected in the Earth's sedimentary cover as a cyclically repetitive sequence of lithological types of rock with each change of day and night. The gradual change of solar energy flux density and the temperature trend during the long palaeoday are obviously imprinted in the carbonate cycles of the Late Proterozoic and the Palaeozoic on a large scale; Late Palaeozoic coal cyclothems which are connected to the duration of day and the level of biosphere development are particularly noticeable. For different durations of day, confined within certain limits, particular climatic and thermal conditions, as well as geological processes, were characteristic and this has been reflected in differences of variations in the content of stratigraphic subdivisions.A rapid increase in the speed of rotation of the planet and a corresponding shortening of the day's duration coincided with the Meso-Cenozoic rebuilding of the Earth's crust. Cyclic and trended changes of the climate, that were consequences of slow and accelerating rotation of the Earth in the geological past, had an extremely important influence on the biological revolution and evolution of the biosphere as a whole. 相似文献
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地质历史中有两种性质不同的陆源区:一是格林威尔期或更早期的构造事件,导致陆块拼合、固结、基底克拉通化,在边缘形成古老剥蚀区,称之为古陆;二是震旦纪至显生宙期间,由于洋陆转换、盆山转换构造事件,原沉积盆地反转成隆起,形成新的物源区,称之为隆起,可分为克拉通边缘隆起和克拉通内隆起。克拉通内隆起具穿时性,制约下伏盆地沉积物进积和上覆晚古生代海侵上超边界。穿时的界面在三维空间上即是沉积和层控矿床的储集空间,也是油气成藏的关键因素之一。而克拉通边缘隆起则具有构造障壁的作用。 相似文献
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Philip E. LaMoreaux 《Environmental Geology》1989,13(3):181-182
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旧供水井化学处理方法介绍--以加德满都市旧供水井修复为例 总被引：1，自引：0，他引：1
章伟民 《水文地质工程地质》2005,32(6):100-101,107
本文以加德满都市旧供水井修复项目为例,针对因滤水管缝隙被化学物质堵塞,导致井出水量逐年减少的旧供水井。通过井下电视摄像系统检查,采用六偏磷酸钠、氨基黄酸等有机酸,结合刷洗、高压喷射等机械方法进行处理,使旧供水井出水量得到明显提高。 相似文献
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The spatial structure of the intermediate and outer regions of the old open cluster NGC 2420 is analyzed using data from the catalog of Paparó. The differential and integrated distributions of the projected [ΔF(r) and F(r)] and spatial [Δf(r) and f(r)] stellar densities are obtained for various subsystems of cluster stars using Kholopov’s star-count method. Analysis of these curves shows that: (1) the cluster has at least three distinct spatial zones with different stellar-density gradients, (2) the each cluster subsystem has a layered structure, and (3) the spatial structure of the cluster changes systematically in the transition to subsystems containing fainter main-sequence stars. Empirical relations describing the structure of the cluster are also derived. Similar structural features can also be found in other globular and open clusters. 相似文献
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Seth Stein Joseph F. Engeln Douglas A. Wiens Robert C. Speed Kazuya Fujita 《Tectonophysics》1983,99(2-4)
The Lesser Antilles subduction zone is an extreme case of the subduction of old (~ 90 m.y.) lithosphere at a slow (~ 2 cm/y) convergence rate. Focal mechanisms of the largest earthquakes in the area have been obtained using body and surface wave data. During the time period (1950–1978) studied the subduction seismicity appears to represent primarily intraplate rather than interplate deformation. All three large (magnitude seven) earthquakes were from intraplate normal faults; no large thrust faulting earthquakes and few small ones occurred. These observations suggest that the plate boundary is largely decoupled, that subduction is at least partially aseismic, and that the downgoing slab is in a state of extension. 相似文献
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通过对旧水泥混凝土路面引起加铺沥青混凝土面层反射裂缝的机理分析,提出了旧水泥混凝土路面改造的几种处理方法,并列举了工程实例.以上方法可为旧水泥混凝土路面加铺沥青混凝土面层时基层处理提供参考. 相似文献
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JENS TYGE MØLLER 《Boreas: An International Journal of Quaternary Research》1987,16(4):381-385
Relict spits shown on the first contour maps of Northern Jylland indicate that in postglacial times there were several straits linking Limfjorden to the North Sea across what is now a single island. At least two generations of spits can be seen on the uplifted marine plain. The spits at the higher elevation were formed by forces coming from northerly directions, while the lower spits were subjected to forces coming only from Limfjorden. 相似文献
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A. V. Loktin 《Astronomy Reports》2005,49(9):693-700
We report an analysis of the kinematic properties of stars in the old open cluster M67 based on proper motions taken from a master catalog made up of nine different catalogs containing proper motions of stars in the cluster field. A modified Sanders method is used to identify 511 probable cluster members. The dependence of the mean radial components of the proper motions of cluster members on clustercentric radius indicates that the cluster core is expanding with a velocity of 0.4 km/s. The radial dependence of the mean tangential components of the proper motions suggests the possible rotation of the cluster core. The dispersions of the velocity components of the cluster members show no evidence for the dominance of elongated stellar orbits in the cluster. The kinetic energy of the cluster stars depends strongly on their mass. 相似文献
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