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This paper focuses on the formative processes of limestone pseudoconglomerates in the Gushan and Chaomidian Formations (Late Cambrian) of the North China Platform, Shandong Province, China. The Gushan and Chaomidian Formations consist mainly of limestone and shale (marlstone) interlayers, wackestone to packstone, grainstone and microbialite as well as numerous limestone conglomerates. Seventy‐three beds of limestone pseudoconglomerate in the Gushan and Chaomidian Formations were analysed based on clast and matrix compositions, internal fabric, sedimentary structures and bed geometry. These pseudoconglomerates are characterized by oligomictic to polymictic limestone clasts of various shapes (i.e. flat to undulatory disc, blade and sheet), marlstone and/or grainstone matrix and various internal fabrics (i.e. intact, thrusted, edgewise and disorganized), as well as transitional boundaries. Limestone pseudoconglomerates formed as a result of soft‐sediment deformation of carbonate and argillaceous interlayers at a shallow burial depth. Differential early cementation of carbonate and argillaceous sediments provided the requisite conditions for the formation of pseudoconglomerates. Initial deformation (i.e. burial fragmentation, liquefaction and injection) and subsequent mobilization and disruption of fragmented clasts are two important processes for the formation of pseudoconglomerates. Burial fragmentation resulted from mechanical rupture of cohesive carbonate mud, whereas subsequent mobilization of fragmented clasts was due to the injection of fluid materials (liquefied carbonate sand and water‐saturated argillaceous mud) under increased stress. Storm‐wave loading was the most probable deformation mechanism, as an external triggering force. Subsequent re‐orientation and rounding of clasts were probably prolonged under normal compactional stress. Eventually, disrupted clasts, along with matrix materials, were transformed into pseudoconglomerates by progressive lithification. Soft‐sediment deformation is prevalent in alternate layers of limestone and mud(marl)stone and/or grainstone, regardless of their depositional environments. 相似文献
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Effects of nonlinearity on theairflow past an urban heat island and precipitationchange downwind, are investigated analytically in thecontext of the weakly nonlinear response of a stablystratified uniform flow to specified heating. Theheating structure is assumed to be bell-shaped in thehorizontal and exponentially decreasing with height.The forcing to the first-order equation exhibitscooling in the concentrated low-level heating region.The linear solution component shows upward motiondownstream as suggested by many previous studies. Theweakly nonlinear solution component shows downward orupward motion downstream depending on the heatingdepth. It is proposed that when the heating depth islarge, but still within a valid range of theperturbation expansion, the linear and weaklynonlinear effects constructively work together toproduce enhanced upward motion on the downstream side,not far from the heating centre. This explains toa greater extent the precipitation enhancement downstream ofthe heat island than is possible from the linear effect alone. Itis also proposed that when the heating depth is small,the linear and weakly nonlinear effects destructivelywork together to reduce upward motion on thedownstream side, not far from the heating centre. Thisexplains to a greater extent the lack of precipitation enhancementdownstream than is possible from the linear effect alone. 相似文献
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Tectonometamorphic evolution of the Chuncheon amphibolite, central Gyeonggi massif, South Korea 总被引:9,自引:0,他引:9
Abstract The Chuncheon amphibolite, part of the Gubongsan Group which overlies the Yongduri gneiss complex, is interlayered with calc-silicate rock, marble, quartzite, biotite schist and quartzofeldspathic gneiss in the central Gyeonggi massif, South Korea. Metamorphic pressures and temperatures estimated from the amphibolite are 5.5–10.6 kbar and 615–714°C. These P—T conditions are close to those defined by the reaction curve between kyanite and sillimanite, and suggest medium-pressure-type metamorphism of the Chuncheon amphibolite. For two metapelites intercalated with the amphibolite, temperatures are estimated to be 607–699° C, consistent with those obtained from the amphibolite. On the other hand, pressures estimated from these metapelites are significantly different, 4–6 kbar and 9–13 kbar, when rim and core compositions of garnet are, respectively, used. These P—T estimates obtained from the amphibolite and metapelite suggest a nearly isothermal decompression of 3–7 kbar during denudation. Rapid decompression is likely on the basis of the results of mineral chemistry, phase equilibria and geothermobarometer. Moreover, in conjunction with the occurrence of kyanite in the adjacent Gyeonggi gneiss complex, P—T estimates of the Chuncheon amphibolite and metapelite suggest a clockwise P—T—t path. This evolutionary path may be related to the amalgamation of continents during the late Proterozoic event which corresponds to the Jinningian orogeny in the Qinling belt of China. 相似文献
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利用Excel实现R型聚类分析 总被引:2,自引:0,他引:2
R型聚类分析是对若干个元素进行数量化相似程度分类的一种数理统计方法,主要步骤包括:原始数据转换;求解相关系数;对结果聚类。利用Excel的数据分析工具实现R型聚类分析的方法和步骤,对野外一线地质人员的工作相当适用。 相似文献
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春乃芽 《物探化探计算技术》2007,29(6):560-564
判别分析是化探常用的一种地质统计学方法,通过建立多变量判别函数,来判断未知地质体的属性。这里通过一个实例,详细介绍了利用Excel的规划求解和有关Excel函数,来建立判别函数的具体操作步骤,该方法对基层地质科技人员相当适用。 相似文献