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排序方式: 共有47条查询结果,搜索用时 15 毫秒
1.
Microbially Induced Sedimentary Structures (MISS) are primary sedimentary structures that arise syndepositionally from microbial community activity. Especially valuable are MISS for the analysis of early Archean (and extraterrestrial) deposits. However, most reports of MISS have focused on the Precambrian and Phanerozoic mass extinction marine sediments, and only a few and terrestrial MISS have been studied. The MISS presented in this paper, which mainly consists of mat growth feature, mat destruction feature and mat decay feature, are well preserved in terrestrial clastic rocks around the P-T boundary in Xiyang area, western Henan. Large U ridges, oriented sand quartz, mica grains and thin clayey laminae arranged parallel to bedding plane are the main features visible under the microscope. Several lines of evidence indicate that the Xingyang MISS are of biogenic origin. Abundant MISS in Xingyang may indicate the degradation of terrestrial ecosystems and proliferation of microbial mats immediately after the severe Permian-Triassic mass extinction. Study aiming at MISS helps to analyze their space distribution in the globe and to probe into links between microbial proliferation and environmental stresses following the end-Permian mass extinction in terrestrial ecosystems. 相似文献
2.
The coast of Kuwait can be divided into nine intertidal geomorphological subunits, of which four are found along the northern muddy shoreline and five along the southern sandy shoreline. In the north the coast is characterized by wide intertidal mudflats, bounded landward by an extensive coastal sabkha which is partly covered by sand drifts. The upper part of the intertidal environment is covered with a mixture of aeolian sands and muddy sediments of marine origin. A number of shallow tidal channels dissect the intertidal flats and small sand bars occur near the low water line. In contrast, the southern shore is characterized by relatively steep sandy beaches fronted by narrow to moderately wide rocky intertidal platforms which are partly covered by sand, bioherms, skeletal debris and algal mats. In some areas the rocky surface is dissected by numerous small gulleys and shallow channels. Multiple sand bars lying either parallel or diagonal to the shoreline are developed near the low water line. This southern intertidal environment is bounded landward by a sandy berm and a wave-cut cliff.Ripple marks are developed almost parallel to the shoreline, showing different flow directions. Energy levels are moderate to high along the southern shore, but low along the northern shore. In the south, waves induced by winds blowing mostly from the north-east and south-east form the dominant energy source, whereas tidal and wind-driven currents are the only tangible process acting along the northern shore. 相似文献
3.
基于GPS技术的大型结构建筑物动态监测 总被引:7,自引:4,他引:7
在回顾传统的结构物震动和位移测量方法的基础上,详细阐述了采用GPS进行大型建筑物动态监测的原理、方法。介绍国内外典型的动态监测实例,提出了监测数据的管理与可视化方案,对未来大型结构建筑物动态监测的技术进行了展望。 相似文献
4.
K. Kusaka K. Hagiya M. Ohmasa Y. Okano M. Mukai K. Iishi N. Haga 《Physics and Chemistry of Minerals》2001,28(3):150-166
The structures of Ca2CoSi2O7, Ca2MgSi2O7, and Ca2(Mg0.55Fe0.45)Si2O7 have been determined in the temperature range between 297 and 773 K with arbitrary intervals. The structures of the incommensurate
phase of the three compounds are characterized by the presence of the six-, seven-, and eight-coordinated Ca–O polyhedra and
of the bundles along the c-axes consisting of four arrays of the six-coordinated Ca–O polyhedra and an array of T1O4 (T1: Co, Mg, or Mg–Fe) tetrahedra in the structures. The number of bundles in each material decreases at elevated temperatures.
The incommensurate phase undergoes a phase transition into the normal phase at 493 K in Ca2CoSi2O7, at 360 K in Ca2MgSi2O7, and at 510 K in Ca2(Mg0.55Fe0.45)Si2O7. The features of the structures of the normal phase are almost the same as those found in the basic structures (the averaged
structures of the incommensurate structures), and this fact implies that the characteristics of the structures, such as the
six-coordinated Ca–O polyhedra or fragments of the bundles, should be partially preserved at higher temperatures both in the
incommensurate structures and also in the structures of the normal phase. Analyses of anisotropic displacement parameters
clarified that disorder of the modulation waves is developed in the structures at higher temperatures. The evolution of a
disorder in the structures was ascertained by observation of the circular diffuse streaks in the vicinity of the transition
temperature between the incommensurate and normal phases.
Received: 3 July 2000 / Accepted: 26 October 2000 相似文献
5.
In southern Taiwan the initial collision of the Luzon volcanic arc with the passive continental margin of China results in the emergence of an accretionary prism of, predominantly, turbidites in composition, thus providing an appropriate place to study the temporal and spatial variation of deformation during the transition of subduction to arc-continent collision. Field surveys have recently been carried out in slightly metamorphosed rocks along the well-exposed Jinlun-Taimali coast in southeastern Taiwan. Three folding phases are identified in the area. The first phase is characterized by gently dipping but widely distributed phyllitic cleavage (S1). The second phase is represented by sparsely distributed crenulation cleavage (S2) that folded the phyllitic cleavage. The third phase is characterized by E–W trending antiforms (F3) that involved both types of pre-existing cleavages. Restoration of such an antiform in the north using a method proposed in this paper reveals that phyllitic cleavage in the overturned beds dips gently towards the southeast or east-southeast before the antiform, in relation to the first-phase thrusting or folding under regional ESE-WNW compression. From the first to third phase, the maximum horizontal compression underwent an about 90° anticlockwise rotation from ESE-WNW to E–W or NE–SW to N–S, and the deformation depth seems to decrease drastically, in terms of the decreasing proportion of pervasive deformation. All these variations are attributed to the oblique arc-continent collision that exhumed the whole accretionary prism and induced a local stress perturbation in southeastern Taiwan. 相似文献
6.
In this paper we present a method for computing the equilibrium structures and various physical parameters of a primary component
of the binary system assuming that the primary is more massive than the secondary and is rotating differentially according
to the law of the w2 = b0 + b1 × s2 + b2 × s4, w being the angular velocity of rotation of a fluid element distant s from the axis of rotation and b0, b1, b2 suitably chosen numerical constants. This method utilizes the averaging approach of Kippenhahn and Thomas (1997) and the
concept of Roche equipotentials in a manner earlier used by Mohan et al. (1997) to incorporate the effects of rotation and
tidal distortions on the equilibrium structures of certain rotationally and tidally distorted stellar models. The use of the
method has been illustrated by applying it to obtain the structures and some observable parameters of certain differentially
rotating and tidally distorted binary systems whose primary component is assumed to be a white dwarf star. 相似文献
7.
豫西地区中元古代汝阳群砂岩中普遍发育微生物形成的沉积构造(Microbial Induced Sedimentary Strutures),简称MISS构造,这些MISS构造在过去通常被误认为前寒武纪后生动物遗迹化石。本文对豫西地区中元古代汝阳群MISS构造的形态、结构及显微构造特征进行了详细地分析研究,结果表明该区发育的MISS构造有4种类型:多边形网状裂隙构造、纺锤形裂隙、鸟足形裂隙和典型的正弦曲线型Manchuriophycus构造。豫西地区中元古代汝阳群微生物形成的沉积构造的发现,不仅表明这些砂岩层面上曾经存在微生物席活动,对今后与一些微生物席活动有关的沉积构造的研究有着重要的借鉴意义,为过去被误认为各种遗迹化石的修定提供了证据,而且对恢复前寒武纪沉积古地理具有重要的意义。 相似文献
8.
The c. 2060 Ma Phalaborwa Igneous Complex forms an elongate intrusion into Archean granitic gneiss. The carbonatite within the central pyroxenite core of the complex (Loolekop) is well-mineralized in copper. Open pit mining operations started in 1965, followed by underground block caving in 2003. Although little attention has been paid to large-scale structures associated with intrusive phases and mineralization, ongoing infrastructure development and block caving, as part of the new Lift II Project, require far greater resolution of structural discontinuities. 3D modelling of these structures, from over 50 years of data, reveals that Loolekop occurs at the confluence of several major shears or fault zones. Of these, five major structures were pivotal in the emplacement of banded carbonatite, transgressive carbonatite and very late-stage, narrow, E-W trending, sulphide veinlets with short down-dip and along-strike extensions, which form the bulk of mineralization. Modelled structures typically have two or more segments, which are rotated with respect to one another, in turn suggesting repeated rotation or torsion of the entire intrusive volume, aided by cross-cutting structures. The oldest structure is the N-S trending Mica Fault Zone, which shows the same trend as the entire carbonatite complex and the nearby eastern edge of the Kaapvaal Craton and the Lebombo Lineament. The youngest structure is the Central Fault, which shows an E-W inflection that is co-incident with the carbonatite and the E-W, vein-hosted Cu mineralization trend. Based on cross-cutting relationships, sinistral movement along the Central Fault Zone and its localized E-W dilational jog is invoked as a mechanism for transgressive carbonatite emplacement and the introduction of late-stage Cu-rich fluids into numerous tensional veinlets. This shearing would have been caused by an E-W trending maximum principal stress orientation. In turn, this corresponds with the orientation of near-field, eastward-directed stress along the eastern lobe of the Bushveld Complex during its emplacement and subsequent deformation. 相似文献
9.
叙述了采用高强度纤维/环氧树脂复合材料对建筑物进行修复或抗震加固方法的特点、施工方法,实例表明该方法有广泛的应用前景,指出,该方法对保证人民财产安全及搞好防震减灾工作有积极作用。 相似文献
10.