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991.
Petrographic and geochemical characteristics of the Upper Triassic sandstones in the western Ordos Basin were studied to provide insight into weathering characteristics, provenance, and tectonic implications. Petrographic features show that the sandstones are characterized by low-medium compositional maturity and textural maturity. The CIA and CIW values reveal weak and moderate weathering history in the source area. The geochemical characteristics together with palaeocurrent data show that the northwestern sediments were mainly derived from the Alxa Block with a typical recycled nature, while the provenance of the western and southwestern sediments were mainly from the Qinling-Qilian Orogenic Belt. The tectonic setting discrimination diagrams signify that the parent rocks of sandstones in the western and southern Ordos Basin were mainly developed from continental island arc, which is closely related to the evolution of the Qinling-Qilian Orogenic Belt. However, the sandstones in the northwestern Ordos Basin show complex features, which may be resulted from a typical recycling process. Overall evidence from petrography, geochemistry and sedimentology, together with previous researches suggest the Kongtongshan and Helanshan areas were the southwestern and northwestern boundary of the Ordos Basin, respectively, and there was no clear boundary between the Hexi Corridor Belt and Ordos Basin, where a large, uniform sediment dispersal system developed during the Late Triassic. 相似文献
992.
柴西南英西地区下干柴沟组上段为一套湖盆含蒸发岩系。文章综合运用薄片、岩心、钻井、测井、化验分析等资
料,对研究区下干柴沟组上段蒸发岩系沉积旋回特征进行了研究。研究表明,平面上由盆地中心向边缘呈现蒸发岩-混积
型碳酸盐岩-碎屑岩的环带状分布,纵向上发育2 个三级旋回及6 个四级旋回期次。各级蒸发岩沉积旋回具有不对称的特
征,即快速湖侵、缓慢湖退。总结出研究区的五种蒸发岩岩相组合类型。研究区蒸发岩为气候干旱、盆地基底快速沉降背
景下,湖退时残留盐湖中以蒸发结晶为主具有一定水深的成因,并建立了沉积旋回发育模式。 相似文献
993.
994.
本文利用古生态研究方法对龙潭组的Taihuellafauna和长兴组的Reichelinafauna等动物群在壳体特征变异和演化阶段上进行了系统的研究与探讨,发现该动物群受地壳运动所造成古环境变迁和沉积岩相的变化所控制,阐述了浙北类在发展上的某些规律,为建立生物系统演化序列和地层沉积模式及准确地划分与对比地层等方面提供了依据。 相似文献
995.
F. J. Bloore 《Mathematical Geology》1981,13(5):461-463
The existence of an angle of repose for sand implies that, in any given wind regime, there is at least one configuration of sand dunes which will not be altered by that wind regime. The existence of implies that the land forms constitute a convex compact subset of a Banach space, and the result then follows from Shauder's theorem. 相似文献
996.
The upper mixed layer (UML) depth obtained from temperature is very close to that from density:the maximum is about 15m. This indicates that temperature is a good indicator of mixed layer during measurements. When the surface heat flux is balanced by a cross-shore heat flux, the surface mixed layer depth obtained from the WM model (Weatherly and Martin, 1978),hPRT, is roughly the same as observed. The mixed layer depth calculated from the PWP model (Price, Weller and Pinkel, 1986) is close to the depth obtained from thermistor chain temperature data. The results show that both the WM model and PWP model can provide a good estimate of stratification in the study area during the cruise. The value of log( h/u3) is about 9.5 in the study area, which shows that the study area is strongly stratified in summer. Observations on the northern Portugal shelf reveal high variability in stability, giving rise to semi-diurnal, semi-monthly and diurnal oscillations, and long term variations. The fortnightly oscillatio 相似文献
997.
998.
通过对山东蒙阴金伯利岩中富含硅酸盐不相容元素的锶钛铁矿族(LIMA系列)、磁铁铅矿族(HAYI系列)矿物及其相关的钛氧化物矿物的探针成分分析,对比南非Debeers,Jagersfontein及Bultfontein等地金伯利岩区的相似矿物研究,发现这类矿物的产出、相互关系及化学成分非常相近,与共生的金云母、碱性闪石等含水矿物一起,反映了富K,Ba,Ti,Zr,Nb,REE等不相容元素的流体对先前亏损的方辉橄榄岩的交代作用.LI-MA,HAYI系列矿物是流体对镁钛铁矿、铬尖晶石等的继承交代产物.不相容元素的局部富集还可形成一些罕见的矿物相,如REE-Ti及Zr-Ti氧化物.与之相关的呈海绵边或基质、空洞充填产出的钙钛矿、富锰钛铁矿、富锰锌尖晶石、柱红石、铬阿玛科矿等,则与碳酸盐化及金伯利岩岩浆晚期不相容元素的浓聚有关.对这类矿物化学成分及相互关系的研究,不但从微观角度揭示了不相容元素在部分上地幔岩石中的富集,提供了卷入交代流体的总成分目录,而且表明南非和山东金伯利岩地球化学性质的相似性 相似文献
999.
Johana Brokešová 《Pure and Applied Geophysics》1996,148(3-4):503-538
The seismic wave field, in its high-frequency asymptotic approximation, can be interpolated from a low- to a high-resolution spatial grid of receivers and, possibly, point sources by interpolating the eikonal (travel time) and the amplitude. These quantities can be considered as functions of position only. The travel time and the amplitude are assumed to vary in space only slowly, otherwise the validity conditions of the theory behind would be violated. Relatively coarse spatial sampling is then usually sufficient to obtain their reasonable interpolation. The interpolation is performed in 2-D models of different complexity. The interpolation geometry is either 1-D, 2-D, or 3-D according to the source-receiver distribution. Several interpolation methods are applied: the Fourier interpolation based on the sampling theorem, the linear interpolation, and the interpolation by means of the paraxial approximation. These techniques, based on completely different concepts, are tested by comparing their results with a reference ray-theory solution computed for gathers and grids with fine sampling. The paraxial method holds up as the most efficient and accurate in evaluating travel times from all investigated techniques. However, it is not suitable for approximation of amplitudes, for which the linear interpolation has proved to be universal and accurate enough to provide results acceptable for many seismological applications. 相似文献
1000.
Abstract The Senonian Ophiolitic Mélange of the Ankara Mélange Supergroup includes numerous blocks of radiolarian cherts. These blocks contain various radiolarian assemblages from the Albian to the Turonian ( Pseudodictyomitra pseudomacrocephala, Thanarla tieneta) , the Lower Cretaceous ( Thanarla conica, Alievium helenae, Pseudodictyomitra carpatica) , the Kimmeridgian-Tithonian ( Ristola altissima, Sethocapsa cetia, Podocapsa umphitreptera) and the lower Jurassic ( Parahsuum simplum). Upper Norian radiolarians were obtained from two of these blocks. The assemblage is represented by Betraccium deweveri Pessagno and Blome, Ferresium triquetrum Carter, Pylostephanidium ankaraense n. sp. (Genus Pylostephanidizi was formerly unknown in the upper Triassic) and other taxa. Thus, upper Norian fauna of Turkey exhibits close similarity to the radiolarian assemblages of western North America, Eastern Russia, Japan and the Philippines. This provides further evidence for the correlation of Mediterranean and Pacific Triassic sequences. These data allow for the conclusion that the sedimentation of radiolarian cherts was common in this part of Tethys during the Late Triassic and the Jurassic. 相似文献