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891.
892.
燕辽地区晚中生代动物君及其古生态和古地理意义 总被引:9,自引:0,他引:9
燕辽地区的中侏罗-早白垩世地层中共有3个动物群贯穿始终,即燕辽动物群、热河动物群、阜新动物群,分别分布于中侏罗世、晚侏罗世及早白垩世,构成多门类化石群的组合序列.根据以昆虫为主的动物群组合序列研究,可以推测中侏罗世燕辽地区处于温带气候条件下,森林沼泽发育,分布广,但水面规模不大,水体不深,地形起伏差异较小,而晚侏罗世相似,陆地植被茂盛,森林极为广布.到早白垩世尼欧克姆期,动物群的种类相对较贫乏,以陆生昆虫为主,出现的昆虫大多为典型亚热带昆虫,说明该地气候仍偏热,但湖泊显著减少,已逐渐向干燥的气候过渡。从昆虫类及其他一些化石的古地理分布特征分析,可以作出如下推断,即:劳亚大陆或欧亚大陆与北美、非洲等大陆分离的最后时限不会早于中侏罗世,以后随着泛大陆解体,昆虫中一些类群(如蚊歇蛉科等)的早期代表扩散到其他大陆,最终现成现今的分布格局。在这一过程中,第三纪白令陆桥虽有一定作用,但并不是主要和唯一的途径。 相似文献
893.
贫信息条件下的多点变形预测模型及其应用 总被引:17,自引:1,他引:17
常用的单点变形分析方法没有利用监测点间相互关系的信息,不足以反映变形体整体的变形规律。本文将单点的变形预测模型扩展为多点的变形预测模型,建立了贫信息条件下的多点预测模型。进行了实例建模与分析,结果表明,多点预测模型为解决少数据,多因子的动态系统预测与分析提供了新的途径。 相似文献
894.
泥炭样品不同有机组分的~(14)C测年的初步研究 总被引:3,自引:0,他引:3
分别用NaClO、NaOH溶液、Na4P2O7和NaOH混合溶液和有机溶剂对采自延庆盆地大王庄两个泥炭样品进行前处理,每个样品获得10个不同有机组分,对这些有机组分的14C年龄测定值进行对比。以探讨泥炭等样品不同有机组分14C测年的可靠性 相似文献
895.
Yin Gongming Xu Xiwei Sun Yingjie Chen Jie and Liu AiguoInstitute of Geology SSB Beijing China 《中国地震研究》1997,(4)
The northern Liulengshan piedmont fault is located along the southern margin of the Yangyuan basin and represents a dip-slip normal fault,generally NEE-trending and NNW-dipping.Landforms offset by the fault are fairly developed and well preserved in the Dushanpu area of Yangyuan County,Hebei Province.Two trenches were excavated in front of a scarp of the northern Liulengshan piedmont fault at Dushanpu and two paleoseismic events were revealed in the trenches,from which several samples were collected for dating.The samples were dated using the IRSL dating technique.The preliminary result shows the possible ages of the two paleoseismic events. 相似文献
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899.
In this paper the incremental nonlinear models are generally discussed, the correlation of this sort of models with others and the difference between them are interpreted, and some basic concepts are clarified. We presented a nonlinear dilatant stress-strain model for soil, which is referred to as KKG model for the sake of simplicity. The experimental results of a sand sample are used to determine the moduli for the following models KKG, KG (the deformation model), and Eν (elastoplastic model) respectively. The comparison of the calculation values of these models with the associated experimental results shows good fittings and prediction of KKG model, and its good simulation of soil dilatant behaviour in particular. The predicted pore pressure and effective stress path have a reasonably good agreement with observed results as well. 相似文献
900.
The effect of the electrical anisotropy on the response of helicopter-borne frequency-domain electromagnetic systems 总被引:4,自引:0,他引:4
Helicopter electromagnetic (HEM) systems are commonly used for conductivity mapping and the data are often interpreted using an isotropic horizontally layered earth model. However, in regions with distinct dipping stratification, it is useful to extend the model to a layered earth with general anisotropy by assigning each layer a symmetrical 3 × 3 resistivity tensor. The electromagnetic (EM) field is represented by two scalar potentials, which describe the poloidal and toroidal parts of the magnetic field. Via a 2D Fourier transform, we obtain two coupled ordinary differential equations in the vertical coordinate. To stabilize the numerical calculation, the wavenumber domain is divided into two parts associated with small and large wavenumbers. The EM field for small wavenumbers is continued from layer to layer with the continuity conditions. For large wavenumbers, the EM field behaves like a DC field and therefore cannot be sensed by airborne EM systems. Thus, the contribution from the large wavenumbers is simply ignored. The magnetic fields are calculated for the vertical coaxial (VCX), horizontal coplanar (HCP) and vertical coplanar (VCP) coil configurations for a helicopter EM system. The apparent resistivities defined from the VCX, VCP and HCP coil responses, when plotted in polar coordinates, clearly identify the principal anisotropic axes of an anisotropic earth. The field example from the Edwards Aquifer recharge area in Texas confirms that the polar plots of the apparent resistivities identify the principal anisotropic axes that coincide well with the direction of the underground structures. 相似文献