天水第三系泥岩地球化学特性研究——以梁家山隧道开挖岩样为例

天水地区第三系地层属于西秦岭甘肃群,梁家山隧道洞身穿越天水盆地第三系泥岩,为确定隧道围岩的地质特性,进行了泥岩样品的地球化学成分与矿物成分测试。将梁家山隧道泥岩的测试结果与天水秦安县下山剖面泥岩的结果进行对比分析和相关分析。结果表明:二者之间存在较好的相关性,能够描述梁家山隧道泥岩的地层岩性、区域地质背景及其演化等工程地质特性,为进一步研究天水盆地的物质组成、风化特征、沉积环境和构造背景提供依据。同时也为利用隧道工程修建研究相关地学问题提供范例和基础数据。     

Model Test on Self-Weight Consolidation of the Red Mud Tailings Placed in the Karsts

The management of tailings depends on its consolidation behavior to great extent. The red mud tailings in Pingguo, Guangxi is of high water content and void ratio. The present paper takes the red mud aluminiferous tailings in Pingguo, Guangxi as prototype. Model tests were carried out to study the consolidation behavior of red mud aluminiferous tailings that were landfilled layer by layer. The layered settlement and the water discharge caused by self-weight consolidation were studied. The influence of the latter landfilled layer of red mud on the previous layer was analyzed. The results show that the settlement at the surface with time can be divided into two stages. During the first stage, a thin layer of water appeared and the thickness kept increasing at the top of the mud surface with the particle of red mud sinking. During the second stage, water drained from the mud and settlement developed slowly. Cracks developed at the surface due to evaporation and the red mud near the surface became unsaturated. When the previous landfilled layer consolidated to the degree that the water content was less than 40%, the later landfilled layer of red mud will have little influence on the settlement of previous landfilled layer.     

Semi-analytical solutions for vertically and laterally loaded piles in multilayered soil deposits

In geotechnical practice, it is of considerable importance to assess the behavior of vertical–lateral coupled loading piles in multilayered soil deposits. This study deals with a semi-analytical formulation for the performance of a pile suffering from combined vertical and lateral loads. The emphasis is on quantifying the mobilization of the subgrade reaction provided by the layered soil stratums. In the proposed method, subgrade reactions, correlated with both the accumulative axial load transfer and side resistances depending upon the pile–soil interaction, are abstracted as a series of nonlinear springs in both vertical and lateral directions. On account of this, an alternative transfer matrix method is applied to characterize the pile reaction along the depth under the identified boundary conditions atop the pile; meanwhile, the condition of static equilibrium, between two specific pile segments located at the border of soil layers, is also essential. On this basis, validation of the solution is conducted by comparing with observations from experiments and predictions obtained from other existing methods. In addition, the influence of properties in shallow soil layer and the vertical load on the lateral response of the pile is also discussed. The results indicate a reduction in the lateral displacement and the maximum bending moment within the pile with the increase in the shallow soil stiffness, but a growth with the increase in vertical load due to the “P-Δ effect.”     

湖南省岳家桥典型岩溶发育区电性特征及构造格架研究

为探讨湖南省益阳市岳家桥地质灾害现状,以区内典型岩溶发育区为研究对象,通过长剖面高密度电法、视电阻率联合剖面法等地球物理方法,研究了地层电性响应特点,利用钻孔数据和综合电法勘探数据建立了三维地层结构模型,揭示了典型区域近地表电性结构形态,构建了区内三维地层构造格架,圈定了岩溶发育范围,并评价了地质灾害程度.研究表明:因地制宜地利用综合电法勘探,有助于在我国南方含水较多的岩溶发育区快速、有效地进行灾害范围的圈定和评价.     

Zircon U-Pb Geochronology,Geochemistry and Petrogenesis of Early Cretaceous A-type Granites in the Mikengshan Area,Southern Jiangxi ProvinceEI北大核心CSCD

In the Mikengshan-Yanbei area, a special region for the tin mineralization in South China, there are some Yanshanian granites and porphyries and associated porphyry tin deposits (e.g., Yanbei). Although the tin mineralization is closely associated with the granitoids magmatism, the age and petrogenesis of the granites remain controversial. The Mikengshan pluton, which intrudes into the rhyolitic tuff and pyroclastic rocks of the Upper Jurassic Jilongzhang Formation, is the largest one in Mikengshan-Yanbei area and mainly consists of K-feldspar bearing granites. In this study, we report new age and geochemical data for the Mikengshan K-feldspar bearing granites. LA-ICP-MS zircon U-Pb age dating shows that they were generated in the Early Cretaceous (~138 Ma). They have high SiO2 (74.42% to 76.69%), low Al2O3 (12.39% to 13.49%) and Mg# (11 to 19), and negative Eu, Sr and Ba anomalies, and are rich in potassium (most K2O/Na2O=1.37 to 1.94) and high field strength elements (HFSEs), and are weakly peraluminous (A/CNK=1.03 to 1.1) with high 10000×Ga/Al ratios (3.46 to 4.96) and slightly high zircon saturation temperatures (807 ℃ to 817 ℃), showing the characteristics of the typical A-type granites. Moreover, they have high Rb contents 842×10-6 to 1295×10-6, Rb/Sr (90 to 255) ratios and show rare earth elements (REE) tetrad effect, which are similar to those of high fractionated granites. Thus, we suggested that the Mikengshan K-feldspar bearing granites are high fractionated and aluminous A-type granite. Their slightly high εNd(t) values (-3.4 to -4.6) indicate that the mantle components should have played a role during their formation. Taking into account regional igneous rocks and tectonic setting data, we suggest that the Mikengshan K-bearing granites were formed in an extensional setting, which was probably related to the roll-back of the subducted Paleo-Pacific plate. © 2018, Science Press. All right reserved.     

Internal Microanatomy and Zoological Affinity of the Early Cambrian Olivooides

The early Cambrian pentamerous microfossil Olivooides/Punctatus in South China, which is characterized by a diagnostic stellate tubular apex, has been well-known for its almost complete development sequence that can be confidently traced from embryos and hatched juveniles, to conical adults. However, its zoological affinity remains highly controversial. Here we describe the internal microanatomic structures of the soft-body inside the peridermal theca of Olivooides multisulcatus Qian, 1977, including interradial pairs of tentacles, adradial and perradial frenula, perradial oral marginal lappets and twins of perradial gastric saccule-like humps as well as a circular velarium with striated coronal muscles. Particularly, one specimen shows bifurcated velarial canals along the bell aperture. Both the components of the soft-body and the external theca (or cyst) are arranged in perfect pentaradial symmetry. These characteristics are more compatible with those of living cubomedusans and co-occurring Cambrian athecate embryonic cubozoans. Concerning the presence of peridermal theca, Olivooides most likely represents an extinct thecate stem-group cubomedusae but devoid of both perradial eyes and specialized pedalia. The well-grown soft body inside the peridermal tube displays a set of mixed features of both polyp and medusa.     

Mathematica软件在计算有限单元法系数矩阵中的应用

以一维分层连续介质大地电磁有限元模拟为例,应用Mathematica软件计算系数矩阵。节约了大量的推导时间。确保快速、准确地得到有限元系数矩阵。展示了mathematica软件在计算有限单元系数矩阵中的强大功能。     

大芦家地区渐新统东二1亚段三角洲前缘砂体微相及储集性研究

通过岩芯、录井、测井资料的综合分析,发现大芦家地区渐新统东二段主要由三角洲前缘亚相组成,砂体的成因类型主要包括三角洲前缘亚相的河口坝、水下分流河道、水下天然堤和决口扇、席状砂、远砂坝。它们不仅具有各自独特的沉积特征和测井相特征,而且其空间储集物性的分布也各不相同。此外,它们还具有较强的层内非均质性,层间非均质性和平面非均质性却较弱。     

Determination of groundwater recharge regime and flowpath in the Lower Heihe River basin in an arid area of Northwest China by using environmental tracers: Implications for vegetation degradation in the Ejina Oasis

Environmental tracers (CFCs, stable isotopes ¹⁸O, ²H, and ³H) and major ions were employed to study river infiltration and groundwater recharge in the aquifer system in the basin of the Lower Heihe River, Northwest China. Three groups of waters have been recognized: (1) young groundwater, connected to the river, with large variation of CFC apparent ages ranging from <10 a to 40 a, and δ¹⁸O and δ²H values which are similar to the river water; (2) regional background water, unaffected by the river, having CFC apparent ages >40 a, and being depleted in ¹⁸O and ²H compared with the river water; and (3) groundwater in Gurinai, a grassland located about 100 km from the river, in which the predominant discharge is from the Badain Jaran desert, with CFC apparent ages ranging from 25 to >50 a and being enriched in ¹⁸O and ²H compared to the river water. The groundwater along the river contains CFCs and ³H down to depths of about 120 m, and the shallow groundwater exhibits CFC apparent ages in a wide range which are not dependent on the well depth. Groundwaters along the river show a similar trend of enrichment in ¹⁸O and ²H as the river water whereas groundwaters in depression cones are depleted in heavier isotopes, and have low CFC and ³H concentrations. The CFC apparent age of the groundwater increases with increasing distance downstream, indicating that the dominant part of the groundwater is from infiltration of river water in the upper reaches. Modifications of groundwater recharge are reflected in variations of stable isotope compositions, as well as CFC and ³H concentrations in the groundwater that was recharged from the river over the last decades. Despite recharging from river water, groundwater abstraction has induced a water balance deficit. The riparian ecosystem in the Ejina Oasis is constrained by both decreased river flow and increased groundwater abstraction. The vegetation degradation in the Ejina Oasis is controlled not only by natural aridification but also worsened by heavy groundwater abstraction and decreased river flow.     

广西糖料蔗寒冻害风险评估与风险区划研究

基于广西1961~2013年冬季寒冻害过程最低气温资料、地理信息数据及地表反射率资料,采用统计学中的多元回归法,构建了基于地理信息与地表反射率相耦合的最低气温降尺度模型及区域250m×250m网格点逐年冬季寒冻害过程最低气温数据库。在此基础上,结合糖料蔗寒冻害等级指标,对广西区域糖料蔗寒冻害时空分布特征进行了分析,并编制了广西区域糖料蔗不同寒冻害等级频率图及糖料蔗寒冻害产量损失率图,同时对广西糖料蔗寒冻害风险等级进行划分及评述。这一结果对糖料蔗种植优化布局及政策性农业保险费率的确定有积极意义。