四川龙门山泥盆纪四射珊瑚     

秦洪宾  蒋飞虎 《地球科学与环境学报》1991,(1)

本文记述了产于四川龙门山地区中、上泥盆统界线附近观雾山组和土桥子组的四射珊瑚。在大量珊瑚标本鉴定的基础上,建立了中泥盆世晚期至晚泥盆世初期的四个四射珊瑚化石组合。根据四射珊瑚的演化规律,确定以Peneckiella珊瑚类的兴起和Pseudozaphrentis hejiazhaiensis,Temnophyllun(Truncicarinulum)beichua-nensis珊瑚类的消失作为龙门山地区识别中、上泥盆统界线的标志。  相似文献   

论弱势群体的法律保护   总被引：3，自引：0，他引：3  

毛晓华 《广东海洋大学学报》2005,25(2):20-23

弱势群体是社会分层的结果,对其进行保护是法律追求正义与秩序的必然要求,具体途径为通过法律再分配社会性资源,缩小强弱差距,保护弱势群体的正当权益。完善我国的弱势群体法律保护制度,须遵循“一个协调,两个结合”的指导原则,即效率与公平相协调,长远措施与短期措施相结合,全面保护与重点保护相结合。  相似文献   

芝罘群岩石地层划分及区域对比          下载免费PDF全文

杨国福  田华  杨夕良 《山东国土资源》2001,17(1):12-18

芝罘群分布于烟台市区北部芝罘岛、崆峒岛、担子岛等岛屿上,自下而上划分为老爷山组、兵营组及东口组.东口组为新建岩石地层单位.该群岩石组合为白云母钾长片麻岩、含电气石钾长石英岩、钾长石英岩、镜铁矿钾长石英岩、石英岩、白云母石英片岩夹黑云片岩、透辉变粒岩及大理岩等.其原岩为富钾、铁、硼的长英质碎屑岩夹粘土岩及富镁碳酸盐岩.兵营组单颗粒锆石U-Pb年龄为2171Ma,其成岩时代属古元古代早期.芝罘群区域上可与辽东地区古元古代榆树砬子群对比.  相似文献   

Three‐dimensional finite element analysis of the interaction between tunneling and pile foundations     

H. Mroueh  I. Shahrour 《国际地质力学数值与分析法杂志》2002,26(3):217-230

This paper concerns analysis of the impact of construction of urban tunnels on adjacent pile foundations. It is carried out using an elastoplastic three‐dimensional finite element modelling. Numerical simulations are performed in two stages, which concern, respectively, the application of the pile axial loading and the construction of the tunnel in presence of the pile foundations. Analysis is carried out for both single piles and groups of piles. Results of numerical simulations show that tunneling induces significant internal forces in adjacent piles. The distribution of internal forces depends mainly on the position of the pile tip regarding the tunnel horizontal axis and the distance of the pile axis from the centre of the tunnel. Analysis of the interaction between tunneling and a group of piles reveals a positive group effect with a high reduction of the internal forces in rear piles. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Sol－gel法制取Al_2O_3系陶瓷涂层的组织与性能     

魏续占 《地球科学与环境学报》1996,(2)

用多种分析手段分析了Ｓｏｌ－ｇｅｌ法制取的Ａｌ２Ｏ３系陶瓷涂层在烧结过程中的组织变化以及烧结后涂层的成分和组织结构；对涂层的高温抗氧化性、耐蚀性、耐磨性以及涂层与金属基体的结合力进行了测试，结果表明，Ｓｏｌ－ｇｅｌ法制取的Ａｌ２Ｏ３系陶瓷涂层由氧化物晶体、过渡相和玻璃体混合而成，涂层与基体之间有很好的结合力，金属基体的抗氧性、耐蚀性、耐磨性能有明显提高．  相似文献   

覆水砂土场地中桥梁群桩基础地震响应离心试验研究     

闫志晓  李雨润  王东升  王永志 《岩土力学》2023,(3):861-872

为探究覆水饱和砂土场地中土-群桩基础-桥梁结构体系动力相互作用规律,自主设计并制作了直（斜）群桩基础-桥梁结构物理相似模型,开展了不同地震动强度和不同特性地震波输入下的离心机振动台试验,分析了群桩基础-桥梁结构动力特性指标,探究了覆水饱和砂土地基超孔隙水压力发展规律和桩-土相互作用动力响应特性。研究结果表明：覆水的存在对地基土-桥梁结构体系的基本周期和阻尼影响很小,但会导致直群桩基础桥梁结构的振动幅值增加20%,而斜群桩基础桥梁结构的振动幅值降低10%;斜群桩基础模型阻尼比是直群桩基础模型的2倍。上覆水导致饱和砂土地基由受低频振动液化深度更大变为受高频振动地基液化深度更大,同时导致小震作用下促进超孔隙水压力发展,而大震作用下则反之。上覆水会增大桥梁上部结构的动力响应和桩身弯矩。上述研究结果可为覆水场地中桥梁工程抗震设计提供关键参考依据。  相似文献   

特高位远程危岩群破坏成因及稳定性评价——以滇东北乌峰山地区为例     

胡君春  彭军  陈志军  焦德光 《地质与资源》2022,31(2):206

特高位远程危岩崩塌具有突发性强、速度快、势能大、摧毁力强、冲击性大、影响范围广等特征. 滇东北地区镇雄县5处危岩位于乌峰山南缘斜坡地带, 地层近水平, 崩塌区地形坡度达70°以上. 崩塌区和危岩区基岩裸露面积为0.07 km², 坡脚与坡顶高差达222 m, 危岩体平均高差159 m, 落石水平最大位移216 m, 属典型特高位远程危岩群. 采用定性和定量方法, 结合内外部条件, 综合分析危岩的10项基本影响因子, 评价其稳定性. 5处危岩在不同工况下稳定性差, 破坏模式为倾倒式, 高速远程动力崩塌易产生碎屑流, 呈散态扇形高速冲击流动, 裸露区面积大, 生态环境脆弱, 亟待治理.  相似文献   

Extinctions, Morphological Gaps, Major Transitions, Stem Groups, and the Origin of Major Clades, with a Focus on Early Animals     

XIAO Shuhai 《《地质学报》英文版》2022,96(6):1821-1829

Systematic extinctions can leave major morphological gaps between living crown-group clades. Such morphological gaps would be perceived, from a neontological point of view, as major evolutionary transitions. In order to fill these morphological gaps and to map the evolutionary steps toward major evolutionary transitions, we need to integrate extinct stem-group taxa in phylogenetic studies. However, the recognition of stem group has not been widely adopted in the study of early animal fossils, despite that all fossils are stem groups at one level or another. Part of the difficulty is that stem groups may not have all features that collectively diagnose the respective crown group, and they can have unique (autapomorphic) features, making them tantalizingly similar to and frustratingly different from the crown group (e.g., stem-group eukaryotes can be prokaryotic and stem-group animals can be protistan). The need to embrace stem groups and to implement the PhyloCode, in order to achieve phylogenetic clarity and to offer key paleontological insights into the origin and early animal evolution, is illustrated in debates on several controversial Ediacaran and Cambrian fossils.  相似文献   

Haitaite-(La), LaU4+Fe3+2(Ti13Fe2+4Fe3+)Σ18O38, a New Member of the Crichtonite Group     

WANG Fenggang  FAN Guang  LI Ting  GE Xiangkun  WU Yu  WANG Tao  YAO Jian 《《地质学报》英文版》2022,96(6):2007-2014

Haitaite-(La), (La, Ce)(U4+, U6+, Fe2+)(Fe3+, Al)2(Ti, Fe2+, Fe3+)18O38, is a new member of the crichtonite group. It is named after the Haita Village in the Miyi County of Sichuan Province, China, where the mineral was discovered. The mineral occurs as black opaque centimeter-sized aggregates in the external contact zone between the Neoproterozoic (~800 Ma) alkali feldspar granite and the Mesoproterozoic (~1700 Ma) micaschist. In the studied sample, haitaite-(La) is associated with other minerals, including ilmenite, magnetite, rutile, zircon, brannerite and uraninite. The new mineral is a black, metallic phase and has a Mohs hardness of 6, with a density of 4.99 g/cm3 (calculated) and 5.03 g/cm3 (measured). Haitaite-(La) is opaque in transmitted light and grayish-white under reflected light, with a reflectivity between 22.5% and 16.42% in the 400–700 nm band (SiC, in the air). The compositions of the mineral were measured by EPMA, the U4+/U6+ ratio was determined by X-ray photoelectron spectroscopy and the Fe2+/Fe3+ ratio was determined by M?ssbauer spectroscopy. Haitaite-(La) is trigonal, belongs to R3ˉ and has unit-cell parameters a = 10.3678(5) ?, c = 20.8390(11) ?, V = 1939.9(2) ?3, Z = 3. The crystalline structure is composed of octahedra with 9 layers of close-packed octahedra (M1, M3, M4, M5), tetrahedra (M2) and contains large 12-coordinated M0 sites.  相似文献   

The Statherian itabirite-bearing sequence from the Morro Escuro Ridge,Santa Maria de Itabira,Minas Gerais,Brazil     

《Journal of South American Earth Sciences》2015

The itabirite-bearing metasedimentary sequence from Morro Escuro Ridge comprises the basal units of the Espinhaço Supergroup and makes up a small tectonic inlier developed during one of the Brasiliano orogenic events (800-500 Ma), amongst horses of the Archean TTG gneisses, including sheared granites of the anorogenic Borrachudos Suite (∼1700 Ma). The metasedimentary rocks are comprised of low-to intermediate-amphibolite facies schists, quartzites, conglomerates and banded iron formation (itabirite) correlatable with the sequences of the Serro Group, which underlies the metasedimentary rocks of the Espinhaço Supergroup in the Serra da Serpentina Ridge. A maximum Statherian deposition age (1668 Ma) was established using SHRIMP U–Pb isotopic constraints on zircon grains from conglomerate and quartzite units overlying the itabirite. The itabirite is predominantly hematitic and its geochemical characteristics are typical of a Lake Superior-type BIF deposited in a platformal, suboxic to anoxic environment distant from Fe-bearing hydrothermal vents. Close to the contact zone with amphibolites of the Early Neoproterozoic Pedro Lessa mafic suite, an increase of the magnetite content and crystallization of metasomatic Mg-hornblende and Ce-allanite can be observed. These mineralogical changes developed preferentially along the igneous contact zone but are probably co-genetic with the formation of alteration haloes in zircon grains during the Neoproterozoic Brasiliano orogeny (506 ± 6 Ma).  相似文献