Structural evolution of the Téfidet trough (East Aïr,Niger) in relation with the West African Cretaceous and Paleogene rifting and compression episodes

Located in northern Niger, the NW–SE Téfidet trough is the western branch of the Ténéré rift megasystem.Here we present a tectono-sedimentary analysis of the Téfidet trough, based on the combined use of satellite imagery, field observations and measures, and available literature. We use these data to analyse the sedimentary facies and the tectonic deformations (faults, folds, basins) in the Téfidet trough, and derive their relative chronology. Doing so, we characterize synrift and postrift deformations and their interactions with sedimentation.Altogether our analyses suggest that the Téfidet trough was affected from the Cretaceous to the Paleogene by three major tectonic periods.

• •The first period was a rifting stage with extension and transtension during the Albian–Aptian times. The mean extension was ∼N60° and dominantly produced NW–SE-trending normal faults, a few strike-slip faults locally associated with small folds with sigmoidal axis and small reverse faults, and progressive unconformities.
• •the second period was also a rifting time, which prevailed during the Upper Cretaceous. The regime was marked by transtensional to extensional tectonics, under a ∼N130° shortening and a ∼N60° trending stretching. The end of this period saw the closure of the Téfidet trough.
• •the third period was a postrift stage. It was characterized by a ∼N70° extensional to transtensional regime during the Oligocene–Pliocene. It mainly produced post-sedimentary extensional faults and fractures and alkaline volcanism. We eventually discuss these deformation phases in relation with the Cretaceous Gondwana breakup and its related rifting events in West and North Africa, and with the subsequent Africa–Europe collision.

     

南水北调中线西四环暗涵工程暗挖施工对环境的影响研究

以南水北调中线北京段西四环暗涵工程为研究背景,通过详细分析在复杂工程环境下进行浅埋暗挖施工对既有工程环境产生的严重影响及关键控制因素,得到有效控制暗挖施工对既有环境影响的措施,如初期支护方案的勘测设计方法、施工控制监测措施、监测控制效果分析检验等。实践证明,既使是在复杂的工程环境下,地下岩土工程开挖影响也可以得到有效控制。     

Interaction of Oblique Waves and A Rectangular Structure with An Opening Near A Vertical Wall

With the method of separation of variables and the eigenfunction expansion employed, an analytical solution is presented for the radiation and diffraction of a rectangular structure with an opening near a vertical wall in oblique seas, in which the unknown coefficients are determined by the boundary conditions and matching requirement on the interface. The effects of the width of the opening and the angle of incidence on the hydrodynamic characteristics of a rectangular structure with an opening near a vertical wall are mainly studied. The comparisons of the calculation results with wall-present and with wall-absent are also made. The results indicate that the variation trends of the heave added mass and excitation force with wall-present are almost the same as those with wall-absent, and that the peak values in the former case are obviously larger than those in the latter due to the reflection of the vertical wall.     

南水北调中线工程对汉江中下游流域生态环境影响的综合评价

南水北调中线工程的实施,对汉江中下游流域的生态环境会造成一系列的影响,对其进行综合评价具有重要意义。在探讨评价指标体系建立原则的基础上,构建了南水北调中线工程对汉江中下游流域生态环境影响的综合评价指标体系;对各指标的影响分值进行了计算,并采用层次分析法了计算各指标的权重,在此基础上采用指标加权求和法对生态环境影响进行综合评价。评价结果表明:南水北调中线工程的实施,对汉江中下游流域生态环境的综合影响程度为-37.91%～-64.46%,相比调水前,生态环境处于强烈或明显负影响状态;分变量的影响程度排序依次为水质变量、土壤地质变量、社会生产变量、水生生物变量、水资源变量和气候变量,其中对水质变量、土壤地质变量、社会生产变量和水生生物变量的影响幅度上限均超过了-40%,对水资源变量的影响幅度也超过了-20%,影响较大,而对气象变量的影响幅度几乎为零。     

关于裂纹柱壳韧性断裂的研究

本文基于实验结果,利用壳单元有限元方法,对周向壁穿裂纹圆柱壳在不同初始裂纹长度条件下的弯曲韧性断裂进行了模拟,计算了裂纹尖端张开位移（ＣＴＯＤ）的裂纹起裂临界值以及裂纹连续扩展条件下裂纹尖端张开角度（ＣＴＯＡ）Ｒ曲线,考察了这些断裂参数作为材料特性的适用性。     

Consequences of artificially opening coastal lagoons on their fish assemblages

The consequences of artificially opening lagoon entrances on the fish assemblages of coastal lagoons in south-eastern Australia were investigated. Impacts of lagoon opening were assessed by comparing changes in the fish assemblages of Werri and Shellharbour Lagoons, both of which intermittently opened to the sea with that of Lake Illawarra, a third coastal lagoon which remained closed during the study period. Numbers of fish species and individuals did not differ significantly after lagoon openings at Werri Lagoon and Shellharbour Lagoon. However, higher numbers of species and individuals were found in Lake Illawarra before the other lagoons had opened. Abundances of some economically significant species (namelyMugil cephalus, Myxus elongatus andLiza argentea) significantly increased after openings, mainly due to small juveniles (<40 mm FL) recruiting to the seagrass beds. In contrast, these species were caught as larger juveniles (>70 mm FL) in Lake Illawarra. Furthermore, their abundance in Lake Illawarra declined during successive months, coinciding with declining salinity. Abundances of resident species (such asPseudomugil olorum andAfurcagobius tamarensis) remained largely unchanged after openings. Although it was clear that marine-spawning species must benefit from lagoon openings, the number and composition of species able to move into lagoons from adjacent waters may be dependent upon the frequency, duration and time of year that the entrance is connected to the sea. The present study thus provides data which may be useful for fisheries management in intermittently open lagoons. However, these results should not be cited as reason to artificially open lagoon entrances as further detailed studies of other aspects of lagoon biota, such as their invertebrate and avian faunas, are also needed to provide sufficient basis for broader management frameworks.     

一种简单的岩体地下洞室地震安全评价方法

提出了动应力集中因子代表值的概念,以合理反映地震荷载作用下地下洞室围岩的动应力集中程度,并将动应力集中因子代表值,作为洞室地震响应的关键特征来衡量洞室地震响应的大小。应用显示有限差分法,讨论了地震动加速度幅值、洞室埋深、围岩岩体级别、衬砌混凝土厚度、衬砌混凝土强度等级与动应力集中因子代表值的相关关系。研究表明,动应力集中因子代表值与这5个因素均近似呈线性关系。在此基础上给出了有（无）衬砌支护结构两种情况的地震安全评价公式,提出了岩体地下洞室的地震安全评价方法。应用提出的评价方法,分别对唐山余震地震作用下溪洛渡水电站超大型地下洞室群的地震安全性进行了评价,所得结果与Dowding-Rozen及Sharma-Judd的评价方法结果一致。分析还表明,文中提出的岩体地下工程的地震安全评价方法的评价结果是偏于安全的。     

南水北调中线干渠浮游植物群落时空格局及其决定因子

为了解南水北调中线干渠浮游植物群落的时空格局,自2018年8月开始分4个季度对干渠沿程的11个样点进行采样调查,同步开展水环境调查;共检出浮游植物7门83属145种,物种丰富度上,硅藻种类数最多,绿藻和蓝藻分别占第2和第3位,且春季＞秋季＞冬季＞夏季;优势种包括极小曲丝藻(Achnanthidum minutissim...     

节理围岩特性及其锚固效应模型试验研究

通过堆砌尺寸为１８０ｃｍ×１４０ｃｍ×１５ｃｍ的大比尺结构模型，依据两组正交节理的不同倾角和间距、地应力及洞周有无锚杆等不同组合的１６种工况进行地下洞室分步开挖模型试验，研究节理对洞室围岩变形破坏的影响及锚杆对节理围岩的锚固效应．试验首次应用ＣＣＤ画像处理法和光学照相法进行位移观测．结果表明，岩体的变形大部分是由节理变形引起的，围岩塌落区完全由开挖自由面与节理的不利组合所控制，围岩变形主要由洞室尺寸、节理倾角及间距、地应力等决定．锚杆能大幅度减少围岩的变形破坏，垂向位移减少更甚，预应力锚杆使围岩变形进一步减小．     

桐柏-大别造山带加里东期构造热事件及其意义

桐柏－ 大别造山带是多旋回发展的复合造山带,至少有晋宁期、加里东期和印支期三个造山旋回。加里东旋回结束洋壳发展历史,经历了广泛的区域变质作用和局部强烈的高压超高压变质作用,具有划时代意义。桐柏－ 大别造山带加里东期具小洋盆、微古陆、多岛海古地理面貌,总体向北俯冲,最终形成陆 陆碰撞造山带。进一步可划分为三个各具特色的单元：北淮阳构造带是一个板块碰撞混杂带;中间隆起区相当于岛弧性质,但它部分地段曾一度伴随小洋盆俯冲至深处,形成高压超高压变质带;随应褶皱带为大陆裂谷性质,并具某些弧后盆地特征。它们共同构成了大陆造山带复杂的内部结构构造特征。桐柏－ 大别造山带向东被后期的郯庐断裂所截;向西与秦岭造山带相连。通过区域地质和古地磁对比,加里东期秦岭造山带开裂规模更大,蛇绿岩更发育,构成一个向西开口的喇叭形;碰撞时大别造山带先碰,然而逐渐向西迁移