深圳地区花岗岩球状风化体地下分布规律统计分析

深圳花岗岩发育地区球状风化体(俗称孤石)广泛分布,对地下工程建设产生了不利的影响.通过对深圳地区花岗岩孤石大样本的统计分析,得到如下统计结论:深圳地区花岗岩孤石主要成份是微风化花岗岩,60％以上分布在强风化花岗岩层中,残积层和全风化层中也有分布,孤石层面分布高程集中在40.00～70.00m(黄海高程)区间内;80％的孤石揭示“厚度”不超过2.50m,三分之二花岗岩孤石主要发育一层,随着发育层数的增多,出现频率锐减.     

广西田林龙江垌上石炭统黄龙组珊瑚礁古生态

广西田林县龙江垌见晚石炭世的珊瑚格架礁,分三层旋回式生长于海百合碎屑滩上。造礁生物为丛状群体珊瑚Diphyphyllum sp.,附礁生物主要是海百合、腕足动物、藻类和有孔虫。造礁生物种群间仅是共同栖息生存,缺乏长期、稳定、复杂的生态关系,礁体生物群落成熟度低,除Diphyphyllum sp.搭建格架外,缺少其他造礁方式,在当时多变的水动力条件下,只形成了未成熟的层礁。对于龙江垌珊瑚礁生态特征形成原因归纳为以下几点:石炭纪中期全球地质构造变化影响、微生物群团和藻类造礁作用不明显、海百合的强大竞争作用使底栖生物群落受到抑制、Diphyphyllum sp.生态特点使其造礁能力差。     

Seismic fragility assessment of low-rise stone masonry buildings

Many historic buildings in old urban centers in Eastern Canada are made of stone masonry reputed to be highly vulnerable to seismic loads.Seismic risk assessment of stone masonry buildings is therefore the first step in the risk mitigation process to provide adequate planning for retrofit and preservation of historical urban centers.This paper focuses on development of analytical displacement-based fragility curves reflecting the characteristics of existing stone masonry buildings in Eastern Canada.The old historic center of Quebec City has been selected as a typical study area.The standard fragility analysis combines the inelastic spectral displacement,a structure-dependent earthquake intensity measure,and the building damage state correlated to the induced building displacement.The proposed procedure consists of a three-step development process:(1) mechanics-based capacity model,(2) displacement-based damage model and(3) seismic demand model.The damage estimation for a uniform hazard scenario of 2% in 50 years probability of exceedance indicates that slight to moderate damage is the most probable damage experienced by these stone masonry buildings.Comparison is also made with fragility curves implicit in the seismic risk assessment tools Hazus and ELER.Hazus shows the highest probability of the occurrence of no to slight damage,whereas the highest probability of extensive and complete damage is predicted with ELER.This comparison shows the importance of the development of fragility curves specific to the generic construction characteristics in the study area and emphasizes the need for critical use of regional risk assessment tools and generated results.     

Effects of land use,slope gradient,and soil and water conservation structures on runoff and soil loss in semi-arid Northern Ethiopia

April lightning production in Richmond County, Georgia, from 1995 to 2003 is considered with regard to the associated risk to golfers and spectators at the Master's Golf Tournament and courses throughout the county. An examination of the April lightning climatology of Georgia, focusing on Richmond County, reveals a minimum in lightning activity during the time of the tournament (the first full week of April). A discriminant analysis of Richmond County lightning production utilizes several meteorological variables in order to discern between three categories of April lightning days: little or no lightning activity, minimal lightning activity, and high lightning activity. The analysis distinguishes relatively well between the categories with only 13.5% of the events misclassified. A composite regional analysis of the three lightning categories illustrates the environmental differences between these events. Although the little or no lightning and high lightning categories are somewhat similar environmentally, the intensity of features separates these events and allows for interpretation. The statistical and synoptic analyses together emphasize the importance of low-level instability and frontal proximity and intensity in enhancing lightning production in thunderstorms during April in and surrounding Richmond County. A multitude of meteorological conditions can lead to thunderstorm development. Localized studies of these environments, especially during times of major outdoor sporting events, are needed to help mitigate the risk associated with lightning.     

P/Ca in coral skeleton as a geochemical proxy for seawater phosphorus variation in Daya Bay, northern South China Sea

The P/Ca ratio in coral skeletons is considered to be a direct proxy for the nutrient P in seawater. We examined the reliability of this proxy by analyzing P/Ca in a Porites coral collected from a eutrophic area in the northern South China Sea. P concentrations were significantly higher compared to previously reported values from pristine and open seas, corresponding to the elevated nutrients from the study site. We compared coral P/Ca against recent in-situ records of seawater P concentrations. Our results show that P/Ca was primarily a function of TP sw rather than PO₄sw, and that the signal of skeletal P included not only phosphate, but also organic phosphorus. Besides the form of skeletal P, sub-sampling and analytical procedures and the distinctive nutrient regime were the most reasonable explanations for our results. We suggest that total P in coral skeletons may be an efficient proxy for seawater P variations and associated phytoplankton dynamics in eutrophic environments.     

Aragonite loss in a cold‐water coral mound: mechanisms and implications

Selective dissolution of aragonitic grains is emerging as a volumetrically significant process that affects a broad range of modern carbonate settings. This study explores mechanisms and implications of aragonite loss in Challenger Mound, a giant cold‐water coral (Lophelia pertusa) mound of Pleistocene age, which lies on the continental slope off south‐west Ireland. A comprehensive sampling scheme allowed the integration of petrographic data with geochemical analyses of sediment and pore water. The mound remains virtually unlithified and consists of stacked, fining‐upward cycles of silty coral floatstone–rudstone and bafflestone grading into wackestone. Whereas calcitic grains appear unaltered, aragonitic grains are corroded and fragmented. Aragonite dissolution is attributed to organic matter oxidation at/near the sediment–water interface and, at greater depths, to the initial stages of bacterially mediated sulphate reduction, when alkalinity production is outpaced by the generation of H⁺. Pore water profiles indicate that undersaturated waters are diffusing towards the mound interior from two centres of sulphate reduction: one located in the upper 10 m of the sediment column and a second that lies below an erosional unconformity which marks the base of the mound. Continued aragonite dissolution is expected to gradually lower the diagenetic potential of the Challenger Mound and delay lithification until deep burial, when solution‐compaction processes come into play. Despite a fundamental role in predestining the final taphonomic and textural characteristics of Challenger Mound, the processes described here are expected to leave little trace in the geological record due to a lack of cementation and calcitization. Assuming that similar processes have been active throughout the Phanerozoic, results imply that the understanding of diagenetic processes in carbonate systems may be incomplete.     

Submerged reefal deposits near a present‐day northern limit of coral reef formation in the northern Ryukyu Island Arc,northwestern Pacific Ocean

High‐resolution single‐channel seismic reflection surveys were carried out in the northern Ryukyu Island Arc during an NT05‐14 cruise of the R/V Natsushima. The survey area is located northeast of Amami Oshima and southwest of Kikai Shima immediately south of the current northern limit of coral reef formation in the northwestern Pacific Ocean. The main purpose of the surveys was to ascertain whether coral reefs formed during glacial periods and, if so, to determine their three‐dimensional distribution. We collected 784 km of high‐resolution single‐channel seismic data during the cruise. The acoustic basement is clearly observed under the Amami Spur, off Amami Oshima. The seismic profiles show two anticlines, each with an axis trending northeast to southwest. Thin Quaternary stratified sediment overlies the acoustic basement in the northwestern and southeastern slope areas, as well as between the anticlinal axes. The stratified sediment can be divided into several sedimentary units. The mound‐shaped reflections are found within the stratified sedimentary units in the central to eastern parts of the spur. Because the mound‐shaped reflections are characterized by strong reflections and chaotic internal structures in profiles, they are considered biogenic ‘reefs’ or banks consisting of coarse‐grained bioclasts. They overlie the acoustic basement or stratified sediment and reach 15 m in thickness and 400 m in width. In contrast, irregularly shaped topographic highs were detected at the shelf edge southwest off Kikai Shima, which are likely to be remnants of coral reefs formed during the last glacial period. Our seismic data indicate probable coral reef formation at low stands during glacial stages, such as the Last Glacial Maximum, even in the northern Central Ryukyus. The occurrence of drowned reefs may indicate that their growth rate was not sufficient to keep up with a rapid rise in sealevel after a glacial period.     

几种具有代表性青田石的矿物学特征初探

对封门矿区七个不同品种的青田石（＂封门青＂＂金玉冻＂＂黄金耀＂＂朱砂＂＂水草＂＂紫罗兰＂＂三彩＂）样品进行X射线粉末衍射、红外光谱、激光诱导离解光谱仪等测试,对其主要矿物组成,矿物组合及颜色成因进行了分析探讨。结果显示,＂封门青＂和＂金玉冻＂均为成分较纯的叶蜡石,属于叶蜡石型青田石;＂黄金耀＂的矿物组合为伊利石＋少量叶蜡石,属于伊利石型青田石;＂朱砂＂的矿物组合为叶蜡石＋石英＋赤铁矿＋高岭石,属于叶蜡石型青田石;＂紫罗兰＂的主要矿物组成是叶蜡石,属于叶蜡石型青田石,其紫色花星成分可能为贫铁蓝线石;＂三彩＂的主要矿物组成为叶蜡石,但其三个不同颜色（灰色,土黄色,黄绿色）部分的矿物组合不同,石英的质量分数较高且结晶较好是＂三彩＂显颗粒感的主要原因。