川西甘孜黄土磁性地层学研究及其古气候意义^*   总被引：11，自引：12，他引：11       下载免费PDF全文

乔彦松  赵志中  王燕  王书兵  傅建利  李朝柱  蒋复初 《第四纪研究》2006,26(2):250-256

文章对川西甘孜地区甘孜寺剖面进行了系统的磁性地层学研究及石英颗粒表面形态特征分析。磁性地层学研究结果显示,B/M界线出现在S₈的顶部,并且在剖面下部12.7~14.0m处出现了松山负向期的贾拉米洛正向极性亚带。本次测试以及结合以前的研究结果表明,甘孜地区典型的风尘堆积形成于约1.15MaB.P.以前。石英颗粒表面形态特征的分析结果说明风尘物质可能经历了风、流水、冰川等多种外动力作用,进一步证明该区的风尘物质主要来源于青藏高原及其周缘地区的冰水沉积。另外,研究结果指示青藏高原及其周缘地区的环境状况大约在1.15MaB.P.发生了很大变化,主要表现为干旱化程度以及高原冬季风的明显增强,而这些变化又与青藏高原在该时期的快速隆升密切相关。磁性地层的研究结果将为在该区进一步开展古环境演化过程的对比分析及阶地地貌发育历史的研究奠定基础。  相似文献   

On laboratory studies of grains from outside the solar system     

U. Ott 《Journal of Earth System Science》1998,107(4):379-390

An overview is given of the identified surviving presolar grains in primitive meteorites. Two of these phases are discussed in more detail: (a) Presolar silicon carbide, with special emphasis on heavy element isotopic compositions which trace the slow neutron capture process (s-process) of nucleosynthesis. It is argued that there are problems either with the grain or neutron capture cross section data or with current basic understanding of heavy element nucleosynthesis, (b) Presolar diamonds, where new developments are discussed concerning the origin of the (supernova) Xenon-HL component thought to be contained within them; in addition, arguments are presented in favor of diverse carrier phases for the various Xe components observed in diamond separates.  相似文献   

澜沧江流域主要断裂断层泥中石英碎砾表面SEM特征及其断裂活动研究   总被引：3，自引：1，他引：3  

俞维贤  安晓文  李世成  周瑞奇  杨继武 《地震研究》2002,25(3):275-280

根据断层泥及地层中石英碎砾表面SEM结构特征的研究，澜沧江断裂带早，中更新世是其主要活动时期，晚更新世活动减弱，全新世以来基本不活动；澜沧－勐遮断裂，孟连断裂晚更新世以来至全新世仍明显活动；木戛断裂，谦迈河断裂，平掌寨断裂及贵基处－瓦窑断裂晚更新世后期以来基本不活动。因此澜沧－勐遮断裂，勐连断裂术及相关地区未来地震地质灾害频度相对较高。  相似文献   

Palynology of Upper Cretaceous (uppermost Campanian–Maastrichtian) deposits in the South Yellow Sea Basin, offshore Korea     

Sangheon Yi  D. J. Batten 《Cretaceous Research》2002,23(6):687

Forty-seven samples from Upper Cretaceous sections penetrated by the Kachi-1 and Inga-1 wells in the South Yellow Sea Basin have been analysed for their spore and pollen content. Thirty-five species of 18 spore genera and 54 species of 28 pollen genera are documented. One new monotypic genus, Diporocolpopollenites, and its type species, D. kachiensis sp. nov., are erected, and Dilwynites Harris, 1965, and its type species, D. granulatus Harris, 1965, are emended. There are also three new combinations: Ephedripites eocaenicus (Selling, 1944), E. praeclarus (Chlonova, 1961), and Retitricolpites anguloluminosus (Anderson, 1960). Two palynological zones are erected: anAquilapollenites attenuatus Assemblage Zone, which encompasses deposits that are considered to be latest Campanian–Early Maastrichtian in age, and an Aquilapollenites eurypteronus Assemblage Zone for sections that have been dated as Late Maastrichtian. The assemblages are typical of the Yenisey-Amur Subprovince of the Aquilapollenites (floral) Province. Lowland floodplain to shallow, commonly mesotrophic, lacustrine environments of deposition are indicated. The climate was probably wet subtropical, with rainfall being somewhat higher during the Late Maastrichtian than through the latest Campanian–Early Maastrichtian.  相似文献   

Optical properties of inhomogeneous media: T-matrix approach (Review)     

P. Bussemer 《Astronomische Nachrichten》1989,310(4):311-314

In der vorliegenden Arbeit wird eine Übersicht darüber geben, wie man die effektive dielektrische Funktion, welche die optischen Eigenschaften heterogener Medien charakterisiert, berechnet. Für Inhomogenitäten kleiner als die Lichtwellenlange kann das entsprechende quasielektrostatische Problem in eine Integralgleichung umgeformt werden, welche die Anwendung des von der Festkörpertheorie her bekannten T-Matrix-Formalismus zur Berechnung von gestattet. Es werden unterschiedliche Näherungen für die T-Matrix diskutiert, die zu unterschiedlichen Effektiv-Medium-Theorien wie die Näherung der mittleren T-Matrix (ATA) oder die Näherung des kohärenten Potentials (CPA) führen.  相似文献   

非等轴颗粒付林图解   总被引：3，自引：0，他引：3  

徐兴旺  马天林  孙立倩  尚玲 《地质力学学报》1997,3(1):63-70

非等轴颗粒付林图解由直线a=1、b=1、a=b和曲线a2b=1、ab2=1分割成10个微区,并对应于不同的e_x、e_y、e_z组合和应变类型。这些直线和曲线分别对应于特殊的e_x、e_y、e_z组合和岩石应变类型。岩石的应变类型有18种。函数a.b的表征方程有4种类型,并分别表征直线a=1/k₁和b=1/k₂所分割的4个区间。a,b表征方程的确定取决于岩石总的变形行为。此图解可用于非等轴颗粒标志体应变测量和应变类型的确定和图示,文章给出了应用实例.   相似文献   

Laboratory and theoretical evaluation of impact of packing density,particle shape,and uniformity coefficient on erodibility of coarse-grained soil particles     

Hyunwook Choo  Qian Zhao  Susan E. Burns  Terry W. Sturm  Seung Ho Hong 《地球表面变化过程与地形》2020,45(7):1499-1509

Sedimentation – including erosion, transport, and deposition of coarse-grained particles – is a primary and growing environmental, engineering, and agricultural issue around the world. Soil erosion occurs when the hydrodynamic force induced by flowing water exceeds the geotechnical resistance of soils, as measured by critical shear stress for initiation of soil-particle motion. Even though various quantitative methods have been suggested with respect to different types of soil, the most widely accepted formula to estimate critical shear stress for coarse-grained soil is a direct function of the median grain size of the soil particles; however, the erosion resistance of soils also varies with other geotechnical properties, such as packing density, particle shape, and uniformity coefficient. Thus, in this study, a combined rolling–lift model for particle detachment was derived based on theoretical analysis. A series of experimental flume tests were conducted with specimens prepared with standard soil types, as well as laboratory-prepared mixtures of coarse-grained soil to validate the theoretical model and determine the effect of other geotechnical properties on the erosion characteristics of coarse grains, coupled with the effect of median particle size. The results indicated that the median grain size is the primary variable determining the resistance of coarse grains, but the critical shear stress also varies with the packing density of the soil matrix. In addition, angular particles show more erosion resistance than rounded particles, and the erosion potential of a soil decreased when the grain is well graded (higher value of uniformity coefficient). Additionally, regression analysis was performed to quantify the effect of each parameter on the critical shear stress of coarse grains. © 2020 John Wiley & Sons, Ltd.  相似文献   

会同县漠滨金矿“聚集式”乳滴状自然金及其成因初探     

余大龙 《湖南地质》1989,8(3):54-57

漠滨金矿的可见金中,有一种呈聚集式乳滴状结构的自然金集合体。本文就其形成机理进行了探讨。这种结构显示的自然金的运动趋势和历史,为原生粗粒金的形成提供了一种可以探讨的途径。  相似文献   

金矿物统计研究中容易忽略的问题   总被引：4，自引：2，他引：2  

韦龙明 《地质与勘探》2000,36(1):29-30

当前的金矿物统计工作大多局限于颗粒数百分比计算,而且常常把粒比简单地等同于重量比,这在理论上的实践上均是错误的。金矿物配分的本质是重量上的配分。根据物质的三维尺度特性,在光片中可以用面积比代替重量比;而在重砂分析中应尽量直接测定金矿物的质量,否则只能用体积比代重量比。  相似文献   

风尘堆积物中石英颗粒表面微结构特征及其沉积学指示   总被引：9，自引：1，他引：8  

孙有斌  安芷生 《沉积学报》2000,18(4):506-509

通过对黄土-沙漠交接带的定边县、黄土高原中部偏南的灵台县表土样品及甘肃灵台剖面不同层位的黄土-古土壤-红粘土样品中石英颗粒的形态特征及表面微结构的观察测试,结果表明红粘土、古土壤及灵台表土原样中石英颗粒表面具有较丰富的次生硅质沉淀和明显的溶蚀痕迹,指示了碎屑石英在沉积之后,由于适宜的温湿气候条件而经历了较强烈的风化成壤改造作用;而定边县表土样及上粉沙层(L9)土样中的石英颗粒表面干净,具有较多的撞击浅坑等风力搬运痕迹。经过双氧水和盐酸清洗过后的石英颗粒的形态特征及表面微结构非常清晰,多为次棱角至次圆状,均具有较丰富的撞击麻点和浅坑,少数样品可见裂纹分布,说明红粘土和上覆的黄土和古土壤一样,主要为风力搬运堆积;但红粘土样中石英颗粒表面所具有的丰富硅质沉淀和明显的溶蚀痕迹,似乎暗示了晚第三纪沉积气候环境显著不同于第四纪的冷干、暖湿气候组合演化格局。  相似文献