共查询到20条相似文献，搜索用时 953 毫秒
1.
We present a new index of carbonate fragmentation based on the size distribution of bulk sediments in core MD962094 from Walvis Ridge (SE Atlantic Ocean). The carbonate fragmentation index is constructed by taking a ratio of the two coarsest fractions in the grain size distributions of the bulk calcareous ooze. The coarsest two fractions (25–90 μm and >90 μm) of the bulk sediments consist primarily of complete shells and fragments of adult foraminifera shells, and juvenile foraminifera shells and fragments, respectively. The ratio of the proportions of the two fractions is interpreted as a measure of fragmentation of the foraminifera shells caused by carbonate dissolution. Downcore changes in our carbonate fragmentation index compare very well with those in the coarse-carbonate fragmentation index in sediments from a nearby core on Walvis Ridge. The latter commonly used fragmentation index is defined as a ratio of foraminifera fragments over whole foraminifera in the >150-μm fraction as seen with a light microscope. Fragmentation is relatively high during glacial stages and relatively low during interglacial stages during the last 300 kyr, caused by the combined effect of wind-driven upwelling of corrosive water and increased production of organic matter, decreasing the preservation potential of carbonates both during and after deposition. The carbonate fragmentation index we present here provides a precise and fast method to establish a downcore fragmentation record. It can be applied to bulk sediments that are carbonate-rich (CaCO3>68%) and to all other deep-marine sediments of which the grain size distribution of the carbonate-free fraction is available. 相似文献
2.
沉积物颗粒与下覆颗粒间转动角是制约沉积物颗粒起动的一个重要因素。本文样品采集于1987年。作者通过一系列实验探明了沉积物转动角同颗粒形状、相对粒径比以及迭瓦状构造等因素之间的相互关系。在均匀粒径条件下,球状砾石转动角的测量数值同理论数值相吻合,但随粒径的减小而增大。这一结果同前人利用球状砂粒进行实验所获得的结果相一致。利用球状、椭球状及棱角状砾石进行的实验表明,沉积物转动角φ随相对粒径的增大而减小,随颗粒扁平度及颗粒棱角度的增大而增大。扁平砾石的迭瓦状构造将导致转动角的增大,其增大值约等于砾石的迭瓦角。若其它因素相同,沉积物起动的难度自球状、椭球状、棱角状及迭瓦状构造而依次增强。这些结果将有助于对颗粒粒径、形状、构造同沉积物搬运临界状态以及沉积物选择性起动之间的相互关系进行定量分析。 相似文献
3.
黄河河口段与海河河口段沉积物碳酸盐对比分析 总被引：1，自引：1，他引：1
利用筛析-沉降法对黄河系及海河系沉积物进行了粒度特征分析,黄河系沉积物以极细砂-粗粉砂为主,分选性中等,粒度分布正偏,峰态曲线尖窄;海河系沉积物以细粉砂为主,分选性较差,粒度分布正偏,峰态曲线较平缓。测定黄河系及海河系沉积物碳酸盐的粒度百分含量及碳酸盐加权粒度百分含量,结果表明:黄河系沉积物碳酸盐粒度百分含量加权平均值为11.36%,细砂碳酸盐粒度百分含量较高(15.24%),随粒度越细波动式降低后逐步增加,并在黏土富集,达20.67%;海河系沉积物中碳酸盐粒度百分含量加权平均值为15.05%,比黄河系略高,呈两端高中间低不对称鞍形粒度分布。黄河系与海河系碳酸盐粒度百分含量受粒度控制,对全样碳酸盐贡献最大的粒度黄河系为粗粉砂,海河系为细粉砂。黄河系全岩碳酸盐平均粒度百分含量与马兰黄土相近,与黄渤海泥质区相当,表明黄河沉积物的主要来源是马兰黄土,黄河在沉积物搬运过程中对黄土碳酸盐没有明显改造,黄河沉积物黏土组分是黄渤海泥质区沉积物高碳酸盐的主要影响因素。 相似文献
4.
The shape parameter helps determining the shape of equilibrium beach profile in terms of offshore distance and water depth. The shape parameter therefore, should represent the effect of all the environmental factors involved in beach profile formation, such as wave climate and sediment properties. However, all the previous studies carried out to define shape parameter only consider the effects of sediment characteristics in their definitions. The aim of this study is to add the effect of wave climate also in the definition of shape parameter. This is achieved by integrating wave energy dissipation rate per unit volume at the surf zone. The result yields equilibrium wave energy dissipation rate that leads to theoretical definition of equilibrium beach profiles involving the effects of both the grain size and the wave climate parameters. It is found that the sediment grain size and the incoming wave height affect the value of shape parameter; whereas, the effects of wave period can be neglected. By means of energy equation, it is also possible to observe in macro scale the strength of wave energy on beach profile for different grain sizes. The findings also bring about the possibility of defining shape parameter such that any two arbitrary beach profiles owning the same sediment grain sizes can have the opportunity to have different beach profile formations. Finally, by adding the effect of wave height in the definition of shape parameter the graphical representation of the parameter, previously given by Moore (1982) is improved herein. 相似文献
5.
Manoj Datta G. Venkatappa Rao Shashi K. Gulhati 《Marine Georesources & Geotechnology》2013,31(4):307-341
Abstract This paper presents the results of a laboratory investigation undertaken to study the nature of two submarine carbonate soils from Bombay High off the west coast of India, as well as to study the shear and plasticity behavior of their sand and silt‐clay fractions, respectively. Scanning electron micrographs reveal that the carbonate content in both soils is comprised primarily of nonskeletal particles of various types. X‐ray diffraction and infrared absorption analyses indicate that in one soil the carbonate fraction consists of calcite and aragonite minerals, whereas in the other soil dolomite is also present. The non‐carbonate fraction of both soils is comprised primarily of quartz and feldspar, and also some clay minerals. The nature of the carbonate fraction of the two soils indicates that they were formed by different depositional processes. During drained triaxial shear the nonskeletal sand grains of both soils exhibit a lower degree of crushing when compared with that of the skeletal carbonate sands, and thus appear to be stronger foundation material. Although the carbonate contents of the silt‐clay fractions of the two soils are similar, they exhibit markedly different plasticity characteristics . This is probably because of the microlevel cementation produced by carbonate material in one soil. This study leads one to the conclusion that carbonate content alone should not be treated as a parameter which controls the engineering behavior of submarine soils; the nature and form of carbonate material must also be identified. 相似文献
6.
对中国北方莱州湾南岸钻孔上部54m海陆交互相沉积物的亮度进行研究,探讨其作为海陆交互相沉积物的环境指标的可行性,同时通过对比不同样品处理方式所得的亮度值探讨影响亮度的几个因素。测量分2次进行,分别使用Minolta CM-2002分光光度计针对柱状原样及Minolta CR400/410色差计针对风干研磨后的散样进行。研究结果表明,海陆交互相沉积物的亮度,尤其是经过风干处理后样品的亮度值,与碳酸钙含量及粒度两个古气候代用指标均具有显著相关关系,可以将其作为碳酸钙含量的替代指标应用于海陆交互相沉积物的环境演化研究。而亮度值与碳酸钙含量不一致性,可归因于沉积物中非碳酸钙组分的性质及含量。粒度与亮度的相关性显示,钻孔砂质沉积中含有的大量深色的有机质使得钻孔中粒度0～31μm的部分比例越高,亮度会越大,而粒度>31μm的部分比例越高,亮度会越小。2次亮度值的对比表明,水分、氧化作用及研磨是沉积物2次测量所得亮度值存在差异的主要原因。 相似文献
7.
不同前处理方法对南方红土粒度测量的影响——以安徽宣城第四纪红土剖面为例 总被引：7，自引：0，他引：7
以安徽宣城官塘村第四纪红土剖面为例,研究了不同前处理方法对南方红土粒度测量的影响。结果表明:(1)南方红土中所含的有机质对粒度测量结果会产生明显影响,在进行粒度测量前处理时,必须加入双氧水去除有机质;(2)南方红土因淋溶强烈,碳酸钙含量极低,对粒度测量结果无影响,无需加入盐酸进行去钙处理。加入盐酸反而使得所测粒径偏粗;(3)与六偏磷酸钠相比,氢氧化钠作为分散剂因其强碱性产生的复杂化学反应,会导致所测得的粒度频率曲线峰态出现异常,且<1μm的黏粒组分含量减少,故不宜用作南方红土粒度测量的分散剂;(4)在对南方红土进行粒度测量时,建议使用H2O2+(NaPO3)6的前处理方法,即先使用双氧水去除有机质,再使用六偏磷酸钠作为分散剂,并用超声波清洗仪震荡后上机测试。 相似文献
8.
海洋暖池的发展、变化及其效应与沉积环境有密切关系。文章对北部湾暖池主要水域进行表层沉积物取样, 测试鉴定其粒度、化学元素、微体古生物化石, 并对数据进行分析比较。结果表明: 研究区物源来自陆区上陆壳风化, 在水动力作用下粒度组成分异明显, 平均粒径为1.1Φ~6.9Φ (Φ=-log2d, d为直径, 单位: mm)。常量元素以SiO2占优, 其平均质量分数最高达到66.61%, 其次为Al2O3; 微量元素的质量分数平均为9.05~297.00μg•g-1, 稀土元素的平均质量分数为0.34~69.43μg•g-1, 化学蚀变指数(CIA)平均为47.33, 轻重稀土元素分馏比为7.46~10.07。古生物多样性指数(H°)为0~2.52。在海湾尺度下化学要素分布的空间异质性显著。在研究区西部, 大部分化学元素质量分数高, 沉积物颗粒最细, 稀土元素分馏显著, CIA较高, 物质来源多样, 古生产力较高; 而东部则几乎表现相反, 以砂质沉积物为主, 除了CaO、MnO、Sr较高之外, 大部分元素质量分数低且稀土元素分馏弱, CIA低下, 古生产力偏低, 显示出物源有限和海洋自生碳酸盐沉积的可能性。浮游类有孔虫以表层暖水种占优, 硅藻为热带和亚热带种, 属种内在结构显示出暖水、高盐等特征。该暖池兼具一定的独立性和开放性, 对生物活动、生物多样性乃至碳酸盐沉积等具有维护作用。 相似文献
9.
前处理步骤与方法对风成红粘土粒度测量的影响 总被引：37，自引：1，他引：37
中国北方晚第三纪红粘土堆积为研究古气候与古环境提供了很好的地质记录,其粒度测量作为一个重要的代用指标被广泛应用。粒度测量结果受到前处理方法的影响,但是,现在各个实验室的前处理方法还不一致,这就为粒度数据分析和古气候古环境解释带来了困难。在黄土高原从北到南选择了3个具有代表性的红粘土剖面,对每个剖面从下向上取10块样品总计得到30块样品,对每个样品用不同的前处理方法与步骤（包括化学分离石英的方法）处理后用激光粒度仪进行颗粒测量。结果表明,前处理方法与步骤可以使同一个样品粒度参数发生几倍甚至于二十几倍的变化。综合理论和经验分析,推荐了一种较好的进行风尘堆积粒度测量的前处理方法（正文中方法C）。化学分离的纯石英的粒度分布比本文推荐的方法处理同一个样品的粒度结果偏粗,表明在提纯石英的过程中较细的不稳定矿物已经被剔除。 相似文献
10.
为了解南海北部末次间冰期以来的沉积环境演化,分析了西沙海槽83PC柱状沉积物的浮游有孔虫氧碳同位素、碳酸钙、有机碳和粒度组成。浮游有孔虫的δ18 O值具有冰期-间冰期旋回特征,记录了海平面的升降和古气候的变化,而海平面变化控制了沉积物的碳酸钙和有机碳含量。冰期,海平面下降,陆源物质输入增多,带来了大量的碎屑物质和陆源有机质,沉积物具有低碳酸钙含量和高有机碳含量;间冰期,海平面上升,陆源物质输入减少,碎屑物质的稀释作用减弱,沉积物具有高碳酸钙含量和低有机碳含量。南海北部83PC柱状沉积物记录了末次间冰期以来的多次海平面升降旋回,还记录了气候变冷事件以及低碳酸钙沉积事件,其中,150、510、660和740cm处的低碳酸钙含量和相对重δ18 O值记录了全球性气候变冷事件,而冰后期的低碳酸钙沉积事件,则主要反映了季风降雨的增强,出现了洪水高发期,陆源碎屑物质对碳酸钙沉积的稀释作用明显增强。 相似文献
11.
12.
黄河三角州沿岸及相邻渤海海域碳酸盐研究(英文) 总被引：2，自引：0，他引：2
对黄河三角州陆地上河道,河口、潮间带及毗邻渤海海域沉积物中的碳酸盐含量作了分析,在此基础上划分出含量不同的沉积区和亚区。沉积区的划分和其物源有十分良好的对应关系,同一沉积区内的亚区则主要和粒度有关,从而间接反映了水动力环境与生物作用的控制性影响。黄河口沉积物中碳酸盐含量与粒度成反比,其他物源的沉积物则各不相同。黄河口及邻近渤海海域中粘土粒级和碳酸盐含量等值线反映出黄河细粒级沉积物扩散的方向、强度和范围。海洋生源沉积是影响渤海东部和中部沉积物中碳酸盐含量分布的主要因素。 相似文献
13.
AbstractSporosarcina pasteurii (ATCC 11859) is a nitrogen-circulating bacterium capable of precipitating calcium carbonate given a calcium source and urea. This microbially induced carbonate precipitation (MICP) is able to infill inter-granular porosity and act as a biological clogging agent, thus having a wide potential application in strengthening coastal foundations, preventing erosion by seas and rivers and in reducing sand liquefaction potential in coastal areas. A successful MICP application requires the understanding of the primary parameters that influence the microbially mediated process to achieve its engineering goals, such as injection scheme, chemical concentrations, retention times, and injection rates. However, the granular morphology has generally been oversimplified to ideal shape without enough consideration in previous studies. The following explores the critical micro-scale influence of particle morphology on mechanisms of microbially induced clogging. Spherical, non-spherical and angular particles were used as granular aggregates in permeating column experiments with the resulting permeability and calcium carbonate content of the treated aggregates examined. Microscopic examination (SEM) defines the features of the distribution of microbially precipitated calcium carbonate and the forms of clogging. The results show: (1) given a fixed duration of treatment, the calcium carbonate content for the spherical particle aggregate is significantly higher than that for near-spherical and angular particle aggregates; (2) for identical durations of treatment, the maximum permeability reduction occurs for angular particles (rather than for spherical particles with the highest carbonate content). This suggests that the microscopic distribution of calcium carbonate is significantly influenced by particle morphology, exerting a critical control in the effectiveness of clogging. SEM images indicate that the microbial calcium carbonate precipitates encapsulate the spherical particles as a near-uniform shell and occlude the pore space only by increasing the shell thickness. In contrast, the near-spherical and angular particles are only partially coated by a calcium carbonate film with scattered crystals of vaterite and calcite further clogging the void space. The polyhedral nature of the non-spherical particles tends to result in a slot-shaped pore structure which critically defines the hydraulic conductivity of the ensemble medium. As the microbial vaterite and calcite continue to accumulate on the particle surface, these slot-shaped pore structures become increasingly more tortuous – resulting in a noticeable reduction of permeability at a lower calcium carbonate content. 相似文献
14.
In this study, simple shear tests on breakable polydisperse granular materials were simulated using two-dimensional discrete element method (DEM). A new technique of generating polydisperse DEM samples with a smooth and continuous particle size distribution curve was proposed. A modified breakage criterion was introduced to reflect the contact force anisotropy of particles in the numerical sample. The simulation results showed that during the simple shearing, grain crushing in the sample mainly occurred in the contraction process and decreased gradually when the sample began to dilate. As the shearing proceeded to a larger strain, the grain crushing tended to a stable value. This grain crushing trend was in accordance with the evolution of the average normal contact forces of particles in the sample during shearing. The average normal contact forces of potential breakage particles increased in the contraction process and decreased in the dilatancy process. A decrease in the average normal contact forces of potential breakage particles resulted in the decrease in grain crushing during the later stage of shearing. 相似文献
15.
Willem J. M. van der Linden 《新西兰海洋与淡水研究杂志》2013,47(1):26-37
Grain‐size and carbonate analyses have been carried out on bottom sediment samples of Wellington Harbour. From grain‐size parameters it was possible to establish a number of facies types and to outline sediment sources and directions of transport. 相似文献
16.
对日本海西部大陆坡沉积物柱状样中的自生碳酸盐样品进行了X射线衍射、扫描电镜、地球化学和碳氧同位素组成的系统研究。X射线衍射和扫描电镜分析结果表明,碳酸盐主要组成矿物为颗粒状自生高镁方解石微晶,放射状自生文石微晶仅在一个层位出现。结合碳酸盐的地球化学组成,认为研究区碳酸盐来自于富Ca2+、Mg2+和HCO3-流体的沉淀。中度亏损的13C(-33.85‰～-39.53‰)表明碳来自于甲烷的厌氧氧化,同时,这也是研究区海底存在甲烷冷泉的重要证据。重氧同位素比值(5.28‰～5.31‰)则指示着富18O流体来源,而该流体应源于天然气水合物的分解。综上可知,研究区碳酸盐来自于研究区甲烷冷泉上升流的沉淀,指示着海底更深处天然气水合物的存在与分解。 相似文献
17.
Multi-sensor core logger data and index properties were measured onboard the JOIDES resolution during ODP Leg 157 and compared with grain size distribution and carbonate contents measured in the on-shore laboratory. Cored sediments are similar in grain size, but very variable in carbonate content. Magnetic susceptibility clearly defines the volcanic turbidite layers, whereas GRAPE density and acoustic velocity help to define the coarser (silty) bases of some organic or calcareous turbidite layers. Index properties are mostly controlled by consolidation effects. 相似文献
18.
Multi-sensor core logger data and index properties were measured onboard the JOIDES resolution during ODP Leg 157 and compared with grain size distribution and carbonate contents measured in the on-shore laboratory. Cored sediments are similar in grain size, but very variable in carbonate content. Magnetic susceptibility clearly defines the volcanic turbidite layers, whereas GRAPE density and acoustic velocity help to define the coarser (silty) bases of some organic or calcareous turbidite layers. Index properties are mostly controlled by consolidation effects. 相似文献
19.
The Oolithe Blanche Formation was studied in three quarries, located at the south-eastern edge of the Paris Basin (France). Heterogeneities in reservoir properties were assessed through a sedimentological, diagenetic and petrophysical study. The relationships between depositional settings, diagenesis and petrophysical properties were analysed using detailed petrographic studies, image analysis, Nano CT-scans and petrophysical measurements.The carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso- and macroporosity.Early cementation vs. early compaction processes (mainly grain interpenetration) may have considerable influence on fluid-flow properties and parameters such as permeability, acoustic velocities and tortuosity. Better reservoir properties are found when compaction processes begin before cementation.From statistical analyses, e.g. Principal Component Analysis and Linear Discriminant Analysis, a sedimentological/diagenetic and petrophysical model is proposed that is in a good agreement with the geological model developed from field work. 相似文献
20.
Geotechnical properties of carbonate sediments result from several factors such as the particular constituents comprising
the sediment, the mineralogy, fabric, and effective stress. Investigating the effects of increasing effective stress by mechanical
consolidation using permeability, porosity, and porometry determinations reveals fabric changes that could not be determined
in scanning electron micrographs. Porometry changes, determined using an image analyzer, are a function of matrix composition
and grain support. Samples that were predominantly matrix-supported exhibited an increase in pore numbers per unit area and
a pore size decrease resulting from consolidation. Samples composed predominantly of aragonite needle matrices displayed opposite
behavior. 相似文献