共查询到20条相似文献，搜索用时 121 毫秒
1.
黄土高原全新世风成沉积的岩石磁学性质及其古气候意义 总被引：9，自引：0，他引：9
对黄土高原NW-SE断面上的现代沙丘砂，原生黄土，全新世黄土和黑垆土的к-T曲线及其磁滞性质和X射线衍射特征进行了系统分析，结果表明，不论是在源区还是沉积区，磁铁矿都是对磁化率贡献最大的磁性矿物，源区风化作用没有使磁赤铁矿含量显著增加，黄土中的赤铁矿至少有一部分是原生的，黄土中的磁赤铁矿以成土成因为主，土壤化程度越高，磁赤铁矿含量越高，由于磁赤铁矿分解导致的磁化率下降越明显，к-T曲线上510℃附近的磁化率峰越不显著，к-T分析能非常灵敏地反映热处理过程中磁性矿物的转化情况，而且这种转化与样品所经历的土壤化作用强度密切相关，因此，к-T分析可作为研究成土作用强度和古气候变化的一种新方法。 相似文献
2.
佳县红粘土堆积序列频率磁化率的古气候意义 总被引：18，自引：0，他引：18
佳县红粘土剖面的磁性地层学研究证明，黄土高原北部风尘堆积的起始年代可以追溯到8．35Ma以前，通过进一步的磁化率测量和频率磁化率分析，发现佳县红粘土及上覆部分午城黄土—古土壤序列的磁化率和频率磁化率之间存在良好的正相关关系，表明成壤作用过程中由生物作用或风化作用形成的超顺磁颗粒和磁性矿物对磁化率和频率磁化率的增大具有重要贡献；同时，剖面中红粘土频率磁化率的百分含量明显高于上部午城黄土，指示了红粘土堆积较强的成壤作用，表明黄土高原普遍发育的红粘土堆积具有相似的磁学性质和古气候意义，并在空间尺度上可以对比。佳县风尘堆积的频率磁化率年代序列指示了3．6Ma以来，尤其是2．7Ma后气候波动加剧和北方干旱化增强。 相似文献
3.
青海湖湖东沙地全新世风成沉积物磁化率特征及其环境意义 总被引：1，自引：0，他引：1
在亚洲季风控制区,黄土-古土壤序列中的磁化率能够很好地反映土壤成壤强度和区域沉积环境变化,但在风成砂-古土壤序列中磁化率的古气候意义仍有待研究。选取青海湖湖东沙地典型风成砂-古土壤序列,基于AMS14 C和光释光测年结果,结合土壤学中传统的土壤发育指标,对沉积物的磁化率特征及环境意义进行分析。研究表明在青海湖盆地风成砂-古土壤序列里,磁化率与成壤强度密切相关:(1)剖面磁化率总体表现为古土壤层最高、弱发育古土壤层次之和风成砂层最低的规律。相较低频磁化率χlf,频率磁化率χfd%能够更好、更细致地反映沉积环境的变化;(2)剖面中磁化率与成壤强度有关(正相关),因成壤作用对两剖面原始物源各粒级组分的改造程度不同,磁化率与黏粒和粉砂正相关;(3)基于剖面磁化率以及粒度特征的综合分析,将青海湖湖东沙地全新世以来气候环境划分为3个阶段:10kaBP以前气候冷干,成壤作用微弱;10~4kaBP气候暖湿,成壤作用显著;4kaBP至今,气候逐渐趋于冷干,成壤作用渐弱。 相似文献
4.
邙山黄土Laschamp事件的缺失及成因探讨 总被引：5，自引：0，他引：5
邙土黄土岩石磁学研究表明，其岩石磁学性质与黄土高原的黄土基本一致，而古地磁学的研究表明其中本记录“Laschamp”事件。研究发现，样品加热到300℃时的乘磁强度与其频率磁化率之间具有极好的相关性。以此为出发点，提出了邙山黄土剩余磁性的部分化学乘磁成因的认识。结合已有的研究成果，认为黄土剩余磁性由碎屑剩磁和化学剩磁叠加而成，它们对剩磁贡献的相对大小，可能决定了黄土-古土壤磁性记录受“Smoothing”效应影响的程度；而其各自贡献的大小与成壤作用密切相关，成壤作用越强，化学乘磁的贡献相对越大。解释了邙山黄土未能记录“Laschamp”事件的原因。并试图将这些认识推而广之，认为它们在黄土－古土 中可能具有普遍意义。 相似文献
5.
南海南部NS93-5孔沉积物磁化率特征及其对全球气候变化的记录 总被引：21，自引：1，他引：21
对南海南部长533cm的NS－93孔连续采取423块样品，测量低场下的质量磁化率。并间隔取样202块，测量ARM。通过与沉积层序、氧同位素和矿物特征对比分析，我们认为NS－93孔磁化率的变化主要受控于外源磁性矿物浓度的变化，其值的高低与沉积物中碎屑矿物的含量相关，与碳酸盐的含量反相关，说明碳酸盐矿物对磁性矿物浓度具有稀释作用。在磁化率特征变化曲线上，与氧同位素阶段和Heinrich变冷事件、D－O旋回有好的对应关系。磁化率的相对高值与氧同位素奇数阶段和气候的暖期相对应，而相对低值则与气候冷期对应。这一规律反映了东亚季风、大洋环流强弱和陆源碎屑输入对沉积物磁化率的控制作用。同时，从ARM和磁化率的关系分析，南海南部在氧同位素阶段6沉积时期处于相对稳定的环境，南面的Borneo海峡可能是封闭的。 相似文献
6.
黄土高原黄土是第四纪古气候研究的主要对象之一,磁化率是黄土古气候研究的主要代用指标。然而,黄土地层磁学特征的主控因子依然存在争论。本文选取黄土高原中部的安塞黄土剖面为研究对象,对地层进行系统的磁学特征分析。安塞剖面在早全新世至中全新世早期(~10000~8500a)黄土层中磁性矿物含量较低且呈递增趋势,中全新世(8000~3000a)古土壤层中磁性矿物含量较高,在中全新世中期(7000~5000a)达到最高随后呈递减趋势,晚全新世(3000a以来)黄土层中磁性矿物含量很低并呈递减趋势。此外,地层的磁学特征表现出3次快速变化:6500a前后,地层中磁性矿物含量迅速增加;4500a前后和2700a前后,地层中磁性矿物含量快速降低。通过与全新世降水和气温等气候因子对比发现降水量是控制安塞剖面中次生强磁性矿物含量变化的关键性气候因子,低温并不能增加地层中强磁性矿物含量,而高温则可能限制地层中强磁性矿物的形成。土壤中强磁性矿物含量变化对气候好转响应迟缓,对气候恶化响应迅速。 相似文献
7.
我国黄土高原第四纪风成黄土序列为研究不同时间尺度(构造和轨道尺度)的环境演变提供了理想材料,其中轨道尺度上冰期-间冰期气候变化是第四纪以来气候周期性演变的重要特征。粒度和磁化率分别作为冬季风和夏季风指标被广泛应用于亚洲内陆干旱化和古季风演化研究。然而,磁化率作为古气候代用指标在解释区域环境演化时存在差异性,并不能将其总视为暖湿信号。以黄土高原西部地区的兰州皋兰山和西津岩心为研究对象,详细分析了倒数第二次冰期以来的粒度和磁化率特征,并与洛川剖面进行空间对比。研究表明,间冰期的磁化率总体高于冰期,但在冰期向间冰期转换的过渡期,皋兰山和西津岩心磁化率值并没有降低到冰期水平,而与弱发育古土壤磁化率水平类似。我们推测该时段兰州黄土磁化率增加并非由成壤作用增强贡献,而是源区粗颗粒磁性矿物增加所致,其磁化率增强模式可能同阿拉斯加、新疆黄土类似。由此可见,磁化率增强模式不仅在冰期时黄土高原东西部存在显著差异,而且在同一区域的不同沉积时期也存在较大差别。 相似文献
8.
土壤中潜在有毒元素(PTEs)易通过食物链的累积对人体健康构成严重威胁，探究其浓度对于生态环境安全具有重要意义。为查明浙江三门湾沿岸土壤中PTEs含量、分布特征及主要来源，在三门湾沿岸4个小流域采集了36个站位土壤样品，进行了土壤黏土矿物、土壤酸碱度、10种PTEs及Si、Al、Fe和TOC含量分析。利用相关性和主成分分析进行了来源分析，并采用《土壤环境质量》（GB 15618-2018）、富集因子（EF）、内梅罗污染指数（PI）及潜在生态风险污染指数（RI）评价模型进行了环境风险评价。结果表明，不同地貌单元土壤黏土矿物组成差异明显，山间平原土壤高岭石和绿泥石占比相对高(平均值>30%)，海积平原伊利石占比相对高（>60%）。山间平原土壤主要为原地母岩风化成壤，而海积平原区土壤主要为历史时期长江来源沉积物改造而成。土壤PTEs整体上呈现流域上游向下游增加的分布趋势。平均富集程度依次为Hg>Cd>Sb>As>Pb>Ni>Cr>Co>Zn> Cu。Hg元素轻微富集、中等富集和中等严重富集站位占比分别为27.8%、2.8%和2... 相似文献
9.
环境磁学是一门介于地球科学、环境科学和磁学之间的新兴边缘学科。在环境系统中,土壤、岩石、沉积物、大气尘埃等自然物质以及人类活动所产生的次生物质往往表现出不同的磁性特征,它们与物质内含矿物的磁性类型、铁磁晶粒含量、大小构成及配比组合有关,在一定程度上反映了其来源母质、生成环境、搬运过程和沉积作用等综合信息。环境磁学旨在分析物质的磁性矿物组合和特征,探索其在不同环境条件下的转化规律,利用环境系统中的物质在磁性特征上的差异和联系及其所指示的环境内涵,研究不同时空尺度的环境过程、环境作用和环境问题,进而… 相似文献
10.
为了准确解释环境磁学参数记录的极地古气候环境变化信息,本研究对白令海和西北冰洋61个站位的表层沉积物进行了高、低频质量磁化率(χ)、非磁滞磁化率(χARM)和磁化率-温度(k-T)分析,以探明该区沉积物中磁性矿物的种类、来源与搬运路径。结果显示,样品的χ具有明显的地域分布特征。白令海的χ值整体高于楚科奇海,并在育空河口外侧和圣劳伦斯岛南侧较高,向北和向西南方向逐渐减小。楚科奇海中东部陆架上表层沉积χ值高于阿拉斯加沿岸,而西北冰洋深海平原和洋脊区的χ值最低。χARM的变化趋势与质量磁化率相似,但频率磁化率的变化趋势与质量磁化率正好相反。k-T分析结果显示阿留申海盆沉积物中的铁磁性矿物以磁赤铁矿占主导,白令海陆架育空河口外侧和圣劳伦斯岛南北两侧为磁铁矿,白令海陆架西部和楚科奇海陆架中东部为磁赤铁矿和磁铁矿,楚科奇海阿拉斯加沿岸为黄铁矿,而西北冰洋陆坡、深海平原和洋脊区为胶黄铁矿和黄铁矿,但高纬度区沉积物中的胶黄铁矿含量更高。沉积物中磁性矿物的区域性分布受沉积物来源、洋流和底质环境等因素的控制。白令海和楚科奇海陆架磁赤铁矿来源于亚洲大陆,白令海陆架东部的磁铁矿来自育空河流域,阿拉斯加沿岸沉积物中的黄铁矿,应为阿拉斯加西北部陆源侵蚀来源的或早期成岩作用形成的,西北冰洋深海盆区的胶黄铁矿,为自生成因的。 相似文献
11.
Coastal inundation associated with extreme sea levels is the main factor which leads to the loss of life and property whenever a severe tropical cyclonic storm hits the Indian coasts. The Andhra and Orissa coasts are most vulnerable for coastal inundation due to extreme rise in sea levels associated with tropical cyclones. Loss of life may be minimized if extreme sea levels and associated coastal flooding is predicted well in advance. Keeping this in view, location specific coastal inundation models are developed and applied for the Andhra and Orissa coasts of India. Several numerical experiments are carried out using the data of past severe cyclones that struck these regions. The simulated inland inundation distances are found to be in general agreement with the reported flooding. 相似文献
12.
Hoi-Soo Jung Kap-Sik Jeong Yong-Shik Chu Sung-Hyun Park Ki-Hyune Kim 《Marine Georesources & Geotechnology》2001,19(3):181-195
Grain size and water content in box-core sediments from the Clarion-Clipperton fracture zone (C-C zone) in the northeast equatorial Pacific were analyzed in detail to understand the downcore variations across a hiatus between Quaternary and Tertiary layers. Grain-size distributions in the topmost core sediments show two modes: a coarse mode (peaked at 50 μm) and a fine mode (at 2-25 μm). The coarse mode disappears gradually with depth accompanied by the dissolution of siliceous fossil tests, whereas the fine mode coarsens due to the formation of authigenic minerals. Water content increases abruptly across a color boundary between an upper pale brown layer and a lower dark brown layer that is the hiatus between Quaternary and Tertiary layers. Abundant smectites and microvoid molds, which are created by the prolonged fossil dissolution in the underlying sediment, are attributed for the abrupt downcore variation of water content. Overall variations in grain size and water content in the topmost core sediments in the western C-C zone are possibly constrained by the dissolution of biogenic siliceous fossils. Variations in geotechnical properties related to these changes must be considered in the design of nodule collectors. 相似文献
13.
Shigehisa Nakamura 《Marine Geodesy》2001,24(1):27-33
This article concerns an interrelation between the sea levels and the western boundary flow near a tectonic boundary in a local zone in the Northwestern Pacific. In this zone, sea level variations at stations located on the coast facing the Pacific are studied to find the interrelation between variations of the Kurosio flow as an index of the distance of the flow axis off a specific coast. The result is discussed after data processing of the monthly means of the sea levels, and a notice is taken of variations caused by active crustal upheavals during a seismic event, a local earthquake. 相似文献
14.
This study tests the hypothesis that the in situ void ratio of surficial marine sediments may be predicted from shear wave velocity-depth data with a reliability equal to that of other methods currently available. Shear wave velocity is fundamentally controlled by the number of grain-to-grain contacts per unit volume of material and by the effective stress across those contacts. In this study, three previously established empirical formulae are used to predict void ratio from velocity-depth data. Field data were acquired along a transect off the northern Californian coast across which water depth increased from 35 to 70 m and seafloor sediment type varied from sand to silty-sand, respectively. A towed seafloor sled device was used to collect shear wave refraction data, and a marked, systematic decrease in velocity was observed along the line, ranging from 35-70 m/s for the coarse, near-shore material to 25-40 m/s for the finer, offshore deposits. Void ratios predicted from these velocities were compared with data measured directly from box-core samples. Of the formulae used for prediction, two agree remarkably well with the control data. Both predicted and control values increase from 0.6-0.8 for the sandy material to 1.1-1.5 for the silty-sand. Thus, this study does not disprove the hypothesis set and demonstrates the potential of field shear wave velocity-depth data as a means of delineating spatial variation in void ratio for surficial marine sediments in a remote, nondestructive manner. 相似文献
15.
Particulate samples were collected from the Changjiang river system during a flood period, in May 1997, and POC, stable isotope and lipids associated with particles were examined. Results showed the decrease (0.84% ～ 1.88%) of organic carbon content from the upper reaches to the estuary.δ13C values of particulate organic carbon was in the range of -24.9×10-3 to -26.6×10-3, which were close to the isotopic signature of continental C3 vegetation. Total particulate n-alkanes concentrations varied from 1.4 to 10.1μg/dm3,or from 23.7 to 107μg/g of total suspended matter. Fatty acids were present in all the samples, from 1.4 to 5.4μg/dm3, with saturated and unsaturated straight-chain and branched compounds in the carbon number range from C12 to C30. Both δ13C and the ratio of carbon content to nitrogen content indicate the predominance of terrestrial inputs (soil organic matter) among the particles. The biomarker approach has been used to identify the relative portion of terrigenous and autochthonous fraction in the particulate samples. The distribution of fatty acids suggests a striking phytoplanktonic and microbial signal in most particle samples. The terrestrial alkanes are used to estimate the contribution of terrestrial inputs along the mainstream. 相似文献
16.
Andrzej Chybicki 《Marine Geodesy》2018,41(1):1-23
Current trends of development of satellite derived bathymetry (SDB) models rely on applying calibration techniques including analytical approaches, neuro-fuzzy systems, regression optimization and others. In most of the cases, the SDB models are calibrated and verified for test sites, that provide favorable conditions for the remote derivation of bathymetry such as high water clarity, homogenous bottom type, low amount of sediment in the water and other factors. In this paper, a novel 3-dimensional geographical weighted regression (3GWR) SDB technique is presented, it binds together methods already presented in other studies, the geographically weighted local regression (GWR) model, with depth dependent inverse optimization. The proposed SDB model was calibrated and verified on a relatively difficult test site of the South Baltic near-shore areas with the use of multispectral observations acquired by a recently launched Sentinel-2 satellite observation system. By conducted experiments, it was shown that the proposed SDB model is capable of obtaining satisfactory results of RMSE ranging from 0.88 to 1.23[m] depending on the observation and can derive bathymetry for depths up to 12m. It was also shown, that the proposed approach may be used operationally, for instance, in the continuous assessment of temporal bathymetry changes, for areas important in the context of ensuring local maritime safety. 相似文献
17.
N. H. Khadge 《Marine Georesources & Geotechnology》2000,18(3):251-258
As a part of the environmental impact assessment studies, geotechnical properties of sediments were determined in the Central Indian Basin. The undrained shear strength and index properties of the siliceous sediments were determined on 20 box cores of uniform dimension collected from various locations in five preselected sites. The maximum core length encountered was 41 cm and most of the sediments were siliceous oozes consisting of radiolarian or diatomaceous tests. The shear strength measurements revealed that surface sediments deposited in recent times (0-10 cm) have a shear strength of 0-1 kPa; this value increases with depth, reaching 10 kPa at 40 cm deep. Older sediments have greater strength because of compaction. Water content varies in the wide range of 312-577% and decreases with depth. The clay minerals such as smectite and illite are dominant and show some control over water content. Wet density, specific gravity, and porosity do not indicate any notable variation with depth, thereby indicating a uniform, slow rate of sedimentation. The average porosity of sediments is 90.2%, specific gravity 2.18, and wet bulk density 1.12 g/cm 3 . Sediments exhibit medium to high plasticity characteristics, with the average plasticity index varying between 105% and 136%. Preliminary studies on postdisturbance samples showed an increase in natural water content and a decrease in undrained shear strength of sediments in the top 10- to 15-cm layer. 相似文献
18.
Extreme sea levels associated with severe cyclonic storms are common occurrences along the east coast of India. The coastal districts of Orissa have experienced major surges in the past. The recent Paradip super cyclone is one of the most severe cyclones, causing extensive damage to property and loss of lives. Extreme sea levels are major causes for coastal flooding in this region. Damages can be minimized if the extreme sea levels are forecast well in advance. In the present study, we develop a location specific, fine resolution model for the Orissa coast on the lines similar to that of IIT-D storm surge model (Dube et al. 1994). The model runs on a personal computer. The bathymetry for the model is extracted from very fine resolution naval hydrographic charts for the region extending from the south of Orissa to south of West Bengal. A simple drying scheme has also been included in the model in order to avoid the exposure of land near the coast due to strong negative sea surface elevations. An attempt was made in this study to simulate extreme sea levels along the Orissa coast using the data of past severe cyclones. The model results reported in the present study are in good agreement with available observations or estimates. 相似文献
19.
An Improved Calibration of Satellite Altimetric Heights Using Tide Gauge Sea Levels with Adjustment for Land Motion 总被引：2，自引：0，他引：2
Gary T. Mitchum 《Marine Geodesy》2000,23(3):145-166
Several major improvements to an existing method for calibrating satellite altimeters using tide gauge data are described. The calibration is in the sense of monitoring and correcting temporal drift in the altimetric time series, which is essential in efforts to use the altimetric data for especially demanding applications. Examples include the determination of the rate of change of global mean sea level and the study of the relatively subtle, but climatically important, decadal variations in basin scale sea levels. The improvements are to the method described by Mitchum (1998a), and the modifications are of two basic types. First, since the method depends on the cancellation of true ocean signals by differencing the altimetric data from the tide gauge sea level time series, improvements are made that produce a more complete removal of the ocean signals that comprise the noise for the altimetric drift estimation problem. Second, a major error source in the tide gauge data, namely land motion, is explicitly addressed and corrections are developed that incorporate space-based geodetic data (continuous GPS and DORIS measurements). The long-term solution, having such geodetic measurements available at all the tide gauges, is not yet a reality, so an interim solution is developed. The improved method is applied to the TOPEX altimetric data. The Side A data (August 1992?February 1999) are found to have a linear drift component of 0.55 + / 0.39 mm/yr, but there is also a significant quadratic component to the drift that is presently unexplained. The TOPEX Side B altimeter is estimated to be biased by 7.0 + / 0.7 mm relative to the Side A altimeter based on an analysis of the first 350 days of Side B data. 相似文献
20.
J. N. Pattan Ch. M. Rao A. A. Migdisov S. Colley N. C. Higgs L. Demidenko 《Marine Georesources & Geotechnology》2001,19(3):155-165
The rare earth element (REE) distribution in nine deep-sea ferromanganese nodules and their associated siliceous sediments from the Central Indian Ocean Basin (CIOB) have been studied to elucidate the REE relationship among them. Total REE concentration varies from 398-928 ppm in the nodules and 137-235 ppm in the associated sediments, suggesting two- to four-fold enrichment in the nodules compared to associated sediments. REE of nodules and their associated sediments show a positive correlation, suggesting REE are supplied from a common source such as seawater. The positive correlation between REE of nodules and sediments from the CIOB is contrary to the competitive scavenging of REE between nodules and sediment in the equatorial Pacific Ocean. REEs in the nodules are carried by Fe, P, and Ti, whereas in the sediment they are carried by P and Mn phases. A similar REE fractionation pattern with middle REE enrichment over heavy and light REE in both the nodules and their associated sediment suggest fractionation is independent of REE abundance and their carrier phases. 相似文献