澳大利亚线形沙丘的粒度特征

前言不同沙丘地间的风成沙沉积结构特征差异在许多领域里具有根本的意义。这些领域包括风成分选过程的理论模型、沙丘或沙丘地的形态动力学性质和演化过程,以及沉积相环境和石油勘探中盆地规模的分析(例如;特沙尔1982,1983;斯奈和韦斯勃罗德1983;兰卡斯特尔1985;鲁宾和休特尔1985;沃特逊1986)。     

柴达木盆地耙状线形沙丘沉积物粒度特征及其对沙丘形成的意义

耙状线形沙丘是一种新发现的沙丘类型,形态上既有线形沙丘特征,又有新月形沙丘的特征,但目前对该类沙丘的研究相对较少,从而限制了对此沙丘的认识。为此,文中选择柴达木盆地的耙状线形沙丘为研究对象,收集地表沉积物样品,探讨沉积物粒度特征,为阐明沙源对耙状线形沙丘的形态演化过程提供支撑。研究表明,受砾石覆盖和盐分的影响,该地区的沙源欠丰富。耙状线形沙丘粒度具有明显的空间差异。在沙丘断面上,脊线最细,且迎风坡坡脚比背风坡粗。分选系数随平均粒径变细而变好,偏度随风选变好而趋于正偏。除分选系数与峰度相关性较差外(R²=0.37,P=0.1),其余所有的粒度参数之间均有明显相关性(P<0.001)。沉积物粒度的空间差异反映了沙源和沉积物搬运过程的差异。综合风况、沉积物和下垫面特征,研究区沙丘物源包括戈壁和干涸湖盆,其中蠕移质主要来源于戈壁,而跃移质则敖阔戈壁和干涸湖盆。     

雅鲁藏布江中游风沙灾害区地表沉积物养分特征

雅鲁藏布江贡嘎县至乃东区是雅江流域沙地分布面积最广的地区,也是防沙治沙的重点区域,目前风沙灾害严重.对雅鲁藏布江流域中游地区河道、河漫滩和沙质地表沉积物取样,分析其速效氮、速效磷、速效钾、有机质等养分含量,为生态恢复提供依据.结果 表明:1)不同类型沉积物在区域上具有明显空间异质性,总体表现为河道土壤养分含量最高,沙丘...     

新疆策勒沙漠与砾质戈壁新月形沙丘表面沉积物粒度特征及其沉积环境

不同下垫面对同种类型的沙丘的表面风沙沉积物特征产生重要影响,通过数理统计法对新疆策勒沙漠与砾质戈壁新月形沙丘表面不同地貌部位表面沙物质的粒度进行分析,探讨不同下垫面形成的相同的沙丘类型而导致沙丘的粒度特征存在的空间差异及其原因。结果表明:沙漠新月形沙丘比砾质戈壁新月形沙丘表面沙物质的平均粒径更细,分选性较好,偏度更趋于粗偏,峰态更趋于宽峰态。沙漠新月形沙丘表面沙物质主要由极细沙、细沙、极粗粉沙组成,百分含量分别为58.67%、20.23%、16.83%,其侧翼表面沙物质平均粒径最粗,约为118.99μm,砾质戈壁新月形沙丘表面沙物质主要由中沙、细沙、极细沙、极粗粉沙、粗沙组成,百分含量分别为26.53%、26.43%、26.36%、9.58%、9.14%,其顶部表面沙物质平均粒径最粗,约为291.48μm。沙漠新月形沙丘表面沙物质分选系数介于1.45-1.73之间,属于中等-较好分选性,偏度值介于-0.03-0.07之间,主要表现为对称,峰态值介于0.96-1.01之间,属于常峰态,砾质戈壁新月形沙丘表面沙物质分选系数介于1.99-2.44之间,主要属于较差分选性,偏度值介于-0.32...     

渭河宝鸡市区段沉积物的粒度特征分析

利用沉积物的粒度特征可以有效地揭示河流的沉积环境和水动力条件。选取了渭河干流宝鸡市区段、清姜河、金陵河和千河4个河床沉积物的76个样品进行了粒度测量。结果表明:渭河干流,清姜河和千河沉积物主要以砂为主,金陵河以黏土为主。渭河干流、清姜河、金陵河和千河沉积物平均粒径分别为3.89Φ、3.71Φ、3.79Φ和3.56Φ,分选系数较好,偏度总体上为负偏,个别样品为正态,金陵河以正偏为主,峰度都以较窄和极窄为主,表明沉积物优势粒级突出。通过分析渭河干流与支流河床沉积物的粒度特征,揭示了渭河干流宝鸡市区段及其主要支流均属于间歇性河流,物源以上游携带和沿岸侵蚀为主,两岸支流存在部分供给;根据渭河干流宝鸡市区段的粒度特征将其划分为两段,第一段宝鸡峡到神龙大桥,第二段神龙大桥至千河入渭口。     

大同土林地貌沉积物粒度特征分析

土林是在干旱-半干旱地区典型的流水侵蚀地貌,研究其物质组成可揭示土林沉积环境演变过程,为进一步探究土林的发育演化奠定基础.本文采用粒度分析方法,对其地层剖面沉积物组成特征进行了研究.结果表明:(1)大同土林沉积物的粒度组成以粉沙为主,平均含量高达50.6％,其次为黏土,平均含量为36.01％,粗颗粒组分的含量较低.(2...     

河岸沙丘粒度分布特征

沙丘沉积物粒度特征分析是研究风沙地貌过程的主要内容之一。通过野外实地考察与测量,并沿盛行风向对西辽河平原西部响水河两岸的河岸沙丘进行样品采集,经室内激光粒度仪测试,研究河岸沙丘的粒度分布规律。结果表明:1响水河东岸沙丘粒径粗于西岸沙丘。东岸沙丘由迎风坡脚到背风坡中下部粒径总体变细,从两侧坡脚到丘顶分选性逐渐变好。西岸沙丘由两侧坡脚到丘顶粒径变细,偏度趋于正偏,分选均较好。河流砂最细,其平均粒径总体细于东、西岸沙丘砂,分选性好于东岸沙丘,差于西岸沙丘。2东岸沙丘受河流与风力作用可以从较深地层获取沙源,西岸沙丘主要受风力作用从较浅地层获得沙源。     

乌鲁木齐河下游地区湖泊沉积物的粒度特征与沉积环境

根据乌鲁木齐河下游尾癌湖泊东道海子钻孔沉积物＾１４Ｃ年代和粒度分析,表明沉积物的粒度特征随着入湖水量的波动而发生有规律的变化。最近３０ｋａＢＰ以来该钻孔基本上处于比较稳定的湖泊沉积环境,说明东道海子至少有３万年的发育历史,这也说明古尔班通古特沙漠边缘地带的纵向沙垄具有相当程度的稳定性。最后几十年的湖泊变４干、环境退化过程主要是人类活动造成的。     

敦煌月牙泉景区沙丘表面沙物质的粒度特征

结合风况和蚀积监测数据,系统分析月牙泉南侧线性沙丘、北侧金字塔沙丘表面沙物质粒度特征及其环境指示意义。结果表明:(1)线性沙丘SW坡面以风蚀为主,NE坡面以风积为主,由此导致NE坡面表面沙物质较SW坡面细、分选性好。(2)月牙泉北侧金字塔沙丘SW坡面以风蚀作用为主,沙物质粒径最粗,分选最差。NW坡面也是主要的风蚀面,但由于靠近绿洲防护林,底部以风积为主。E坡面以风积作用为主,沙物质粒径最细、分选最好。(3)从风场、粒度和蚀积变化监测结果来看,对月牙泉危害最大的是南侧线性沙丘NE坡面的积沙。金字塔沙丘SW坡面中部的持续积沙也会对月牙泉构成潜在的威胁。因此,为了更好的保护月牙泉这一自然奇观,应该加强景区周边环境监测与管理。     

Near-surface wind environment in the Yarlung Zangbo River basin,southern Tibetan Plateau

Aeolian processes have been studied extensively at low elevations, but have been relatively little studied at high elevations. Aeolian sediments are widely distributed in the Yarlung Zangbo River basin, southern Tibetan Plateau, which is characterized by low pressure and low temperature. Here, we comprehensively analyzed the wind regime using data since 1980 from 11 meteorological stations in the study area, and examined the interaction between the near-surface wind and aeolian environment. The wind environment exhibited significant spatial and temporal variation, and mean wind speed has generally decreased on both annual and seasonal bases since 1980, at an average of 0.181 m/(s·10a). This decrease resulted from the reduced contribution of maximum wind speed, and depended strongly on variations of the frequency of sand-driving winds. The drift potential and related parameters also showed obvious spatial and temporal variation, with similar driving forces for the wind environment. The strength of the wind regime affected the formation and development of the aeolian geomorphological pattern, but with variation caused by local topography and sediment sources. The drift potential and resultant drift direction were two key parameters, as they quantify the dynamic conditions and depositional orientation of the aeolian sediments. Wind affected the spatial variation in sediment grain size, but the source material and complex topographic effects on the near-surface wind were the underlying causes for the grain size distribution of aeolian sands. These results will support efforts to control aeolian desertification in the basin and improve our understanding of aeolian processes in high-elevation environments.     

雅鲁藏布江曲水-乃东段沙化空间特征研究

雅鲁藏布江曲水-乃东段地处"一江两河"核心区域,土地沙化对区域经济发展和生态安全造成重大影响。通过收集多源数据,采用RS、GIS和数理统计方法,研究沙化分布特点及驱动机理。结果表明:沙地分布呈现北重南轻、西重东轻的格局,总面积621km2,占全区面积15%;沙化从轻度到极重度的面积大致呈现正态分布,极重度沙地面积95km2,占沙地总面积的15%;重度沙地153km2,占25%;中度沙地314km2,占51%;轻度沙地58km2,占9%;近东西向断层破碎带成为沙地发育和发展主体;海拔≤4200m的沙地占沙地总面积98%,坡度≤15°的沙地占沙地总面积85%,平地及全阳坡沙地占沙地总面积的77%;极重度沙地的沟壑密度平均值达659m/km2;近年来,雅鲁藏布江北岸及拉萨河东岸沙化大致维持扩散态势,与之隔河而望的区域因工程防治,沙化面积收缩。     

Study of the intensity and driving factors of land use/cover change in the Yarlung Zangbo River,Nyang Qu River,and Lhasa River region,Qinghai-Tibet Plateau of China

Land use/land cover (LULC) is an important part of exploring the interaction between natural environment and human activities and achieving regional sustainable development. Based on the data of LULC types (cropland, forest land, grassland, built-up land, and unused land) from 1990 to 2015, we analysed the intensity and driving factors of land use/cover change (LUCC) in the Yarlung Zangbo River, Nyang Qu River, and Lhasa River (YNL) region, Qinghai-Tibet Plateau of China, using intensity analysis method, cross-linking table method, and spatial econometric model. The results showed that LUCC in the YNL region was nonstationary from 1990 to 2015, showing a change pattern with fast-slow-fast and U-shaped. Built-up land showed a steady increase pattern, while cropland showed a steady decrease pattern. The gain of built-up land mainly came from the loss of cropland. The transition pattern of LUCC in the YNL region was relatively single and stable during 1990-2015. The transition pattern from cropland and forest land to built-up land was a systematic change process of tendency and the transition pattern from grassland and unused land to cropland was a systematic change process of avoidance. The transition process of LUCC was the result of the combined effect of natural environment and social economic development in the YNL region. This study reveals the impact of ecological environment problems caused by human activities on the land resource system and provides scientific support for the study of ecological environment change and sustainable development of the Qinghai-Tibet Plateau.     

Spatial heterogeneity for grain size distribution of eolian sand soil on longitudinal dunes in the southern Gurbantunggut Desert

The grain size composition, distribution characteristics and spatial variation of eolian sand soil on distinct positions across two longitudinal dunes and interdune areas were studied by means of conventional grain size analysis and geostatistical methods. In the study, 184 samples of eolian sand soil from the 0-30cm layer were systemically collected and measured from two longitudinal dunes and interdunes in the southern Gurbantunggut Desert. The results show that the dominant grain sizes are fine and very fine sands, and the differences of grain size compositions between the distinct geomorphologic positions are significant. The contents of clay and silt are highest on the interdune areas and lowest on the crests, and higher on the leeward slopes than on the windward slopes. The contents of very fine and fine sands are highest on the windward slopes and lowest on the crests. The contents of medium, coarse and very coarse sands are lowest on the interdune lands, and highest on the crests, and are identical on the two slopes. The coarser sizes (φ1) and mean sizes (Mz) for eolian sand soil all have a varying tendency from fine to coarse sizes with interdune area → leeward slope → windward slope → crest, and the sorting (σ) are poorly to well sorted. The results of geostatistical analysis reveal that φ1, Mz and σ values are moderately to strongly spatially autocorrelated. The values of the spatially correlated ranges are φ1<σ相似文献   

Morphology and formation mechanism of sand shadow dunes on the Qinghai-Tibet Plateau

The formation and development of dunes depend on wind-blown sand movement which is affected by the characteristics of sand material, topography, wind regimes and other factors. In this paper, we investigated two sand shadow dune groups in Shigatse and Za’gya Zangbo of Tibet and an individual dune in Da Qaidam of Qinghai, and analyzed their topographies and morphologies, and the physical characteristics of the sand, wind regime and sand transport. Formed under harsh conditions behind hills, these mature sand shadow dunes are hundreds of meters long, have significant ridges and crescent dunes downwind, and have a hill pass on one or both sides. Wind tunnel experiments revealed that the hill gap and wind velocity are important factors in the formation of these dunes. Sand shadow dunes formed only when the gap spacing is two-thirds of the hill height. When wind velocities are 20 m/s, the sand body is divided into two parts. The hill pass allows the transport of sand by wind, creating a "narrow-pipe effect", which causes the transported material to gradually accumulate in the center of the shadow zone. We observed that the following are needed for sand shadow dunes to form:(1) strong winds, sufficient sand, suitable obstacles and a dry climate;(2) one or both sides of the obstacle forming the shadow zone must have a hill pass; and(3) the windward side of the obstacle must have a wide, flat area, providing adequate spacing for wind flow and transport of material and the leeward side must have a sufficiently broad, flat area to allow the release of the transported material. Research results on these newly discovered dunes on the Qinghai-Tibet Plateau could contribute to the understanding of dune geomorphology.     

Sand source and formation mechanism of riverine sand dunes: a case study in Xiangshui River,China

Riverine sand dunes develop as a result of fluvial-aeolian interactions. The primarily barchan dune chains along the Xiangshui River (a branch of the Xar Moron River in the western part of the Horqin Sandy Land of China) form a typical riverine dune field. We collected a series of samples from the riverine sand dunes parallel to the direction of the prevailing wind and investigated the sand sources and formation mechanisms of these dunes by determining the grain size, heavy mineral content and optically stimulated luminescence (OSL) of the samples. The sand of the near-river dunes was coarser than the sand of the dunes distant from the river, indicating that coarse sand of the valley mainly deposited on near-river dunes. The heavy mineral analysis suggested that wind-sand activity levels were intense on the upwind dunes, but relatively weak on the downwind dunes. This indicated that the sand sources for the near-river dunes were more abundant than those of the distant dunes. Our OSL analysis of samples suggested that the deposition rates on dunes near the river were greater than the deposition rates on dunes distant from the river. The development of dunes along the river indicated that the river played an important role in dune formation and development. In addition, airflow fluctuation and the formation of the waveform dunes had a type of feedback relationship. Grain size, heavy mineral and OSL analyses are widely used methods in wind-sand research. Sand dune grain size characteristics reflect the effects of airflow on the transport and separation of sand materials, as well as the physical characteristics of the sand sources. Heavy mineral characteristics are often used to investigate the relationships between sediments and sand sources. OSL indicates dune age, revealing formation of dunes. Therefore, it is useful to explore dune sand sources, as well as the mechanisms underlying dune formation, by determining grain size, heavy mineral content and OSL. This study investigated the sand sources of riverine dunes and provided new information about riverine dune formation and development.     

3.34Ma以来河北平原衡水地区沉积物粒度特征及沉积环境意义

通过对河北平原衡水地区JZ孔的粒度测试与分析,探讨了3.34Ma以来该地区沉积物粒度特征、水动力条件及沉积环境演变历史.研究表明:3.34Ma.以来,沉积物平均粒径在0.74～4.80φ之间,粒径偏粗;分选系数处于0.88～2.21之间,属差-较好分选性;偏态在-0.2～2.89之间,以正偏为主;峰态范围处于1.88～...     

西拉木伦河流域地表沉积物粒度、化学元素分布特征

通过对内蒙古西拉木伦河流域沉积物的采样分析,结果表明:西拉木伦河地表沉积物的粒度组成以63~250μm粒径为主,粒度特征表现出一定的风成特点;化学组成以Si、Al为主,与上陆壳平均化学组成相比,除Si O_2、Co、As Ni、Ba、Ce等元素外,均处于不同程度的亏损;不同河段沉积物粒度参数、化学元素的分布具有一定相似性,且化学元素含量之间存在高度的相关性,均表明其具有相似的的物源;不同河段A-CN-K图解及CIA(化学蚀变指数)揭示了西拉木伦河不同河段地表物质化学风化程度均较低,处于较弱的去Na、Ca阶段。不同河段化学风化程度差异与其局地气候及地貌格局息息相关;不同地貌单元沉积物粒度组成、地球化学过程的递变规律与距河道远近、地貌、植被等因素有关;西拉木伦河平均粒径与一些元素的相关性,说明粒度和化学元素之间存在一定关系。总之,在不同空间尺度上,西拉木伦河地表沉积物理化特征的分异实质上反映了风动力和水动力的差异性分选。该研究对于构建风水两相沉积物综合判别指标等问题有着重要的意义。     

沙柳方格沙障对库布齐沙漠沙丘粒度分布的影响

为定量探讨沙柳方格沙障对沙粒粒度组成与特征的影响,以流动沙丘(LS)、设障2a沙丘(TS)和设障6a沙丘(SS)为研究对象,在沙丘不同部位、不同土层和障格内不同位置进行取样,分析样品的粒度组成与特征。结果表明:1)随着设障年限的增加,粘粒和粉粒含量增加,细砂含量下降,SS粘粒和粉粒含量与TS和LS的含量差异显著,而TS和LS二者间差异不明显;LS、TS各粒级含量在三个层次间差异均不明显,而SS 0-5cm的粘粒、粉粒以及极细砂粒体积含量较其他2层差异显著。2)SS的频率分布曲线变化幅度小于TS和LS的频率分布曲线变化幅度。各沙丘的平均粒径MZ、分选系数δ、偏度SK、峰度KG的大小顺序均表现为SS相似文献   

黄河晋陕峡谷吉县段全新世古洪水平流沉积特征研究

鉴别古洪水沉积物是古洪水水文学研究中最基本的任务。古洪水沉积物特征的研究对于识别古洪水沉积以及利用古洪水沉积物来恢复古洪水的水位,流量和发生规律都有十分重要的意义。通过对黄河晋陕峡谷吉县段流域深入调查,在黄河中游峡谷发现具有典型的古洪水平流沉积夹层的全新世黄土古土壤剖面。利用地貌学和第四纪地质学、沉积学,进而通过磁化率、粒度分析深入揭示了古洪水沉积物与风成黄土堆积物之间的主要区别。