灌丛沙丘形成演化及环境指示意义研究的主要进展

干旱半干旱区风沙活动较强烈, 风沙地貌十分发育, 环境演变过程对气候变化响应敏感。由于缺乏高分辨率载体, 在这些地区进行环境变化重建的手段及获得的结果相对贫乏。但是在这些区域发育的灌丛沙丘是风沙堆积体, 其形成演化记录了相对丰富的区域环境演变信息。本文综述了目前在灌丛沙丘形态学特征、发育过程、以及其在区域环境变化重建中的意义等方面的研究进展。我们认为, 灌丛沙丘形成演化研究在揭示干旱区环境演变过程方面有重大的意义, 但还没有形成系统的体系, 这一方面的研究仍有较大的空间。     

河西走廊新月形沙丘表层沉积物的理化性质

沙丘表层沉积物的理化特征是风沙地貌研究的重要内容。选取了河西走廊沙漠中部戈壁地表发育的新月形沙丘、灌丛沙丘及附近的湖相沉积物和戈壁表层沉积物的38个样品，对其物理性质（平均粒径、分选程度、峰度、偏度）和化学性质（常量元素和微量元素）进行分析。结果表明：河西走廊新月形沙丘表层沉积物粒度以中沙为主（21.65%~57.39%），其次是细沙（23.22%~52.96%）；平均粒径为0.27~0.43 mm，大于其他沙漠。分选性以中等较好为主，粒度曲线近对称，峰度中等。常量元素以CaO和SiO₂为主，分别为5.55%和66.12%；微量元素含量在同一沙丘具有相似性，但不同的沙丘之间的含量有所差异。     

黑河下游地区柽柳沙丘的气候与环境记录

对黑河下游地区柽柳沙丘沉积剖面进行AMS¹⁴C定年及沉积物粒度和Hg含量的综合分析,探讨了该区域从18世纪中期到21世纪初的气候与环境变化。结果表明:沙丘沉积物以细沙为主,粒度频率分布曲线呈明显的单峰形态,反映了单一的风力沉积作用;>100 μm的粗颗粒含量变化很好地指示了该区域冬季风的强弱变化,并记录了小冰期末期以来气候转暖的过程以及现代暖期中两个相对寒冷时期——20世纪10-20年代和50-60年代。沙丘沉积物中Hg主要来源于人类的工业活动,剖面Hg含量存在3个峰值,分别对应18世纪末的西班牙美洲地区银矿开采、19世纪中后期的北美淘金热、二次世界大战及战后经济复苏。此外,剖面中有两个样品Hg含量异常升高,其原因可能是1815年和1883年印尼的两次大规模火山喷发而引起的全球Hg沉降增加。     

中纬度荒漠区河西走廊沙丘地貌的演化特征及其环境指示

北半球中纬度地区的沙丘地貌变化和粉尘活动历史是探索全球环境变化与景观响应问题的良好档案。本文从风沙地貌学、粒度沉积学、地球化学和气候学等方面综合分析了中纬度典型荒漠区河西走廊的典型沙丘动态变化、物质来源、粉尘活动历史及其影响因素等。结果表明,20世纪60年代以来研究区典型新月形沙丘和新月形沙丘链等发生了较大的移动或摆动,平均移动速度介于0.8~6.2 m/a之间。沙丘的动态变化主要受年降水量、年平均风速和年大风日数的影响,表明气候是沙丘地貌变化的首要影响因素。沙丘沙（三段式）与戈壁沉积物的两段式粒度曲线模式明显不同,揭示了后者在沉积学上的“不成熟性”而前者经历了高效的风成分异作用且非局地起源。古地理、沉积学和地球化学综合证据揭示沙丘沙的母源物质主要是冲洪积物和古河流沉积物等,包括南北山麓剥蚀带的碎屑沉积等。地表细颗粒物质的比例、表层盐结皮的覆盖率和可蚀性砂质物质含量等指标指示了西部戈壁区不是中东部风尘的主要来源区。沙丘移动方向与区域性主导风向在空间分布上具有相似性,表明河西走廊东、西部间之间在沙丘地貌动态演化上的差异应受控于区域尺度的环流风系,即受控于动力机制而不是物质来源上的差异。区域气候的暖湿化是对全球增温和亚洲夏季风增强的同步响应,也是研究区沙尘暴减少的主要原因,同期河西走廊潜在的逆沙漠化过程亦受控于气候变化;但绿洲区沙漠化过程还是起因于人类活动影响的地下水波动。     

柴达木盆地灌丛沙丘稀土元素地球化学特征与物源

分析了柴达木盆地灌丛沙丘剖面风沙沉积物中稀土元素及其相关特征参数、分布模式和（La/Yb）_N-REE（稀土元素）物源特征。结果表明：灌丛沙丘剖面风沙沉积物中REE值100.52~163.47 μg·g^-1,接近于新疆灰钙土,而略低于中国黄土;LREE（轻稀土元素）值87.80~144.65 μg·g^-1,占总量86.62%~90.53%,决定了稀土总量的变化。总体表现为LREE相对富集,而HREE（重稀土元素）丰度相对较低,分馏特征基本相似,呈斜"L"型缓右倾斜,Eu大致呈现中度负异常的分配模式,而Ce未表现出明显异常,且更多地反映了其物源特性。其物源主要由东昆仑北麓冲积扇碎屑沉积物质经过风化、搬运、沉积而成,而并非来自于干旱期的湖底剥蚀物。总体而言,灌丛沙丘沉积过程稀土元素分异特征反映了灌丛沙丘发育时期柴达木盆地总体处于干燥的气候环境,化学风化作用弱,植被发育相对较差,成壤作用不明显。     

青海湖湖东沙地沉积记录的全新世以来风沙活动变化

青海湖湖东沙地典型剖面的AMS¹⁴C测年数据表明该剖面记录了当地约10 ka BP的风沙活动及环境变化。对沉积物的粒度组成特征、粒度参数、粒度环境敏感指标等分析,并结合沉积物磁化率和青海湖盆地相关研究中风成砂、黄土和弱发育古土壤、古土壤的OSL、AMS¹⁴C年代数据等,进行全新世以来的风沙活动及气候环境变化讨论。结果表明：（1）粗颗粒敏感组分（138~156μm）可以用来指示风沙活动的强弱,细颗粒敏感组分（2~5 μm）可以用来指示成壤作用。（2）10~9ka青海湖盆地气候状况较全新世之前略有好转,暖湿程度增加,部分区域开始发育古土壤,但总体上古土壤、弱发育古土壤、黄土、风成砂共存;9~4.2 ka青海湖盆地水热组合条件较好,风沙活动弱,大部分沙丘固定成壤,但9~8 ka和4.2 ka左右风沙活动较为频繁的特征可能指示了8.2 ka和4ka冷事件;4.2 ka之后特别是2 ka之后风沙活动显著增强,气候朝干冷化发展。     

基于倾斜摄影技术的戈壁灌丛沙丘形态反演及其对粉尘释放研究的意义

灌丛沙丘是广泛分布于西北干旱区的风沙地貌。戈壁上发育的灌丛沙丘在戈壁沙尘释放和固沙能力方面具有重要的指示意义和应用价值。本研究采用倾斜摄影技术对戈壁上的灌丛沙丘形态特征进行观测和提取,并分析沉积物特征,计算戈壁灌丛沙丘的固沙能力,为沙尘释放研究提供依据。结果表明:(1)戈壁上发育的灌丛沙丘有明显的空间分布格局,即主要分布在干河床的两侧和地势低洼地区。(2)戈壁灌丛沙丘在形态上和其他地表灌丛沙丘类似,但沙丘的长度、宽度、底面积、体积等小得多,而且参数之间具有明显的相关关系。(3)沉积物的累积概率曲线表现为三段式,跃移组分的粒度范围(50~700 μm)明显与以往研究不同。沙丘内部和表层的粉沙和黏土含量分别为4.47%和5.24%,从而说明灌丛沙丘能够捕获戈壁上释放的粉尘物质。(4)戈壁地区单个灌丛沙丘的粉尘释放量约0.05~0.08 m³,固沙能力最大可达18.71 m³。     

乌兰布和沙漠流动沙丘下风向降尘粒度特征

选择乌兰布和沙漠典型流动沙丘进行定点野外观测,分析了沙丘下风向不同距离及不同高度降尘的粒度特征及其来源。结果表明:乌兰布和沙漠降尘空间变化大,降尘以细沙为主,随着距离的增加,细沙物质逐渐减少,粉沙和极细沙含量显著增加。降尘平均粒径2.5~3.1 Φ,且随距离、高度的增加而变大。分选系数随着距离、高度的增加而变差; 2 m高度偏度近乎对称,若设沙丘高度为H,则只有在距离为8 H时正偏,高0.5 m处降尘在距沙丘0.5~1 H近对称,2~8 H皆是正偏;峰度随距离的增加逐渐变窄,且2 m高度的变化晚于0.5 m高度。乌兰布和沙漠降尘以局地物质为主,远源物质及区域物质比例很低。<70 μm的远源物质及区域物质的降尘与下风向距离呈正相关,主要来源于沙漠边缘的荒地、河湖沉积物、农田草地,而>70 μm的局地物质的降尘与下风向距离呈负相关,主要来源于沙丘下垫面沙粒的气流短距离输送。     

若尔盖盆地沙漠化驱动机制

作为世界上最大的高寒泥炭沼泽湿地,若尔盖盆地是黄河水源的重要补给区,素有黄河"蓄水池"之称.作为生态敏感区,在自然环境和不合理的人为活动的影响下,若尔盖盆地出现了湿地萎缩、草场退化、沙地增加等一系列严重的生态环境问题.本文通过分析若尔盖盆地沙漠化现状及其驱动因素,进而阐述和分析沙漠化驱动机制.结果表明:若尔盖盆地广泛分布的古风沙沉积物是现代沙漠化的沙物质来源,地表致密草皮层的机械破坏,使下伏松散的古风沙沉积物暴露,是形成沙漠化的关键一步;随后在风蚀、雨水冲刷及生物因素的共同作用下,松散的古风沙沉积物被侵蚀,引起草皮层坍塌,导致古沙丘活化,风沙活动加剧,形成风沙沉积;若尔盖沙漠化是人为因素与自然因素共同作用的结果,其中人为因素是其主导驱动因素,鼠类活动和热融沉陷、滑塌是沙漠化的诱发因素.     

青海高原沙漠化研究进展

20世纪50年代末到21世纪初,对青海高原沙漠化的分布、基本特征、沙丘类型、形成演化、风沙移动规律、野外观测、沙化监测的科学考察研究到防沙治沙试验的过程;从地域上涉及了青海的柴达木盆地、共和盆地、青海湖盆地、黄河源区和长江源区全部5个沙漠化土地分布地区,全面综述了高原沙漠化研究的成果、防沙治沙经验和研究进展,提出了存在的问题及今后研究的内容。     

Nebkha （coppice dune） formation and significance to environmental change reconstructions in arid and semiarid areas

Environments in arid and semiarid regions are extremely sensitive to climate changes.High wind activity in these regions has resulted in an extensively developed arid geomorphology,but past environmental changes are poorly understood because of the absence of relatively high-resolution proxies.The accumulation characteristics of nebkhas,which have developed extensively in these regions,can be used as a method of reconstructing environmental changes.Here we summarized recent advances in research on the formation,development,and sediment characteristics of nebkhas and their significance to environmental changes in arid and semiarid regions.Based on the studies of our colleagues,we suggested that research on nebkha formation can provide distinct clues about environmental changes in arid and semiarid regions;however,continued studies are needed.     

毛乌素沙地西南缘灌丛沙丘沉积物的粒度和元素特征

对毛乌素沙地白刺(Nitraria tangutorum)灌丛沙丘沉积物粒度和元素特征进行了采样分析.结果表明:灌丛沙丘沉积物来源单一,几乎全部由丘间地物质组成,其粒度和元素特征与丘间地物质极其相似;相对而言,灌丛沙丘沉积物比丘间地物质含有更多粗颗粒物,主要因丘间地可做跃移运动的中沙和细沙更易被灌丛阻挡而堆积;灌丛沙丘沉积物中大部分元素含量比丘间地物质低,主要因这些元素易被淋溶迁移到丘间地富集;灌丛沙丘发育以来,虽然其沉积环境存在波动,但相对稳定,未发生过显著变化.     

Formation and evolution of sand deserts in Xinjiang,Northwest China: I. Provenances ofdesert sands简

Sandy desert landscape is a geological product of arid climate and abundant sand materials supply in natural conditions, therefore the formation of sandy desert is an ideal studying object for understanding the interaction between various stratigraphic/epigenetic spheres of the earth system. However, until now, the knowledge about the provenance and formation of these deserts in Xinjiang, Central Asia is diverse and inconsistent, a systematic review is necessary. Ancient aeolian sand sediments in the internal areas of these deserts and their twin dust deposits in the Cenozoic strata surrounding the Xinjiang deserts are direct and indirect clues reflecting the provenance of sand materials and the formation and evolution of deserts. Based on the geochemical, mineralogical and isotopic evidences of desert sands and relevant deposits in the peripheral regions, this paper reviews the research progress on the development of the sandy deserts in Xinjiang, Northwest China. Many proofs proposed that desert sands in Xinjiang were mainly sourced from the ancient pluvial, alluvial and fluvial sediments and were eventually achieved because of the local sand supply. It pointed out that the settings of tectonic structure in Xinjiang had made sediments both in the Tarim Basin and the Junggar Basin being influenced greatly by regional hydrological system and aeolian processes originated from the planetary wind system of westerly, the East Asian winter monsoon and the topographical mountain-valley winds. However, the directions of transpor- tation paths are different between the hydrological dynamics and the aeolian dynamics, which are decided by the slantwise structures of the basins tectonics and the regional atmospheric circulation routes, respectively, and have determined anisotropies of the transport pathway of these sediments delivered by different agents. This results in a geological cycle of detrital sediment transportation in the two large sediment mixing, alternation and recycle basins and thus largely increases the degree of between younger and older sediment sources, as well as the complexity and diversity of sand provenances.     

晚冰期以来河西走廊花海古湖泊演化过程及其对气候变化的响应

通过分析河西走廊花海古湖泊沉积物中的盐类矿物组成,结合年代序列,重建了花海晚冰期以来湖泊演化过程及其对气候变化的响应。结果表明：晚冰期及新仙女木时期,花海湖泊以芒硝沉积为主,属硫酸盐型湖泊,湖水的盐度较高且周期性波动频繁;全新世早期（10.47 cal ka BP以前）,湖泊以洪泛堆积和风成沉积为主,揭示了湖泊萎缩、甚至干涸;全新世早期至全新世中期（10.47～8.87 cal ka BP）盐类矿物以碳酸盐沉积为主,为碳酸盐型湖泊,湖水淡化,湖泊水位开始逐渐回升;全新世中期（8.87～5.50 cal ka BP）盐类矿物呈现一定的波动变化,其中,8.8 cal ka BP 时期盐类矿物以硫酸盐沉积为主,湖泊由碳酸盐型转化为硫酸盐型,湖水咸化,盐度升高;随后盐类矿物以碳酸盐沉积为主,湖泊由硫酸盐型转化为碳酸盐型,湖水盐度降低、湖泊扩张;全新世中晚期（5.50 cal ka BP以来）出现沉积间断,表明中晚全新世时期湖泊逐渐萎缩。在全新世期间,花海湖泊千年尺度演化过程揭示了该区域气候干湿状况受亚洲季风和西风共同控制的影响。     

黄河源区玛多盆地沙漠化土地粒度特征

为探讨黄河源区玛多盆地风沙沉积物分异特征,采集玛多盆地不同沙漠化程度、不同地貌部位、不同动力条件的沉积物样品进行粒度分析。结果表明：（1）玛多盆地沉积物随沙漠化程度增加,平均粒径增大,粗颗粒组分增多,分选性变好,偏度向负偏靠拢,峰态逐渐转向平坦,频率分布曲线也由双峰态转变为单峰态。（2）流动沙丘以中沙和细沙组分为主,分选性好,偏度近对称,峰度为中等尖锐。各个沙丘不同地貌部位沉积物粒度参数分异受风向改变的影响,变化规律不明显。流动沙丘沉积物相较于流动沙地沉积物的粒径更粗,分选性更好,可能是沙丘形成过程中风对沉积物颗粒的再次分选所致。（3）河流阶地剖面沉积物的主要粒级为中沙和细沙,分选中等偏差,偏度为正偏,峰尖锐,河流阶地沉积物的粒度组成与周围风成作用形成的流动沙丘（地）的粒度组成高度相似,极有可能是当地风沙活动的主要物源。     

Formation and evolution of sand deserts in Xinjiang,Northwest China：Ⅰ. Provenances of desert sands

Sandy desert landscape is a geological product of arid climate and abundant sand materials supply in natural conditions, therefore the formation of sandy desert is an ideal studying object for understanding the interaction between various stratigraphic/epigenetic spheres of the earth system. However, until now, the knowledge about the provenance and formation of these deserts in Xinjiang, Central Asia is diverse and inconsistent, a systematic review is necessary. Ancient aeolian sand sediments in the internal areas of these deserts and their twin dust deposits in the Cenozoic strata surrounding the Xinjiang deserts are direct and indirect clues reflecting the provenance of sand materials and the formation and evolution of deserts. Based on the geochemical, mineralogical and isotopic evidences of desert sands and relevant deposits in the peripheral regions, this paper reviews the research progress on the development of the sandy deserts in Xinjiang, Northwest China. Many proofs proposed that desert sands in Xinjiang were mainly sourced from the ancient pluvial, alluvial and fluvial sediments and were eventually achieved because of the local sand supply. It pointed out that the settings of tectonic structure in Xinjiang had made sediments both in the Tarim Basin and the Junggar Basin being influenced greatly by regional hydrological system and aeolian processes originated from the planetary wind system of westerly, the East Asian winter monsoon and the topographical mountain-valley winds. However, the directions of transportation paths are different between the hydrological dynamics and the aeolian dynamics, which are decided by the slantwise structures of the basins tectonics and the regional atmospheric circulation routes, respectively, and have determined anisotropies of the transport pathway of these sediments delivered by different agents. This results in a geological cycle of detrital sediment transportation in the two large basins and thus largely increases the degree of sediment mixing, alternation and recycle between younger and older sediment sources, as well as the complexity and diversity of sand provenances.     

新疆地区沙漠的形成与演化——I.沙漠沙的物源（英文）

Abstract:Sandy desert landscape is a geological product of arid climate and abundant sand materials supply in natural conditions,therefore the formation of sandy desert is an ideal studying object for understanding the interaction between various stratigraphic/epigenetic spheres of the earth system.However,until now,the knowledge about the provenance and formation of these deserts in Xinjiang,Central Asia is diverse and inconsistent,a systematic review is necessary.Ancient aeolian sand sediments in the internal areas of these deserts and their twin dust deposits in the Cenozoic strata surrounding the Xinjiang deserts are direct and indirect clues reflecting the provenance of sand materials and the formation and evolution of deserts.Based on the geochemical,mineralogical and isotopic evidences of desert sands and relevant deposits in the peripheral regions,this paper reviews the research progress on the development of the sandy deserts in Xinjiang,Northwest China.Many proofs proposed that desert sands in Xinjiang were mainly sourced from the ancient pluvial,alluvial and fluvial sediments and were eventually achieved because of the local sand supply.It pointed out that the settings of tectonic structure in Xinjiang had made sediments both in the Tarim Basin and the Junggar Basin being influenced greatly by regional hydrological system and aeolian processes originated from the planetary wind system of westerly,the East Asian winter monsoon and the topographical mountain-valley winds.However,the directions of transportation paths are different between the hydrological dynamics and the aeolian dynamics,which are decided by the slantwise structures of the basins tectonics and the regional atmospheric circulation routes,respectively,and have determined anisotropies of the transport pathway of these sediments delivered by different agents.This results in a geological cycle of detrital sediment transportation in the two large basins and thus largely increases the degree of sediment mixing,alternation and recycle between younger and older sediment sources,as wellas the complexity and diversity of sand provenances.