雅鲁藏布江米林宽谷段爬升沙丘粒度分异特征研究   总被引：3，自引：0，他引：3  

周娜  张春来  刘永刚 《地理研究》2012,31(1):82-94

雅鲁藏布江米林宽谷段爬升沙丘分布广泛。选择卧龙镇西侧雅鲁藏布江右岸典型爬升沙丘,根据沙丘爬升高度和叠置沙丘地貌部位对其表面沉积物进行了系统采样。作为河谷风沙地貌的重要组成部分,相应采集了河漫滩、阶地沙丘沙样品。粒度分析表明,爬升沙丘对河漫滩沙丘、阶地沙丘在物源和形成过程方面具有继承性,其表面沉积物以细沙和极细沙为主(2.07～3.71Φ),分选中等或较好(0.20～1.41Φ),细偏,多峰。由坡脚向丘顶的沉积物粒径变细,分选变好,偏度和峰度降低。爬升沙丘表面叠置沙丘的粒度向丘顶变粗、分选变好。细沙、极细沙等粒级组分与高度相关,反映颗粒爬升能力不同。叠置条带状沙丘脊部和槽部的粒度存在分异。  相似文献   

青海巴颜喀拉山北麓古高位湖相沉积的分布与特征   总被引：3，自引：0，他引：3  

朱大岗  邵兆刚  孟宪刚  雷伟志  王津  韩建恩  余佳  吕荣平  钱程 《地质通报》2009,28(5):549-555

巴颜喀拉山北麓地区古湖岸线分布广泛,湖相沉积与湖成地貌发育。目前,在扎陵湖和鄂陵湖沿岸可清晰地划分出4级湖岸阶地、多级湖相沉积和古高位湖相沉积。古高位湖相沉积出露的最高海拔为4615m,分别高出现代扎陵湖水面328m、鄂陵湖水面346m;在扎陵湖和鄂陵湖谷地分布着多级湖岸堆积阶地或基座阶地、多级湖相沉积和古高位湖相沉积;在小野马岭、大野马岭、扎陵湖北等地的基岩山丘上,也发育有多级湖相沉积和古高位湖相沉积,其古高位湖相沉积高出现代扎陵湖和鄂陵湖湖面50～350m。巴颜喀拉山北麓古高位湖相沉积的形成时代可能为中更新世。  相似文献   

Aeolian dune‐field development in a water table‐controlled system: Skeiđarársandur,Southern Iceland     

NIGEL P. MOUNTNEY  ANDREW J. RUSSELL 《Sedimentology》2009,56(7):2107-2131

Aeolian dune fields characterized by partly vegetated bedforms undergoing active construction and with interdune depressions that lie at or close to the water table are widespread on Skei?arársandur, Southern Iceland. The largest aeolian dune complex on the sandur covers an area of 80 km² and is characterized by four distinct landform types: (i) spatially isolated aeolian dunes; (ii) extensive areas of damp and wet (flooded) interdune flat with small fluvial channels; (iii) small aeolian dune fields composed of assemblages of bedforms with simple morphologies and small, predominantly damp, interdune corridors; and (iv) larger aeolian dune fields composed of assemblages of complex bedforms floored by older aeolian dune deposits that are themselves raised above the level of the surrounding wet sandur plain. The morphology of each of these landform areas reflects a range of styles of interaction between aeolian dune, interdune and fluvial processes that operate coevally on the sandur surface. The geometry, scale, orientation and facies composition of sets of strata in the cores of the aeolian dunes, and their relationship to adjoining interdune strata, have been analysed to explain the temporal behaviour of the dunes in terms of their mode of initiation, construction, pattern of migration, style of accumulation and nature of preservation. Seasonal and longer‐term flooding‐induced changes in water table level have caused episodic expansion and contraction of the wet interdune ponds. Most of the dunes are currently undergoing active construction and migration and, although sediment availability is limited because of the high water table, substantial aeolian transport must occur, especially during winter months when the surface of the wet interdune ponds is frozen and sand can be blown across the sandur without being trapped by surface moisture. Bedforms within the larger dune fields have grown to a size whereby formerly damp interdune flats have been reduced to dry enclosed depressions and dry aeolian system accumulation via bedform climb is ongoing. Despite regional uplift of the proximal sandur surface in response to glacial retreat and unloading over the past century, sediment compaction‐induced subsidence of the distal sandur is progressively placing aeolian deposits below the water table and is enabling the accumulation of wet aeolian systems and increasing the likelihood of their long‐term preservation. Wet, dry and stabilizing aeolian system types all co‐exist on Skei?arársandur and the dunes are variously undergoing coeval construction, accumulation, bypass, stabilization and destruction as a result of interactions between localized factors.  相似文献   

Temporal variation of soil seed banks in two different dune systems in northeastern Inner Mongolia,China     

Q. L. Yan  Z. M. Liu  J. J. Zhu 《Environmental Geology》2009,58(3):615-624

To assess the potential contribution of soil seed banks to seedling recruitment, and to the vegetative processes of dune systems in semi-arid areas, a comparison of temporal variation in soil seed bank was made between active and stabilized dune systems in northeastern Inner Mongolia, China. The results showed that between-year difference in seed density for the stabilized system was smaller than that for the active one, but there were similar variations with season in seed bank for both dune systems. Furthermore, seed densities of the dominant species on the respective dune type (i.e., annuals on the stabilized dune and psammophytes on the active dune) varied more sharply with season, but more gently in annual variation than those of other phytogroups. These findings suggest that (1) seeds of annuals in the soil of the stabilized dune, or seeds of psammophytes in the soil of the active dune contributed much to seedling recruitment or plant species colonization, (2) the relationship between soil seed bank and seedling recruitment was complex in both dune systems.  相似文献   

华南泥盆纪古地理环境对宁乡式铁矿床时空分布、矿石特征的制约   总被引：1，自引：0，他引：1  

周家云  郑荣才  张裕书  朱志敏  李潇雨  罗丽萍  周满庚 《地质科技情报》2009,28(1)

泥盆纪宁乡式铁矿床是我国分布最广、储量最多的沉积型铁矿床,广泛分布于我国华南的鄂、湘、赣、川、滇、黔、桂等省(区)及甘南等地,矿床的时空展布和矿石组合受控于沉积盆地的古地理环境.根据宁乡式铁矿床的分布情况划分出8个成矿区,根据华南地区泥盆纪构造格局划分出8种盆地类型.在详细分析各盆地内矿床特征的基础上,总结出陆内凹陷盆地对成矿最为有利,晚泥盆世铁矿床相对集中,规模较大,矿化强度高;在同一盆地内,盆地边缘矿床的矿石为碱性矿石,多为贫矿,磷含量较低,靠近盆地中心的矿床规模巨大,矿石为酸性矿石,品位较高,富矿所占比重较大,磷含量较高.最后,针对不同类型矿石提出了其不同的可利用性和不同的矿物加工利用技术.  相似文献   

3.50Ma BP以来河北衡水地区古植被与环境演化     

范淑贤  刘海坤  徐建明  郑宏瑞  赵华  毕志伟  杨振京  林防  张静 《现代地质》2009,23(1)

依据河北衡水南张庄600 m深HS1钻孔中529块岩心样品的孢粉分析,结合古地磁、光释光测试建立的年代地层格架,初步建立了河北平原中部衡水地区3.50 Ma BP以来孢粉组合的更迭序列。在3.50~2.58 Ma BP期间,研究区沉积环境稳定,主要是极浅水泛滥平原与浅湖相沉积,孢粉不丰富,孢粉组合结构简单,反映降水、气温等变化幅度小,气候由温暖湿润逐渐过渡到冷干;2.58~0.78 Ma BP期间,植被出现频繁波动,我国东部古季风气候格局已经基本形成,表现出气候频繁变化的不稳定性,具有早期温和偏干、中期温暖湿润、晚期温凉偏干的气候演化特征;780~15 ka BP期间,孢粉带组成成分较为丰富且复杂,在不同时期乔木植物与草本-灌木植物互为消长、相互更迭,反映气候变化幅度大、频率高的特点;15 ka BP至今,气候总体表现为干,其波动频率较快,植被属森林和草原兼而有之的类型。  相似文献   

高密度电阻率法在铝土矿床上的应用   总被引：4，自引：0，他引：4  

李水平 《物探与化探》2009,33(1):8-9

沉积岩地层中,石炭系中统本溪组在奥陶系古风化面的凹陷地段（溶蚀盆 地、溶洼和溶斗）沉积厚度大,利于铝土矿的形成,为铝土矿的赋存场所。通过 高密度电阻率法在某矿区的成功勘探实例,说明高密度电阻率法在探测古岩溶盆 地、间接寻找铝土矿方面有好的应用效果。  相似文献   

Modern-style Subduction Processes in the Archean: Evidence from the Shangyi Complex in North China Craton   总被引：3，自引：0，他引：3  

WANG Renmin  WAN Yusheng  CHENG Suhu  FENG Yonggang 《《地质学报》英文版》2009,83(3):535-543

Abstract: Three fragments of the Archean oceanic crust have been found between the Archean granulite belt and the Paleo-Proterozoic Hongqiyingzi group in North China craton, which spread along the Shangyi-Chicheng ancient fault. This paper presents integrated field, petrology, geochemistry and geochronology evidence of the ancient oceanic fragments. The magma crystallizing age of the tonalite in the Shangyi complex is 2512±19?Ma and the geochemical characteristics suggest that the Nb-enriched basalts may be related to crustal contamination and formed in the intra-oceanic arc of the supra subduction zone setting.  相似文献   

石英光释光测年揭示的晚第四纪毛乌素沙地演化   总被引：12，自引：11，他引：1       下载免费PDF全文

何忠  周杰  赖忠平  杨林海  隆浩  梁剑鸣 《第四纪研究》2009,29(4):744-754

本研究利用石英光释光测年的单片再生法(Single­aliquot Regenerative­dose Protocol,简称SAR)对毛乌素沙地内部西北－东南方向5个风成砂－砂质古土壤剖面进行了年代测定,结合年代框架和剖面沉积相、磁化率及粒度特征探讨了晚第四纪以来毛乌素沙地演化和气候变化。研究表明毛乌素沙地在晚第四纪以来经历了多次沙地固定与活化的交替演化： 距今91.0ka,71.0ka,48.0ka,22.0ka,11.6ka,5.0ka,1.1ka,1.0ka和0.4ka前后风成砂沉积,沙地活化,指示气候干旱,植被覆盖度低; 在距今65ka和全新世适宜期(8.5～5.0ka),沙地固定成壤,砂质古土壤发育,指示气候湿润。另外,剖面中风成砂层数变多、厚度增加、粒径变粗指示了晚第四纪以来毛乌素沙地干旱化趋势加强。  相似文献   

基于不完整点云数据的3D柱状模型快速重建   总被引：2，自引：1，他引：1  

罗德安  廖丽琼  丁岩辉 《测绘科学》2006,31(4):100-102

在对古建筑仿真的特点和柱状目标重建中存在的技术问题进行充分地分析基础上,提出了一种基于不完整点云数据的3D柱状目标重建算法,并给出了算法的基本思想和实现方法。实验表明:算法对激光点云中的柱状目标探测和重建,具有良好的稳定性和较高的效率。  相似文献