The Horqin dunefield is situated in the southeast of Inner Mongolia Autonomous Region which is the transition zone of Inner Mongolia Plateau and North East China Plain.The geographic coordinates is about 42°15'～45°45 'N, 118°15' ～123°30'E which extend to Shuangliao County and Qian'an County to the east,Lindong County and Linxi County to the west,the east of Daxing'anling Mountain to the north and loess hill of northern Yanshan Mountain to the south.Sixteen profiles, which are located at three north-south routes, were taken at critical points.Thirteen of them are aeolian sequences,and three of them are loess deposits.The study of grain-size ,magnetic susceptibility and sediment color were applied to sequence of dark sandy soil and the underlying sand at 5 ～ 10cm intervals.24 samples just below the boundary between dark sandy soils and sand were collected and dated by OSL methods.The age span of 13 ～ 10ka of the aeolian sand is part of the last late glacial.The cold and dry climate leaded to continuous reworking of aeolian sand of last glacial maximum ( 26.5 ～ 19.0ka).The dune field was not totally stabilized by vegetation cover until Holocene Optimum (10～5kaB.P.).The results of environmental proxies such as grain size and magnetic susceptibility for the two featured profiles are presented as follows.Median grain size decreased from 150 ～ 200μm in last late glacial to 100 ～ 150μm in Holocene, and the silty sand (<63μm) increased from 10% to 40% , which indicated that mobile dunes developed under the control of strengthened wind in last late glacial.The increase of magnetic susceptibility from 15 SI to 20 -25 SI also indicated that cold and dry last late glacial turn to warm and humid in Holocene.The area of present Horqin dunefield is 42, 000km , 10% of which is mobile dune.Comparatively, the mobile sand area amounted to 85,000km2 during LGM including the current stable dunes,sandy plain and nearby marshland.So the sand expansion in the last late glacial was 20 times bigger than that of today.The sand supply for the dune expansion in LGM resulted from two factors; 1 ) Cold and dry climate in glacial resulted in poor vegetation cover.Loose surface deposits were eroded by wind and turned into mobile sand; 2) river system inside the Horqin dunefield is abundant.Exposed river bed during glacial period supplied sand source for dune extension.%对中国东北地区科尔沁沙地13个风成沙剖面和3个黄土剖面进行了研究,测试分析了黑色砂质土壤和下伏古风成沙的OSL年龄及粒度、磁化率、色度数据；OSL测年获得的古风成沙数据位于末次冰期晚期-全新世期间(13 ～1Oka),小于26.5 ～19.Oka的末次冰盛期时段.末次冰盛期干冷气候背景下沙丘持续不断的活化翻动,风成沙在进入全新世气候转暖后才被固定,沙地内全新世黑色砂质土壤下伏的疏松流沙为末次冰盛期产物,其分布范围可代表末次冰盛期流动沙丘的分布范围.现今科尔沁沙地面积约为42000km2,活动沙丘面积约占10％.在末次冰盛期不仅原固定沙丘活化,沙质平原与部分甸子也被流沙覆盖,面积约85000km2,活动沙丘或流沙面积相对目前扩大了约20倍.末次冰盛期沙地活化扩张的控制因素主要有两方面:一方面冰期气候干旱寒冷,降水减少,地表植被覆盖下降,地表松散沉积物遭受风力剥蚀而活化成流沙；另一方面科尔沁沙地内部水系发育,河流流经途中会沉积大量松散物质.在冰期干冷环境下,河流水位下降,河流沙暴露并遭受风蚀改造,为流沙扩张提供物源,沙漠沿西拉木伦河流域扩展.
展开▼
