乌海盆地内末次冰期砂楔/冰楔铸型的发现及古气候意义  

Discovery of Sand Wedge/Ice Wedge Cast of Last Glaciation in Wuhai Basin and Its Paleoclimatic Significance

作　　者：李大伟[1] 李德文[1] 沈晓明[1] 孙昌斌[1] 康艳蕊 张亚娇[1] 

机构地区：[1]中国地震局地壳应力研究所地壳动力学重点实验室,北京100085

出　　处：《地球科学与环境学报》2016年第3期410-419,共10页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(41171001;41471002)

摘　　要：砂楔/冰楔铸型等具有定量古环境意义的冰缘现象在中国北方已有多处报道,但多集中在末次冰期晚冰阶。报道了首次发现于乌海盆地的冰缘现象,从楔体形态特征、填充物粒度特征和光释光测年等方面对其成因和发育年代进行了深入研究。楔体和填充物剖面穿插关系、物质组成和形态特征分析等指示其形成过程大致可分为两个阶段:早期原生砂楔发育与楔壁近平行的充填-挤压构造;晚期冰楔铸型(包括冰楔形成、融化和填充)在砂楔之上进行叠加。冰楔切穿早期砂楔,导致楔壁物质发生强烈挤压变形,结构扰动,楔体表现为弯曲的不规则形态。光释光测年结果显示,原生砂楔发育的年代主要集中在(62.69±6.81)^(66.45±7.08)ka B.P.,即末次冰期早冰阶,对应于MIS4阶段,并可能部分延续至MIS3b阶段;冰楔铸型填充物年代为(5.95±0.61)^(6.62±0.73)ka B.P.,对应于全新世中期。由于冰楔铸型的填充晚于冰楔发育年代,推测冰楔发育年代可能为末次冰期晚冰阶。基于砂楔/冰楔铸型的发育过程及对环境条件的要求,初步估算出砂楔和冰楔发育时期年均气温比现在低12.1℃~13.6℃,砂楔发育时期(即末次冰期早冰阶)年降水量与现在相当。乌海盆地砂楔/冰楔铸型的发现为研究中国北方末次冰期尤其是末次冰期早冰阶纬度多年冻土分布及古气候环境提供了新的依据。The periglacial phenomena like sand wedge/ice wedge cast have been discovered with the paleoclimatic and paleoenvironmental significances in the northern China.But most of them are dated to the late stage of last glaciation.The periglacial phenomenon discovered firstly in Wuhai Basin was reported.Characteristics of morphology,grain size analysis of filler and OSL dating were applied to identify the origin and age,including that the early primary sand wedge encompasses a set of structures almost parallel with the wall around it,and the late ice wedge cast（including its formation,melt and fill）is superposed on the sand wedge.The ice wedge cuts through and damages the structure of the primary sand wedge,and the wedge is characterized with bend and irregular boundary as a whole.OSLdating results show that the primary sand wedge is formed during the early last glaciation（（62.69±6.81）-（66.45±7.08）ka B.P.,MIS4）,and may go down to MIS3b;the filler of ice wedge cast is formed during the Middle Holocene（（5.95±0.61）-（6.62±0.73）ka B.P.）.Because the filling of ice wedge cast is later than the formation of ice wedge,it is probably that the formation of ice wedge is during the late last glaciation.Based on the formation process of sand wedge/ice wedge cast and their environmental requirement,it is estimated that the annual mean temperature has dropped 12.1℃-13.6℃from the formation of sand and ice wedges to present,and the annual precipitation is of no significant difference from the formation of sand wedge（the early stage of last glaciation）to present.The discovery of sand wedge/ice wedge cast in Wuhai Basin could provide a basis for studying the distribution of permafrost and the paleoclimate during the last glaciation（especially the early stage）in the northern China.

关 键 词：冰缘现象 砂楔 冰楔铸型 古气候 末次冰期 光释光测年 粒度分析 乌海盆地 

分 类 号：P931.4[天文地球—自然地理学]