呼伦贝尔沙地末次冰盛期晚期至全新世风成沙表面矿物特征及环境意义
作者简介:杨利荣(1978- ),女,山西新绛人,讲师,研究方向为干旱区第四纪环境与光释光年代学。E-mail: lryang@163.com
收稿日期: 2014-11-28
要求修回日期: 2015-03-13
网络出版日期: 2015-07-12
基金资助
国家自然科学基金项目(40802039,4172036)
The environmental implication from microscopic texture of eolian sand of Hulun Buir duneland centred on late last glacial maximum and Holocene
Received date: 2014-11-28
Request revised date: 2015-03-13
Online published: 2015-07-12
Copyright
运用扫描电镜与能谱分析,研究呼伦贝尔沙地末次冰盛期晚期以来全样风成沙的微区形态和粘土矿物成分。呼伦贝尔沙地的沙粒磨圆度较好,在扫描电镜观察下保存了水成沙粒的特征,意味着沙地物源曾经流水作用到达该区域。颗粒表面同时留有风力搬运的碟型坑等撞击痕迹,为干枯河床沙丘活化、风力搬运流动扩张的过程提供证据。末次冰盛期晚期风成沙颗粒大且表面光滑洁净,未见次生粘土矿物,反映出冰期地表无植被发育,区域沙漠活化、流动性加强。而全新世适宜期的褐色沙质土壤砂粒表面同时发育鳞片状自生粘土矿物和同沉积粘土颗粒及团块。能谱分析表明:全新世适宜期,风化自生粘土矿物有蒙脱石和伊利石,在相对温湿气候条件下,发育干旱碱性土壤,反映出冰后期植被发育、土壤化作用增强。
杨利荣 , 岳乐平 , 弓虎军 . 呼伦贝尔沙地末次冰盛期晚期至全新世风成沙表面矿物特征及环境意义[J]. 地理研究, 2015 , 34(6) : 1066 -1076 . DOI: 10.11821/dlyj201506006
Scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) have been applied simultaneously in order to observe micromorphology and clay mineral for the whole grains from aeolian sand of Hulun Buir dunefield since the late last glacial maximum. Based on the OSL age of the alternate layers, climatic proxies including grain size, magnetic susceptibility, organic carbon content and chroma have also been measured to correlate with the environmental indications from SEM and EDS. The fairly roundness indicated the fluvial sedimentary origin. The collision pits were also been observed which are typical eolian evidence. The coexistence of fluvial and eolian surface texture of the depositing sands in this duneland implies that the dried fluvial sand in river-bed was reworked by wind erosion. Glacial sand has clear surface without any clay mineral attachment, which suggests slightly weathering resulting from intensified winter monsoon erosion and barren mobile desert. However, sandy soil of Holocene optimum has not only developed flaky authigene clay, but also adhered immigrated clay grain and block. The authigene clay minerals are montmorillonite and illite evidenced from EDS, which are typical indicative clays of alkaline soil. The abundance of clay minerals states that relatively humid and warm climate and developed vegetation cover. The depositing alternations of aeolian sand of last glacial maximum and sandy soil of Holocene optimum were also developed in other eastern China dunefields. The combination of SEM and EDS aiming to observe clay mineral in this study can definitely be referred to the environmental research in other dunefields. The analyses of grain surface are effective methods to reveal the sand source and transportation process apart from environmental information. Fixed dunes under the vegetation cover in Holocene optimum not only decreased the output of sand grains, but also degraded the grain-size resulting from physical and chemical weathering. Hence, being finer of accumulated sandy soil was mainly affected by sand decrease and degradation of regional output rather than weakened winter monsoon during the humid and warm Holocene optimum.
Fig. 1 Map of the study area and sampling locations图1 研究区采样位置图 |
Tab. 1 OSL age of samples表1 测试样品年代清单 |
点号 | 样品名 | 深度(m) | 岩性 | 光释光年龄 (a) |
---|---|---|---|---|
1 | EWK | 0.6 | 风成沙 | 13400±2100 |
4 | XBEH-2 | 0.8 | 砂质土壤 | 7900±1100 |
8 | CG-7 | 0.6 | 风成沙 | 50±10 |
8 | CG-6 | 0.9 | 砂质土壤 | 680±120 |
8 | CG-4 | 1.4 | 风成沙 | 2300±310 |
8 | CG-3 | 1.6 | 砂质土壤 | 4900±500 |
8 | CG-1 | 2.5 | 风成沙 | 11800±1500 |
9 | XYQ | 0.6 | 风成沙 | 15300±2900 |
11 | XZQ-2 | 0.5 | 砂质土壤 | 8300±1500 |
12 | HLR-2 | 8.1 | 风成沙 | 12500±2300 |
14 | BYCG | 0.6 | 风成沙 | 11400±1400 |
16 | YM | 0.6 | 风成沙 | 10400±2000 |
18 | HDG | 0.5 | 风成沙 | 9500±1800 |
Fig. 2 Environmental proxies and SEM of CG profile图2 嵯岗剖面环境指标及颗粒扫描电镜结果 |
Fig. 3 SEM and EDS of flaky authigene clay on the sureface of feldspar (CG-2)图3 长石表面鳞片状自生粘土矿物扫描电镜—能谱(CG-2) |
Fig. 4 SEM and EDS of adhered immigrated clay grain on the sureface of quartz (CG-2)图4 石英表面附着外来粘土矿物颗粒扫描电镜—能谱特征(CG-2) |
Fig. 5 SEM and EDS of adhered immigrated clay grain on the sureface of quartz (CG-2)图5 石英颗粒表面附着的粘土颗粒的扫描电镜—能谱特征(CG-2) |
Fig. 6 SEM and EDS of montmorillonitizated grain (CG-4)图6 颗粒表面蒙脱石化的扫描电镜—能谱特征(CG-4) |
Fig. 7 SEM and EDS of unweathered feldspar grain (CG-5)图7 颗粒表面未风化长石的扫描电镜—能谱特征(CG-5) |
Fig.8 Microscopic texture of eolian sand of late last glacial and holocene图8 末次冰盛期晚期至全新世风成颗粒表面特征扫描电镜(a:颗粒整体磨圆;b:颗粒团块;c:土壤团块;d和e:蝶形坑;f:蝶形坑、表面原化;g:表面原化;h:鳞片状自生粘土;i:粘着的外来粘粒) |
Fig. 9 SEM and EDS of flaky authigene clay on the sureface of feldspar (XBEH-2)图9 长石表面鳞片状自生粘土矿物的扫描电镜—能谱特征(XBEH-2) |
The authors have declared that no competing interests exist.
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