冰川沉积类型识别与ESR测年样品采样规范  

Genesis Types of Glacial Sediments and Sampling Procedures for ESR Dating

作　　者：易朝路[1] 毕伟力[1] 杨海军[2] YI Chaolu;BI Weili;YANG Haijun(Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Belting,100101;Department of Chemistry,Tsinghua University,Beijing,100084)

机构地区：[1]中国科学院青藏高原研究所,北京100085 [2]清华大学化学系,北京100084

出　　处：《地质论评》2019年第1期151-167,共17页Geological Review

基　　金：一带一路计划(编号:XDA20070102);国家自然科学基金资助项目(编号:41230523)的成果~~

摘　　要：电子自旋共振(ESR)技术是一种确定物质成分和结构的顺磁性质的分析方法,也能够用于沉积物定年。该方法的测量技术和测年的物理机制等还处于发展阶段。冰川作用过程十分复杂,形成各种类型的冰川沉积物,其顺磁信号的归零机制有显著差异,ESR测年的实验方案也有所差异。因此,识别冰碛物类型,采集合适的样品对于ESR测年的准确性十分重要。冰下融出碛和滞碛经过了冰下磨蚀过程,结构致密,细颗粒基质含量高,石英砂中的一些杂质芯的ESR信号能够衰退。许多冰上融出碛,结构疏松,但细颗粒基质含量高,不但经过了搬运过程中的冰下磨蚀过程使ESR信号衰退,又经历了沉积时的冰上阳光直射过程使信号衰退,一些样品的ESR信号能够完全晒退。冰水湖泊和冰水河流沉积的细砂和粉砂来源于冰下研磨的产物,信号会衰退;在搬运沉积过程中又可能被阳光直射,信号进一步衰退。其它类型的冰碛物的ESR信号衰退机制不明,或粒径不适合用ESR方法测年。采集冰碛物ESR年代样品时,最好同时采集信号衰退机制相同的现代冰碛物样品,以便对照,并用于扣除可能的残留信号。Electron spin resonance( ESR) technique is a method of paramagnetic analysis for the determination of elements and structure of matters. It can also be used for dating of sediments to solve some problems in sediment age which cannot be solved by other dating techniques. The techniques in measurement of paramagnetic signal and principle for sediment dating are in state of development. Glacial geological processes are complicated and produce a complex glacial sediment with various subtypes. The mechanisms for resetting ESR signal are different from subtypes of the sediments,and the experimental procedures should be chosen properly. Therefore,it is important to identify glacial sedimentary types and collect proper samples for the accuracy of ESR dating. Subglacial meltout till and lodgment till are abraded and crushed in subglacial environment,and they are compacted and contain fine particles in matrix so that ESR signals in some impurity centers in quartz grains are decayed. Superglacial meltout till forms in ice surface environment. It is loose and contains large particles. But some material in superglacial meltout till comes beneath ice and contains concentrated fine particles which sustain subglacial abrasion to decay ESR signal,and exposes to sunlight during deposition to further decay the signal. ESR signal in some quartz grains can completed bleached. Fine sand and silt in glacial lake deposit and glacial meltwater sediment are the producta of subglacial comminution/abrasion. ESR signal in quartz grains would be decayed during transportation,and would be further decayed during sedimentation. The mechanism for ESR signal resetting is not clear for other types of glacial sediments and some grains in sediments are too large for measurement of ESR signal. They are not suitable for ESR dating. It is strongly suggested to collect contemporary glacial sediments with the same sedimentary processes with the samples for geological dating so as to reduce possible residual signal for more accurate results.

关 键 词：冰川沉积类型 ESR测年 沉积物采样 

分 类 号：P343.6[天文地球—水文科学]