云南大理点苍山末次冰期冰碛物石英砂扫描电镜形态特征分析

云南大理点苍山是大理冰期的命名地,保存有确切的末次冰期冰川作用遗迹.对点苍山冰碛物石英砂进行了扫描电镜形态特征分析,获得了其石英砂形态特征及其频率,并在冰川成因的典型特征的频率上取得了新的认识.扫描电镜分析表明,点苍山冰碛物石英砂形态特征主要为:石英砂形状主要为次棱角状、尖棱角状和多棱角状,边缘多可见次棱脊和棱脊磨损,表面起伏度高;机械特征主要有贝壳状断口、平行解理面、裂隙、粘附碎片、擦痕、机械V形坑;化学特征主要有蚀坑和蚀缝、蜂窝状溶蚀表面、无定形硅沉淀和硅质薄膜.在石英砂表面与冰川作用密切相关的擦痕的频率为8%~32%;粘附碎片的频率为16%~40%;裂隙的频率为12%~32%.通过对点苍山冰碛物的石英砂扫描电镜分析,得出该第四纪海洋性冰斗冰川和悬冰川的石英砂形态特征及其频率.该冰碛物石英砂原始形态特征明显,机械特征频率不高,是近源堆积的冰碛物石英砂的典型形态特征.

Quartz grains SEM surface microtextures of Quaternary glacial sediments along the Diancang Mountain in Yunnan,Southwest China

Diancang Mountain is the place where the concept of Dali Glaciation was put forward,and it is synon-ymous with the Last Glaciation in China. In this study,we applied Scanning Electron Microscopy(SEM)to the samples of Quaternary glacial sediments from the Diancang Mountain. According to the SEM analysis,the main surface microtextures of quartz grains from the Quaternary glacial sediments in Diancang Mountain are as fol-lows:the quartz grains are mainly subangular and sharp angular outline,subedge ridge,high relief in shape;mechanical characters are mainly conchoidal fractures,parallel cleavages,crevasses,adhering particles,stria-tions,V-shaped percussion cracks;chemical features are dissolution pits and grooves,honeycombed solution surface,SiO2 precipitates and silicon film. The features most related to glacial genesis are striations,with its fre-quency of 8%- 32%;adhering particles,with its frequency of 16%- 40%;cracks with its frequency of 12%-32%. According to the SEM of glacial sediments of Diancang Mountain,we obtained the microtextures and its frequency of maritime cirque glacier and hanging glacier. The quartz grains of the glacial sediments are characterized by original features,and glacial mechanical microtextures are not well developed.