云南西北部丽江—剑川地区古近纪宝相寺组石英砂颗粒表面特征

石英砂具有丰富的颗粒表面特征,是判别沉积环境的重要标志。利用扫描电镜对云南丽江—剑川地区宝相寺组(E2b)的石英砂颗粒表面特征进行了系统分析:下部样品具水成特征,中部样品具风成特征,上部样品则具经水流改造后的风成特征。结合野外观察结果,从宝相寺组石英砂颗粒表面特征的变化规律可以看出,下部为近源洪积环境、中部为风成沙丘环境、上部为湖泊环境。其中中部样品的石英砂磨圆、分选极好,普遍具有标准的碟形、新月形撞击坑和毛玻璃化表面,是典型的沙漠砂沉积。

Surface microscopic characteristics of quartz sand grains in the Paleogene Baoxiangsi Formation of Lijiang-Jianchuan area, northwestern Yunnan

Quartz sand grains have a variety of surface characteristics, which could be used as the main indicators of their depositional environment. In the present study, the surface characteristics of quartz sand grains were systematically analyzed on the basis of the samples from varying levels of the Baoxiangsi Formation (E2b) in Lijiang-Jianchuan area, Yunnan Province, by using electronic scan microscope. The results show that the grain surfaces of the samples from the lower part of the Baoxiangsi Formation have aqueous characteristics, those from the middle part have eolian characteristics, and those from the upper part have reworked eolian characteristics. It is thus concluded that the lower part is a proximal diluvial environment, the middle part is an eolian dune environment, and the upper part is a lake environment. Moreover, the quartz sand grains of the samples from the middle part are well sorted and rounded, and commonly have standard dish-shaped impact scars, crescent-shaped impact scars and frosted surface, suggesting typical desert sand sediments.