青藏高原北缘古近纪石英砂表面特征及其古环境意义

中国西北干旱化和风成记录的研究已取得重要进展，但对亚洲内陆干旱化和亚洲冬季风开始时间的认识目前仍存在分歧。利用扫描电镜，通过对青藏高原北缘广大典型地区古近系中类似风成堆积的红色砂层石英砂微形态详细研究，发现这些红色砂层中绝大部分石英砂颗粒表面具有流水搬运和改造的磨光面与V型坑微形态特征组合，与现代塔克拉玛干沙漠、阿尔金山北缘洪积扇上的现代风沙沉积物石英砂颗粒表面的麻面与蝶形坑组合不同。粒度分析也显示这些沉积物的粒度曲线特征与风成黄土和现代沙丘粒度曲线有明显差别。结合沉积特征认为青藏高原北缘古近纪期间不存在大范围的风沙沉积物，推断亚洲冬季风此时可能尚未激发，而该期的干旱环境可能是由行星风系副热带高压控制的干旱炎热气候以及全球变冷事件造成。

The Eogene Surface Texture of Quartz Sand and Paleoclimatic Change in Northern Margin of Tibetan Plateau

The start time of the Asian interior aridification and East Asian monsoon is a research hotspot. The quartz sand grains which are taken from the Eogene red sandstones in the northern margin of Tibet Plateau were examined under Electronic Scanning Microscope for their external morphological characteristics in the paper. The result shows that the samples almost have the texture of subaqueous polished surface and V-shape impact pits which is the typical feature of hydraulic action, and it is obviously differen...