青藏高原东缘盐源盆地古近纪风成沙丘及其古地理意义*

盐源盆地始新世丽江组沉积时期发育了一套具大型高角度交错层理的红色砂岩，其确切成因对于厘定青藏高原东缘古近纪古地理格局、恢复东亚新生代干旱带与古气候演化过程具有重要意义。文中通过对盐源盆地始新统丽江组红色砂岩的沉积特征进行系统分析，证明该套砂岩的岩性、粒度分布、石英颗粒表面特征与沉积构造等明显不同于水成沉积，而与典型风成沙丘相应特征完全一致，表明其为风成沙丘沉积。结合古近纪研究区的古气候条件、大气环流样式与大地构造背景，笔者进一步推断盐源盆地始新世风成沙丘可能沉积于中国古近纪干旱带内的沙漠环境。根据目前相关研究资料，确认青藏高原东缘存在一个厚度稳定的古近纪风成沙丘富集带。

The Paleogene aeolian dunes and their palaeogeographic significance in Yanyuan Basin,eastern margin of the Tibetan Plateau

Red sandstones with large-scale cross-beddings in high dip angles were developed in Yanyuan Basin during the sedimentary period of Eocene Lijiang Formation.Its exact origin is significant for revising the Paleogene palaeogeographic pattern in the eastern margin of the Tibetan Plateau and reconstructing the evolutionary process of the Cenozoic arid belt and palaeoclimate in East Asia.Sedimentary characteristics of these red sandstones from the Eocene Lijiang Formation in　Yanyuan Basin were systematically analyzed in this paper.The results show that their lithology，grain size distribution，surface features of quartz grains and sedimentary structures are clearly different from aqueous deposits，but perfectly consistent with the corresponding sedimentary characteristics of typical aeolian dunes，indicating that these red sandstones should be attributed to aeolian dunes.Combined with the Paleogene palaeoclimate state，atmospheric circulation pattern and geotectonic setting of the study area，it is further inferred that the Eocene aeolian dunes in Yanyuan Basin could be deposited in the desert environment，which was located in the Chinese Paleogene arid belt.Furthermore，on the basis of existing relevant research data，it is also confirmed that there was an aeolian dune enrichment zone in eastern margin of the Tibetan Plateau during the Early-Mid Paleogene epoch.