Discovery and significance of the Palaeogene eolian deposits in Lijiang, Yunnan

The lower part (formerly Meile Formation) of the Baoxiangsi Formation (E₂b) in Lijiang, Yunnan has long been interpreted as the hydrogenic deposits. The integration of lithology, sedimentary textures and structures in this study indicates that the tremendous sandstones in the lower part of the Baoxiangsi Formation consist of purplish red, well-sorted and rounded medium-to fine-grained quartz sandstone characterized by large-scale high-angular tabular cross-bedding and foreset bedding of the eolian dunes. The characteristic features of dish-shaped, crescent-type impact craters and frosted surface under an electronic microscope demonstrate that the lower part of the Baoxiangsi Formation may be assigned to the eolian dune deposits deposited in desert environments. The sedimentary characteristics also show that there were gradations from dry to humid climates in eastern Qinghai-Xizang plateau. It is inferred that this climatic change may be the sedimentary responses to the Eocene-Oliocene global cooling-drying events, the rapid uplift of the plateau and formation of the palaeomonsoon in East Asia.