Study on the microstructure characteristics of Late Cretaceous aeolian sand in the playa from Chuxiong Basin

Cretaceous greenhouse, a long-lasting typical warminginterval in the history of the earth, and the regional paleotopography effect triggered a wide spread arid-climate belt in East Asia accompanying with extensive paleo-desert outcrops and evaporite deposits. The Upper Cretaceous Jiangdihe Formation in the Chuxiong Basin is characterized by a set of red clastic rocks interbedded with gypsum, being atypical playa environment. Through multiple approaches including optical microscopy, Scanning Electron Microscopy (SEM) and Energy Spectrum (EDS) analysis, the structural morphology and surface micro-morphology characteristics of quartz grains from the Jiangdihe Fm. sandstones from the Chuxiong basin have been studied. The results show that the quartz grains of the Jiangdihe Fm. sandstone has high roundness and wellsorting, dish-shaped impact scars, "desert varnish", and groups of intense chemical corrosion pores (caves), all of which show the typical characteristics of aeolian sand. In addition, the evolution rule of micro-morphology on the quartz grains under different sedimentary environment has been systematically summarized, based on physical interaction, chemical (dissolution, precipitation) interaction, and their combination characteristics of the quartz grains surface. This study will contribute to the further understanding for the characteristics of aeolian sand deposited in the playa environment and the mechanism of the interacting aeolian-aqueous deposition.