Abstract: Abundant megaspores were discovered from 13wells in hinterland of Junggar basin. They are grouped into two assemblages, namely Badaowan formation-Lower Sangonghe formation assemblages with abundant fossils of Kuqqia megaspore of Early Jurassic and Upper Sangonghe formation-Xishanyao formation assemblage of Middle Jurassic. Based on the distribution and existing era of these two assemblages, integrated with plants and bivalve fauna classification, this paper suggests that the boundary of Early Jurassic and Middle Jurassic should be placed at the contact between the Lower and Upper Sangonghe formation.

Key words: Junggar basin, Jurassic, megaspore, formation classification