The Middle Jurassic palynoflora and its implication for paleoclimate in the western margin of Longjiang Basin

Based on the systematic analysis of palynological fossils collected from the coal-bearing strata of the Middle Jurassic Wanbao Formation in the Longjiang Basin, totally 73 species of 45 genera, including 16 species of 15 genera in pteridophyte spores and 57 species of 30 genera in gymnosperm pollen were recognized in the Longjiang Basin, and 3 palynological assemblages Alisporites-Chasmatosporites-Cyclogranisporites, Chasmatosporites-Piceites-Cyclogranisporites and Cyclogranisporites-Baculatisporites-Protopinus assemblage were established in the Middle Jurassic strata in ascending order.The palynoflora is dominated by gymnospermous pollen, followed by fern spores.In addition, the pollen of gymnosperms is mainly composed of the bisaccate pollen of conifers and monosulcate pollen of cycads, bennettitales and ginkgophytes.Based on the analysis of palynological data, the age of the Wanbao Formation in the Longjiang Basin should be assigned to the Middle Jurassic.Combined with the features of the ecological environment, the Middle Jurassic Wanbao palynoflora may reveal a subhumid to humid warm temperate-subtropical climate with a certain paleoenvironment of low mountains.