Late Triassic palaeoclimate and palaeoecosystem variations inferred by palynological record in the northeastern Sichuan Basin, China

The end-Triassic is characterized by enhanced rates of biotic turnover, but the terrestrial records of the Triassic-Jurassic transition are relatively rare in Asia. In this study, a detailed investigation of well-preserved palynomorphs of Late Triassic terrestrial deposit in northeastern Sichuan Basin, China, has been conducted to reconstruct the palaeoclimate and palaeoecosystem variations. The palynoflora of the Xujiahe Formation in Xuanhan of Sichuan shows a high diversity of spores and pollen grains, including 151 species of 64 genera. The palynological assemblage is characterized by a dominance of spores and abundance of gymnosperm pollen grains, dated as Norian-Rhaetian (Late Triassic) in age. Palaeovegetation reconstruction shows a predominance of fern floras, followed by gymnosperms represented by conifers. This palynoflora indicates that a tropical-subtropical humid and warm climate generally prevailed during the Late Triassic. However, further Sporomorph EcoGroup model (SEG) analysis suggests that the overall humid and warm climate condition was not static and unchanging throughout the Late Triassic episode, but was punctuated by several climatic and ecosystem variations: two warm and humid climate events, accompanied by a cool and dry trend in the end-Triassic episode. The study reveals the terrestrial ecosystem variations before the Triassic/Jurassic boundary in the Sichuan Basin, and thus provides important evidence for understanding the response of terrestrial vegetation to regional and global environmental changes across the Triassic/Jurassic transition.