Palynological study reveals palaeovegetation and palaeoclimate changes across the Triassic-Jurassic transition in south China

　　The Triassic–Jurassic (T–J) transition interval (ca. 200 Ma) is characterized by a major mass extinction, one of the five largest Phanerozoic extinctions in Earth history. Major biotic turnover occurred in both marine and terrestrial realms. Much emphasis has been placed on the marine Triassic–Jurassic successions, however, studies on the terrestrial response to this event is still limited, especially in the eastern Tethys region of eastern Asia. In the northeastern Sichuan Basin of South China, the Upper Triassic and the Lower Jurassic successions are well exposed and continuously developed, yielding diverse fossil plant remains, providing important material for exploring the continental ecosystem conditions across the T–J transition in the eastern Tethys. In recent decade, a research team leading by Prof. WANG Yongdong from the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Science (NIGPAS) has conducted a series investigations in this region. 

　　Recently, Dr. LI Liqin, Prof. WANG Yongdong from NIGPAS, Prof. Wolfram M. Kürschner from the University of Oslo, Dr. Micha Ruhl from the University of Dublin and Prof. Vivi Vajda from the Swedish Museum of Natural History, published a new study in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, which reported about palaeovegetation and palaeoclimate changes across the Triassic–Jurassic transition in the Sichuan Basin, China. 

　　A detailed palynological study was performed from the Qilixia section in Xuanhan County of the Sichuan Basin, China, spanning the Upper Triassic (Norian–Rhaetian) (Xujiahe Formation) to the Lower Jurassic (Hettangian–Sinemurian) (lower Zhenzhuchong Formation). Five palynological assemblages were identified, in combination of Principal Components Analysis (PCA) and Sporomorph EcoGroup (SEG)  model, they reveal significant ecosystem fluctuations across the Triassic–Jurassic transition. The palynological analysis indicates a lowland fern flora and a warm and humid climate in the Late Triassic (Norian to Rhaetian), interrupted by a cooler interval at the Norian–Rhaetian transition, and followed by a mixed mid-storey forest under cooler and drier condition in the latest Rhaetian. This is followed by a fern-dominated lowland vegetation and a warmer and drier climate during the Triassic–Jurassic transition, and a flora with abundant cheirolepid conifers in the Hettangian–Sinemurian. 

　　Most interestingly, the significantly dominant fern vegetation at the Triassic–Jurassic transition interval is similar to the changes reported from geographically widespread sites. The short cooling at the end Triassic and preceding a period of warmer condition at the Early Jurassic, is comparable with records from the western Tethyan realm. It likely reflects (global) vegetation turnover and climatic fluctuations at this time. This global response in vegetation and climate may suggest that, the CAMP emplacement, with a significant influx of SO2 and sulphate aerosols into atmosphere, causing an initial cooling at the latest Triassic. It was later outpaced by global warming from elevated CO2 release in the Triassic–Jurassic transition interval.  

　　This study represents the best and higher resolution palynological records of the Triassic and Jurassic transition in siuthern China, providing important evidence for terrestrial ecosystem response to the Triassic–Jurassic event from the eastern Tethys area. 

　　This research was supported by the National Natural Science Foundation of China, the Strategic Priority Research Program (B) of the Chinese Academy of Sciences, the State Key Laboratory of Palaeobiology and Stratigraphy, and the Swedish Research Council. 

　　Reference: Li L., Wang Y*., Kürschner, W.M., Ruhl, M., Vajda V.*, 2020. Palaeovegetation and palaeoclimate changes across the Triassic–Jurassic transition in the Sichuan Basin, China. Palaeogeography Palaeoclimatology Palaeoecology. https://doi.org/10.1016/j.palaeo.2020.109891.  

Late Triassic spores and pollen representative taxa from Xuanhan of Sichuan Basin

　　Early Jurasic spores and pollen representative taxa from Xuanhan of Sichuan Basin

　　Late Triassic–Early Jurassic palynological assemblages and palaeovegetation reconstruction of the Sichuan Basin

　　Late Triassic–Early Jurassic palynoflora and palaeoclimate implications for the Sichuan Basin