Palaeovegetation and palaeoclimate changes across the Triassic–Jurassic transition in the Sichuan Basin, China

Abstract

The Triassic–Jurassic transition interval is marked by enhanced biotic turnover rates in both marine and terrestrial realms. However, limited data from Asia hampers the understanding of global ecosystem response to the end-Triassic mass extinction event. Here, we present significant vegetation and climate changes across the Triassic–Jurassic transition in the eastern Tethys region (southern China). A detailed palynological study was performed from the Qilixia section 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 reveal significant ecosystem fluctuations across the Triassic–Jurassic transition. Our study 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. These long term changes in vegetation and inferred climatic conditions are comparable with records from the western Tethyan realm, and possibly reflect global terrestrial environmental changes associated with Central Atlantic Magmatic Province volcanism during the Triassic–Jurassic transition.