Dinoflagellate cyst and vegetational dynamics during the Early Jurassic (late Pliensbachian–early Toarcian) in Tibet

The late Pliensbachian–early Toarcian (Early Jurassic) marks a critical interval in Earth history, characterised by major palaeoclimatic, palaeoenvironmental, and palaeoceanographical perturbations. This study examines the Pliensbachian–Toarcian Quse Formation at the Qixiangcuo section in the Southern Qiangtang Basin (Tibet), using palynological analysis to investigate dinoflagellate cyst evolutionary patterns and vegetation dynamics prior to and during the Jenkyns Event. Palynological data showed a clear record of late Pliensbachian dinoflagellate cyst radiation, likely owing to cooler climatic and enhanced water mass circulation between the Arctic-Boreal and Tethyan realms. Prior to the Jenkyns Event, a dinoflagellate cyst acme is observed, possibly controlled by sea-level rise, increased seawater salinity, and well-ventilated conditions. During the Jenkyns Event, a blackout event of dinoflagellate cysts occurred in the Southern Qiangtang Basin, consistent with records from the central Tethys and Boreal regions, likely triggered by global warming and rising seawater temperatures. Pollen assemblages across the Pliensbachian-Toarcian transition are dominated by Cheirolepidiaceae conifers (Classopollis), compared to reduced cycadophytes, bennettites, and ginkgophytes, and sparse fern spores. This reflects a vegetation turnover towards xerophytic, drought-tolerant vegetation in arid lowland environments, likely linked to the initial phase of Karoo-Ferrar volcanism. During the Jenkyns Event, Cheirolepid coniferous pollen remained dominant before temporarily disappearing, indicating a demise of mixed wet mire-conifer communities and a shift towards drought-adapted flora. Similar patterns of deforestation and vegetation crisis are observed across the Tethys and Boreal realms, contemporaneous with the main phase of the Karoo-Ferrar volcanism and rising atmospheric CO2. Regional comparisons of vegetation response across the Jenkyns Event reflect different magnitudes of predominance and recovery patterns in Cheirolepid conifers.