PALYNOLOGY AND PALEOENVIRONMENT OF THE TERRESTRIAL PERMIAN-TRIASSIC TRANSITION IN WESTERN GUIZHOU AND EASTERN YUNNAN, SOUTH CHINA

While numerous efforts to resolve the Permian–Triassic boundary (PTB) have been conducted in marine successions, the PTB interval and the end-Permian extinction event (EPE) remains poorly resolved in the terrestrial realm. Terrestrial outcrops in South China offer a unique opportunity to investigate organic-rich sediments deposited in a warm, humid climate. We present a new dataset including sedimentological analysis, paleobotany, palynology, organic geochemistry and XRF, from the re-investigation of four terrestrial PTB sections from western Guizhou (Chahe, Zhejue, Jiucaichong) and eastern Yunnan (Mide).

Stratigraphic and sedimentological analysis shows major differences in the depositional settings between the Xuanwei and Kayitou formations. Changes from terrestrial fluvial-lacustrine to coastal marine setting are observed, with a clear segregation supported by major element XRF geochemistry. Exact stratigraphic placement of the PTB remains unclear, although current data indicates that the PTB is likely occurring at the top of the Xuanwei Fm. Recent radiometric dates bracketing the PTB from the Meishan GSSP are within range of bed 68 at Chahe. The disappearance of the Gigantopteris flora cannot be used as a reliable marker for the EPE as this plant group persists into the Triassic. However, plant fossils reveal two distinct assemblages: A Late Permian (Changhsingian) Gigantonoclea guizhouensis – Annularia pingloensis assemblage in the upper Xuanwei Formation, and an Early Triassic (Induan) Annalepis – Peltaspermum assemblage associated with relicts of Permian gigantopterids in the uppermost Xuanwei and basal Kayitou formations. The Early Triassic age of the Kayitou Formation is further supported by the occurrence of typical Triassic marine fauna. Palynological assemblages are almost exclusively composed of spores, and a ~1 meter zone with fungal spores including Reduviasporonites has been identified near the top of the Xuanwei Fm. This interval also corresponds to a prominent δ13CTOC carbon-isotope excursion which altogether may correspond to the EPE ecosystem collapse and "fungal spike" event. It is yet to demonstrate whether diversity changes are related to paleoenvironmental change coeval the transition between the Xuanwei and Kayitou formations, or rather linked to the EPE.