Fig.1 Geological sketch map of tectonic units in Guizhou Province ((a),modified after reference [21]), and Guanba area ((b), modified after reference [20])

Fig.2 Stratigraphic column of P-T boundary at Guanba (a) and location of the profile (b)

Fig.3 Field photos (a-b), and optical (c) and SEM (d) microphotographs of the P-T boundary claystone at Guanba, Guizhou Province

Fig.4 Zircon CL images of the P-T boundary Guanba claystone(Red circle and white number denote laser spot and U-Pb age, respectively)

Fig.5 U-Pb concordant diagram (a) and weighted average age (b) of zircons from the P-T boundary claystone at Guanba

Fig.6 Nb/Y-SiO2 ((a), base map modified after reference [23]) and AFM ((b), base map modified after reference [24]) diagrams for the P-T boundary claystone at Guanba

Fig.7 Harker diagrams of major element oxides for the P-T boundary claystone at Guanba

Fig.8 Chondrite-normalized REE patterns (a) and primitive mantle (PM)-normalized multi-element spider diagram (b) for the P-T boundary claystone at Guanba (Chondrite and PM normalizing values are from reference [28])

Fig.9 Comparison of marine facies of the P-T boundary in the Guanba,Guizhou and its adjacent areas and Changxing, zhejiang (modified after reference [16])

Fig.10 Paleogeographic reconstruction ((a), modified after reference [50]) and lithofacies paleogeographic map ((b), modified after reference [56]) of South China during the Permian-Triassic transition