The Global Stratotype Section and Point(GSSP) for the Permian-Triassic boundary was placed in Bed 27 of Meishan section D where the conodont species Hindeodus parvus first occurs.Bed 27 was usually considered comprising continuouslydeposited,homogeneous silty limestone,with no depositional hiatus near the boundary.Detailed study on the boundary sequence revealed that a typical firmground characterized by Glossifungites ichnofacies developed about 2 cm below the Permian-Triassic boundary in Bed 27.Fossil content and lithology show apparent differences across the firmground crust.The abundance of the Permian bioclasts decreases significantly across the firmground,and is accompanied by a shift of dominating carbonate precipitation from calcite to dolomite.The firmground marked a rapid transgression at the very end of the Late Permian and significant shifts of sedimentary environment and paleoclimate.This transgressive submerging surface is also observed at the Huangzhishan section of the shallow-water carbonate platform facies in Zhejiang Province,the Jiangya section of the lower-slope to basinal-margin facies in Hunan Province,the Pingdingshan section of the basinal facies in Anhui Province of South China,as well as the Selong section in Tibet of the northern peri-Gondwana.The transgressive submerging surface marks the onset of a rapid global transgression at the latest Permian.
