Petrologic evidence for sea-level drop in latest Permian in Jiangxi province, China and its meanings for the mass extinction
江西修水二叠纪·三叠纪界线地层海平面下降的岩石学证据

A new-found Permian-Triassic boundary section in Xiushui,Jiangxi Province,China shows evidence for sea-level drop during the latest Permian.Evidence for sea-level drop was preserved in a 2.1 m thick interval of limestone,and is 1 m from the P-T boundary.The basal 0.1 m of this interval is a reddish sparry-cemented grainstone.The grains are rounded,dolomitized,all having a black coating.Microprobe analysis indicates that the coating is limonite,which indicates a weathering event in subaerial environments after a sea-level drop event.The internal structure of most grains has been destroyed by diagenesis.Some remained structures of foraminifers and fusulinids.So,this bed is formed before the mass extinction.The 2.0 m thick bed overlying the reddish grainstone is a dedolomitized limestone.The shapes of some original finely-crystalline dolomite rhombus were preserved.The occurrence of dedolomitization is generally related to meteoric water.So,this bed recorded a sea-level drop event.Fossils in this bed are simple: fusulinids and large foraminifers such as Colaniella are absent.It is clear that mass extinction began before this bed.The 1 m thick limestone between the dedolomitized bed and the P-T boundary is composed of grainstone and lime mudstone.Study of this section reached two points:(1)sea-level drop occurred in latest Permian;(2)The end-Permian mass extinction began in the earliest episode of the sea-level drop event.Thus,we cannot exclude the possibility that the mass extinction was caused by a dramatic environmental change which triggered the end-Permian sea-level drop.