Stratigraphic And Isotopic Records Of Tarim,NW China During Late Mississippian To Early Permian:Implication For Palaeoclimatic Changes

The Late Paleozoic was a critical period of extreme environmental changes in Earth's history.Little attention has been focused on the stratigraphical imprints of the Late Paleozoic Ice Age on the Tarim in Paleo-Tethys.A study of lithostratigraphy,biostratigraphy,and isotope stratigraphy was carried out on Late Mississippian to Early Permian carbonates of the Sepabayi section in the Tarim Block,Northwestern China.Microscopic observation and sedimentary environmental analysis remove samples that did not represent the original seawater signal.Sepabayi section records twice Gondwana Glacial in Serpukhovian(Glacial II)and Kasimovian(Glacial III).The Serpukhovian isotopic pattern exhibits similar negative ?13C excursions(from-2.2 ‰ at the base to +4.4 ‰ at the top)compared with other sections globally,suggesting the sea-level lowstands triggered by onset of Glacial II.Alluvial fan and marine carbonate deposits followed marked the melting of this Gondwana glacier.Moreover,isotope excursions and sediments reveal multi-pulsed melting of Glacial II.A weak ?13C excursion occurred around the boundary of Asselian and Sakmarian satge in Sepabayi section.Furthermore,the ?18O curves in all four sections exhibit increasing trend from Gzhelian to Asselian,which is followed by a global decreaseing ?18O trend from Asselian to Sakmarian.These isotopic fluctuations are interpreted as related to the Glacial III.The onset and waning of this Gondwana glacier leads the regression around the boundary of Asselian and Sakmarian,and formation of the huge horseshoe-shaped reef limestone in middle Sakmarian in Northwestern Tarim.