Palaeoclimatology, Provenance and Tectonic Setting during Late Permian to Middle Triassic in Mahu Sag, Junggar Basin, China

Huang Yunfei; Zhang Changmin; Zhu Rui; Yi Xuefei; Qu Jianhua; Tang Yong

doi:10.3799/dqkx.2017.559

Abstract：A series of distinct biological and environmental events have occurred during the Permian-Triassic transitional period,which are mainly indicated by marine geological record.However,little study has been done on palaeoclimate and palaeoweathering on land in Early Triassic.In order to reconstruct the palaeoclimatological information,provenance and tectonic setting from Late Permian to Middle Triassic in Mahu sag,Junggar basin,bulk-rock major and trace elemental analyses were carried out on the core mudstone samples.Palaeoweathering condition and palaeoclimatology were reconstructed through various chemical weathering indices,while the provenance and tectonic setting were inferred from various discrimination diagrams.The chemical weathering switched from lower level to middle level from Late Permian to Early Triassic,and remained steady during the Early Triassic with minor weakened trend in the late Early Triassic,indicated by the CIA (Chemical Index of Alteration),CIW (Chemical Index of Weathering),WIP (Weathering Index of Parker) and PIA (Plagioclase Index of Alteration),which agrees with the global weathering evolutionary trend shown by Sr isotopes.The palaeoclimatology from Early to Middle Triassic was warm and wet seasonally,in comparison with the cool and dry environments during the Late Permian.However,the chemical weathering of Middle Triassic in Mahu sag did not weaken simultaneously with the global trend,but increased slightly,which might be a local event.In addition,the provenance of the Upper Permian Wuerhe Formation,Early Triassic Baikouquan Formation and Middle Triassic Kelamayi Formation should be felsic igneous rocks,and the tectonic setting during the formation of source rocks probably was the oceanic island arc setting.