Discovery of Permian tuff from the northern margin of the Qaidam Basin and its geological implications

Abstract

Whether the Permian sedimentary records are still preserved in the northern Qaidam Basin is an open issue with various viewpoints. Most regional geological correlations imply that those Permian successions have been wholly eroded or that there is no Permian deposition in this area. These arguments were partly derived from the contrasting interpretations of the age of the fossils obtained from the Zhabusagaxiu formation. Other scholars consider that the lower unit of the Zhabusagaxiu formation, composed of alternating sandstone, mudstone, and limestone, belongs to the Carboniferous. In contrast, its upper limestone member should be assigned an early Permian sedimentary age, hinting that Permian successions are preserved in the northern Qaidam Basin. Therefore, it is still unclear whether the Permian sedimentary records are still preserved in the northern Qaidam Basin. In this study, the Keluke and Zhabusagaxiu formations in the Wanggaxiu-Dongdagou section were investigated in the field and measured in detail, and several volcanic tuff interbeddings were identified. Zircon LA-ICP-MS U-Pb geochronological studies were undertaken on zircons retrieved from a collected tuff sample. A high-precision weighted mean age of 295±2 Ma(MSWD=0.035)was obtained for the first time. This firstly reported age estimate solidly constrains the existence of the Permian strata in the northern Qaidam Basin. This clue will provide new insight into the following oil-gas exploration concerning the Permian successions and also provide a crucial limit on the studies of Carboniferous-Permian global climate change and sea level change.

Keywords

• early permian
• zhabusagaxiu formation
• zircon geochronology
• northern qaidam
• tuff