Redefinition of Stratigraphic Sequence of Type Section of Pleistocene Qigequan Formation in Qaidam Basin:New Evidence from Lithologic and Petrographic Studies and ESR Dating
Ke Xue
Yang Wenjun
Zeng Wen
Zhang Zongyan
Zhang Jinming
Song Taizhong
Li Jing
Zhang Xiaojin
Abstract：In response to the previous problems of unclear lithologic and petrographic meanings of the Qigequan Formation in Qaidam Basin,especially the controversial issue of whether its depositional age extends to the Middle Pleistocene.In this paper it re-conducted a fine study of the auxiliary type section(Section Y)of the Qigequan Formation located in the north of the type section(Section Z)in the Qigequanzi area of Mangya City,Qinghai Province.It obtained for the first time four ESR ages from the bottom to the top of the section,which are 562±64 ka,511±90 ka,438±32 ka,and 379±33 ka,respectively,further confirming the existence of the Middle Pleistocene sedimentary sequences in the Qigequan Formation.Based on a detailed analysis of the lithological and petrographic assemblage of the Section Y and Section Z,the Qigequanzi Section is divided into two parts,the upper fine and the lower coarse.The lower part of the section is assigned to Member 1 of Qigequan Formation for the mud-sand lake sequences,and the upper part is assigned to the Member 2 of Qigequan Formation for the gravel-sand rhythmic sequence of the alluvial fan stratigraphy.Combined with the paleomagnetic age obtained in Section Z and ESR ages obtained in Section Y,the depositional age of the Member 1 of Qigequan Formation is limited mainly to the Early Pleistocene,and that of the Member 2 of Qigequan Formation mainly to the Middle Pleistocene.Although Member 1 of the Qigequan Formation is at the lower part and Member 2 is at the upper part,there is a phase transition between the late Early Pleistocene and the early Middle Pleistocene,which means that the stratigraphic interface between the two members is time-disconnected.In this paper it compares the type section of Qigequan Formation with other contemporaneous stratum in the Qaidam Basin,and provides new stratigraphic materials for the analysis of Quaternary petrographic paleogeography in the region as well as for the exploration of Quaternary potassium salts and other important minerals.
Keywords：Qigequan Formationtype sectionESR datingPleistoceneQaidam Basingeophysics
Publication Date：2025-04-30
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：17( 1514-1530 )