Sedimentary response to the Indosinian movement—a case study of the Mid-Upper Triassic in the Zigui basin, Hubei

Abstract：The authors made measurements of sections of the Middle-Upper Triassic Badong and Shazhenxi Formations on the south margin of the Zigui basin and 1:100,000 geological mapping of the Zigui Sheet and found that the Middle Triassic Badong Formation is missing to different degrees on the southeastern margin of the basin and that only the first and second members of the formation were deposited in the vicinity of Guojiaba, Zigui. The whole Badong Formation is absent in Nanjiawan; as a result, the Upper Triassic Shazhenxi Formation directly rests on the Lower Jialingjiang Formation. However, the Badong Formation is complete in Shazhenxi and Jiziyan on the western margin of the basin. The aforesaid phenomena indicate that there occurred appreciable difference in the Badong Formation because of the influence of the Indosinian movement at the end of the Early Triassic. The Shazhenxi Formation, varying greatly in thickness, inherited the characteristics of rugged ancient landforms of the Badong Formation when it was deposited. The authors suggest that the Middle Triassic Badong Formation and Late Triassic Shazhenxi Formations in different areas of the basin are not in fault contact but in conformable or disconformable contact.