Tectonic sequences of Triassic strata in the southern Ordos Basin, China

摘要

The Triassic is an important transition period in the structural evolution of North China. The structural features and their controlling action over the sedimentation in the southern Ordos Basin were studied. In combination with modern sedimentology and sequence stratigraphy, the Triassic basin fills have been classified into four second order tectonic sequences bounded by unconformities and erosional surfaces. Tectonic sequence 1 (TS1) is composed of the Liujiagou and Heshanggou Formations. It represents the early stage before the formation of prototype of the foreland basin. Tectonic sequence 2 (TS2) is composed of the Zhifang Formation. The foreland basin formed in this stage. Tectonic sequence 3 (TS3) consists of the lower Yanchang Formation (Chang 10-chang 8). It represents the initial stage of the foreland basin development. Tectonic sequence 4 (TS4) consists of the upper Yanchang Formation (Chang 7-Chang 1). It represents the peak phase of the foreland basin development. The evolution of the Ordos Basin is associated with movement of the Indosinian plate and through analysis of the tectonic sequence, the characteristics of the subsidence and sedimentation in this region are documented.