Stratigraphic framework and model for the Permian -Triassic strata in the Xikou region, Shaanxi

The stratigraphic and sequence stratigraphic characteristics are examined for the Permian-Triassic strata in the Xikou region, Shaanxi in terms of modern sedimentological and sequence stratigraphic theories. The Permian-Triassic strata in the study area may be arranged into four sequence units. The systems tracts are divided on the basis of sequential architectures formed during sea-level rises and falls, and the stratigraphic framework and model are constructed for the Permian-Triassic strata in this area. The four phases of eustatic fluctuations and regional tectonic subsidence are responsible for the formation of four type-2 unconformities. From the latest Early Permian onwards, the development of the basin during its formation and evolution displayed the palaeogeographic framework of being shallower in the western part and deeper in the eastern part of the basin. The results of research in this study may give a good example for the construction of the stratigraphic framework and model for the tectonically stable areas.