Structural characteristics and evolution of the Shulan Basin

Located in the middle south segment of the Jia-Yi graben and northeast Yitong Basin, the Shulan Basin is a NE-trending narrow faulted basin. Previous studies only carried out preliminary geological survey in the Shulan Basin, whereas researches on the structural characteristics and evolution of the basin were insufficient. This paper focused on the correlations of Cenozoic strata between the Shulan Basin and Yitong Basin on the basis of all research data collected, e.g., sporopollens and stratigraphy. Moreover, the electrical and seismic profiles from the Shulan Basin suggest that the southern section of the basin shows half-graben type structure, the middle basin shows graben type structure, and the northern section becomes increasingly deep step by step southwestward. In addition, the basement of the basin is slightly different in different parts and characterized by upper Permian Yangjiagou Formation, Cretaceous granites and Cretaceous strata in the southern, middle and northern parts, respectively. A comprehensive analysis suggests that the Shulan Basin underwent three tectonic evolutional stages, e.g., the initial faulted phase (Early Paleocene), the main faulted phase (Paleocene-Oligocene), and the extrusion-reversion phase (Oligocene-Miocene).