Gravity and magnetic field features and basement relief of the Sanjiang Basin in Heilongjiang Province, China

The Sanjiang Basin has received more attention in Mesozoic stratum and petroleum potential research because of its particularity in geographic and tectonic position. There remains debate on the basement structure of the basin since igneous rocks and faults make the structure and stratigraphy more complicated. In this paper we utilize gravity and magnetic data as well as petrophysical properties and drilling logs to understand the structure of the Sanjiang Basin. The study is focused on the comparison between the western and eastern parts of the basin. The comparison reveals that there are distinct differences in the gravity and magnetic field between the western and eastern parts. The integrated analysis of the gravity, magnetic, geological, petrophysical data and drilling logs indicates that the difference in the gravity and magnetic field results from the different basement structure and caprock formation of the two parts of the basin. The basement consists of three parts from west to east, the Proterozoic crystalline basement, the Neopaleozoic fold basement and the Lower Mesozoic fold basement separately. The Tongjiang–Yingchun Fault and the Qinglongshan–Xiaoheyan Fault controlled the formation and development of depressions and uplifts and also affected the sedimentation and volcanic activities of the basin. The Sanjiang Basin has relatively thin and stable crust thickness, varying around 33 km, and the deep structure has control and constraint over the shallow conformations