Basement characteristics of Yinggehai Basin in pre-Cenozoic

Combining basin margin outcrops with basement drilling and geophysical data,a comprehensive study is conducted on the basement characteristics of basement in Yinggehai Basin for pre-Cenozoic. Based on the sequence stratigraphic data of 18 outcrop sections,density data of 166 rock samples,and 2 800 sets of magnetic susceptibility data collected from the Song Da zone at the northwestern margin of the basin,a density-magnetic susceptibility crossplot is constructed. These data additionally provide geological constraints for the interpretations of the seismic profiles and geophysical anomalies within the basin. A basement geologic map is subsequently drafted with a combination of marine and terrestrial perspectives. The pre-Cenozoic basement is composed of Presinian,Cambrian-lower Upper Triassic,and upper Upper Triassic-Cretaceous. Spatially,they distribute along the Red River fault zone in a NW orientation. Chronostratigraphically and lithologically,they are characterized by a gradual aging trend from the middle to the two sides,and by a lithologic pattern of Mesozoic sedimentary rocks at west and Paleozoic epi-metamorphic rocks at east.