Differential control of syndepositional faults on sequence stratigraphy and depositional systems during main rift I stage in the southeastern fault zone of Qingxi Sag, Jiuquan Basin, Northwestern China

摘要

In active rift basins, syndepositional faults exert a major control on sequence stratigraphic patterns and depositional system features, which together determine reservoir distribution, geometry, and quality. In this study, we analyze syndepositional fault characteristics of the main rift I stage in the southeastern fault zone of the Qingxi Sag, Jiuquan Basin. The syndepositional faults are marked by boundary fault with high dip angle and strong activity in the western section, and both boundary fault and associated secondary fault with relatively low dip angles and weak activity in the eastern section. In response to these different fault patterns and activity intensities, the resulting sequence stratigraphic and depositional system features are different in the western and eastern fault zones. The southeastern basin margin is divided into steep slope fault belt in the west and fault terrace belt in the east, and two corresponding types of sequence stratigraphic patterns developed. Contrastive analysis of the depositional systems highlights that they differed in sediment dispersal patterns, distribution scales, development positions, and sediment physical properties. Reservoirs associated with the depositional systems were further differentiated into four types. Analyzing the characteristics of the four types of reservoirs and their corresponding traps provides a useful reference for the deployment of future hydrocarbon exploration in the study area.