STRUCTURAL STYLES ASSOCIATED WITH MULTIPLE DETACHMENT LEVELS IN THE EASTERN SICHUAN BASIN, SOUTH CHINA

Sichuan Basin is located in the northwest of Upper Yangtze platform of South China, and East Sichuan is situated between Huaying Mountain fault and Qiyue Mountain fault. The surface Jura type folds are very famous with barrier parallel folds, but few researches are concentrated on the structural styles of subsurface in the eastern Sichuan Basin. Surface and subsurface data are integrated to characterize the structural styles in the region. Multiple detachment levels are developed in the eastern Sichuan and result in distinct structural domains. In addition to the basal, Triassic and Silurian system detachment levels, we recognize a regionally extensive detachment level in the Middle and Lower Cambrian. The lithology of the detachment level is gypsum and salt by the synthetical studies of outcrop, drilling well, and chaotic seismic reflection configuration. The Middle and Lower Cambrian detachment level forms a structural domain boundary that can be observed by seismic reflection profile in subsurface. The stratigraphic intervals above and below the detachment develop characteristic patterns of deformation. The detachment level is folded by flow in and flow out of salt movement. Above the detachment, the thrust fault-related folds were generated by the contractional action from southeast to northwest, including the fault-bend fold, fault-propagation fold, and thrust wedge fold, and so on. Below the detachment, the broad anticlines were formed due to the basal detachment. Hydrocarbon traps are formed above and below the detachment, in particular, the broad anticline below the detachment is a potential gas exploration domain in eastern Sichuan Basin.