Structural Characteristics and Favorable Target Prediction of Ultra-Deep Salt-Related Structures: A Case Study of the Madong Structural Belt

Madong structural belt in the Tarim basin is one of the best-preserved Early Paleozoic fold-thrust belts in the world. However, significant controversy persists regarding the characteristics and deformation mechanisms of Middle Cambrian salt-related structures due to complicate structures, which has constrained ultra-deep hydrocarbon exploration in the region. This study delineated the styles of salt-related structures based on 2D seismic data, determined their deformation phases and evolutionary sequence, established the response relationship between structural evolution and plate activities, discussed the deformation mechanisms, and predicted favorable sub-salt hydrocarbon targets. In the Madong structural belt, the post-salt strata predominantly developed hinterland-vergent break-thrust folds, while the sub-salt strata were dominated by basement-involved pop-up structures formed through shear folding (including flattening folding). The main deformation periods occurred at the end of the Ordovician and the Silurian, controlled by the amalgamation and collision of the Altun-Qilian Terrane and the Qaidam Block with the Tarim Plate. The Middle Cambrian gypsum-salt layer is one of the most critical driving factors for the formation of back-thrust faults in the belt. Shear folding can indirectly lead to the development of steeply dipping or vertical fractures, and the assemblage of "post-salt break-thrust folds and sub-salt pop-up structures" represents the most favorable exploration target for ultra-deep sub-salt strata.