Characteristics and Formation of Salt Structures in Baicheng Sag, Kuqa Fold-and-Thrust Belt

The role of differential sedimentary loading in deformation of viscous rock salt in contractional setting is unclear. Combined with field observation, well and seismic data, salt structures in Baicheng sag, Kuqa fold-and-thrust belt were constrained, and their formation mechanisms were investigated. The structural map of top salt shows that two depocenters were developed in Baicheng sag, eastern depocenter near Baicheng County and western depocenter to the south of well BZ1, respectively. Dawanqi salt pillow and saddle of Baicheng sag were developed between two depocenters. Seismic and well data reveals that: (1) the salt layer below two depocenters is very thin, while thick salt layer has accumulated between two depocenters; (2) Dawanqi salt pillow formed from the Late Pliocene to present; (3) the saddle of Baicheng sag, which is an antiform structure in E-W trend, formed from the end of Late Pliocene to present. Based on our investigations and previous studies, we propose a model showing salt flow related to salt structures in Baicheng sag, Kuqa fold-and-thrust belt, and it suggests that differential sedimentary loading plays an important role in Kuqa fold-and-thrust belt: (1) under bulk shortening and differential sedimentary loading, salt flew out of depocenter in three-dimensional; (2) salt flew dominantly along the direction of contraction (N-S) and also obviously along strike (E-W).