Influence of preexisting structures on salt structures in the Kuqa Depression, Tarim Basin, Western China: Insights from seismic data and numerical simulations

The preexisting structures that developed in the basement and subsalt strata play a key role in the salt structural deformation in the Kuqa Depression, Tarim Basin. The characteristics of preexisting structures and their controls on the salt structure are investigated via the latest three-dimensional seismic data and numerical modelling. The results show that the preexisting structures that developed in the Kuqa Depression mainly consist of basement faults, palaeouplifts, subsalt slopes and early passive salt diapirs. Basement faults are mainly distributed in the Kelasu and Qiulitag structural belts and control the position of development and deformation style of the Miocene compressive salt structure. The differences in styles and reactivation degrees of basement faults lead to great diversity in the salt structure. The palaeouplifts mainly include the Wensu, western Qiulitag, Xinhe and Yaha-Luntai palaeouplifts. The original sedimentary range and later deformation space of the salt layer are limited by the palaeouplift, resulting in strong salt thrusting in the Awate sag in the western part of the Kuqa Depression. The heterogeneous spatial distribution of the palaeouplift promoted the development of regional strike-slip transform belts. Subsalt slopes are located mainly on the northern edge of the western Qiulitag low uplift and block the southward flow of the salt, causing the salt to form salt domes; the size of these domes is closely related to the subsalt slope. Early passive salt diapirs mainly developed in the Quele and Bozidun areas of the western Kuqa Depression, and they were preferentially active during the compression period, inducing the formation of a piercement salt nappe. Numerical modelling revealed that the preexisting structure strongly controlled the stress-strain distribution during the deformation of the salt structure. The spatial distribution heterogeneity of the basement structure is an important factor in the structural zonation along the north-south strike and segmentation along the west-east strike in the Kuqa Depression, as well as an important inducer of the piercement salt structure. Different salt structural deformation models controlled by preexisting structures in the Kuqa Depression. (a) In the Wensu segment, the sedimentary range and deformation space of the salt layer are restricted, resulting in the strong thrust of the subsalt faults and piercement of the salt. (b) In the Quele segment, progradational sedimentary load induces a passive salt diapir. Influenced by the blocking of the steep subsalt slope and the reactivation of the preexisting salt diapir, a piercement salt wall was formed on the right edge of subsalt slope. (c) In the Dabei segment, a salt dome was formed at the northern edge of the western Qiulitag palaeouplift due to the blocking of the steep subsalt slope. (d) In the Keshen segment, the subsalt slope and preexisting salt diapir are not developed, and finally, two salt domes are formed at the top of the basement faults in the Kelasu and Qiulitag structural belts.image