The effects of salt flow on the cross-section restoration of salt-bearing fold-and-thrust belts: An example from the Kuqa depression

Abstract

Thrust sequence analysis using cross-section restoration is critical for understanding the evolution involved in folds and thrusts as well as kinematics, the distribution of strain, and hydrocarbon accumulation. However, the application of cross-section restoration is challenging in salt-bearing fold-and-thrust belts. Salt flow causes uncertainty and difficulty in quantifying the geometry because of salt mobility and poorly constrained deformation kinematics. In this paper, we first analyze the role of salt flow in the cross-section restoration of salt-bearing fold-and-thrust belts using a synthetic model. Then an applicable method has been systematically described to quantify the effect of salt flow on the cross-section restoration. The method is efficient in determining the sub-salt thrust sequence, whereas accurate fault throw can be restored when the history of salt flow is known. Two well-constrained seismic profiles in the western Kuqa salt-bearing fold-and-thrust belts are restored sequentially to analyze the evolutionary process of sub-salt faults. The results show that the sub-salt thrust system propagates forward in sequence in the Bozi segment and out of sequence in the Dabei segment. The differential evolution of the sub-salt thrust between the Bozi and Dabei segments forms an oblique transfer zone. This study shows that understanding salt flow is the key point for cross-section restoration in salt-bearing fold-and-thrust belts, and relationships between supra-salt deformations and sub-salt thrust can be built by clarifying the contribution of salt flow.