Geometry, kinematics and mechanism of growth unconformities in the Biertuokuoyi piggy-back basin: implications for episodic growth of the Pamir frontal thrust

Piggy-back basins are characterized by growth stratigraphic sequences bounded by growth unconformities and record the complete deformational history of the related structures. The Biertuokuoyi piggy-back basin, located in the hanging wall of the Pamir frontal thrust (PFT), provides a remarkable example documenting the geometry, kinematics and mechanism of growth unconformities. High-resolution seismic data reveal that multiple growth sequences were folded with constant-dip kink band migration and their dips are equal to the change in the fault-bend angle of the PFT, indicating their kinematic coupling. Divided by a basal Cenozoic detachment, the PFT system contains five lower thrust ramps that cut Paleozoic–Mesozoic strata and an upper thrust ramp that cuts Cenozoic strata. The growth strata and unconformities record c. 4425 m of dip-slip and six stages of episodic thrusting for the PFT. We propose a coeval thrusting style for the five lower thrust ramps. The present seismic section reveals at least 31.1 km of total shortening at the northeastern Pamir front. In particular, the latest shortening of c. 8.0 km is recorded by the Biertuokuoyi Basin and the Mushi anticline. Our results show that multiple growth sequences bounded by growth unconformities are powerful resources for documenting the evolution of deformation. Supplementary material: Supporting figures and data, including seismic profiles and kinematic simulation results, are available at https://doi.org/10.17605/OSF.IO/DNQBS . Thematic collection: This article is part of the Fold-and-thrust belts collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts