A piggyback basin, which is characterized by growth stratigraphic sequences bounded by growth unconformities, records the complete deformation history of related structures. The Biertuokuoyi piggyback basin located in the hanging wall of the Pamir Frontal Thrust (PFT) provides a remarkable example for 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 fault-bend angle of the PFT, indicating their kinematic coupling. Divided by a basal Cenozoic detachment, the PFT system contains 5 lower thrust ramps that cut Paleozoic–Mesozoic strata and an upper thrust ramp that cuts Cenozoic strata. The growth strata and unconformities record ∼4,425 m of dip-slip and 6 stages of episodic thrusting for the PFT. We propose a coeval thrusting style for the 5 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 ∼8.0 km is recorded by the Biertuokuoyi basin and Mushi anticline. Our results emphasize multiple growth sequences bounded by growth unconformities as 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