Structure, Biostratigraphy, and Numerical Modelling of the Nizampur Basin (Pakistan): Implications for Deformation in the Himalayan Fold‐Thrust Belt

ABSTRACT The Nizampur Basin in northern Pakistan preserves a structurally important segment of the Himalayan fold‐thrust belt between the Attock‐Cherat Range (ACR) and the Kalachitta Range. Its architecture records interaction among the Hissartang Fault, the Main Boundary Thrust (MBT), blind thrusting, and fault‐related folding, but the relative contributions of blind thrusts, inherited structural weaknesses, and mechanical stratigraphy to basin structural development have not previously been evaluated through integrated field mapping and numerical modelling. Here we integrate geological mapping, litho‐biostratigraphy, cross‐section construction, and discrete element modelling to reconstruct basin structure and to evaluate whether inherited fault zones were active during Himalayan shortening and whether the principal detachment surface (interpreted as a major crustal‐scale thrust within the thrust belt, possibly corresponding to the MBT) exerted first‐order control on thrust propagation, fold geometry, and the localization of deformation within the basin interior. The basin contains east–west‐trending anticlines and synclines, south‐verging blind thrusts, and localized structural tightening toward the western margin near Janakor Valley. The structural architecture comprises fault‐cored folds, all underlain by blind faults, consistent with the absence of evaporite décollement horizons in the Nizampur Basin stratigraphy. Numerical experiments demonstrate that pre‐existing faults localize strain at lower shortening magnitudes and promote more organized imbricate thrusts with subsidiary conjugate back‐thrusts compared with models lacking inherited weaknesses; in both cases, the principal detachment surface exerts first‐order control on thrust propagation and fold geometry. Field structural data indicate that Jurassic–Eocene strata are strongly deformed, while younger fluvial deposits are comparatively weakly affected, implying only limited coupling between recent sedimentation and the principal shortening phase. Basin evolution was therefore governed by the interaction of inherited structures, blind thrusting, and detachment‐controlled shortening, with broader implications for structural predictions, hydrocarbon exploration, seismic hazards, and tectonic evolution in the northwestern Himalayas.