A record of the transition from foreland to piggy-back basin from the western Churia Range in Central Nepal: Evidence from luminescence dating and geomorphology

The development of the Himalayan foreland basin at the mountain front is shaped by the interactions between tectonic uplift, climate, and fluvial sedimentation. This study examines the tectonic evolution of the western Churia Range in central Nepal using terrace mapping, sedimentary analysis, and Optically Stimulated Luminescence (OSL) dating. Our findings indicate that terrace formation in the Chitwan Dun area reflects episodic thrust activity and alluvial processes that were also influenced by climate shifts from the Late Pleistocene to Holocene. Analysis of terrace gradients, lithology, and OSL dates reveals that tectonic uplift and river incision played a central role in shaping terrace surfaces and fluvial morphology. New OSL ages in the western Churia Range, when compared to published ages in the eastern Churia, suggest that topographic growth initiated in the east around 10–7 ka and progressively extended westward with sustained uplift throughout the Holocene; fluvial terraces formed in response to this westward propagation of uplift. This east-to-west growth pattern and the effects of regional climatic events have collectively influenced the geomorphology of the Chitwan Dun, shifting river channels and sedimentation patterns. Our study proposes a model of foreland to piggyback basin transition, contributing valuable insights into the Himalayan frontal thrust's structural and sedimentary evolution.