Flexural tectonics and lithological controls on landscape evolution in a forebulge region: Insights from Central India

Abstract

Forebulge regions represent slowly deforming intraplate settings where the relative roles of flexural tectonics, lithological variability and climate in shaping landscapes remain poorly constrained. We investigate the Central Indian Forebulge (CIF), which formed in response to Himalayan loading and despite low erosion rates (2–7 m/Myr), hosts widespread transient landforms, including waterfalls, canyons and escarpments that are generally associated with tectonically active settings. To evaluate the controls on landscape evolution in CIF, we integrate morphometric analyses (normalized channel steepness index k_sn, chi profiles), catchment-averaged cosmogenic ¹⁰Be erosion rates, field-based rock strength measurements, lineament and stream orientation analysis, and flexural stress modelling. Our results show that flexural tectonics exerts a primary control on landscape organization through the generation of fracture networks that guide rivers. Modelled fibre stress magnitudes on the CIF exceed 14.2 MPa, which is sufficient to overcome the tensile strength of the lithologies present on the forebulge. These stresses are enough to generate and reactivate extensional fracture networks associated with flexural uplift. Stream orientations and lineament trends show a dominant NW–SE direction, which aligns with forebulge-parallel fracture systems. The majority of structurally controlled knickpoints also align with these NW–SE lineaments. The k_sn values are broadly similar across lithologies in spite of their different rock strengths (uniaxial compression strength range, 16–199 MPa), indicating that channel steepness does not relate directly with substrate erodibility at basin scale. Erosion rates show positive relationships with basin-averaged slope, relief and k_sn but weak relationships with precipitation and drainage area, suggesting that denudation is largely governed by the topographic gradients established under long-term tectonic forcing. These observations indicate that flexural tectonics controls the structural framework and topographic boundary conditions for river incision, whereas lithological contrasts modulate erosion efficiency and the expression of transient landforms. The weak coupling between channel steepness and lithologic erodibility demonstrates that the CIF represents a transient landscape that is not yet in steady state.