Alluvial Stratigraphic Response to Abruptly Increasing and Variable Sediment Supply: Insights From Stratigraphic Forward Modeling

Abstract Understanding how alluvial stratigraphy responds to sediment supply perturbations is critical for interpreting past environmental changes from the sedimentary record, characterizing subsurface reservoirs, and forecasting future landscape evolution. However, identifying and quantifying sediment supply signals preserved in the rock record remain challenging, leaving their stratigraphic imprint insufficiently understood. To help address this issue, we use a process‐based numerical model to simulate alluvial stratigraphy under different sediment supply scenarios, independently testing the effects of supply magnitude and variability. Our results show that sediment supply variability has a stronger impact than magnitude: increased variability leads to much thicker channel‐belt deposits and elevated yet alternating high and low down‐valley slopes. In contrast, greater total sediment supply results in only slightly thicker channel‐belt deposits and uniformly elevated down‐valley slopes. These results reconcile diverse fluvial stratigraphic responses to sediment‐supply changes across basins during climatic perturbations.