Sediment grain size as a carrier of climate and tectonic signals from orogenic topography to foreland basin stratigraphy

Foreland basins archive the erosion history of adjacent orogenic belts, but how foreland stratigraphy preserves history of orogenic landscape evolution remains poorly understood. To explore this, we use a landscape evolution model goSPL to simulate the coupled evolution of orogenic topography and foreland basin formation driven by erosion, vertical crustal displacement (rock uplift, lithospheric flexure), and sediment transport. We implement Sklar et al. (2017)’s approach to simulate grain size of hinterland hillslope sediment supply at each timestep and transmit this signal to foreland alluvial fans using Fedele and Paola (2007) self-similarity downstream fining model. Results show that, as orogenic relief grows, both the flux and grain size of material derived from the orogen increase until topographic steady state is reached. Grain size produced on hillslopes responds sensitively to mountain relief: higher and steeper topography caused by faster uplift, drier climate, or more resistant bedrock generates greater volumes of coarser debris delivered to the foreland basin. Thus, the advance or retreat of coarse-sediment facies relative to the mountain front generally reflects changes in orogenic relief driven by tectonic and climatic forcings over geological timescales. We also find that gravel-front migration rate correlates with the pace of topographic adjustment. Faster uplift or wetter climates accelerate erosion in the orogen and gravel facies migration in the basin. However, propagation of coarse facies is limited by spatially and temporally variable flexural subsidence coupled with evolving topographic loads. Our findings highlight grain size as a carrier of paleo-topographic signals transmitting tectonic and climatic imprints from source to sink but also suggest that similar foreland grain-size patterns may occur from differing uplift and rainfall histories if topography evolves similarly, cautioning interpretations of paleo-climate and tectonic signals solely from physical stratigraphy.