<p>Over geological timescales, we often assume the export of sediment, from mountainous source regions to depositional basins, is relatively instantaneous. As such, stratigraphic units are thought to capture erosional trends in their upstream catchment. The export of sediment from mountain basins, however, is a process heavily modified by sediment transport.</p><p>Here, we exploit a well-constrained field site in the Argentine Andes to demonstrate how the connectivity between hillslopes and mountain rivers modulates long-term sediment export in post glacial landscapes. We map out erosion trends in upstream catchments by combining an analysis of river profiles with geomorphic mapping of sediment deposits. We then use a comprehensive catalogue of clast lithology data to test to what extent upstream erosion trends are recorded downstream.</p><p>Despite their proximity to each other, we find adjacent catchments supplying sediment to the Iglesia basin have distinctly different degrees of hillslope-river connectivity, evident from the morphology of terraced and fan deposits within the catchments. Catchments with good hillslope-river channel connectivity also have a higher abundance of clasts sourced from the upper cordillera downstream of their mountain front. We place these observations within the context of a strong precipitation gradient across the cordillera and demonstrate the importance of climate and climate-controlled base-level on the spatial distribution of erosion within mountain catchments and fundamentally, on sediment export.</p><p>This work has implications for those using gravels to reconstruct the history of mountain ranges. Furthermore, it highlights the need to better constrain the potential for a disproportionate increase in sediment export to populated areas under future climate scenarios</p>
