Direct response of small non-glaciated headwater catchments to Late Quaternary climate change: The Valle de la Fueva, southern Pyrenees

Abstract

Topographic depressions in mountain regions function as sediment traps and their morpho-sedimentary archives provide important insight into erosion and sediment dynamics in mountain ranges. In order to establish the (direct) drivers and timing of erosion phases in the southern central Pyrenees, small non-glaciated headwater catchments in the highly erodible Valle de la Fueva drainage basin were investigated as to their morphogenetic development.Geomorphic mapping revealed three morphogenetic complexes associated with the Valle de la Fueva drainage basin development: (i) high-lying talus plateaus and lateral slopes, (ii) extensive glacis and pedimentation surfaces, and (iii) deeply incised ravines with late-stage fluvial-cut terraces. The talus slopes are the oldest preserved geomorphic units of the Valle de la Fueva and potentially denote the initial drainage basin topography. Talus bedrock and boulder exposure ages cluster yet between 21 and 40 10Be-ka, indicating that the carbonate-dominated talus surfaces were rejuvenated during the last glacial cycle (MIS 4–MIS 2). The younger morphogenetic complexes (ii, iii) point to successive basin erosion stages from diffusive surface pedimentation under cold climate conditions (ii) to rapid linear fluvial dissection and late-stage terrace formation (iii). Denoting the abandonment of pediments as actively eroding surfaces, 10Be depth profiles of glacis cover sediments yielded consistent late MIS 2 exposure ages. The abandoning of pediments marks the onset of rapid fluvial downcutting of deep ravines (iii) around the Holocene climate transition, which involved substantial sediment routing and basin scale erosion. Lower fluvial-cut terraces denote the termination of intense catchment erosion at around 14–8–10Be-ka and minor fluvial incision during Middle-Late Holocene.This research shows that small non-glaciated mountain catchments feature valuable high-resolution morpho-sedimentary archives that are useful for assessing the direct impact of major climate transitions on surface processes and landscape transformation in mountain regions. Improvements in quantifying the timing and rates of (paleo-) surface processes are vital for enhancing regional glaciofluvial chronologies and large-scale basin erosion models that are possibly afflicted with time-averaging biases.