QUANTIFYING BEDROCK EROSION AND COARSE SEDIMENT TRANSPORT IN THE TECTONICALLY QUIESCENT, LIMESTONE LANDSCAPE OF SOUTHEASTERN SPAIN

Limestone rocks form > 10% of Earth's surface, yet are poorly studied relative to siliclastic rocks. The long-term evolution of limestone landscapes and the consequent contribution of sediment and soil to fluvial systems is beginning to be better understood. In limestone landscapes, the accumulation of overland flow along hillslopes is patchy, due to subterranean pathways. Semi-arid to arid climates further limit the surface connectivity of hillslopes and fluvial systems and the availability of water, a key ingredient in the chemical erosion of limestone. These features together suggest that coarse sediments (or rock fragments, coarse clasts) will remain on hillslopes with limited overland flow. We predict sediment transport to be primarily driven by local hillslope characteristics. Here, we present results from four fluvial, four bedrock, and six hillslope clast cosmogenic 36-Chlorine measurements from a semi-arid limestone area in south-east Spain, the Navarrés Valley. In this landscape, tilted limestone uplands bound the valley; relief persists in the resistant bedrock in dipslope plateaux and scarps along river gorges. Vegetation today is maquis -- shrubs and wild herbs -- but early Holocene forests abounded. Soils on the limestone bedrock uplands are shallow and contain abundant rock fragments. To quantify the spatial distribution of erosion from along-dip slope limestone plateau and scarps, we measured cosmogenic 36-Cl from four primarily-limestone watersheds in the Navarrés Valley. The fluvial material we collected includes watersheds solely from dipslope areas and from the larger rivers. A detailed examination of a moderate-relief hillslope provides bedrock erosion rates, which we compare to 36-Cl concentrations in coarse clasts (2-16 cm and >16 cm) collected along a downslope transect. These measurements guide our bracketing of local coarse sediment production rates, coarse clast residence time, and hillslope contribution to fluvial systems. Using the national 5 meter digital elevation dataset, we use local curvature and surface roughness of this hillslope to inform our model of sediment transport.