Investigating Source to Sink Processes with Cosmogenic 10Be Concentrations in Multiple Alluvial Grain Sizes

Recent studies suggest that concentrations of terrestrial cosmogenic nuclides (TCN) in varying grain sizes can provide important information about sediment source to sink pathways. However, some basic questions remain regarding the role that geomorphic processes play in determining TCN concentrations in alluvial sediment. As a result, there exists a critical need for an increased understanding of how sediment transport histories effect the interpretation of TCN concentrations in alluvium, and hence, the denudation rates and surface exposure ages derived from these data sets. We are using 10Be TCN concentrations in various alluvial sediment grain sizes to investigate the geomorphic processes responsible for eroding and transporting sediments from hillslopes, through drainage networks, and ultimately to sedimentary depocenters in two contrasting tectonic and climatic environments. The first is Red Wall Canyon in northern Death Valley, California, an arid tectonically active region. The second is the Blue Ridge Escarpment in the southern Appalachian Mountains, a humid tectonically inactive region. We collected sand (0.025-0.050 cm) and gravel (3-6cm) from active channels within the study areas for analysis of 10Be concentrations in the two distinct grain sizes; 19 samples were collected from Red Wall Canyon and 16 samples from the Blue Ridge Escarpment. By analyzing TCN concentrations in multiple alluvial grain sizes this project will explore the geomorphic processes responsible for transporting sediments from source area to depocenter, determine the geomorphic controls on TCN concentrations among variable grain size fractions in alluvial sediment, and ultimately help establish the most appropriate sample material for dating alluvial fans and measuring catchment-wide denudation rates.