WIDELY DISTRIBUTED SMALL DEFLATION SCOURS IN HOLOCENE SEDIMENTS EXHIBIT INTERACTIONS BETWEEN EOLIAN AND FLUVIAL PROCESSES

Small deflation scours are identified in closed basins across northern Chihuahuan desert. They for in a variety of settings, including distal alluvial fans, gentle slopes and more rarely in basin floors. The features exhibit large patches of bare earth. Morphologically, they form deflation scours, usually less than a meter below the adjacent surface, with widely scattered, or absent vegetation and with small lunettes composed of eolian sand along their downwind margins. The floors of the deflation scours are either deflationary, with lags of coarser material, or are eroding depositional surfaces containing thin layers of fluvially deposited silt and clay. The upwind margins are typically abrupt steps up to the surrounding vegetated surface. Up slope from the floors of the scours are commonly bare slopes, with rills showing erosion and transport toward the floor of the scours. In alluvial fans, there is typically a scatter of pebbles on this surface. These features are typically widely distributed on silty Holocene sediments that are less permeable, allowing repeated flooding of the deflationary hollow. An initial reconnaissance in the area immediately adjacent to El Paso and Las Cruces identified these features in most of the closed basins in the region. A preliminary analysis indicates that areas containing them cover 1,180 km² in these basins. These features are potentially a poorly understood contributor to eolian dust emissions. I am still hunting for a term for these features, but a searching for one that combines the eolian and fluvial processes that shape them.