Sedimentological and Geochemical Assessment of Dust Sources in the Pluvial Lake Palomas Basin

The Chihuahuan Desert is a major and underappreciated dust production region in North America. Mineral aerosol production in the Chihuahuan Desert may be increasing as a result of varied causes, including native ecosystem (grassland) degradation due to a drying climate tendency and anthropogenic effects including cattle overgrazing and rapid human habitat expansion. The Pluvial Lake Palomas Basin (PLPB) includes the prime dust “hotspots” in this desert. Detailed sedimentological and geochemical properties of dust-producing sediments in eight PLPB sub-basins (Bolson de los Muertos, central PLPB, Laguna Santa Maria, Laguna El Fresnal, Laguna Guzman, Casas Grandes River Valley, Laguna Palomas, and Laguna de Patos) and one adjacent basin (Laguna Ascension) have been investigated. These basins are characterized by flat, barren playa surfaces located in the basin center (except Laguna Santa Maria). Flat playa surfaces and lack of roughness elements provide increased dust potential along with the perfect sediment textural distribution formed by abundant surface clays and silts along with sands and fine gravels, potentializing dust production via sandblasting and bombardment of surface crusts. Playa edges are dominated by a heterogeneous Gobi-type texture, while playa shorelines contain soft efflorescent crusts and abundant coarse sediments serving as abrading elements for the fines covering most playa surfaces. Playa-surface ped tops display very fine (to submicron grain size) thinly-crusted clays forming easily-deflated upcurled flakes: ped undersides are also rich in fines which may be liberated by disturbance. Geochemically, some PLPB playa sediments (especially Laguna Ascension) show enrichment in potentially hazardous elements such as As, Br and Mo, along with evaporite-related elements such as S and Cl which may contribute to salinization of downwind agricultural areas. These results complement ongoing regional dust sampling and analysis for assessment of environmental hazards posed by PLPB's dust emissions, and source comparison and identification of aerosols collected downwind.