Airborne Dusts in the Edwards Plateau Region of Texas

As part of a larger study to estimate the impact of airborne dust on pedogenesis, seven dust traps were installed across a 100 000 km 2 region in central and western Texas. Contents of the traps were collected and analyzed at 120‐d intervals. Total annual infall was approximately 12 g/m 2 with significant seasonal variations occurring. The average clay content is near 60% and is primarily mica and quartz with lesser amounts of smectite and kaolinite. The medium silt (5–20 µm) comprises approximately 25% of the dust and is dominantly quartz with moderate amounts of alkali feldspars. Particulate carbonates were not observed and Ca values for water from the dust traps indicate that if present, carbonates constitute only a small portion of the total infall. Analyses of medium silt grains using SEM and microprobe indicate that quartz and feldspar grains have both smooth conchoidally fractured surfaces and rough pitted morphologies. Grain surface morphology is not adequate for mineralogical identification. Although some materials from local soils may be collected as dust, analyses indicate that the primary source is external to the study area. Grain morphologies suggest multiple source areas for the dust. Substantial uniformity in total infall, particle size distribution, mineralogy, and silt grain morphology was observed across the study area, indicating that the dust depositions are regional in character.