New Mexico Geological Society Annual Spring Meeting — Abstracts

Atmospheric dust is recognized as an ubiquitous component of soils that form semi-arid and arid regions. The Carrizozo volcanic field in the Tularosa Valley, south-central New Mexico provides an opportunity to characterize the dust accumulation (loess) on a 5,000 year old surface (PhiHips et al., 1997). Variations in climate, topography, dust source and ecology have a pronounced effect on the chemical and physical nature of loess. A more complete study incorporating chemical and physical composition, rate and origin of modern loess is essential for understanding the mechanisms of global climate change.

Samples were collected incrementally with depth from three distinct surface cover catchments characterized by (1) desert pavement, (2) grasses and cacti, and (3) juniper tree vegetation within the northern portion of the flow boundaries. The catchments wereI measured for surface area and depth, and accumulation rates over 5,000 was calculated. Accumulation rates range from 3 cm³yr^-1 to 166 cm³yr^-1 with an average rate of 46 cm³yr^-1. Accumulation rates varied with surface cover through out the flow. ConsistantIy greater rates are observed with tree cover (avg. 62 cm³yr^-1) than with grasses/ cacti vegetation (avg. 38 cm³yr^-1) and high variability exists (5-166 cm³yr^-1, avg. 61 cm³yr^-1) with desert pavement cover. These results suggest that accumulation rates are controlled with surface cover type. The samples were analyzed for major and trace elements by x-ray fluorescence spectroscopy. The analysis indicates a dacitic composition (68 wt. % SiO₂ and 4 wt.% Na₂O+K₂O). Little or no significant chemical variability is seen incrementally with depth or within the flow boundaries suggesting a uniform,
homogeneous atmospheric dust source that has remained unchanged pedogenically over the last 5,000 years.