2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 12
Presentation Time: 8:00 AM-12:00 PM


DIXON, John C., Geosciences, University of Arkansas, Fayetteville, AR 72701, jcdixon@uark.edu

The role of eolian addition in the development of weathering profiles is a poorly understood component of the weathering system. Traditionally, evaluation of the transformation of solid bedrock to regolith and ultimately to soil has been based on a mass balance approach to tracing the fate of weathering products in an essentially closed system. However, examination of trends in chemical weathering indices obtained from the systematic sampling of weathering profiles commonly reveal patterns which strongly suggest that the Critical Zone of the weathering system is profoundly influenced by the addition of chemical constituents in the form of windblown mineralogenic material.

Commonly used chemical weathering indices (alkalis: resistates, alkali earths: resistates, and silicon: resistates) were calculated from whole rock chemical analyses of weathering profiles from three sites in Arctic alpine Scandinavia. Rather than finding consistent increases in mobile: immobile chemical weathering indices with increasing depth in weathering profiles there is commonly a marked increase in surface horizon index values compared to values from deeper within the profile. Occasionally, weathering index values exceed those of the fresh bedrock from which the weathering profile has been derived. The increase in weathering index values is interpreted to be a reflection of the addition of relatively fresh mineral matter to the surface of the weathering profiles thus enriching the surface in relatively unweathered mineral grains. X-ray and light microscope analyses of silt and clay size fractions from surface horizons of weathering profiles reveal the presence of relatively fresh grains of primary rock forming minerals.

A more complete understanding of the processes operating in the Critical Zone of the global weathering system will require the assessment of the contribution of eolian-derived inputs into the soil/regolith system. This can initially be achieved by identifying the likely presence of eolian sediments using techniques discussed in this paper and subsequently calculating mass input of chemical species delivered in sediment to the weathering system.