Digital processing of back-scatter electron imagery: a microscopic approach to quantifying chemical weathering

This paper introduces digital processing of back-scattered electron (BSE) imagery as a microscopic approach to measure porosity from in situ dissolution of minerals. Four case studies exemplify this technique. In case one, alveoli start in the Sedona area of Arizona when sandstone porosity exceeds ~32%. Case two examines the maintenance of gnamma pits and polygonal cracks on a basalt boulder on the island of Maui, Hawaii. Cases three and four involve measuring rates of dissolution over thousands of years. Case three concerns rock dissolution in weathering rinds formed on ventifacted aplite boulders. Case four addresses the classic topic of which variable is most important in chemical weathering: temperature, precipitation, or microenvironment. Microenvironment is a more important control on plagioclase dissolution; organic-rich positions (under lichens) weather two to seven times faster than adjacent organic-poor positions away from epilithic organisms and rock coatings. Cases three and four illustrate that in situ measurements of rock and mineral porosity can yield data on mass weathered per unit area over time. This information is comparable to mass balance approaches in watershed- and soil-based weathering research. -from Author