Weathering rinds as a relative-age criterion: Application to subdivision of glacial deposits in the Cascade Range

Abstract

The thickness of weathering rinds on surface and near-surface clasts of Teana-way Basalt from alpine drift sheets in the southeastern North Cascade Range varies systematically with age of deposit. The rinds, which can be measured to the nearest 0.1 mm, result from oxidation of mafic minerals and mineraloids. Rind thicknesses for outermost moraines of three principal Pleistocene drift sheets are 1.96 ± 0.24 mm, 1.10 ± 0.11 mm, and 0.71 ± 0.12 mm. Sample variance may result from differences in composition and texture of clasts, microclimatic differences at sample sites, and incorporation of previously weathered stones. Weathering rinds can be used to construct relative time-distance curves for Cascade glaciers, but because rate of rind formation appears to be nonlinear, the true age of drift sheets cannot be obtained unless the weathering rate is calibrated by radio-metric dating.