Particle-size analyses of more than 300 samples of drift from Nisqually, Paradise, and South Cascade Glaciers in the Cascade Range of Washington, from Athabasca Glacier in Alberta, Canada, and from other alpine glaciers show that textural differences exist both between glaciers and between glacier subenvironments. Differences between glaciers probably reflect bedrock terrane and are shown by the percentage of silt + clay in the < −1.00 ϕ fraction, which increases in the following order: Nisqually and Paradise (volcanic bedrock), South Cascade (metamorphic and plutonic bedrock), and Athabasca (sedimentary bedrock). Differences between subenvironments are shown best by analyses of samples which include clasts as large as −6.67 ϕ average frequency curves of these samples show that basal tills lack dominant modes in the coarse fraction and may have dominant modes in the fine fraction at about 4.00 ϕ, whereas sediments of other subenvironments possess dominant modes in the coarse fraction at or above about −5.00 ϕ. Mean size and sorting increase, and percentage of silt + clay decreases in the following order: basal till, recessional-moraine till, end-moraine till, ablation drift, and stratified drift. Skewness, but not kurtosis, also varies with subenvironment.
A comparison of alpine drift with continental ice-sheet drift from Ontario shows that, in general, alpine drift is coarser, but that alpine basal till is comparable to ice-sheet basal till. When comparing nonglacial diamictons to alpine drift, it may be possible to distinguish the former from the sediments of one glacier subenvironment but not from those of another.
↵* Present address: Department of Chemistry and Geology, Clemson University, Clemson, South Carolina 29631.
- Geological Society of America