NUTT, Wesley V., and STRASSER, Jeffrey C., Augustana College, 639 – 38 St., Rock Island, IL 61201; EVENSON, E. B., and ENSMINGER, S. I., Lehigh University, 31 Williams Dr., Bethlehem, PA 18015; LAWSON, D.E., USA CRREL, Ft. Richardson, AK 99505

In an effort to determine if the depositional processes of glacial diamictons can be distinguished by the physical characteristics of their clasts, clasts were sampled and analyzed from two types of glacial deposits as well as from glacier ice at the Matanuska Glacier, Alaska. Diamictons studied included ice-marginal and inferred subglacial deposits. Clasts were sampled from debris-rich basal ice at two localities at the terminus as well as from a pebble horizon at the boundary between the basal ice and the clean englacial ice. For each clast, size, general lithology, shape, degree of striation, and roundness were quantified visually. Clast sizes ranged from 3 to 68 cm. Lithologies and shapes were fairly consistent throughout all localities. Clasts sampled from the ice exhibit a marked variability between sites in degree of roundness and the percentage of striated clasts. This possibly reflects different degrees of subglacial abrasion and fluvial transport in the basal system prior to incorporation in the ice. Clasts within the basal ice were nearly identical in all aspects to those from the pebble horizon at the top of the basal ice at the same site, suggesting similar pre-freeze-on histories of those clasts. Clasts sampled from two contrasting diamictons exhibit similar percentages of striated clasts, similar shapes, and slight differences in the degree of roundness. This study suggests that there is no clear method of distinguishing depositional processes of glacial diamictons based on clast physical characteristics.