Identification of basal layer debris in ice-marginal moraines, Russell Glacier, West Greenland

Different processes of ice formation and deformation at the glacier bed create distinctive basal ice facies. The geographical distribution of these facies at the glacier margin can indicate the distribution of subglacial environments. Previous research has shown that debris in dispersed facies basal ice at the margin of the Greenland ice sheet has a distinctive particle-size distribution that can also be recognised in moraines deposited where the dispersed facies is present. This permits reconstruction of the distribution of basal ice characteristics and subglacial conditions from moraine sediments. Here, we study stratified and debris-band facies of the basal ice layer at the same site. We find that, contrary to previous suggestions, these two facies can also be distinguished sedimentologically. Co-variant plots of the C-40 (aggregate shape) and RA (aggregate roundness) indices show that pebble and cobble sized clasts (-2phi to -7phi) in the debris bands are statistically more angular than those in the stratified facies. Sedimentological characteristics of the parent facies are retained in ice-marginal moraines. Combined with previous work, these new observations suggest that the geographical distribution of basal ice facies at a glacier margin can be reconstructed from sedimentological characteristics preserved in moraines. (C) 2003 Elsevier Science Ltd. All rights reserved.