A hypothesis on the relative roles of crushing and abrasion in the mechanical genesis of a glacial sediment

Relatively new techniques of optical microscopy and interferometry have been used combined with fractal and modal analyses to study possible deformation mechanisms in glacial sediment from Langjökull, Iceland. Previous studies have shown that the Langjökull till has reached an ultimate grading during deposition and transport. The results presented here add information on the deformation mechanisms that it may have suffered until and after reaching this ultimate grading. The modal and fractal analyses suggest high mechanical weathering. This is supported by the shape and texture of particles determined using the different imaging techniques of laser scanning, optical microscopy combined with three-dimensional image construction, interferometry and scanning electron microscopy. The larger particles have highly weathered surfaces, indicating severe abrasion to their surface during transport. The finer particles show less abrasion stamp and higher angularity. They also bear evidence of relatively fresh fractures. This seems to indicate that as the sediment became better distributed during transport, breakage moved from the larger to the smaller particles, with the larger grains only suffering abrasion. This supports the hypothesis of fractal breakage in this type of soil.

Research highlights
► Higher fractal dimension than other glacial sediments.
► Bi-modal particle size distribution cannot be reached solely by crushing.
► Evidence of chipping and wearing out in larger particles.
► Smaller particles less abraded with evidence of fresh fractures.
► Micro-morphological features show sediment suffered fractal breakage.