Basal ice facies: a review and unifying approach

Over the past 30 years numerous basal ice facies have been identified, named and classified. However, the resulting facies descriptions and names are inconsistent and no single scheme encompasses all of the different ice types that exist at different ice masses. In this paper, we review and critique existing basal ice facies names, descriptions and classification schemes, and propose a new, non-genetic approach that has the capacity to name and describe all basal ice types. We define six fundamental basal cryofacies and a further 12 composite cryofacies which can all be defined on the basis of a cursory evaluation of debris disposition and concentration. More detailed cryofacies description is based on characterizing three sets of ice properties that can also be estimated visually in the field: (a) the thickness of the basal ice facies and its constituent sub-layers, (b) the concentration and texture of debris included within any or all of those layers, and (c) the concentration and size of bubbles included within any or all of those layers. We also propose a shorthand method for the presentation of this descriptive information. Here, codes for the layer thicknesses are presented as standard text, and codes for the included debris characteristics and included bubble characteristics are presented as superscripts and subscripts respectively. Sub-layers are characterized similarly, but within a nested sequence of brackets. We evaluate the effectiveness of these two schemes by using them to rename and reclassify several existing basal ice facies. Results indicate that the schemes are robust and that they provide a coherent, non-genetic framework for the effective naming and description of basal cryofacies.