Glacial terrain zone analysis of a fragmented paleoglaciologic record, southeast Keewatin sector of the Laurentide Ice Sheet

Abstract

A highly fragmented subglacial landscape is recognized at the regional to sub-regional scales in northeastern Manitoba, Canada, in the southeast Keewatin Sector (a core region) of the Laurentide Ice Sheet. New field-based ice-flow indicator measurements, mapping of subglacial landforms (remote-sensing and aerial photograph), and a re-examination of previously published data from an 8100km2 area in northeastern Manitoba show that the preserved subglacial record reflects a complex and potentially long glacial history. Five streamlined landform flowsets are mapped. A much higher degree of inheritance in the field-based ice-flow indicator data, than previously reported, allows for recognition of multiple ice-flow phases. Analysis of the characteristics of the subglacial landscape combined with a relative-age chronology established with field-based indicators, led to the recognition of disjoint zones with internally-consistent glacial histories – termed glacial terrain zones (GTZ). These GTZ were then classified as (1) relict glacial, (2) palimpsest, or (3) deglacial in nature.Our data suggest that while the southern Keewatin Sector was affected by regional ice-divide translocation, this alone cannot explain the fragmented, high inheritance landscape. We suggest that the subglacial landscape was continually evolving and subject to spatio-temporal variations in intensity of erosion, transportation and/or deposition throughout multiple glacial events (subglacial bed mosaic). Preservation of relict and palimpsest terrain likely occurred under large ‘sticky’ low-erosion regions. These regions could have formed by at least two different mechanisms: heterogeneous switch from warm-based to cold-based ice or within a warm-based subglacial environment from wet to stiff, dewatered till. Establishment of the regionally extensive (∼700km wide by at least 500km long) dendritic esker channel-system may have caused rapid spatially-variable dewatering of the substrate far back under the ice sheet. The GTZ approach integrates all available data (e.g. flowsets and other landform data, striations) to advance our interpretation of the spatio-temporal evolution of subglacial dynamics in areas where the degree of landscape inheritance and overprinting is spatially highly variable. This mosaic may be a characteristic net-effect of landscape evolution beneath the core regions of ice sheets.