A better understanding of the Northwest Territories surficial geology is important for addressing topics such as natural resource extraction, permafrost change, infrastructure development, and land use management. The area surrounding southwestern Great Slave Lake (NTS 85C/85F) is one such region requiring greater surficial geological understanding. This region includes several towns and communities, important infrastructure (highways, railroads), is within the discontinuous permafrost zone, and is considered to host a significant mineral resource potential. Our research aims to improve understanding of Laurentide Ice Sheet (LIS) dynamics and evolution of glacial Lake McConnell, as well as the nature and distribution of surficial sediments, regional stratigraphy, and permafrost landforms.
Previous interpretations of ice-flow in the area indicated a generalized westward trajectory. New ice-flow erosional indicators (n=66) provide evidence for an oldest southwest flow (230°), followed by an intermediate westward flow (280°), and a later northwestward flow (305°). Stratigraphic observations and sediment properties (n=160) indicate three distinct till units. The lowest (oldest) till observed is a grey diamicton sourced mainly from local Paleozoic sedimentary rocks. A southwestward ice flow direction is interpreted for this unit based on clast fabrics and is consistent with the oldest erosional ice-flow indicators. The lower till is overlain by a brown diamicton containing a higher proportion of far-travelled Canadian Shield clasts. This brown till contains lodged, elongate boulders with parallel striations on their upper surface and clast fabrics indicating a west to northwestward ice-flow direction, broadly consistent with the interpreted intermediate ice-flow phase. The third till, with a dominant local bedrock provenance, forms a discontinuous unit at surface across the study area. Although no clear stratigraphic constraints were found, the third till appears to be related to the final ice-flow phase. Streamlined landforms, moraines, and other sediment-landform assemblages previously understudied in the region have now been mapped and analyzed in greater detail and further supporting LIS dynamics interpretations and deglacial history.
Minimum deglacial age estimates are better constrained through optical dating of medium-sand deposits in a well-developed raised beach (n=2) and relict aeolian dunes (n=7). Optical dating results indicate distinct shoreline development associated with the retreat of glacial Lake McConnell, and phases of dune development following lake drainage. Interpretation of local LIS dynamics and ice-margin retreat enhances our understanding of the western LIS and will inform practical applications of surficial geology in the southwestern Great Slave Lake area.