Reconnaissance surficial geology of the Rivière Grandin map area (NTS 86-D) and the legacy of glacial Lake McConnell, Northwest Territories: GEM-2 Mackenzie Project, report of activities 2018

Abstract

This report provides information on progress for three North Bear activities: (1) reconnaissance surficial geology mapping of the Rivière Grandin area, (2) ongoing compilation of mapped glaciolacustrine features associated with glacial Lake McConnell, and (3) surficial geology mapping and Holocene landscape investigations at Whitebeach Point, Northwest Territories. These activities contribute new geological knowledge and improve our understanding of the distribution and nature of the surficial geology cover and the glacial history of this region. The Rivière Grandin map area (NTS 86-D; 1:125,000 scale) is characterized by three glacial terrains defined by different surficial sediments. Along and inland from the shores of Hottah Lake in the northeast, glacial Lake McConnell deltas, beaches and offshore sediments occur between 180-350 m elevation. Farther west, terrain near or above 500-600 m elevation is defined by hummocky glaciofluvial sediments, a few moraine ridges, abundant radial meltwater channels, and an absence of ice-flow indicators, which may indicate local cold-based glacial ice regimes. On the eastern edge of the Ortona Lake highlands, rare drumlins trend northwestward, perpendicular to the flutings at lower elevations to the north and south. The remaining and most extensive map areas are generally covered by streamlined till with interspersed minor moraines composed of ridged till. Drumlins, crag-and-tails and drumlinoids record northwestward and southwestward divergent and convergent ice flows. The area north, west, and south of Rome Lake has a greater concentration of ridged till. Late during deglaciation, a minor ice-flow shift occurred in the southwest map area, indicated by small, superimposed streamlined landforms. Compilation of glaciolacustrine features attributed to glacial Lake McConnell is ongoing. These features are from surficial maps that conform to the Surficial Data Model of the Geological Survey of Canada. To date, two NTS map sheets have been added in 2018 (86-D, L) and 17 NTS map sheets were added in 2017. Continuing compilation will improve knowledge of previous glacial lake limits and the associated surficial geology. The Whitebeach Point area was previously inundated by glacial Lake McConnell and more recently by ancestral Great Slave Lake. Surficial geology mapping of the area has identified a complex array of deposits, including widespread eolian sand dunes and sheets, beach ridges, and peatlands. The ongoing work will also examine the Holocene lake level history and landscape development of the area, which includes high-grade silica sand deposits.