Drift composition and glacial dispersal trains, Baker Lake area, District of Keewatin, Northwest Territories

Abstract

In the District of Keewatin, glacial dispersal trains defined by lithology and geochemistry are mapped at regional (hundreds of kilometres), local (tens of kilometres), and detailed (kilometres) scales. The trains reflect glacial dynamics and the bedrock composition. Despite complex ice flow near the Keewatin Ice Divide, they have a prominent southeastward trend, although there is evidence for older regional southward and eastward flows, and for later flow northward and westward from the divide. In till, trace element concentrations are low, reflecting glacial erosion of metal-poor sedimentary and volcanic bedrock of the Dubawnt Group, Thelon Formation sandstone in particular. Glacial dispersal trains impoverished in trace elements extend into crystalline terrain masking the geochemical expression of underlying bedrock. In sections and drill cores, vertical compositional variations record differences in provenance related to either change in ice flow, glacial erosion, or both. The models of glacial dispersal trains provide a context for mineral exploration based on drift prospecting.

Evidence from Keewatin (Central Nunavut) for Paleo-Ice Divide Migration*

“…In the 1990s, Clark (1990a, 1990b) used satellite imagery over North America to reveal crossing drift lineations, namely in the area of the Keewatin Ice Divide, and to infer mobility of outflow centres within the Laurentide Ice Sheet throughout the last glacial cycles. Based on till composition near Baker Lake, Klassen (1995Klassen ( , 2001 showed strong evidence for southeastward dispersal under the Keewatin Ice Divide area, hence supporting the southeastward migration of the divide. Based on the examination of stratigraphic sections of till along the Kazan River, Klassen (1995) observed differences in provenance related to changes in the location and orientation of the Keewatin Ice Divide, but he also reported that correlations with overburden drill-core information in the area (i.e.…”

“…The dispersal of Dubawnt erratics as far south as the Manitoba border provides a better support for southward glacial transport in the region. Geochemical composition of till collected in the lower parts of drill core south of Pitz Lake also point to an early southward flow (Klassen, 1995).…”

“…Till stratigraphy along the Kazan River led Klassen (1995) to suggest an early eastward flow in the region (Lower till at his section KC, p. 50). Examination of two Kazan River sections (KR-A and KR-B) indicates at least three distinctive till units, of which the lowest till is thought to have a provenance from the west (McMartin and Henderson, 2004).…”

“…It builds on previous surficial mapping in the area by the GSC at 1:125 000 scale (Arsenault et al, 1981;Aylsworth et al, 1981aAylsworth et al, , 1981bAylsworth et al, , 1981cAylsworth et al, , 1981dAylsworth et al, , 1984Aylsworth et al, , 1986, and drift compositional studies at local and regional scales (i.e. Shilts, 1971Shilts, , 1973Shilts, , 1977Klassen, 1995Klassen, , 2001. Prior to our recent mapping, cross-striations and streamlined landforms indicated diverse ice-flow trends but their relative ages and significance to the regional ice-flow history remained poorly known.…”

“…Thus far, the history of the Keewatin Ice Divide, and its relative stability throughout the last glaciation, is still subject to debate (e.g. Klassen, 1995;Dyke et al, 2002), and most modelling exercises have yet to attempt to explain ice divide migrations (e.g. Tarasov and Peltier, 2004).…”