Uncovering the hidden part of a large ice stream of the Laurentide Ice Sheet, northern Ontario, Canada

Abstract

Abstract This investigation was prompted by an enigmatic ice-flow anomaly (Area A) on the Glacial Map of Canada which covers about 10 000 km 2 in the Hearst/Kapuskasing area of northeastern Ontario. It consists of streamlined landforms and striations indicative of a major ice flow toward 130° oriented at right angle to another toward 220°. Both are late glacial flows but long-lasting disagreement exists regarding their relative age. The analysis of aerial photographs and satellite images in conjunction with a detailed survey of bedrock cross-striated surfaces over an area of about 30 000 km 2 within and around Area A clearly indicate that the 130° flow preceded the 220° flow. The earlier conflicting interpretations within Area A are attributed mainly to the sporadic occurrence of relict striated surfaces formed by older southwestward (220°–240°) Wisconsinan ice flows that have locally escaped destruction by late glacial flows, with the result that the southwestward flows are older (Wisconsinan) at some sites and younger (late glacial 220°) at others relative to the 130° flow. When considered with other factors such as the maximum elevation reached by the youngest late glacial flow, these ice-flow relationships indicate that Area A is the outcropping southern part of a much larger ESE ice-flow system, which is probably related to a large fluted belt located to the north and that was identified as the Winisk Ice Stream. The distal part of the ice stream, except for Area A, escaped detection by remote sensing mapping methods because depositional and erosional features associated with it are masked by deposits laid down by the younger (220°, Cochrane) ice flow and/or by postglacial marine and organic deposits (or were destroyed by the younger ice flow). The only reliable indicators of the passage of the ice stream in this “buried” section are ESE relict striations crossed by SW striations. The advancing ice stream toward the ESE not only preceded the late Cochrane 220° flow but probably outlasted it, as suggested by the mapping of several thousand iceberg furrows in Quebec and Ontario, also directed toward the ESE and overprinted on flutes formed by the last glacial flow. If this interpretation is correct, this makes the Winisk Ice stream the largest terrestrial ice stream in the Hudson Bay basin. An alternative interpretation associates this fluted belt to the exposed western fringe of streamlined bedforms from a late Hudson lobe buried by younger sediments.