10BE DATES OF FLOOD DEPOSITS WEST OF LAKE NIPIGON: EVIDENCE FOR AN EARLY HOLOCENE MELTWATER EVENT

Extensive channels incised into bedrock west of Lake Nipigon, Ontario, may have served as the first possible eastward drainage routes of glacial Lake Agassiz. We investigated flood deposits within this channel system and 10Be dated two deposits located in a southern and northern channel complex. Four 10Be dates from a location near the Roaring River yield a mean surface exposure age of ≈10,400±240 yr and five 10Be dates from a location near Mundell Lake yield a mean surface exposure age of ≈10,700±640 yr. These ages indicate that occupation of the channels postdates initiation of the Younger Dryas event by ≈2500 years and are in agreement with an existing basal radiocarbon date near the Mundell Lake location (Teller et al., 2005). Preliminary paleohydrological estimates based on clast sizes and channel geometry are velocities and discharges between 2.8–19.8 ms-1 and 4200–30,000 m3s-1 at the Roaring River location and 2.5–17.5 ms-1 and 49,000–349,000 m3s-1 at the Mundell Lake location. Our results suggest that significant melting of the Laurentide Ice Sheet was occurring during Early Holocene time.