FLOOD-INDUCED TURB1DITES FROM NORTHERN HUDSON BAY AND WESTERN HUDSON STRAIT: A TWO-PULSE RECORD OF LAKE AGASSIZ FINAL OUTBURST FLOOD?

摘要

In Hudson Bay and Hudson Strait, the rapid collapse of the Laurentide Ice Sheet (LIS) culminated in the catastrophic drainage of proglacial Lake Agassiz into the North Atlantic around 8500 cal BP. It has been suggested that this catastrophic event may have triggered the 8200 cal BP cold event recorded in Greenland ice cores. Evidence for that outburst flood was the identification of a centimeter to decimeter-thick hematite-rich red layer that was observed in Hudson Strait sediments around 8000 yr BP. In this paper, we have identified a sequence of two flood-induced turbidites (i.e., hyper-pycnites) in a reddish layer from two cores collected in northern Hudson Bay (core AMD0509-27bLEH) and western Hudson Strait (core AMD0509-28PC) in 2005 onboard the ice-breaker CCGS Amundsen. These two reddish layers can be correlated to a red bed previously identified as a regional isochron in Hudson Strait and associated with the final drainage of Lake Agassiz around 8500 cal BP. Regardless of the exact timing of the catastrophic drainage, the hyperpycnites described in this paper suggest that they were deposited following two pulses, which is in agreement with the one of the scenarios proposed by Clarke et al. (2003) [Science 301, 922-923] for the drainage of Lake Agassiz. Finally, this study demonstrates for the first time the turbiditic and the flood-induced nature of the Hudson Strait red bed isochron.