Ice-rafted detritus evidence from Ar-40/Ar-39 ages of individual hornblende grains for evolution of the eastern margin of the Laurentide ice sheet since 43 C-14 ky

During the last glacial interval, the North Atlantic ice sheets expanded and contracted in approximate synchronicity with orbitally forced global climate change. Variation in ice rafted detritus content in North Atlantic marine sediment cores record the waxing and waning of glaciers, as well as the abrupt temperature changes at millennial time scales. The background variations of ice rafting are punctuated by Heinrich layers, which appear to record the catastrophic collapse of the Laurentide ice sheet through the Hudson Strait. The objective of this paper is to document the evolution of glaciation on Laurentia during the last 43 C-14 kyr. We present a provenance study based on Ar-40/Ar-39 dates of individual hornblende grains from 57 samples taken at 2 ern spacing between 4 and 134 cm from core V23-14 (43.4degreesN, 45.25degreesW, 3177 m). Sedimentation rates outside of the Heinrich layers are very low in this core, but the Heinrich layers are easily identified. Laurentide glaciation did not extend into the ocean south of 55degreesN until about 26 C-14 kyr, and retreated to the coastline or beyond by 14 C-14 kyr. Documenting the history of this major ice sheet has significant implications for understanding ice rafting sources in more distal locations where mixing among different ice sheets is likely. (C) 2002 Elsevier Science Ltd and INQUA. All rights reserved.