TIMING AND SOURCES OF ABRUPT GLACIAL EVENTS ON THE LABRADOR SHELF

High peaks of detrital carbonate in Holocene and Late Glacial sediments in the Cartwright Saddle of the Labrador shelf record deglaciation events of the NE margin of the Laurentide Ice Sheet, particularly events in Hudson Strait and Hudson Bay, well to the north. The carbonate likely comes from glacial erosion of Paleozoic carbonate bedrock in the Hudson Strait and Southeastern Baffin Shelf, upstream, as there is no carbonate bedrock in the local drainage area feeding Cartwright Saddle. Core MD99-2236 was collected from Cartwright Saddle to develop a high-resolution record of deglaciation events and associated hydrographic changes; in particular, the catastrophic drainage of Laurentide glacial lakes, associated with the 8,200 year cold event, and the lack of evidence for an H-0 event in Younger Dryas-aged sediments of Cartwright Saddle are investigated.

The age model of this 21.15 m long core is based on 18 calibrated radiocarbon dates on mollusks and foraminifers. Carbonate and mass magnetic susceptibility (MMS) were measured on average at a 30 yr time resolution. There are six pronounced high carbonate spikes (>30%) in MD99-2236. Each spike corresponds to a relative MMS low. Age estimates of these peaks are: 11.5, 10.6, 9.5, 9.1, 8.7, and 8.2 cal kyr BP. The duration of the carbonate peaks ranges between 50 and 200 years. The 11.5 cal ka spike (end of Younger Dryas chron) corresponds to an 18-O depletion in benthic foraminifera; the full 18-O record is in progress. The carbonate spikes at 11.5 cal ka and a pronounced peak at 8.2 cal ka were not resolved in earlier research in Cartwright Saddle.

A ‘red bed' associated with a carbonate spike lies between 570 and 620 cm depth, ca. 8.57 cal ka, in the core; very close to the estimated age of the timing of the final outburst drainage of lakes Agassiz and Ojibway: ca. 8.47 cal ka BP. Bulk mineralogy, by X-ray diffraction, is tested on samples from the ‘red bed' of core MD99-2236, and the ‘red beds' of upstream sites in Hudson Strait (90023-045; 90023-101; AMD0509-28PC) and Hudson Bay (AMD0509-27bLEH), and samples of red Labrador and Keewatin (Dubawnt Group of northern Hudson Bay) tills. Estimations of the weight % of clay and non-clay minerals from the XRD are compared to help determine a potential source for the ‘red bed' sediments in MD99-2236.