Paper No. 4
Presentation Time: 9:45 AM
ICE RAFTED DEBRIS FROM REID LAKE, ONTARIO RELATIVE TO THE VARVE STRATIGRAPHY OF LAKE OJIBWAY
EVANS, Gianna L., Department of Geology, University of Cincinnati, 345 Clifton Court, Cincinnati, OH 45221, LOWELL, Thomas V., Department of Geology, University of Cincinnati, Cincinnati, OH 45221 and BRECKENRIDGE, Andy J., Department of Natural Sciences, University of Wisconsin - Superior, Belknap and Catlin, P.O. Box 2000, Superior, WI 54880, evansgi@mail.uc.edu
After the last glacial maximum, meltwater from the final retreat of the Laurentide Ice Sheet formed extensive, but short lived, bodies of water such as Lake Ojibway. The sequences of glacial sediments deposited in these lakes can be used to determine changes in water influx, changes in sediment influx, and ultimately the ice margin position. There are three prominent thickness changes in the Lake Ojibway varve sequence: varve 1528 which is thought to be the influx of Lake Agassiz water, years ~1800-2000 which is thought to correspond to the Cochrane Advance, and the Connaught varve series from years ~2060-2090.
Reid Lake, located just south of the furthest extent of the Cochrane advance, has an excellent varve record from varve years 1385 to 2115. Within these varve sediments are an IRD signal representing changes in the amount of icebergs at this location. X-rays of the Reid varve sequence allowed the IRD to be quantified and considered in a temporal sequence.
From this data we can conclude that there is a marked increase in IRD frequency ~30 years preceding varve 1528. There is also increased IRD deposition per varve thickness during varve years that coincide with the latter half of the Cochrane Advance. During the Connaught varves, there is an increase in the raw IRD counts but the frequency of IRD normalized by the varve thickness decreases. A possible ~10-20 periodicity in IRD deposition seen in the IRD record as a whole remains to be investigated.
