CGRG Bibliography of Canadian Geomorphology
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Author : Godfrey-Smith, D.I.; King, E.L.; and Li, M.
Date : 2003.
Title : Establishing medium and long-term sand ridge stability and migration on Sable Island Bank using optically stimulated luminescence dating.
Publication : Joint Annual Meeting of the Canadian Quaternary Association and the Canadian Geomorphology Research Group. Halifax, Nova Scotia, June 8-12, 2003.
Issue :
Page(s) :
Abstract
On Sable Island Bank the presence of large bedforms of various orders of magnitude (up to 15 m relief), often with superimposed, smaller scale bedforms (sandwaves and megaripples) has been recognized for more than two decades but their stability conditions and timing of reactivation have remained uncertain. The formation of the large bedforms is time-transgressive, initiating, evolving (with dominantly eastward migration), and "drowning" as a result of Late Wisconsinan deglaciation and consequent post-glacial sea-level rise. Well-developed sand ridges in the immediate Sable Island shoreface (10 - 30m water depth) probably formed within the last 3 to 6 ka, though precise dating is generally lacking. Short-term morpho-dynamics studies are underway, yet until now, age dating by 14C has been ambiguous, largely due to the fact that old shell material is being reworked and incorporated into ridges formed at a later date. Using optical dating (optically stimulated luminescence) of quartz grains, we have begun to establish the mid- and long-range mobility of the Sable Island Bank sand ridges. Optical dating was applied to sequences of storm-reactivation units and underlying horizons identified in four cores on two ridges. Undisturbed, pre-sand ridge sands yield old apparent ages of ~45 ka. These ages reflect a large residual optical signal due to deposition without exposure to light, and are consistent with the subglacially derived origin of the sands. Basal sand ridge horizons yielded 3.1 and 5.8 ka, appear in correct stratigraphic order with respect to overlying reactivation horizons, and agree with limited 14C ages. Three of the cores show a reactivation horizon which had stabilized at 1.1-1.3 ka, at just over 1 m depth below the seabed. It may be that the weather patterns ameliorated at that time, following an earlier period of storminess. Another stabilization surface, dated at 400-600 years, was identified in two cores. Luminescence dating also yielded apparent zero ages (confirmed by a 14C age on soft organics) in the uppermost, active horizons, thereby confirming adequate exposure to light during bedform mobility and their apparent modernity. We therefore conclude that the luminescence method is very powerful tool in the study of process geomorphology within the shallow marine environment.
Bibliography of Canadian Geomorphology