CGRG Bibliography of Canadian Geomorphology
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Author : Godfrey-Smith, D.I.; and Stea, R.R.
Date : 2003.
Title : The luminescence properties of raised beaches and related modern deposits in north-central Nova Scotia: Can optical dating pinpoint the timing of isostasy in Atlantic Canada?
Publication : Joint Annual Meeting of the Canadian Quaternary Association and the Canadian Geomorphology Research Group. Halifax, Nova Scotia, June 8-12, 2003.
Issue :
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Abstract
The Bay of Fundy shoreline of Nova Scotia provides ample evidence of glacial and deglacial processes attributed to the late Pleistocene. Stranded beach shingle and sandy beaches are encountered along the Bay's southern shores. Some are located at spectacular elevations of nearly 40m a.s.l., as at Squally Point near the head of the Bay, trending to far more modest elevations of 10 m a.s.l. towards the southwestern tip of the Bay's shoreline. This gradient provides an opportunity to study the rate of deglaciation and isostatic uplift of the province. As a first step towards the absolute dating of these organic-poor deposits, we have investigated the luminescence properties of quartz grains extracted from raised beach deposits identified at Bennett Bay and Turner Brook, N.S. At Turner Brook, a sequence of four samples from 0.3 to 1.2 m depth yielded apparent ages of 0.55 to 23.3 ka, in correct stratigraphic order. We feel that it's unlikely that the lowest of these reflects the time of deposition; rather, the structure of the deposit suggests gradual infilling of the coarse, open gravel beach shingle by downward winnowing of finer quartz grains. The earliest of these may have originated directly from a glacially derived, poorly zeroed proximal source. A single sample from Bennett Bay yielded an age of 15.5 ± 2.5 ka, which is consistent with the end of Late Wisconsinan time of deposition of this beach. In order to understand how depositional and transportation processes within the Bay of Fundy affect the luminescence dating of similar sediments, we have examined the luminescence properties of a sequence of modern sediments bordering the Bay of Fundy at Rainy Cove, N.S. The source of these sediments is a unit of fluvial sand and gravel of Triassic age. Residual apparent past doses of 9.3 Gy, 1.1 Gy, and 0.2 Gy were detected, equivalent to apparent depositional ages of 4.5, 0.5, and 0.1± 0.06 ka. The apparent ages decrease monotonically with an increase in the number of reworking cycles and with increasing distances of up to 1km from the source, consistent with the expectation that longer exposure to light results in more complete signal zeroing in quartz. These results highlight how different depositional environments can affect apparent luminescence ages. By continuing to study late glacial and Holocene coastal deposits and modern depositional analogues we expect to develop appropriate procedures for the accurate dating of coastal Quaternary deposits, and ultimately to focus these on the investigations of deposits attributed to MIS3 and older, for which other chronological methods are frequently lacking.
Bibliography of Canadian Geomorphology