ABSTRACT: A comparison of dating methods used for the interpretation of a significant lithostratigraphic unit overlying the Last Interglacial (MIS 5e) Muir Point Formation, southwestern British Columbia.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Sedimentary units exposed in the sea cliffs at Muir Point, southern Vancouver Island, comprise some of the most widely-studied and climatically significant units in Western Canada. The Muir Point formation is the regional holostratotype for the last interglaciation (marine oxygen isotope substage, MIS 5e, c. 130-116ka) and is overlain by a complex association of fluvial sand and gravel, peat lenses and wood up to 6 m thick in some locations, also known as unit 6. A sample of poorly-preserved wood from unit 6 yielded a radiocarbon age of 43.6 ka BP, suggesting that the unit was deposited during the Olympia non-glacial interval (MIS 3); this interpretation is supported by palynological data that indicates that sub-alpine to treeline vegetation was present when climate was cool-cold and moister than present (Alley & Hicock 1986). However new high pressure radiocarbon ages from well-preserved wood within this unit were indeterminate (>52ka BP). In light of this age discrepancy the paleoecology from unit 6 could be interpreted as representing the cool and moist period that existed immediately before the onset of the Fraser Glaciation (MIS 2), and the organic matter represents glacially reworked material from the underlying Muir Point Formation. Optically-stimulated luminescence ages from unit 6 support this latter interpretation: a quartz SAR protocol provided two ages of approximately 23 ka. The suitability of luminescence ages derived from feldspar, and using different laboratory protocols, as a means to further support this interpretation will also be discussed.

Bibliography of Canadian Geomorphology