OPTICAL DATING STUDIES OF QUATERNARY ORGANIC-RICH SEDIMENTS FROM SOUTHWESTERN BRITISH-COLUMBIA AND NORTHWESTERN WASHINGTON-STATE

The suitability of optical dating using 1.4 eV (infrared) excitation for determining the time of deposition, or compaction, of organic-rich sediments and peat is assessed with measurements on seven samples from six different lithostratigraphic units. One is of zero age, two have associated C-14 ages, three are known to have been deposited during an interglaciation, and one is similar to 1 Ma old. The samples yield satisfactory optical ages ranging from 0 to over 100 ka. We conclude that the Muir Point Formation (southern Vancouver Island) and the Whidbey Formation (northwestern Washington State) were both deposited during delta(18)O stage 5, as previously deduced from other evidence. The age obtained from the similar to 1 Ma sample was significantly too low. The optical dating method is simpler and more precise than thermoluminescence dating, and is recommended for future work.