Pleistocene aminostratigraphy of the Georgia Depression, southwest British Columbia

Abstract

Amino-acid ratios of certain taxa of molluscs and wood were determined for Quaternary sediments in the Georgia Depression, southwest British Columbia. The stratigraphy and proposed ages of established major units are confirmed in all but one case by the amino-acid results. Aspartic-acid ratios in Clinocardium, Serripes, Nuculana, Mya, Macoma, and Hiatella averaged about 0.22, 0.23, 0.37, 0.28, 0.28, and 0.27, respectively, in late Wisconsinan Capilano Sediments and 0.37, 0.35, 0.44, 0.44, 0.56, and 0.44, respectively, in early Wisconsinan Dashwood and Semiahmoo sediments. D/L ratios of aspartic acid in Abies averaged about 0.14 in late Wisconsinan Fraser drift, 0.24 in the middle Wisconsinan Cowichan Head Formation, and 0.37 in the early Wisconsinan Dashwood and Semiahmoo drifts, whereas D/L ratios of aspartic acid from Picea averaged about 0.13 in the Cowichan Head Formation and 0.27 in the Sangamonian (?) Muir Point Formation. Ratios for the Muir Point Formation are judged to be much too low for the age of the sediments and, therefore, not reliable.Molluscan results from the Georgia Depression area were compared with D/L ratios of aspartic acid from the same mollusc taxa from the Puget Lowland to the south. Results are encouraging and appear to distinguish four Quaternary units within the combined region. Capilano Sediments correlate with Everson glaciomarine sediments, and Dashwood and Semiahmoo with Possession glaciomarine sediments. D/L ratios of wood samples from the Puget Lowland are poorly correlated with sediment age and so could not be compared with those of the Georgia Depression.