A TALL TALE OF TILLS: EVIDENCE FOR MULTIPLE HOLOCENE ADVANCES OF LILLOOET GLACIER, SOUTHERN COAST MOUNTAINS

Lateral moraine stratigraphy at Lillooet Glacier, a large valley glacier in the southern Coast Mountains, is characterized by stacked tills separated by organic horizons containing in-situ paleosols and large wood macrofossils. Natural exposures are locally present where streams flowing from adjacent slopes have eroded through the moraine. Examination of several such gullies revealed two laterally continuous organic horizons and associated lines of detrital wood. More continuous exposures have been created by slopewash and minor gully erosion on the steep proximal slope of the moraine. Up to four organic horizons with abundant woody debris were identified at these exposures. Radiocarbon dating of detrital wood at one exposure suggests that Lillooet Glacier advanced between ca. 1600 and 1100 ¹⁴C yr BP, and again after 440 ¹⁴C yr BP. Forthcoming radiocarbon ages from other gullies, including sites with a complete sequence of four stacked tills separated by continuous organic horizons, should provide additional insight into the Holocene fluctuations of Lillooet Glacier. Dendrochronological techniques are being used to facilitate chronostratigraphic correlation of gully exposures along a ca. 3-km length of the lateral moraine.