A PALEOECOLOGICAL RECORD OF CLIMATIC DETERIORATION FROM MIDDLE TO LATE WISCONSINAN TIME ON THE INTERIOR PLATEAU OF BRITISH COLUMBIA, CANADA

The Indianpoint section, 90 km southeast of Prince George, presents a >25 ka record of paleoenvironmental changes from non-glacial Middle Wisconsinan time to just before Late Wisconsin ice from the Cordilleran Ice Sheet overran the site. Detailed plant and insect macrofossil analyses of a 5-6 m thick fine grained unit reveal that it represents a small lake, based on aquatic plants and insects, and taxa indicative of riparian or shoreline environments. Radiocarbon ages of 33.3 ka (TO-9159) and 46.5 ka (CAMS 93938) were obtained on willow (Salix) twigs near the base. The lower 30 cm of the unit is characterized as shrub tundra dominated by willow with some shrub birch (Betula), and no macrofossil evidence of conifers. Directly above 30 cm, abundant needles, seeds and seed wings of spruce (Picea) indicate that this tree was locally present, probably in small groves. Further analyses of samples from the lower portion of the section will be carried out to clarify the record of forest vegetation. The middle portion of the section indicates tundra with willow and minor birch. In the upper 2.5 m of the section, between 24.5 ka (CAMS 93940) and 20.4 ka (CAMS 93939), the vegetation changes to dry shrub tundra, dominated again by willow with minor birch. Characteristic insects such as the weevil Vitavitus thulius and the ground beetles Trichocellus mannerheimi, Pteriostichus (Cryobius) nivalis, and Amara alpina are presently only found in dry tundra habitats. The upper 40-50 cm of the lacustrine unit shows a decrease in the occurrence of willow and represents dry herb tundra. An age of 19.9 ka (AA44045) has been obtained on a willow twig 20-30 cm below where the unit is truncated by a Late Wisconsinan till. More AMS radiocarbon ages and a pollen diagram to complement the macrofossil evidence are in progress.

The lacustrine unit of the Indianpoint section spans >25 ka and records climatic deterioration associated with the growth of the Cordilleran Ice Sheet during the Late Wisconsinan. The increasingly dry and cold conditions indicated by the macrofossil assemblage likely reflect the growth of ice in the Coast Mountains which would reduce the availability of moisture to the Interior Plateau from Pacific air masses.