TERRESTRIAL SEDIMENTS AND THE ¹⁸O RECORD: CORDILLERAN ICE SHEET DYNAMICS, VANCOUVER, BRITISH COLUMBIA

Terrestrial sediments across continental northwestern North America record Late Quaternary Cordilleran glaciation. Sedimentological and paleontological studies of these sediments have facilitated reconstruction of local and regional Cordilleran Ice Sheet dynamics. While these studies provide a wealth of data concerning this ice sheet, continental sedimentary deposits are, by nature, difficult to date and difficult to correlate beyond a regional scale. Littoral marine records provide a sedimentary record of terrestrial events containing biogenic carbonate from which age constraints can be established through radiocarbon dating. Planktonic foraminiferal oxygen isotope data provides a local climate record. MD02-2496, drilled off Vancouver Island, Canada, (48^o 58’ N; 127^o 02’ W; 1190m water depth; 38.38m core length) provides the first high resolution Late Quaternary sedimentary record from the northeastern Pacific. Results indicate MD02-2496 preserves a significant record of climate variability, similar to the Greenland δ¹⁸O records. Terrigenous sediments dominate from the core base to 31.5m. Numerous dropstones, high magnetic susceptibility, increased delivery of sediments >150 um, and heavy oxygen isotopes provide evidence of glacial activity in the Juan de Fuca Lobe during MIS 4. Between 25 and 31.5m color reflectivity and low magnetic susceptibility suggest glacial sediment input diminishes while C_org concentrations increase, likely representing decay of the Cordilleran Ice Sheet. During this interval δ¹⁸O decreases and demonstrates extreme variability, similar to the widely documented MIS 3 interstadial events. Glacial sediment returns at 25m (25.2 ¹⁴C kyr) coincident with the Coquitlam advance. Bedded turbidites and heavy oxygen isotopes beginning at 19.5m core depth appear to be coincident with the Last Glacial Maximum (16.8 ¹⁴C kyr), advance of the ice sheet onto the continental shelf providing a proximal source for terrigenous sediments. A dramatic shift in δ¹⁸O values occurs at 9.5m (12.5 ¹⁴C kyr), co-incident with the Bolling, and indicating rapid decay of the Cordilleran Ice Sheet. There is no evidence for glacial sedimentation at the site after 7m (9.3 ¹⁴C kyr).