Late glacial and Holocene sedimentary environments of Quesnel Lake, British Columbia

At 512 m Quesnel Lake is the third deepest in North America and at 100 km long its drainage basin spans from the arid interior plateau to the high mountains of the eastern Cordillera where small glaciers are a significant source of sediment. In most of the lake sediment is 0 to 40 m thick, reaching a maximum of just over 100 m thick near the junction of the three arms. Cores from three locations in the lake provide evidence that the entire Holocene record is contained in the upper 4 to 6 m of the sedimentary record where rates of accumulation have been constant or have decreased slowly. The highest rates (0.35 to 0.72 mm/a) occur near points of inflow, while the lowest rate (0.22 mm/a) occurs in a sheltered environment with limited inflow, and significant hypolimnic circulation which may flush water and suspended sediment from the water column. Late Pleistocene sediment beneath has a similar acoustic signature to the cored Holocene record above, suggesting that the sedimentary processes governing its deposition were not greatly different than in the present lake but that extensive glacial and paraglacial sources contributed to a significantly higher rate of accumulation. Mazama ash analyzed from two locations near points of inflow has an age of 7576 ± 60 cal. BP according to our chronology. Vivianite, which is uncommon in lakes of the Cordillera, occurs in the middle of the cores mainly associated with macroscopic wood fragments and indicates reducing conditions within the sediment.

► Assessment of the late glacial and post-glacial history of Quesnel Lake ► Holocene sedimentation in the upper 4 to 6 m at 0.2 to 0.7 mm/a ► Mazama ash is documented and dated very near the northern limits of its occurrence. ► The deep trench in which the lake lies is evidence of intense glacial erosion.