Geomorphic and climatic interpretations of abrupt changes in glaciolacustrine deposition at Moose Lake, British Columbia, Canada

Abstract

Sediments deposited in Moose Lake, British Columbia exhibit three abrupt transitions during the Holocene. Basal diamicts are unconformably overlain by coarse sand and silt deposited as turbidity currents in an ice-dammed lake during final retreat of Wisconsinan ice. Rapid withdrawal of the valley glacier resulted in a fully developed Moose Lake followed by low rates of sediment input for much of the early and middle Holocene until approximately 4,100 years BP. At that time, sediment input doubled and then tripled by 3,120 years BP in response to cooling and several phases of regionally documented glacier expansions. The transition from the Altithermal dry/warm period to the Neoglacial cooling is coincident with the formation of varves at Moose Lake which provide a chronology of changing Neoglacial sediment inputs. The glacier-climate signal recorded in Moose Lake sediments suggests distinct thresholds for changes in sedimentation style that are dependent on both climatic and geomorphic conditions affecting the watershed. Early in the record, direct connection to glaciogenic sediment production produced highly variable sedimentation rates that ended abruptly as the ice-front retreated. In the middle record, climate conditions that led to greatly reduced ice extent and lower sediment production in the upper Fraser and Moose river watersheds, changed abruptly resulting in varve formation. The change in style and increased sedimentation was caused directly by greater seasonal variations in sediment input due to climate-controlled glacier advances beyond modern limits. While sediment supply is a factor, comparison of the sediment record with tree-ring responses to climate change suggest both summer temperature and winter precipitation are important controls of Holocene variations in sediment yield.

Key Words:

• Varves
• facies
• Holocene
• climate change