CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Bond, J.D.; and Kennedy, K.E.
Date : 2007.
Title : When ice sheets meet mountains: Late Wisconsinan McConnell ice-flow history in the Pelly Mountains, south-central Yukon.
Publication : CANQUA Ottawa 2007. Canadian Quaternary Association Conference, June 4-8, 2007. Carleton University, Ottawa, Ontario, Canada.
Issue :
Page(s) :
Abstract
Drift prospecting in high relief areas of the Cordillera requires consideration of paleo-ice-flow reversals. In the Pelly Mountains of southern Yukon, Late Wisconsinan McConnell (ca. 26.3-11 ka) ice flow occurred in four phases. Phase 1 marked the onset of ice accumulation in cirques above 1524 m a.s.l. These local glaciers expanded and fed valley glaciers that extended beyond the mountain front and into surrounding lowlands (after 26.3 ka). At glacial maximum or phase 2, the development of ice-divides to the east and south of the Pelly Mountains allowed Cordilleran ice lobes to invade the lesser glaciated Pelly Mountains, which resulted in up-valley ice-flow, and in some areas, topographically uncontrolled ice-flow across the massif. This ice-flow pattern continued into phase 3 or early deglaciation, a period characterized by recessional pauses and re-advances of the invading Cordilleran ice sheet. Following retreat of the ice sheet from the Pelly Mountains, local cirque glaciers above 1600 m a.s.l. expanded and resumed down-valley ice-flow (phase 4). This limited advance may have been sourced by remnant ice from the Cordilleran ice sheet. In light of the multi-phase ice-flow model, stratigraphical and sedimentological studies were applied in order to characterize drift dispersion in the mountain valleys. Results indicate that the composition of drift deposits is largely derived from the most recent ice-flow phase that glaciated a particular area. This was particularly evident on valley flanks where thin, homogenous moraine deposits are directly on bedrock, suggesting complete glacial reworking during each phase of ice flow. This has important implications for mineral exploration programs that are attempting to determine the source of anomalous float and soil samples. Finally, the effects of meltwater erosion from the retreat of the Cordilleran ice sheet from the Pelly Mountains were examined. Retreat of the Cordilleran ice sheet to the south and east of the regional drainage divides resulted in ponding of meltwater against the ice sheet. The initial outlets for this water were across the mountain passes and into the ice-free western and northern drainages. The large volumes of water released from the ice sheet resulted in significant erosion of surficial deposits in valley bottoms and potential complete reworking of pre-late Wisconsinan placer gold deposits.
Bibliography of Canadian Geomorphology