WET Hydrology & Hydrogeology

Theories on the origin of the valley-fill architecture and age of the Okanagan basin sediments remain divided between those favouring a pre-Fraser Glaciation and those favouring a post-Fraser Glaciation genesis. Regionally, landforms related to large meltwater discharges are continually being recognized, but sediment packages demonstrating those processes were previously unknown. Glacial sediments and landforms on the University of British Columbia campus near Kelowna BC were studied using surficial mapping, shallow seismic, and lithologic logs. Analysis revealed basin architecture consisting of fluvial valley fills, tributary fans, and subglacial flood deposits. The lowest valley sequence includes coarse fluvial sediments >65,000 yrs BP. Above are fine-grained sand and layers of organics (woody debris) radiocarbon dated at 35,000 - 23,000 yrs BP. Dates indicate continual deposition leading up to and during glaciation. The upper 10 - 20 m of sediments contains high energy bedforms that include dunes, antidunes, hummocky cross-stratification, and hummocky unconformities. Stacked bedforms are commonly conformably draped by laminated silt and clay couplets, indicating repeated discharge events filling a subglacial reservoir. Esker networks intrude into subglacial bedforms and represent high energy subglacial meltwater conduit erosion and deposition near the ice margins. Waning flow gravel deposits were initially parallel to esker direction, but locally reoriented into clastic dykes. Clastic dyke formation likely resulted from pressure created by regional ice recoupling after drainage of a subglacial lake phase. The following sequence is proposed: 1) The Okanagan Valley operated as a pre-glacial river valley 65,000 - 23,000 yrs BP and filled with clastic sediments and woody debris during glacial onset. 2) During the Fraser Glaciation, several high energy subglacial floods from the north and northwest filled a subglacial lake that repeatedly drained. 3) Esker conduit sedimentation and erosion indicates last stages of rapid flow from the west of the campus. 4) Clastic dykes within the esker indicate massive pressure heads ensued, and were likely caused by regional ice sheet recoupling. 5) Absence of tills in the central part of the valley and truncation of the esker distally indicates a late-stage water flow scoured out glacial sediments, except in the lee of bedrock obstacles.