CHRONOLOGY AND SUBGLACIAL ENVIONMENTS RELATED TO OKANAGAN VALLEY FILLS

The landscape of the Okanagan Valley, BC, is dominated by a suite of landforms and sediments that formed under the advancing and retreating Cordilleran Ice Sheet. Theories surrounding the valley-fill architecture and age of the Okanagan basin sediments remain divided between pre-Fraser Glaciation and post-Fraser Glaciation genesis. Previous researchers concluded the absence of interglacial sediments resulted from complete meltwater scouring of the valley floor and subsequent re-deposition of glacial and post-glacial sediments

Analysis of 2 km of high resolution seismic reflection profiles and over 100 lithologic logs for the Central Okanagan region shows alluvial valley fills are composed of several stratigraphic sequences. Sand and gravel outwash of Wisconsin age comprises the bulk of sediments in the valley. Lower strata are dense coarser sand and gravel with an unconformable upper boundary. They are believed to be of subglacial fluvial origin (>65,000 yrs BP). Above is a fine grained sandy interval that has produced radiocarbon datable wood, showing it was deposited within the last interglacial period (23,000 to 65,000 yrs BP). Upper, thick accumulations of glaciolacustrine deposits represent a period of wide spread lakes in the region (<23,000 yrs BP). Subglacial beaded esker networks interfinger these laminated sediments representing a period of dewatering near the ice margins. Alluvial fans occur at the mouths of tributaries along the valley margin and evidence suggests these fans extend almost half way across the valley from the east, interfingering both interglacial and glacial deposits. Contemporaneous deposits represent fluvial incision into glaciolacustrine silts and clays.

The following sequence is proposed:

1)Valley operated as a pre-glacial braided river valley from 23,000-65,000yrs BP

2)Advancing glaciations deposited outwash deposits starting around 23,000 yrs BP

3)Glaciolacustrine deposits reflect a proglacial lake in the valley

4)Debris flow facies and beaded esker networks dominated late stages of glaciations as pulses of sediment delivery from side valleys into a subglacial position occurred

5)Postglacial lacustrine sedimentation followed

6)Contemporary riverine processes have incised through the valley fill (<10,000 yrs BP) depositing present day fluvial sequences.