CGRG Bibliography of Canadian Geomorphology
Author : Lesemann, J-E.; Brennand, T.A.; and Lian, O.B.
Date : 2007.
Title : New insights on environmental change preserved in the Okanagan Centre stratotype, southern British Columbia, Canada.
Publication : CANQUA Ottawa 2007. Canadian Quaternary Association Conference, June 4-8, 2007. Carleton University, Ottawa, Ontario, Canada.
The Okanagan Centre section consists of a ~100 m thick sediment exposure located on the eastern shore of Okanagan Lake. Current interpretations of sediments at Okanagan Centre suggest a record of environmental change spanning ~44 000 – 50 000 years, possibly encompassing two glacial and interglacial cycles. The Okanagan Centre stratotype is a composite established from numerous smaller component stratotypes located in tributary valleys of the Okanagan Valley. Although some chronological control exists for the component stratotypes, it is generally lacking in the Okanagan Centre section. Also lacking is detailed process sedimentology for each lithostratigraphic unit, especially for diamicton units identified as tills and therefore interpreted as being formed during glacial (stadial) intervals. The only reported chronological marker is a redeposited and diluted tephra layer tentatively identified as a Cascadia tephra. Due to this paucity of datable material, correlation between composite stratotypes and units of the Okanagan Centre section relies mainly on lithostratigraphy. Re-examination of the lithostratigraphy and, especially, detailed sedimentology of diamicton units indicates that they record a glacial advance and debris flows, not separate glacial intervals. In addition, new age information (optical dating and tephrachronology) from lithostratigraphic units at Okanagan Centre suggest a much shorter record of environmental change, limited to the Late Wisconsinan (Fraser) glaciation (MIS 2). Optical ages show that most sediments were deposited 12 000-19 000 yrs BP. Tephra grain chemistry was determined using glass shard chemistry and glass-encased magnetite chemistry techniques. In both cases, tephra dilution limits the number of grains that can be probed. Glass shard chemistry has yielded inconclusive results suggesting a Mt. St Helens (MSH) tephra source. Identifying the exact MSH eruption is difficult as results can be linked to two distinct eruptions separated by ~35 000 years. Glass-encased magnetite chemistry eliminates the Mt. Mazama and Bridge River eruptions as sources for the Okanagan Centre tephra. This presentation highlights the need for careful re-examination of stratotypes in south-central British Columbia and their use in interpreting Quaternary environmental change. We emphasize the need for coupling of detailed process-based sedimentology with multiple chronological controls of units within stratotypes to better constrain the nature and timing of environmental change.
Bibliography of Canadian Geomorphology