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TitleTiming and rates of Holocene eolian deposition in the eastern Canadian Rockies: preliminary results
AuthorWolfe, S AORCID logo; Hugenholtz, C H; Lian, O B; Westgate, J A
SourceCANQUA-CGRG Biennial Meeting Programme and Abstracts Volume; 2009 p. 175 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20080718
MeetingCanadian Quaternary Association and Canadian Geomorphology Resereach Group General Meeting; Burnaby; CA; May 3-8, 2009
Mediaon-line; digital
File formathtml
AreaCanadian Rockies
Subjectssedimentology; eolian deposits; sands; dunes; depositional environment; Cenozoic
ProgramEnhancing resilience in a changing climate
AbstractEolian processes and deposition in the Canadian Rockies are closely tied to the fluvial regime of major river systems, and recent alterations to the fluvial regime have altered rates of eolian deposition. In some areas seasonal fluxes of eolian sediment are suppressed through human modification of the fluvial regime in order to reduce local dust hazards. In other areas fluxes are enhanced by seasonal reservoir drawdown related to hydroelectric production, which can cause local and downwind effects. Dust deposition can also contribute to unique localized ecosystems, through rapid soil accumulation rates and enrichment. The purpose of this study is to establish the timing and rates of Holocene eolian deposition in the Eastern Canadian Rockies. These results will be combined with geomorphic studies and present-day monitoring, to better understand the potential impacts that changes to the fluvial and climatic regimes could have on dust production. We examined 14 stratigraphic sections comprising eolian silts and sands within the Bow, Saskatchewan and Athabasca river valleys. The sections examined were in valley settings, near to the modern rivers such that eolian deposits are expected to be derived mainly from nearby fluvial sediments. Two distinct settings were examined, i) fluvially-proximal bottom-valley settings consisting of dune or loess deposits, ii) fluvially-distal lower-valley settings consisting of loess deposits. Chronological control is provided from 24 radiocarbon ages from wood and charcoal, 15 tephra horizons and 7 optical ages. Radiocarbon ages from all sites are in correct age-depth sequence, and provide good age control for the other methods used. Mazama (ca. 7.63 cal ka BP), Mt. St Helen's Y (ca. 3.66 cal ka BP) and Bridge River (ca. 2.35 cal ka BP) tephras were identified at various sections based on glass compositions of volcanic glass shards. Radiocarbon and tephra ages are in good agreement and establish the timing and rates of eolian deposition. Optical ages determined using the Single Aliquot Regeneration (SAR) protocol on the 180 - 250 µm quartz fraction of eolain silty-sands appear to be too young, based on radiocarbon ages and tephrachronology. At this time, no single explanation can be given for the differences in these ages, which is still being pursued. The radiocarbon ages indicate that eolian deposition began prior to 10 cal ka BP in the Athabasca and Bow river valleys. Loess accumulation rates at sites on the Saskatchewan River valley ranged from between 3 to 15 mm per century for the period between 9.5 and 1.2 ka BP, averaging about 7.6 mm per century. Preliminary results suggest that depositional rates in the last 2000 years may be higher than the average rate over the Holocene, not accounting for changes in soil compaction, with potential causes still being investigated.

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