TIMING, RATES AND GEOMORPHIC CONTROLS ON HOLOCENE EOLIAN DEPOSITION IN THE EASTERN CANADIAN ROCKIES, CANADA

Glacially-fed river systems represent potentially significant sediment sources for eolian processes, owing to the volume of sediment production, seasonality of flow, and synoptic wind conditions within mountain and continental settings. In these settings, eolian deposition can play a major role in influencing local to regional ecosystems. However, the reduction in area of glacial ice during the Holocene, coupled with modern anthropogenic modifications has altered these inter-related processes. We investigate the timing and rate of Holocene eolian loess and dune deposition within three major river valleys of the southern Canadian Rockies, Canada through eolian stratigraphy and dating of sedimentary materials. Source sediments are seasonally-exposed alluvial deposits caused by fluctuating flows of glacially-sourced rivers. Variations in local river morphology promote source-sediment deposition caused by bedrock configuration and deposition from tributary streams and alluvial fans. Two primary settings for eolian deposition are recognized: source-proximal valley-bottom settings and more distal lower-valley sites. Dating is well-constrained by AMS ages and tephrachronology, but optical dating of quartz is complicated in this environment, likely due to varying provenance of quartz. Mass accumulation rate (MAR) determinations are defined mainly from AMS 14C age and tephrachronology for several Holocene intervals. Eolian deposition was initiated soon after deglaciation and has occurred nearly continuously for at least 10 500 years in the Bow, Saskatchewan and Athabasca river valleys. Sandy silt loess MARs have ranged between 100 to 2500 g·m^-2·a^-1 over the Holocene. Rates in the last 3000 to 4000 cal years BP are generally two to three times high than those observed in earlier periods. We attribute the late Holocene increase in MARs primarily to an increase in alluvial sediment supply within these river systems from localized basin and channel deposition.