Bed sediment sources and mixing in the glacierized upper Fraser River watershed, east‐central British Columbia

Abstract

The geochemical, mineralogical and lithological composition of modern stream bed material is examined in order to characterize sources and evaluate downstream mixing of sediments in the upper Fraser River drainage basin, British Columbia. The <63 µm fraction is emphasized for its relative mobility and ease of analysis using instrumental neutron activation. Overall, the composition of the stream sediments closely reflects bedrock distribution. Samples dominated by limestone and dolostone, calcite and dolomite, and related elements (Ca, Mg, Sr etc.) correspond to Lower and Middle Cambrian carbonate bedrock largely confined to the Moose River sub-basin. Clastic and non-quartzite metamorphic lithologies, primary and secondary aluminosilicate minerals and related elements (Al, Cs, Rb etc.) are largely derived from Miette Group bedrock and associated with the uppermost Fraser River sub-basin. Except in the case of the Moose River/Fraser River junction, the determination of proportional tributary contributions is complicated by variable or delayed mixing, localized floodplain or valley side sources, and limited contrast between source areas. At present the Moose River sub-basin contributes a greater proportion of the total and fine-grained sediment loads of the combined Fraser River than would be expected from drainage basin area alone. The imbalance is related to greater relief, precipitation and runoff in the Moose River sub-basin; however, the spatial association of carbonate-rich stream sediments, ice cover and carbonate bedrock exposure indicates that glaciers play a particularly important roll in generating fine-grained fluvial sediment. Since differences in glacier cover and glacier potential in the two major sub-basins are likely to be persistent, and since relative sediment yields from the sub-basins can be determined from sediment composition, a potential indicator of glacier variation and climate change during the Holocene is therein available.

Sediment source changes over the last 250 years in a dry-tropical catchment, central Queensland, Australia

“…Most applications of sediment tracing have involved the analysis of suspended sediment from flood events (e.g., Collins et al, 1997a;Russell et al, 2001), although it has also been successfully applied to river bed sediments (e.g., Olley and Caitcheon, 2000;Dirszowsky, 2004). In the case of Theresa Creek, river bed sediments were sampled as there is no flow for most of the year and no flood events occurred during the study period.…”

“…As with the radionuclide tracing technique, a mixing model is used to determine the relative contribution of the different spatial sources. Geochemical tracing has been used extensively and in a wide variety of settings to determine the provenance of intransport or deposited sediment, including floodplain core sediments (e.g., Owens et al, 1999;Dirszowsky, 2004).…”

Suspended sediment flux downstream of the retreating Castle Creek Glacier, Cariboo Mountains, British Columbia.

“…As such, it is difficult to partition the relative amount o f sediment derived from the two scales o f paraglacial systems and contemporary non-glacial processes solely from a downstream perspective (Church and Slaymaker 1989;Ballantyne 2002a;Dirszowsky 2004). …”

“…Glaciers store water during cool and/or wet periods and release water during warm and/or dry periods. Glaciers are powerful agents of erosion that abrade and fracture substrate, making it available for various erosion processes and transport downstream (Dirszowsky 2004;Haritashya et al 2010). The suspended sediment load o f glaciated rivers (1-90% ice covered watershed) is higher than the global average (Gumell et al 1996); this load can be even higher during deglaciation as a result o f elevated meltwater production and sediment availability (Gumell et al 1999;Menounos et al 2005).…”

“…• fine sediment < 63 pm (silts and clays) are the chemically active component of the solid sediment load; they can transport and store nutrients and contaminants (Brown et al 1996;Dirszowsky 2004;Hodson et al 2004;Owens et al 2005;Walling 2005;Hodson et al 2008;Haritashya et al 2010);…”