Characterization of subglacial till from Robertson Glacier, Alberta, Canada : implications for biogeochemical weathering
Griggs, Russell Kelly.
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Physical and biogeochemical weathering occurring during transport in the subglacial traction zone impacts the lithology and petrology of sediment in tills. Grain size distribution, particulate organic carbon (POC) content, and bulk/clay mineralogy of recently exposed tills from the terminus of Robertson Glacier, Alberta, Canada were characterized via sieving, laser diffractometry, loss-on-ignition, and X-ray diffraction/scanning electron microscopy (SEM) in order to describe physical and mineralogical properties of these tills. The matrix material of all tills exhibit a grain size distribution biased toward medium to coarse sand-sized particles and the dominant minerals are calcite, dolomite, quartz, and K-feldspar with lesser muscovite, pyrite, phlogopite, and chlorite. POC abundance ranges from 1.1 to 3.5 weight percent and is negatively correlated with grain size for grains from 125 - 2000 microns. POC abundance is also positively correlated with calcite abundance, especially for grains from 125 - 2000 microns. Pyrite is present at < 1% bulk abundance, with a significant portion of the pyrite observed via SEM as ~5-15 micron grains. The modal particle size of the till matrix of medium to coarse sand is consistent with limited physical weathering due to the short (< 3 km) subglacial transport distance and is comparable to that from a metasedimentary glaciated catchment in the Swiss Alps. The small grain size of pyrite produces a large reactive surface area, which supports its potential importance as a key chemical energy source for microbially-mediated chemical weathering.