Composition and formation age of the amorphous silica coating glacially polished surfaces

Blackburn, T., Simon-Tov, S., Coble, M.A., Stock, G., Brodsky, E., and Hallet, B., 2019, Composition and formation age of the amorphous silica coating glacially polished surfaces: Geology, v. 47, no. 4, p. 347–350. https://doi.org/10.1130/G45737.1

Amorphous silica layers deposited on bedrock were investigated to determine the timing and nature of their deposition during glaciation in Yosemite National Park, California. The authors found that the amorphous coatings precipitated from chemical weathering of silicate bedrock beneath glaciers during the last glacial maximum at 30-10 ka. This work helped to recognize that glacial polish is comprised of subglacial chemical precipitates which may preserve the timing of formation as well as the compositions of subglacial waters.