Sodium Chloride and Freezing Temperatures Increasing the Weathering of a Shale Bedrock Channel

Abstract

Studies on erodibility in shale channels attribute slaking as the primary weathering mechanism, and consider chemical weathering mechanisms as a secondary agent (Tinkler and Parish, 1998). This research examines the roles of freeze-thaw, cation exchange, and slaking mechanisms. The objectives of this study were to determine if slaking is the primary mode of weathering in a shale bedrock channel, investigate the cumulative effects of cation exchange, freeze-thaw and slaking upon weathering and ascertain the contribution of chemical weathering due to anthropogenic sources.

The impact of slaking, freeze-thaw and geochemical weathering on Georgian Bay Formation (GBF) shale was assessed in the laboratory using shale samples collected from Humber Creek (Toronto, Ontario). A modified version of the slake durability test (Franklin and Chandra, 1972) and the weatherability test (Unrug, 1997) was employed to investigate the slaking characteristics of the shale. Three-way ANOVA tests revealed that significant effects from air temperature, NaCl concentration and the interaction effect of the two conditions on Weatherability Index and Inverse Slake Durability Index.

The results of this study indicate that slaking is not the primary weathering agent in shale bedrock channels and suggest that changes to water quality from anthropogenic inputs may be increasing the erodibility of these channels. Despite its exploratory nature, this study offers conditional insight into possible revisions required to the conceptual model of erosion and erodibility within a shale bedrock channel environment.