Recent Geotechnical and Sedimentological Investigations between Inuvik and Tuktoyaktuk, NWTTuesday, November 19, 2019 - 11:00am to 11:20am Theatre Three
The Anderson Plain and Tuktoyaktuk Coastlands, between Inuvik and Tuktoyaktuk in the western Canadian Arctic, are characterized by ice-rich Pleistocene morainal, glaciofluvial, lacustrine and marine sediments. Permafrost is continuous and ranges in thickness from approximately 100 m near Inuvik to over 500 m near Tuktoyaktuk. Knowledge of the geology and Quaternary sedimentology of this region has been developed primarily through investigations between the 1950s and 1980s, often incorporating data from exploration by the oil and gas industry. Additional geotechnical data have been collected in this region since 2012 to support construction and monitoring of the Inuvik to Tuktoyaktuk Highway (ITH). Given their value for future multidisciplinary research and for informing decisions about land use and regional infrastructure development, the objective of this presentation is to introduce and partially synthesize these recent data.
The data being presented were obtained from geotechnical drilling at 18 alignment and 29 stream crossing sites along the proposed ITH route in 2013, 232 bridge piling installation sites during highway construction, and 16 highway embankment and 16 permafrost Sentinel research sites offset from the ITH investigated shortly before highway completion in 2017. Drilling depths were typically 10 or 20 m. Over 700 additional boreholes were advanced since 2012 near the proposed route to identify aggregate supplies for highway construction, however data from those investigations are not presented here.
Analyses of geotechnical borehole logs and samples obtained by solid stem auger and coring indicate that near-surface materials typically include organics and peat, often in combination with ground ice, while silt, clay and sand generally occur at greater depths. Clay is the dominant substrate type at depths greater than 4 m beneath riparian terrain, with peat at the surface and often an intermediate layer of pure ice, ice-rich silt, or ice-rich clay. Clay and sand characterize the top 20 m of substrate at hilltop sites. Investigations in stream channel banks show surficial material as primarily fluvial sand and gravel, with a general increase in fines in the underlying ground moraine till. Weathered shale bedrock was encountered at two drill sites, and mudstone at six, all less than 50 km north of Inuvik. Geochemical analyses were conducted on sediment samples obtained from the 16 Sentinel sites. Conductivities were mostly between 0 and 4000 μS cm-1, and samples were marginally basic with pH generally between 7.5 and 8.0. Dissolved organic carbon concentrations were generally between 0 and 15 mg C L-1, with greater concentrations in some peatlands between approximately 4 and 6 m depths.
Publication of these geochemical, physical, and related ground temperature data by the Northwest Territories Geological Survey and Geological Survey of Canada is intended to support multidisciplinary applied research on the terrestrial and aquatic ecosystems, hydrology, and sensitivity of this permafrost landscape. This resource is also expected to inform regional infrastructure management, and climate change adaptation.