Ground ice stratigraphy of the Inuvik-Tuktoyaktuk corridor
Creators: Alejandro, Alvarez
Publisher: name: University of Alberta Library
Year: 2022

<p>In order to understand permafrost and paleoenvironmental conditions in the Mackenzie Delta Region, permafrost cores were collected in the winter of 2017, near the newly developed Inuvik-Tuktoyaktuk Highway (ITH), NWT, by the NWT Geological Survey, NWT Department of Infrastructure, the University of Alberta’s Permafrost Archives Science Laboratory (PACS Lab), and partners as part of the Sentinel Drilling program. This study analyzed five cores (BH-1, BH-2, BH-3, BH-4, and BH-8) located within hilltops, riparian, and peatland terrains, recording various depositional environments. Cores were analyzed for stratigraphy, density, cryostructures, water isotopes (𝛿18O and 𝛿2H) and radiocarbon dating to determine the origin of the sedimentary records and associated ground ice.</p>

<p>This study highlights that the Mackenzie Delta region and its ground ice history have been extensively preconditioned by deglaciation, landscape evolution and climatic change, resulting in a landscape with reduced ground ice relative to the late Pleistocene surface. Collectively, these results indicate that deposits within low-relief areas (such as peatlands, lacustrine and riparian zones) are characterized by hosting ice-poor sediments with isotopic values, similar to modern-day, local isotopic composition. BH-1 and BH-3 are comprised of ice-poor diamicts with an isotopic composition between 𝛿18O -23‰ to -19‰, with a co-isotope slope lower than the local meteoric water line. These isotopic values indicate deep thaw following deglaciation, and subsequent talik formation, and likely enhanced by the Early Holocene thaw followed by stabilization and permafrost aggradation. Likewise, BH-4 and BH-8 are underlain by modest ice contents, in the form of Holocene-aged segregated ice within lacustrine and glaciolacustrine deposits. Radiocarbon dates and sedimentary structures indicate a changing landscape following deglaciation. Local lakes from ~11,500 to 9000 years ago, subsequently drained or lowered, developing epigenetic permafrost, and transitioning to syngenetic peat in the early Holocene. Lastly, deposits within high-relief areas, such as hummocky and ice-cored terrain, show little evidence of being affected by Holocene thaw. The ice within BH-2, located on a hilltop remnant of glaciofluvial outwash deposits, had depleted Pleistocene values ranging between 𝛿18O -30‰ to -27‰, at depths greater than 6-meters below the surface. This borehole included buried glacier ice and primary till below 11m depth, likely buried by glaciofluvial outwash in an ice-marginal landsystem.</p>

<p>Overall, these results highlight the ground ice heterogeneity within the Mackenzie Delta region. This heterogeneity is primarily a function of landscape geologic history, including, first and foremost, the preservation or eradication of relict ice during deglaciation processes such as talik development within lakes and fluvial networks, and mass-wasting processes, and subsequent climatic warming during the early Holocene. The result of these landscape-wide processes over the Holocene suggests that the landscape today is less ice-rich than the late Pleistocene landscape. Since the distribution and abundance of ground ice are strongly related to the geologic history of permafrost regions, future work will focus on placing these observations into a Quaternary geologic context and allow future trajectories of thermokarst to be identified.</p>