GEOSCAN Search Results: Fastlink

GEOSCAN Menu


TitleContemporary sand wedge development in seasonally frozen ground and paleoenvironmental implications
AuthorWolfe, S A; Morse, P D; Neudorf, C M; Kokelj, S V; Lian, O B; O'Neill, H B
SourceGeomorphology vol. 308, 2018 p. 215-229, https://doi.org/10.1016/j.geomorph.2018.02.015
Year2018
Alt SeriesNatural Resources Canada, Contribution Series 20170301
PublisherElsevier BV
Documentserial
Lang.English
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
NTS85J/06
AreaGreat Slave Lake
Lat/Long WENS-115.2961 -115.2958 62.4303 62.4300
Lat/Long WENS-115.2958 -115.2958 62.4303 62.4300
Subjectsenvironmental geology; surficial geology/geomorphology; stratigraphy; geochronology; sedimentology; Nature and Environment; Science and Technology; permafrost; ground ice; periglacial features; sand wedges; paleoenvironment; meteorology; precipitation; snow; temperature; sediments; sands; peatlands; vegetation; thermal conductivity; frost cracks; radiometric dating; radiocarbon dating; stratigraphic analyses; subsidence; sedimentary structures; ground temperatures; thermal regimes; Great Slave Plain High Boreal Ecoregion; climate change; sand veins; snow cover; optical dating; fill sediments; lacustrine beach sediments; eolian sediments; eolian sand sheets; surface furrows; chronostratigraphy; Phanerozoic; Cenozoic; Quaternary
Illustrationsgeoscientific sketch maps; photographs; tables; time series; schematic representations
ProgramClimate Change Geoscience, Permafrost
Released2018 02 15
AbstractContemporary sand wedges and sand veins are active in seasonally frozen ground within the extensive discontinuous permafrost zone in Northwest Territories, Canada. The region has a subarctic continental climate with 291 mm/a precipitation, -4.1 °C mean annual air temperature, warm summers (July mean 17.0 °C), and cold winters (January mean -26.6 °C). Five years of continuous observations indicate that interannual variation of the ground thermal regime is dominantly controlled by winter air temperature and snow cover conditions. At sandy sites, thin snow cover and high thermal conductivity promote rapid freezing, high rates of ground cooling, and low near-surface ground temperatures (-15 to -25 °C), resulting in thermal contraction cracking to depths of 1.2 m. Cracking potentials are high in sandy soils when air temperatures are < -30 °C on successive days, mean freezing season air temperatures are less than or equal to -17 °C, and snow cover is <0.15 m thick. In contrast, surface conditions in peatlands maintain permafrost, but thermal contraction cracking does not occur because thicker snow cover and the thermal properties of peat prolong freezeback and maintain higher winter ground temperatures. A combination of radiocarbon dating, optical dating, and stratigraphic observations were used to differentiate sand wedge types and formation histories. Thermal contraction cracks that develop in the sandy terrain are filled by surface (allochthonous) and/or host (autochthonous) material during the thaw season. Epigenetic sand wedges infilled with allochthonous sand develop within former beach sediments beneath an active eolian sand sheet. Narrower and deeper syngenetic wedges developed within aggrading eolian sand sheets, whereas wider and shallower antisyngenetic wedges developed in areas of active erosion. Thermal contraction cracking beneath vegetation-stabilized surfaces leads to crack infilling by autochthonous host and overlying organic material, with resultant downturning and subsidence of adjacent strata. Sand wedge development in seasonally frozen ground with limited surface sediment supply can result in stratigraphy similar to ice-wedge and composite-wedge pseudomorphs. Therefore, caution must be exercised when interpreting this suite of forms and inferring paleoenvironments.
Summary(Plain Language Summary, not published)
Within discontinuous permafrost, significant differences in ground thermal regimes, permafrost conditions and processes may occur over short distances, due to variations in moisture conditions, vegetation cover, surficial sediment types, and in depth to bedrock. In these and other permafrost environments, studies of present-day processes and landforms provide information for paleoenvironmental and geomorphic reconstructions, and applied geotechnical purposes including hazard and environmental assessments. Herein, we examine contrasting contemporary settings of sand wedges and peatland terrain developed in sand within the extensive discontinuous permafrost environment in the Great Slave Lake region of southern Northwest Territories, Canada, where the historical (1980-2010) mean annual air temperature is approximately -4.1°C.
GEOSCAN ID310678