Cryostratigraphy and Permafrost Evolution in the Lacustrine Lowlands of West‐Central Alaska

Abstract

The influence of permafrost growth and thaw on the evolution of ice-rich lowland terrain in the Koyukuk-Innoko region of interior Alaska is fundamental but poorly understood. To elucidate this influence, the cryostratigraphy and properties of perennially frozen sediments from three areas in this region are described and interpreted in terms of permafrost history. The upper part of the late Quaternary sediments at the Koyukuk and Innoko Flats comprise frozen organic soils up to 4.5 m thick underlain by ice-rich silt characterised by layered and reticulate cryostructures. The volume of visible segregated ice in silt locally reaches 50 per cent, with ice lenses up to 10 cm thick. A conceptual model of terrain evolution from the Late Pleistocene to the present day identifies four stages of yedoma degradation and five stages of subsequent permafrost aggradation-degradation: (1) partial thawing of the upper ice wedges and the formation of small shallow ponds in the troughs above the wedges; (2) formation of shallow thermokarst lakes above the polygons; (3) deepening of thermokarst lakes and yedoma degradation beneath the lakes; (4) complete thawing of yedoma beneath the lakes; (5) lake drainage; (6) peat accumulation; (7) permafrost aggradation in drained lake basins; (8) formation of permafrost plateaus; and (9) formation and expansion of a new generation of thermokarst features. These stages can occur in differing places and times, creating a highly complex mosaic of terrain conditions, complicating predictions of landscape response to future climatic changes or human impact.

Permafrost soils and carbon cycling

“…Thaw lakes are most abundant on icerich, fine-grained deposits, such as abandoned floodplains, colluvial lower slopes and basins, peatlands, and lowland loess deposits (Veremeeva and Gubin, 2009;Grosse et al, 2013;Jorgenson, 2013). The age of thaw lakes can be extremely variable with some thaw lakes in Yedoma persisting since the late Pleistocene , Kanevskiy et al, 2014, while others are newly formed. Veremeeva and Gubin (2009) identified two stages of active thaw-lake formation in Northern Russia; one during the early Holocene around 9000 to 8000 years BP and the second one during the late Holocene around 5000 to 4000 years BP.…”

“…Much of this relic permafrost is polygenetic in that syngenetic permafrost developed on epigenetic permafrost. Examples include the Yedoma formations in northeastern Russia, Arctic and boreal Alaska (Reyes et al, 2010;Schirrmeister et al, 2011a, b;Kanevskiy et al, 2011Kanevskiy et al, , 2014, and the Yukon regions in Canada (Froese et al, 2008). Yedoma is also called "Ice Complex" because of the huge ice wedges formed in thick deposits of syngenetic origin (i.e., concurrent upward growth of deposits and the permafrost surface).…”

“…But, considering the whole cryostratigraphy, the profile also should include a fourth layer -the "true permafrost", which often contains buried or paleo-genetic horizons (Höfle and Ping, 1996;Schirrmeister et al, 2002aSchirrmeister et al, , 2008Schirrmeister et al, , 2011aKanevskiy et al, 2014). The active layer is defined as the zone of the soil profile above the permafrost that is subject to annual freeze-thaw cycles (Burn, 1998).…”

Cryostratigraphy, sedimentology, and the late Quaternary evolution of the Zackenberg River delta, northeast Greenland

“…The distribution of ground ice in the Zackenberg River delta is similar to that described by Pollard (2000a, b). The presence of the layered cryofacies in epigenetic permafrost has also been described by Kanevskiy et al (2014) in lacustrine sediments in interior Alaska. The suspended cryofacies is likely a more developed form of the layered cryofacies, forming during increased moisture availability or slower rates of freezing.…”

“…The presence of the pore cryofacies in frost-susceptible material is characteristic of epigenetic permafrost (Stephani et al, 2014). However, ice-rich cryofacies may form in epigenetic permafrost if an external water source is available to recharge the local groundwater system (Pollard, 2000a;Kanevskiy et al, 2014). In addition to the mode of permafrost aggradation, sediment characteristics and the availability of moisture have a controlling influence on the presence and morphology of ground ice (Stephani et al, 2014).…”