Southwest Banks Island Research Articles

Quaternary geology of the Duck Hawk Bluffs, southwest Banks Island, Arctic Canada: a re-investigation of a critical terrestrial type locality for glacial and interglacial events bordering the Arctic Ocean

Duck Hawk Bluffs, southwest Banks Island, is a primary section (8 km long and 60 m high) in the western Canadian Arctic Archipelago exposing a long record of Quaternary sedimentation adjacent to the Arctic Ocean. A reinvestigation of Duck Hawk Bluffs demonstrates that it is a previously unrecognized thrust-block moraine emplaced from the northeast by Laurentide ice. Previous stratigraphic models of Duck Hawk Bluffs reported a basal unit of preglacial fluvial sand and gravel (Beaufort Fm, forested Arctic), overlain by a succession of three glaciations and at least two interglacials. Our observations dismiss the occurrence of preglacial sediments and amalgamate the entire record into three glacial intervals and one prominent interglacial. The first glacigenic sedimentation is recorded by an ice-contact sandur containing redeposited allochthonous organics previously assigned to the Beaufort Fm. This is overlain by fine-grained sediments with ice wedge pseudomorphs and well-preserved bryophyte assemblages corresponding to an interglacial environment similar to modern. The second glacial interval is recorded by ice-proximal mass flows and marine rhythmites that were glacitectonized when Laurentide ice overrode the site from Amundsen Gulf to the south. Sediments of this interval have been reported to be magnetically reversed (>780 ka). The third interval of glacigenic sedimentation includes glacifluvial sand and gravel recording the arrival of Laurentide ice that overrode the site from the northeast (island interior) depositing a glacitectonite and constructing the thrust block moraine that comprises Duck Hawk Bluffs. Sediments of this interval have been reported to be magnetically normal (<780 ka). The glacitectonite contains a highly deformed melange of pre-existing sediments that were previously assigned to several formally named, marine and interglacial deposits resting in an undeformed sequence. In contrast, the tectonism associated with the thrust block moraine imparted pervasive deformation throughout all underlying units, highlighted by a previously unrecognized raft of Cretaceous bedrock. During this advance, Laurentide ice from the interior of Banks Island coalesced with an ice stream in Amundsen Gulf, depositing the interlobate Sachs Moraine that contains shells as young as ∼24 cal ka BP (Late Wisconsinan). During deglaciation, meltwater emanating from these separating ice lobes deposited outwash that extended to deglacial marine limit (11 m asl) along the west coast of Banks Island. Our new stratigraphic synthesis fundamentally revises and simplifies the record of past Quaternary environments preserved on southwest Banks Island, which serves as a key terrestrial archive for palaeoenvironmental change.

Paraglacial fluvial landscape change in a continuous permafrost environment around the ‘Twin Creeks’ catchment, Banks Island, western Canadian Arctic

Following Late Wisconsin glaciation of southwest Banks Island, four stages of landscape change are reconstructed for a small (c. 2km2) tundra catchment draining a south facing slope in an environment underlain by continuous permafrost. Initially, during deglaciation, glaciolacustrine silts and sands were deposited on a proximal slope underlain by till (Unit A). Subsequently a cyclic sub-aerial fluvial erosional–depositional system developed. First, an alluvial fan aggraded unconformably on Unit A with penecontemporaneous growth of ice and sand wedges (Unit B). Second, deep incision of the fan created a network of steep-sided flat bottomed channels. Third, wetland fens developed on the channel floors and peats with a sandy aeolian component aggraded and largely infilled the channels (Unit C). Synchronously, on the interfluves a soil catena developed under a warmer climate in the early Holocene. This was later buried by coversands (Unit D). Fourth, in the late Holocene, entrenchment recurred and currently fluvial processes are both exhuming and extending the first phase channel networks. A combination of climate and vegetation cover changes appears to control the pattern of geomorphological process responses.

Glaciotectonic deformation and reinterpretation of the Worth Point stratigraphic sequence: Banks Island, NT, Canada

Hill-hole pairs, comprising an ice-pushed hill and associated source depression, cluster in a belt along the west coast of Banks Island, NT. Ongoing coastal erosion at Worth Point, southwest Banks Island, has exposed a section (6 km long and ∼30 m high) through an ice-pushed hill that was transported ∼ 2 km from a corresponding source depression to the southeast. The exposed stratigraphic sequence is polydeformed and comprises folded and faulted rafts of Early Cretaceous and Late Tertiary bedrock, a prominent organic raft, Quaternary glacial sediments, and buried glacial ice. Three distinct structural domains can be identified within the stratigraphic sequence that represent proximal to distal deformation in an ice-marginal setting. Complex thrust sequences, interfering fold-sets, brecciated bedrock and widespread shear structures superimposed on this ice-marginally deformed sequence record subsequent deformation in a subglacial shear zone.Analysis of cross-cutting relationships within the stratigraphic sequence combined with OSL dating indicate that the Worth Point hill-hole pair was deformed during two separate glaciotectonic events. Firstly, ice sheet advance constructed the hill-hole pair and glaciotectonized the strata ice-marginally, producing a proximal to distal deformation sequence. A glacioisostatically forced marine transgression resulted in extensive reworking of the strata and the deposition of a glaciomarine diamict. A readvance during this initial stage redeformed the strata in a subglacial shear zone, overprinting complex deformation structures and depositing a glaciotectonite ∼20 m thick. Outwash channels that incise the subglacially deformed strata record a deglacial marine regression, whereas aggradation of glaciofluvial sand and gravel infilling the channels record a subsequent marine transgression. Secondly, a later, largely non-erosive ice margin overrode Worth Point, deforming only the most surficial units in the section and depositing a capping till.The investigation of the Worth Point stratigraphic sequence provides the first detailed description of the internal architecture of a polydeformed hill-hole pair, and as such provides an insight into the formation and evolution of an enigmatic landform. Notably, the stratigraphic sequence documents ice-marginal and subglacial glaciotectonics in permafrost terrain, as well as regional glacial and relative sea level histories. The reinterpreted stratigraphy fundamentally rejects the long-established paleoenvironmental history of Worth Point that assumed a simple ‘layer-cake’ stratigraphy including the type-site for an organically rich, preglacial interval (Worth Point Fm).

Late-Quaternary cryostratigraphy of a coastal cliff at Martha Point, southwest Banks Island, western Canadian Arctic

A 5 m thick unlithified sequence consisting of sands, silts and minor peats crop out in a coastal cliff within continuous permafrost. A well-exposed 70 m long section displayed a range of epigenetic ice wedges. These could be classified into three generations, each at a different stratigraphic level. The oldest was truncated by a major thaw unconformity which was overlain by a bed of highly involuted silts with peat clasts, interpreted as evidence of a deep palaeoactive layer and associated thermokarst. This bed forms part of a regionally extensive thermokarst phase, correlated with an early-Holocene Climatic Optimum. The other two ice-wedge horizons postdate the thermokarst event with the youngest approximating to the base of the modern active layer.

Genetically complex and morphologically diverse pingos in the fish lake area of south west banks island, n.w.t., canada

An unusually wide variety of pingo landforms located within a relatively restricted 50 km2 area of thick surficial sediments and permafrost is documented. Pingo growth and decay may occur independent of climatic change as witnessed by examples of embryonic, active and collapsed/collapsing features. The presence of deep kettle lakes in the area probably creates a dynamic system of interlinked taliks which influence the groundwater supply to centres of ground ice growth. The field relationships suggest that the pingo growth mechanisms may embrace both hydrostatic and hydraulic processes. All the pingos post‐date the Last Glacial Maximum ice retreat and the youngest was actively growing in AD 1981.

Genetically Complex and Morphologically Diverse Pingos in the Fish Lake Area of South West Banks Island, N.W.T., Canada

Genetically Complex and Morphologically Diverse Pingos in the Fish Lake Area of South West Banks Island, N.W.T., Canada

Nature and origin of ground ice, Sandhills Moraine, southwest Banks Island, Western Canadian Arctic

AbstractThe Sandhills Moraine is a Late Wisconsinan lateral moraine complex on southwest Banks Island. The occurrence of ice‐ablation landforms, ground ice slumps, kettle lakes and catastrophic lake drainage in winter suggests the presence of substantial bodies of massive ground ice. The distinctive hummocky topography of the Sandhills Moraine is thought to reflect partial melt‐out of this ice. Stratigraphic observations indicate that the ice is overlain irregularly and unconformably by glacigenic sediments, notably pebbly clay (till) and/or sandy gravels (outwash), while the ice itself possesses numerous and variable mineral inclusions, faults and foliations. Petrofabric analyses indicate a strongly preferred orientation to the ice crystals. It is suggested that these characteristics are best explained if the ground ice is interpreted as relict glacier ice.

Nature and Importance of Thermokarst Processes, Sand Hills Moraine, Banks Island, Canada

The Sand Hills moraine of southwest Banks Island is extensively affected by backwearing thermokarst in the form of ground ice slumps. Most are initiated by coastal erosion, with the result that 75%...

Headwall retreat of ground-ice slumps, Banks Island, Northwest Territories

The relationship between ice-face ablation and headwall retreat is described for three ground-ice slumps in the Sand Hills moraine, southwest Banks Island. Retreat exceeds ablation by a geometric factor that depends on the slope of the ice and the gradient of the surrounding terrain. Amounts of retreat predicted from ice-ablation calculations compare favourably with field measurements, except at the start of thermokarst activity in the spring or when the ground ice remains covered by debris for long periods.Long-term headwall retreat for slumps in southern Banks Island with different orientations and ice contents can be estimated using a model based on meteorological information. The model predicts headwall recession of 11 m/a for a ground-ice slump facing south and 8.8–9.3 m/a for one facing north, with inputs of a 35 °ice face, a ground slope of 5°, and a volumetric latent heat of 270 MJ/m3. These predictions are close to the maximum rates of retreat over a 10 year period as measured from air photographs.

Rate of Short-Term ablation of Exposed Ground Ice, Banks Island, Northwest Territories, Canada

AbstractEnergy fluxes and resultant short-term ablation rates were measured at a ground-ice slump on south-west Banks Island. Net radiation, as a proportion of the ablation flux, is greatest on days with high incident solar radiation, whereas on overcast days, sensible- and latent-heat inputs may supply more than half the necessary energy. A multiple regression equation using net radiation and a turbulent-energy term as independent variables explains 79% of the variation in the measured ablation fluxes. Overall, at least 60% of the energy used for ablation at the slump is derived from net radiation.

Rate of Short-Term ablation of Exposed Ground Ice, Banks Island, Northwest Territories, Canada

AbstractEnergy fluxes and resultant short-term ablation rates were measured at a ground-ice slump on south-west Banks Island. Net radiation, as a proportion of the ablation flux, is greatest on days with high incident solar radiation, whereas on overcast days, sensible- and latent-heat inputs may supply more than half the necessary energy. A multiple regression equation using net radiation and a turbulent-energy term as independent variables explains 79% of the variation in the measured ablation fluxes. Overall, at least 60% of the energy used for ablation at the slump is derived from net radiation.

Use of an ablatometer to measure short-term ablation of exposed ground ice

An instrument (ablatometer) was developed to measure rates of ablation of exposed ground ice. When the ablatometer is mounted on a melting ice face and linked to a portable micrologger, a continuous record of short-term ablation is obtained.The ablatometer was tested on the headwall of an active ground-ice slump located in southwest Banks Island, Northwest Territories. In general, it performed satisfactorily with little or no instrument-induced melt of the ice. Data for sunny days showed a strong diurnal rhythm of ground-ice ablation and considerable microscale spatial variability. Rates of ablation and their spatial variation were lower on cloudy days, illustrating the importance of solar insolation in inducing melt. Measurements beneath a debris cover following active-layer collapse suggest that ablation soon ceases and does not recommence until after the debris is removed by mud flow.As a result of the high degree of spatial variability in energy inputs and consequently in ablation rates, results from a single ablatometer may not be representative. If two or more instruments are mounted concurrently on exposed ice, an average value of the energy used in ablation can be determined. This value can then be compared with measurements of energy fluxes such as net radiation.