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TitleMarine record of late-glacial readvance and last recession of Laurentide ice, inner Frobisher Bay, Baffin Island
AuthorDeering, R; Bell, T; Forbes, D LORCID logo
SourceCanadian Journal of Earth Sciences 2021 p. 1-18, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200768
PublisherCanadian Science Publishing
Mediapaper; on-line; digital
File formatpdf
NTS25N/07; 25N/08; 25N/09; 25N/10; 25N/15; 25N/16
AreaFrobisher Bay; Baffin Island
Lat/Long WENS -68.8333 -68.0000 63.8333 63.3333
Subjectsmarine geology; sedimentology; marine environments; ice; glaciomarine deposits; glaciology; marine sediments; Laurentian Ice-Sheet
Illustrationslocation maps; tables; bathymetric profiles; images; stratigraphic columns
ProgramPublic Safety Geoscience Assessing landslides and marine geohazards
Released2021 08 25
AbstractThe Cockburn Substage readvance marks the last major late-glacial advance of the northeast sector of the Laurentide Ice Sheet on Baffin Island. The causes of this abrupt, late reversal of retreat are still unclear, but greater chronological controlmay provide some insight. To date, the literature has focused on the large terminalmoraines in the region, providing a date of readvance (circa 9.5-8.5 ka cal BP). In Frobisher Bay, the Cockburn Substage readvance and recession onshore are marked by a series of moraines spread over 20 km along the inner bay. Acoustic marine mapping reveals five distinct transverse ridges, morphologically suggestive of grounding-zone wedges, and two later fields of DeGeer moraines on the floor of the inner bay. These indicate that the style of ice retreat (beginning no later than 8.5 ka cal BP) changed over time from punctuated recession of a floating ice front (20 km over >680 years, with four pauses) to more regular tidewater icefront retreat, reaching the head of the bay 900 years or more after withdrawal from the outer Cockburn limit. The established chronology for final recession in the region is based largely on radiocarbon dating of bulk shell samples and single shells of deposit-feeding molluscs, notably Portlandia arctica, affected by old carbon from carbonate-rich sediments. Sedimentary analysis and judicious sampling for 14C dating of glaciomarine and marine facies in seabed sediment cores enables development of a late- and post-glacial lithostratigraphy that indicates final withdrawal of ice from the drainage basin by 7 ka cal BP.
Summary(Plain Language Summary, not published)
The last glacial readvance of the continental (Laurentide) continental ice sheet from inner Frobisher Bay (near Iqaluit, Nunavut) occurred before 9400 years ago and the ice had disappeared from the bay by 7800 years before present. Seabed mapping and sediment coring show how the style of retreat changed over time from a step process, forming five large, distinct, moraine ridges to a regular tidewater ice-front retreat forming numerous small subparallel ridges known as DeGeer moraines. Radiocarbon chronology from fossil molluscs in the cores refines the timing of these processes.

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