Palaeogeographic Reconstruction of Hecate Strait British Columbia: Changing Sea Levels and Sedimentary Processes Reshape a Glaciated Shelf

a b s t r a c tSea-level history since the Last Glacial Maximum on the Pacific margin of North America is complex and heterogeneous owing to regional differences in crustal deformation (neotectonics), changes in global ocean volumes (eustasy) and the depression and rebound of the Earth's crust in response to ice sheets on land (isostasy). At the Last Glacial Maximum, the Cordilleran Ice Sheet depressed the crust over which it formed and created a raised forebulge along peripheral areas offshore. This, combined with different tectonic settings along the coast, resulted in divergent relative sea-level responses during the Holocene. For example, sea level was up to 200 m higher than present in the lower Fraser Valley region of southwest British Columbia, due largely to isostatic depression. At the same time, sea level was 150 m lower than present in Haida Gwaii, on the northern coast of British Columbia, due to the combined effects of the forebulge raising the land and lower eustatic sea level. A forebulge also developed in parts of southeast Alaska resulting in post-glacial sea levels at least 122 m lower than present and possibly as low as 165 m. On the coasts of Washington and Oregon, as well as south-central Alaska, neotectonics and eustasy seem to have played larger roles than isostatic adjustments in controlling relative sea-level changes.

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“…Riddihough, 1982;Barrie and Conway, 2012). Many authors have commented on the dichotomy between postglacial RSL on Haida Gwaii (Fig.…”

Section: Northern British Columbiamentioning

confidence: 99%

Post-glacial sea-level change along the Pacific coast of North America

Shugar

Walker

Lian

et al. 2014

Quaternary Science Reviews

128

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“…Terraces at 180 m to 170 m bsl are visible to the west of Kruzof Island (Greene et al, 2007(Greene et al, , 2011. These terraces are similar to those described by Barrie and Conway (2012) in Hecate Strait between Haida Gwaii and the British Columbia mainland. We have no core data near these terraces for approximating their age; however, these terraces very likely predate the beginning of the Younger Dryas and mark where the fetch of the sea came into equilibrium with the forebulge front sometime before the glaciers fully retreated from the fjords and straits at ca.…”

Section: Collapse Of the Crustal Forebulgementioning

confidence: 58%

Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

Baichtal¹,

Lesnek

Carlson³

et al. 2021

Geosphere

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We leverage a data set of >720 shell-bearing marine deposits throughout southeastern Alaska (USA) to develop updated relative sea-level curves that span the past ∼14,000 yr. This data set includes site location, elevation, description when available, and 436 14C ages, 45 of which are published here for the first time. Our sea-level curves suggest a peripheral forebulge developed west of the retreating Cordilleran Ice Sheet (CIS) margin between ca. 17,000 and 10,800 calibrated yr B.P. By 14,870 ± 630 to 12,820 ± 340 cal. yr B.P., CIS margins had retreated from all of southeastern Alaska's fjords, channels, and passages. At this time, isolated or stranded ice caps existed on the islands, with alpine or tidewater glaciers in many valleys. Paleoshorelines up to 25 m above sea level mark the maximum elevation of transgression in the southern portion of the study region, which was achieved by 11,000 ± 390 to 10,500 ± 420 cal. yr B.P. The presence of Pacific sardine (Sardinops sagax) and the abundance of charcoal in sediments that date between 11,000 ± 390 and 7630 ± 90 cal. yr B.P. suggest that both ocean and air temperatures in southeastern Alaska were relatively warm in the early Holocene. The sea-level and paleoenvironmental reconstruction presented here can inform future investigations into the glacial, volcanic, and archaeological history of southeastern Alaska.

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“…In the late stages of ice retreat from Hecate Strait, large moraines were formed on the flanks of the strait, their roughly north–south orientations reflecting the retreat from the strait west onto Haida Gwaii and east onto British Columbia (Barrie and Conway, 2016). As deglaciation progressed, much of Hecate Strait was a broad coastal outwash plain fed from retreating ice to the west on Haida Gwaii and to the east on the British Columbian mainland (Barrie and Conway, 2012). Pro‐glacial lakes were formed during the retreat of the CIS in Hecate Strait.…”

Section: Discussionmentioning

confidence: 99%

Deglacial dynamics of the Foxe–Baffin Ice Sheet, Frobisher Bay, Nunavut, Canada revealed by submarine landform mapping

Todd

Dowdeswell

Shaw

et al. 2022

J Quaternary Science

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Previous interpretation of the nature and distribution of subaerial glacial landforms established that Frobisher Bay in southeastern Baffin Island was glaciated in the Late Wisconsinan by ice flowing southeast from the Foxe–Baffin Ice Dome. New seafloor mapping within the bay has revealed submarine glacial landforms that are described and interpreted in the context of their subglacial, ice‐marginal, glaciomarine and marine process environments. Interpretation of the evidence confirms that ice occupied Frobisher Bay, flowing from the northwest to southeast, parallel to the orientation of the bay. Relatively rapid ice velocities are indicated by the presence of ice‐moulded bedrock and megaridges flanking a deep trough (>700 m) along the faulted southern flank of Frobisher Bay. In shallower regions, areal scouring and channelisation indicate the widespread presence of glacial ice. As ice retreated to the northwest towards the Foxe Ice Dome, De Geer and recessional moraines were deposited at the ice front. The latter correlate spatially with the extensive Frobisher Bay Moraine System on land. Two iceberg ploughmark populations are evident, with smaller relict features in shallow water in rare locations in the northwest of the bay, and larger relict and modern ploughmarks in deeper water in outer Frobisher Bay.

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Palaeogeographic Reconstruction of Hecate Strait British Columbia: Changing Sea Levels and Sedimentary Processes Reshape a Glaciated Shelf

Cited by 5 publications

References 25 publications

Post-glacial sea-level change along the Pacific coast of North America

Post-glacial sea-level change along the Pacific coast of North America

Late Pleistocene and early Holocene sea-level history and glacial retreat interpreted from shell-bearing marine deposits of southeastern Alaska, USA

Deglacial dynamics of the Foxe–Baffin Ice Sheet, Frobisher Bay, Nunavut, Canada revealed by submarine landform mapping

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