Records of former land–sea relationships in southwestern British Columbia and adjacent Washington State have been established in considerable detail by terrestrial and marine stratigraphy, by terrestrial and littoral landforms, and by archeological remains, aided by radiocarbon dating of shells, wood, peat, and charcoal from critical sites. These records indicate submergent conditions at the time of retreat of the Vashon ice sheet, 13 000 y ago, followed by an unusually quick emergence of several hundred feet by about 12 000 y ago. In the north-east and north of the area studied, this emergence was followed by a submergence of some hundreds of feet during the next half millennium preceding the Sumas ice advance. During and following this ice advance, land again became emergent, and during the period 9 000 to 6 000 y ago sea level stood approximately 35 ft (10 m) below the present shore in some parts of the area. The shore has stood close to its present level for the last 5 500 y in all parts of the area.Early movements were dominantly isostatic. The pre-Sumas submergence is of problematical origin. Sea level shifts since 8 000 y ago appear to be dominantly eustatic; isostatic movements were evidently essentially complete by this time. In historic time very small changes shown by tide gauges and precise levelling may be tectonic.
Moderately to completely weathered Devonian clastic rocks caver much of central Melville Island, including Dundas Peninsula. The principal Quaternary deposits are till and ice contact gravels, which occur in central and southeastern Dundas Peninsula. Deltaic and marine nearshore and beach sediments are scattered along lowland coasts. Continental ice sheets, dispersing from the south, reached their maximum limits on central Melville Island during at least three episodes; only the age of the last advance has been determined. The oldest and most extensive glaciation recognized covered at least southern Dundas Peninsula up to 300 m a.s.l. and deposited Dundas Till plus a major belt of ice contact deposits. During a subsequent glaciation, ice from Parry Channel overlapped the south-central coast of Dundas Peninsula up to 100 m a.s.l. and deposited Bolduc Till. This deposition may have occurred at the same time that ice entered Liddon Gulf from the south, depositing Liddon Till to 100 m a.s.l. on the outer gulf coast. At 11 700 ± 100 BP, all coasts were rising after crustal depression by ice assumed to have occupied Parry Channel and possibly covered the central Queen Elizabeth Islands. Maximum emergence on the south coast is at least 90 m; on all coasts farther north a prominent (and highest) water plane is recorded at about 55 m a.s.l. Subsequent to this initial emergence, ice from Parry Channel readvanced over, and retreated from, the south coast of Dundas Peninsula probably between 10 340 ± 150 and 9670 ± 150 BP, depositing Winter Harbour Till up to 120 m a.s.l. Because shoreline emergence was not significantly interrupted by this readvance, it is concluded that off shore this ice sheet was probably floating. Local ice caps existed at undetermined times on the uplands of Melville Island, north of Dundas Peninsula.
The Beaufort Formation, in its type area on Prince Patrick Island, is a single lithostratigraphic unit, a few tens of metres thick, consisting of unlithified sandy deposits of braided rivers. Organic beds in the sand have yielded more than 200 species of plants and insects and probably originated during the Pliocene, when the area supported coniferous forest. This Beaufort unit forms the thin eastern edge of a northwest-thickening wedge of sand and gravel beneath the western part of the island. These largely unexposed beds, up to several hundred metres thick, include the Beaufort unit and perhaps other older or younger deposits. On the islands northeast and southwest of Prince Patrick Island (Meighen Island to Banks Island), the name Beaufort Formation has been applied to similar deposits of late Rrtiary age. Most recorded Beaufort beds on these islands are stratigraphically and paleontologically equivalent to the "type" Beaufort, but a few sites that have been called Beaufort (such as Duck Hawk Bluffs and the lower unit at Ballast Brook, on Banks Island) differ stratigraphically and paleontologically from the "type" Beaufort. This paper recommends that these deposits (probably middle Miocene) and others like them be assigned new stratigraphic names and not be included in the Beaufort Formation as now defined. Informal names Mary Sachs gravel (Duck Hawk Bluffs) and Ballast Brook beds are proposed as an initial step. Formal use of the name Beaufort Formation should be restricted to the western Arctic Islands.
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