Reconstruction of late Quaternary sea-level change in southwestern British Columbia from sediments in isolation basins

Abstract

Conway, K. W. 2004 (August): Reconstruction of late Quaternary sea-level change in southwestern British Columbia from sediments in isolation basins. Boreas, Vol. 33, Bracketing ages on marine-freshwater transitions in isolation basins extending from sea level to 100 m elevation on Lasqueti Island, and data from shallow marine cores and outcrops on eastern Vancouver Island, constrain late Pleistocene and Holocene sea-level change in the central Strait of Georgia. Relative sea level fell from 150 m elevation to about -15 m from 14 000 cal. yr BP to 11 500 cal. yr BP. Basins at higher elevations exhibit abrupt changes in diatom assemblages at the marine-freshwater transition. At lower elevations an intervening brackish phase suggests slower rates of uplift. Relative sea level rose to about 1 m about 9000 cal. yr BP to 8500 cal. yr BP, and then slowly fell to the modern datum. The mean rate of glacio-isostatic rebound in the first millennium after deglaciation was about 0.11 m a À1 , similar to the peak rate at the centres of the former Laurentide and Fennoscandian ice complexes. The latter feature smooth, exponential-style declines in sea level up to the present day, whereas in the study area the uplift rate dropped to less than one-tenth of its initial value in only about 2500 years. Slower, more deeply seated isostatic recovery generated residual uplift rates of <0.01 m a À1 in the early Holocene after the late-Pleistocene wasting of the Cordilleran ice sheet. compiled age-altitude relations of marine deltaic features and glaciomarine deposits on the coast of southern British Columbia. They concluded that the upper limit of marine inundation during the initial phase of ice retreat at the end of the late Wisconsinan (Fraser) glaciation was approximately 200 m on the mainland coast, about 150 m on the central east coast of Vancouver Island, and 50 m on the west coast of Vancouver Island.Palaeo-sea levels can be established with some certainty from the age-altitude relations of the topsets of perched marine deltas, but few of these features have been dated in southern British Columbia. The determination of a palaeo-sea level position from glaciomarine sediments is more problematical, because the depth of the overlying water column at the time of deposition is difficult to determine. The fossil assemblage in a glaciomarine deposit may provide information on water depth, but the habitat ranges of neritic species are commonly broad, so depth reconstructions are generally imprecise and are therefore rarely undertaken. The studies conducted on the British Columbia coast in the 1970s and 1980s are no exception to this generalization; the presence of glaciomarine deposits was simply taken as an indicator of a higher sea-level datum. The resultant palaeo-sea level positions consequently have relatively low precision.A second problem, in common with much of the literature of the time, is that the radiocarbon ages of marine taxa from the deltaic and glaciomarine deposits were not corrected for the effects of isotopic fractio...

Relative Sea-Level Change in the Northern Strait of Georgia, British Columbia*

“…Sea-level histories developed recently for Victoria and the eastern Strait of Juan de Fuca Mosher and Hewitt, 2004) and the mid-Strait of Georgia (Hutchinson et al, 2004a) follow this pattern. Although less constrained, the early sea-level history of the Queen Charlotte Islands and adjacent continental shelf areas also features sea-level fall (Barrie and Conway, 2002a) to a pronounced sea-level low (Josenhans et al, 1997), possibly related to a crustal forebulge generated by the retreating ice sheet (Luternauer et al, 1989).…”

“…The first results provided new information for Victoria and Vancouver and have generated a well-constrained sea-level history for mid-Strait of Georgia (Hutchinson et al, 2004a). Here we present a complementary study for the northern Strait of Georgia and briefly discuss the implications for mantle flow properties and projections of future sea-level change.…”

Holocene Relative Sea-Level Changes from Near-, Intermediate-, and Far-Field Locations

“…Deglacial RSL histories of the Pacific coast [75][76][77][78][79][80][81][82][83][84][85] are supplemented by studies of the earthquake and tsunami history of the Cascadia subduction zone along the coasts of British Columbia, Washington, Oregon, and northern California [86][87][88][89][90][91][92][93].…”

Constraints on regional drivers of relative sea-level change around Cordova, Alaska

“…Ingólfsson et al, 1995;Shennan et al, 1995;Svendsen and Mangerud, 1987), reflecting isostatic uplift following deglaciation. In the vicinity of Vancouver, Canada, relative sea level fell from 150 m to --15 m between 14,000 cal yr BP and 11,500 cal yr BP, reflecting rapid uplift resulting from the retreat of the Cordilleran Ice Sheet (Clague et al, 1982;Hutchinson et al, 2004). James et al (2000) Observations and modelling of recent ice retreat and land uplift from a number of locations in south central and southeast Alaska (Larsen et al, 2005;Sauber et al, 2000) suggest that glacial isostatic responses to Little Ice Age and older Neoglacial changes in the mass of local ice caps and glaciers can produce measurable changes in relative sea level.…”

“…This approach, developed along Scandinavian coastlines (e.g. Hafsten and Tallantire, 1978;Krzywinski and Stabell, 1984;Svendsen and Mangerud, 1987), provides reconstructions of late Quaternary relative sea--level change in Scotland (Shennan et al, 1994;, Iceland (Lloyd et al, 2009;Rundgren et al, 1997), Canada (Hutchinson et al, 2004;James, 2005;2009a;Josenhans et al 1995) and Antarctica (Bentley et al, 2005;Zwartz et al, 1998) We investigate two potential isolation basins located above present mean sea level. Cores from Lower Whitshed Lake were retrieved in March 2010 from the frozen surface of the lake using a percussion corer and a gravity surface corer at a single site (60.472°N, 145.922°W; Figure 1).…”