Improved relative sea-level histories for Victoria and Vancouver, British Columbia, from isolation-basin coring

Freshwater sediments in low-elevation lakes and bogs in southwestern British Columbia are commonly underlain by marine and glaciomarine deposits. Radiocarbon ages from the marine-freshwater transition define the time that basins became isolated from the sea. Data from five lakes and bogs in the Victoria area, combined with earlier results, indicate that sea level fell from above 60 m a.s.l. to below present sea level between 12 500 and 11 500 14C years ago. In the Fraser Lowland, data from seven lakes and bogs show that sea level fell from above 180 m a.s.l. to about 80 m a.s.l. between 12 500 and 12 000 14C years ago, to 20–30 m a.s.l. by 11 000 14C years ago, and to about 10 m a.s.l. by 10 000 14C years ago. A previously proposed secondary resubmergence of the Fraser Lowland of 100 m or more is ruled out by the radiocarbon ages and by diatom analyses. Current Research 2002-A16 1 T.S. James et al. Resume : Dans les lacs et les tourbieres a faible altitude du sud-ouest de la Colombie-Britannique, les sediments d’eau douce reposent generalement sur des depots marins et glaciomarins. La datation au radiocarbone de la zone de transition entre les sediments marins et les sediments d’eau douce permet de determiner a quel moment les bassins ont ete isoles de la mer. Des donnees provenant de cinq lacs et tourbieres de la region de Victoria, combinees a celles d’etudes anterieures, montrent que le niveau de la mer est passe de plus de 60 m au-dessus du niveau actuel a un niveau plus bas que le niveau actuel entre 12,5 et 11,5 ka (14C). Les donnees provenant de sept lacs et tourbieres dans les basses terres du Fraser montrent que le niveau de la mer est passe de plus de 180 m au-dessus du niveau de la mer actuel a environ 80 m au-dessus de ce niveau entre 12,5 et 12 ka (14C), puis a 20-30 m au-dessus de ce niveau a 11 ka (14C) et a environ 10 m au-dessus de ce niveau a 10 ka (14C). Une proposition anterieure relative a l’existence d’une nouvelle submersion secondaire des basses terres du Fraser sous 100 m d’eau ou plus est exclue d’apres les radiodatations et des analyses des diatomees.

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