New observations of relative sea level from the Northern Cascadia Subduction Zone: Cordilleran ice sheet history and mantle rheology

• Main Author: Belanger, Kevin Karl
• Other Authors: James, Thomas Sinclair, Spence, George D.
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: relative sea level; Cascadia Subduction Zone; Cordilleran ice sheet; mantle rheology; Sechelt; Barkley Sound; Tofino; glacial isostatic adjustment; Ice Sheet
• Online Access: http://hdl.handle.net/1828/4558

New relative sea-level (RSL) observations dating from the late Pleistocene and early Holocene, during and after the collapse of the Cordilleran ice-sheet (CIS), are provided for two regions in southern coastal British Columbia. They record the glacial isostatic adjustment (GIA) response of the Earth to the changing surface load of the waning CIS. The data provide a new RSL curve for Sechelt, on the mainland coast north of Vancouver, and extend and revise a previously constructed curve for Barkley Sound on the west coast of Vancouver Island. The observations create a new profile of RSL curves oriented southwest-northeast across Vancouver Island and the Strait of Georgia. A previously-defined profile of RSL curves is oriented northwest-southeast profile along the east coast of Vancouver Island. The two profiles intersect in the central Strait of Georgia. The new RSL curves sample different parts of the Cascadia Subduction Zone (CSZ) and provide constraints on the history of the CIS. The Juan de Fuca plate subducts beneath the North American plate in roughly the same southwest to northeast direction as the RSL profile. GIA modelling of the RSL observations along this profile may indicate spatial variations related to the structure of the Cascadia Subduction Zone (CSZ). The CIS flowed roughly from northeast to southwest over the regions of interest. RSL observations along this path indicate how sea-level change differed with distance from the edge of the ice-sheet towards its centre. The CIS model of James et al. (2009b) is refined to fit observed sea levels while applying glacial geological constraints to regional ice sheet advance and retreat. Sea level in Barkley Sound dropped from greater than 27 m elevation before 15 cal kyr BP to -46 m below present around 12 cal kyr BP. At Sechelt, sea level closely follows the same trend as in the central Strait of Georgia, dropping from over 150 m before 14 cal kyr BP and falling past present levels after 12.4 cal kyr BP to a poorly constrained lowstand between 12 and 9 cal ...