Paleogeography, glacially induced crustal displacement, and Late Quaternary coastlines on the continental shelf of British Columbia, Canada

Abstract

Subsequent to the Last Glacial Maximum (LGM), complex isostatic adjustments resulted from deglaciation, eustatic sea level change, tectonic faulting, and a relatively thin, flexible lithosphere in the Queen Charlotte Islands (QCI) region. A geostatistical interpolation model charts the sequence of evolving landscapes and displays temporal changes in the magnitudes and extent of crustal flexure that accompanied forebulge development on the Late Quaternary northeast Pacific continental shelf between 14.2 and 8.7 ka BP. Wavelength and forebulge amplitude are consistent with thermal modeling implying low upper mantle viscosity and thin elastic lithospheric thickness beneath Queen Charlotte (QC) Sound and Hecate Strait. Glacial ice ∼690 m thick began retreating from Dixon Entrance after 14.5 ka BP ( 14C years ago) and prior to 12.6 ka BP, permitting over 100 m of crustal uplift in northern Hecate Strait. A forebulge persisted in Hecate Strait and QC Sound from 13.2 until after 9.7 ka BP, implying fixed glacial ice on the British Columbia (BC) mainland until ∼10 ka BP. Paleogeographic reconstructions show two emergent ice-free terrains, one extending eastward from the QCI and the other in QC Sound. By ∼11.7 ka BP, a landbridge connected the BC mainland and the QCI.