Post glacial sea levels on the Western Canadian continental shelf: evidence for rapid change, extensive subaerial exposure, and early human habitation

Abstract

Grounded piedmont type glaciers inundated and isostatically loaded the deep troughs which indent the Western Canadian continental shelf, as far west as the shelf edge. Glaciers do not appear to have covered the offshore banks east of the Queen Charlotte Islands (Haida Gwaii). Ice retreated from the shelf at approximately 13,500 14C yr B.P. Rapid emergence of the crust followed the ice retreat and resulted in a relative fall of sea level. At 10,400 14C yr B.P. relative sea level on the continental shelf was more than 100 m below that of today and large areas of the Queen Charlotte Basin were subaerially exposed. Eustatic sea-level rise, coupled with subsidence of a glacioisostatic forebulge, allowed sea levels to rise very rapidly, and reach the present shoreline on the Queen Charlotte Islands (Haida Gwaii) by about 9100 14C yr B.P. Dated shoreline deposits (shells), submerged wood remnants, and barnacles on stone tools at elevations between −110 m and +14 m suggest a sea-level rise of 6.3 cm per year between 12,200 and 11,000 calender years. Our reconstructions of the paleogeography and paleoenvironments suggest a hospitable environment for human habitation existed in areas that are now submerged. Stone tools excavated from intertidal deposits support this interpretation. Significant local variations in the depth of synchronous shorelines are described and attributed to localized differences in isostatic load. The documented rates of crustal adjustment are much greater than those used in conventional geophysical (forebulge) models. Regional high-resolution seismic reflection data (3400 line km) shows little evidence for post-glacial faulting and suggest that most crustal adjustments appear to have been isostatically rather than tectonically driven. Subaerial exposure and subsequent sea-level transgression were the dominant post-glacial processes that determined the morphology, texture and paleoenvironment of the Western Canadian continental shelf.