Slowstands, stillstands and transgressions: Paleoshorelines and archaeology on Quadra Island, BC, Canada

Abstract

On Quadra Island, west coast Canada, a series of marine terraces formed during a period of rapid marine regression from 200 m to 1 m above modern levels between ca. 14,500 and 12,000 years ago. Within this period of regional marine regression, evidence points to brief periods of sea level stillstand and even marine transgressions. It is hypothesized that during these anomalous periods, global meltwater events created a local signature on the Quadra Island sea level curve by slowing, halting and/or inversing the regional sea level regression trend. This is revealed through identification of high elevation paleoshorelines, landscape terracing and other stranded marine features from LiDAR Digital Elevation Models (DEMs) and subsurface investigation. These paleomarine terraces are believed to have developed during brief marine stillstands, slowstands and minor marine transgressions. Pauses or slowing periods of regression appear to result from global eustatic rise briefly matching or exceeding local isostatic and tectonic uplift. The ages of these terraces, based on local sea level history and radiocarbon dating of some of the raised marine features, match well to the ages of coral-based marine terraces sequences associated with periods of rapid global sea level rise. A number of early post glacial to earliest Holocene archaeological sites are associated with the Quadra marine terraces. These associations suggest an improved approach to location of early archaeological sites dating to times of rapid sea level change.