Holocene sea-level change on the central west coast of Vancouver Island, British Columbia

Abstract

A new Holocene relative-sea-level (RSL) curve is proposed for the central west coast of Vancouver Island based on topographic surveys of coastal landforms and the stratigraphy of coastal deposits. Six study sites are described on Vargas Island and Esowista and Ucluth peninsulas and 23 previously unpublished radiocarbon ages that constrain mean-sea-level (MSL) position are presented. A long-term rise in RSL from an early Holocene (> 7000 BP) lowstand below −3 m asl is documented from dates on tree stumps in the intertidal zone and salt-marsh peats and forest-floor deposits buried by marine sands and gravels. Submergence culminated in a stillstand from 6000 to 4800 BP, marked by the development of a strandline at 6 m asl (MSL ≈ 3.2 m asl). A fall in RSL is documented by a strandline at 4.0–4.5 m asl, which dates from 2700 to 2000 BP (MSL ≈ 2.0 m asl). Little is known of the dynamics of emergence between 4800 and 2700 BP or from 2000 BP to the present, although the absence of strandlines below 4 m asl suggests continuous emergence during the last two millenia. This submergence–emergence cycle is unique in southern British Columbia. A simple simulation model suggests that late Holocene emergence was induced by tectonic uplift of the edge of the America plate margin.