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Abstract
A refined relative sea level (RSL) history spanning the past 14,300 calendar years is described for the Quadra Island area in the northern Strait of Georgia on the Pacific coast of Canada. Here marine shorelines dating to the time of earliest post-glacial emergence are at least 197 m above present-day sea-level at 14,300 years ago. RSL fell rapidly, reaching two to three metres above present-day by 12,000 years ago. A series of raised marine terraces at ca. 4, 10 and 30 m above present day high tide level suggest the rapid fall in RSL during early post-glacial time may have been briefly interrupted by factors such as regional ice advances and recessions and global meltwater pulses generated by climatic variations. A possible minor sea-level transgression of 1–2 m around 12,000 to 11,400 years ago was followed by slow regression to modern levels. This sea-level reconstruction is providing critical input for efficient discovery and cataloging of late Pleistocene and early Holocene archaeological sites on ancient raised shorelines in the region. Integration of the sea-level history with LiDAR imagery has proven successful in locating a number of archaeological sites on these ancient shorelines.
Highlights
The relative sea level (RSL) history of coastal British Columbia varies greatly from one location to another because of spatially variable vertical land displacements that occurred in response to glacial ice loading and unloading of the Earth's crust
In inferring a refined RSL curve, we assume that tidal ranges on Quadra were similar to present-day (4e5.3 m, see Appendix 1, footnotes) since there were fewer constrained channels associated with much higher sea levels in the Late Pleistocene (e.g. 13,300 to 14,300 years ago) tidal ranges may have been less spatially variable and similar to the ca. 4.8 m range of the open waters of the northern Strait of Georgia
Key revisions to the sea-level curve include: 1) isolation basin results from Assu Bog show that sea-level was above 197 m at 14,300 years ago, placing a minimum age constraint on the early post-glacial high-stand; 2) instead of the previously inferred, tentative shallow lowstand (
Summary
The relative sea level (RSL) history of coastal British Columbia varies greatly from one location to another because of spatially variable vertical land displacements that occurred in response to glacial ice loading and unloading of the Earth's crust. The process, termed glacial isostatic adjustment (GIA), generated large vertical land displacements in British Columbia with significant spatial variability (Mathews et al, 1970; Clague et al, 1982; Clague and James, 2002). A previously developed RSL history for the northern Strait of Georgia (James et al, 2005) provided the general features of postglacial sea-level change. It featured a rapid sea-level fall from a high-stand, but was not well constrained during the early Holocene
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