Late Quaternary landscape evolution in a region of stable postglacial relative sea levels, British Columbia central coast, Canada

Abstract

2018 (July): Late Quaternary landscape evolution in a region of stable postglacial relative sea levels, British Columbia central coast, Canada. Boreas, Vol. 47, pp. 738-753. https://doi.org/10.1111/bor.12297. ISSN 0300-9483.After retreat of the Cordilleran Ice Sheet (CIS) and subsequent glacio-isostatic adjustment of the central coast of British Columbia (BC), Canada, a complex coastline emerged as relative sea level rapidly reached equilibrium and maintained stability over the end of the Late Pleistocene and Holocene. This study provides a late Quaternary reconstruction of the landscape evolution of a geographically distinct location on the central BC coast, northwest Calvert Island, which experienced a re-advance of the CIS near the end of the Late Pleistocene and minimal subsequent relative sea-level change. Geomorphological observations from LiDAR imagery, sedimentological and palaeoecological evidence from exposures, cores and shovel pits, and a robust luminescence and 14 C-based chronology spanning the last 15 000 years are used to reconstruct the landscape of northwest Calvert Island following CIS retreat. A singlealiquot regenerative dose protocol that was developed specifically for luminescence dating of the sediments on Calvert Islandwas utilized in this study. Localized proglacial sedimentation was linked to the glacial re-advance experienced at the end of the Late Pleistocene. Extensive coastal reconfiguration (e.g. rapid shoreline progradation of >1 m a À1 ) occurred in the absence of extensive RSL change, which was the main driver of coastal change elsewhere along the BC coast. Changes in climate, small magnitude changes in RSL, and fire all probably played a role in isolated aeolian landform development and stabilization in the study area. An important contribution of this study is the documentation of the multi-disciplinary approach for reconstructing palaeogeography, using multiple geochronological methods, micro-and macro-sedimentology, the palaeoecology inferred from both macro and microfossils (e.g. diatoms and foraminifers), stratigraphy, field mapping and remote sensing. In addition, these findings inform our understanding of the drivers of coastal sedimentary processes, particularly in the temperate coastal rainforest region of BC, and the role that fire may play in those processes. Coastal palaeogeography studies in the region will become increasingly important as discoveries of Late Pleistocene human habitation along the coastal migration route continue to be documented.

The Role of Large Woody Debris in Beach‐Dune Interaction

“…In terms of the longer‐term evolution of the foredune at this site, the rate of progradation (from 0.4 cal. ka BP to present) was estimated to be about 0.69 m a −1 based on OSL dating of relict foredunes landward of the modern beach (Eamer et al, ). It is uncertain as to what the modern rate is or what the proximal sediment source might be to sustain such progradation within this deeply embayed beach.…”

Retreat of the Western Cordilleran Ice Sheet Margin During the Last Deglaciation

“…Bedrock in the area is composed of diorite, quartz diorite, granite, granodiorite, and tonalite (Roddick, 1996); Quaternary glacial landform and sedimentary deposits are relatively uncommon. Moraines are generally aligned east-west or northeast-southwest ( Figure 2) and in places westward, tracking the receding margin of the Cordilleran Ice Sheet (Eamer et al, 2017(Eamer et al, , 2018Neudorf et al, 2015). Figure 2.…”

Examination of long-term soil development and phosphorus dynamics in a hypermaritime chronosequence, Calvert Island, British Columbia, Canada

“…On the Calvert Island chronosequence this beige organic horizon could not have formed in a bog because the oldest site, (10,760 a BP; CIDS10) is in an upland position in a discharge location. It is possible that fine glacial sediment could have been deposited on the oldest dune from the proximal glaciofluvial plain that contained fine sediment after drainage of the glacial meltwater by aeolian processes (Eamer, 2017;Eamer et al, 2017b).…”

“…Between 14 and 8.5 kya the relative sea level was a few meters lower than today also promoting the formation of dune systems (McLaren et al, 2014). By the early Holocene (11.7 to 8.3 kya), there was erosion of glacial sediments and a warmer, wetter climate that provided a good environment for the stabilization of the oldest dune (10,760 ya; CIDS10; Eamer, 2017;Eamer et al, 2017b). The relative sea level rose a few meters above the current mean annual sea level between 8.5 and 5.6 kya causing erosion on the coast and the redistribution of these sediments at higher locations, creating new beaches (eg., CIDS8 and CIDS15;McLaren et al, 2014;Eamer, 2017;Eamer et al, 2017b).…”

“…By 5.6 to 4.2 kya, the dune complex between 4 th and 7 th beach (3,588 a BP; CIDS8; Fig. 3-2) and the beach formed behind North Beach (4,198 ya; CIDS15) stabilized because of the warm, wet climate (Eamer, 2017;Eamer et al, 2017b). Between 1.8 and 0.4 kya progradation rates were high on West Beach followed by a little ice age (~0.6-0.4 kya).…”