Timing of terminal Pleistocene deglaciation at high elevations in southern and central British Columbia constrained by 10 Be exposure dating Martin Margold a, * , Arjen P. Stroeven b, 1 , John J. Clague c, 2 , Jakob Heyman b a Durham University, Department of Geography, Lower Mountjoy, South Road, Durham DH1 3LE, UK b Stockholm University, Department of Physical Geography and Quaternary Geology, and Bolin Centre for Climate Research,106 91 Stockholm, Sweden c Simon Fraser University, Department of Earth Sciences, 8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada article info Article history: Received 29 January 2014 Received in revised form 18 June 2014 Accepted 19 June 2014 Available online 10 July 2014 Keywords: Cordilleran Ice Sheet Be-10 exposure dating Deglaciation abstract The Cordilleran Ice Sheet (CIS) covered most of British Columbia and southern Yukon Territory at the local Last Glacial Maximum (lLGM) during Marine Oxygen Isotope Stage 2. However, its subsequent demise is not well understood, particularly at high elevations east of its ocean-terminating margin. We present 10 Be exposure ages from two high-elevation sites in southern and central British Columbia that help constrain the time of initial deglaciation at these sites. We sampled granodiorite erratics at eleva- tions of 2126e2230 m a.s.l. in the Marble Range and 1608e1785 m a.s.l. in the Telkwa Range at the western margin of the Interior Plateau. The erratics at both sites are near ice-marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation. The locations of the erratics and their relations to meltwater channels ensure that the resulting 10 Be ages date CIS deglaciation and not the retreat of local montane glaciers. Our sample sites emerged above the surface of the CIS as its divide migrated westward from the Interior Plateau to the axis of the Coast Mountains. Two of the four samples from the summit area of the Marble Range yielded apparent exposure ages of 14.0 ± 0.7 and 15.2 ± 0.8 ka. These ages are 1.8e3.0 ka younger than the well- established lLGM age of ca 17 ka for the Puget lobe of the CIS in Washington State; they are 1.7 ka younger than the lLGM age for the Puget lobe if a snow-shielding correction to their uncertainty- weighted mean age is applied. The other two samples yielded much older apparent exposure ages (20.6 ± 1.4 and 33.0 ± 1.5 ka), indicating the presence of inherited isotopes. Four samples collected from the summit area of the Telkwa Range in the Hazelton Mountains yielded well clustered apparent exposure ages of 10.1 ± 0.6, 10.2 ± 0.7, 10.4 ± 0.5, and 11.5 ± 1.1 ka. Significant present-day snow cover introduces a large uncertainty in the apparent exposure ages from this site. A snow-shielding correction based on present-day snow cover data increases the uncertainty-weighted mean exposure age of the Telkwa Range erratics to 12.4 ± 0.7 ka, consistent with deglacial 14 C ages from areas near sea level to the west. Our exposure ages show a thinning of the southern portion of the CIS shortly after the lLGM and persistence of a remnant mountain ice cap in the central Coast Mountains into the Younger Dryas Chronozone. Our data also show that the summit area of the Marble Range was ice-covered during the lLGM. The presence of an ice body of considerable dimension in north-central British Columbia until, or possibly even after, the Younger Dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the Skeena Mountains in northwest British Columbia and the need for better understanding of the response of the CIS to Lateglacial climate fluctuations. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The evolution of Earth's climate during the Pleistocene was the result of the interplay between known, hypothesised, and yet un- discovered feedbacks in the climate system and has long been a focus of scientific study. An important aspect of this scientific * Corresponding author. Tel.: þ44 191 33 41829. E-mail address: martin.margold@durham.ac.uk (M. Margold). 1 þ46 8 16 42 30. 2 þ1 604 291 4924. Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev http://dx.doi.org/10.1016/j.quascirev.2014.06.027 0277-3791/© 2014 Elsevier Ltd. All rights reserved. Quaternary Science Reviews 99 (2014) 193e202