Postglacial palaeoenvironments of the upper Bow Valley, Banff National Park, Alberta, Canada

Crowfoot Lake sediments provide a sensitive 11,300 C-14 year record of glacial activity and vegetation change in the central Canadian Rocky Mountains. Bow Valley ice had receded from the Crowfoot Lake basin shortly before ca. 11,330 C-14 yr BP. Inorganic sediments associated with an expansion of alpine glaciers (Crowfoot Advance) were deposited in the basin during the Younger Dryas Chron. Prior to ca. 10,100 C-14 yr BP, the local vegetation was a sparse shrub-herb community dominated by Artemisia and Poaceae. Dramatic changes in the palaeobotanical record concomitant with the abrupt onset of organic sedimentation reflect the establishment of an open Pinus-dominated forest at ca. 10,100 (14)Cyr BP. Fires may have accentuated the effects of climate in maintaining an open forest between ca. 9000 and 4160 C-14 yr BP. After ca. 4160 '4C yr BP, Picea and Abies were dominant components of the local closed forest and subordinate xerophytic taxa were in decline. The consistent presence of mesophytic taxa after ca. 4160 C-14 yr BP indicate increases in precipitation associated with the onset of Neoglacial conditions. Sharp declines in local arboreal taxa occurred at ca. 900 C-14 yr BP along with increases in several taxa common to modern alpine tundra and subalpine meadows. These changes probably reflect expansions of valley floor meadows and descending alpine timberline in the drainage and are coincident with renewed glaciogenic sedimentation in the basin. (C) 1999 Elsevier Science Ltd. All rights reserved.