ENVIRONMENTAL HISTORY OF THE MID WISCONSIN OLYMPIA INTERSTADIAL, FRASER LOWLAND, BRITISH COLUMBIA, CANADA

Lithostratigraphic, 14C and palynological analyses reveal a 22 kyr continuous record of the Olympia Interstadial at four nearby sites, Fraser Lowland, British Columbia within ca. 300 km of the Cordilleran Ice sheet limit. Sites are located near the mouths of Lynn Creek valley (115 m asl), Seymour River valley (90 m asl), and in Port Moody (65 m asl) in the western hemlock (Tsuga heterophylla) western redcedar (Thuja plicata) rainforest zone. Lynn Creek sequences rest on diamicton and consist of up to 1 m of compressed woody peat and peaty silt deposited between ca. 48 and ca. 33 ka, sharply overlain by 45 cm of silty sand (between ca. 33 and 27 ka). In Seymour valley a 5 m sequence comprises fluvial pebble gravel and sand separated by 1-2 m thick fossiliferous units of inter-bedded fluvial sand, silt, gravel, and peat. Port Moody section has about 2 m of organic-rich sediment (ca. 31 ka) between 4m-thick sand and gravel units. Lynn Canyon and Port Moody sequences are overlain by Fraser Glaciation sediments or postglacial sand and gravel, and the Seymour sequence is capped locally by fill. At Lynn Creek, Polypodiaceae fern spores and non-arboreal pollen (grasses) predominate in >48 ka mineral sediments reflecting an unstable landscape and cold climate. A brief pine (Pinus)(35-60%) zone with grasses follows, likely representing pine parkland and cool dry climate. Varying values of spruce (Picea) and mountain hemlock (Tsuga mertensiana) pollen characterize most of the Olympia Interstadial during local peat deposition in sedge and Myrica wetlands until ca 33 ka. Valeriana, Gentiana, and Sanguisorba pollen indicates widespread wet meadows under a cool and moist climate. A brief pine-western hemlock zone at Lynn Creek may indicate a regional climatic optimum. A grass and Artemisia dominated assemblage and deposition of silts after 33 ka reflect cooling and drying. A unique Lycopodium spore-dominated assemblage (post 27 ka) may reflect cold arid climate and onset of Fraser Glaciation. Compared to Late Pleistocene-Holocene records, the Olympia has a similar succession from open vegetation to pine parkland to cool mixed conifer forest. There is no progression to vegetation typical of warm, interglacial, Holocene-like climates. The interstade grades through a relatively long (>3 kyr) open tundra-like interval and climatic deterioration into Fraser Glaciation.