Late Pleistocene proboscideans and early Fraser glacial sedimentation in eastern Fraser Lowland, British Columbia

Abstract

Three recently radiocarbon-dated tusk segments from eastern Fraser Lowland indicate Pleistocene proboscideans (probably mammoths) lived there between 22 700 and 21 400 years ago during early Fraser (for the Fraser Lowland) ice advance into the area. Palynomorphs from silty sand adhering to a tusk indicate the animals grazed on open grassy floodplain. Sedimentologic and altimeter studies of tusk-bearing gravel indicate an early Fraser sandur, at least 10 km long and deposited at the same time as Coquitlam Drift, formed in Chilliwack Valley at the same time that a sandur or kame terrace was deposited against the north side of Promontory ridge. Probably about 21 000 years ago (the time of Coquitlam glacial maximum in western Fraser Lowland) ice blocked Chilliwack Valley, creating a glacial lake whose freshwater, Pediastrum-bearing, laminated silt has been observed up to 200 m asl. Stratigraphy and history of the area following deposition of the above gravels and silt are still uncertain without more chronologic control. However, proboscideans could have migrated southward and westward, away from ice advancing into Fraser Lowland, across ancestral Strait of Georgia via the Quadra sandur, and onto southeastern Vancouver Island to which earliest Fraser glacial ice probably advanced after 17 000 years BP.