Abstract

Recently, palaeoenvironmental records, including new plant macrofossil evidence, from the Northern Plains (Alberta and Saskatchewan) have yielded information on the early postglacial landscapes (ca. 11,000-9,000 yr. BP) occupied by Paleoindians. Although coverage is patchy, the records suggest general patterns of vegetation and landscape development that provide the basis for a testable model. Specifically: 1) a recently-completed plant macrofossil record from the Andrews site, southern Saskatchewan, contains white spruce cones and needles at a level radiocarbon-dated from sprucewood to 10,200 yr. BP, 2) in Southeastern Alberta, the Jenner and Webb sites have yielded wood, including aspen, dated between 10,150 and 9,800 yr. BP, 3) in south central Alberta, the Fletcher site (DjOw-1), has produced seeds from wetland and aquatic plants dated around 9,300 yr. BP. Already-published pollen records from northern Montana show predominantly open, probably arid, landscapes between 12,000-10,000 yr. BP. Based on these observations, we propose the following scenario for a transect moving away from the Laurentide ice margin, extending from southern Saskatchewan, through southern Alberta to northern Montana, around 11,000-9,000 yr. BP: a) abundant residual ice and proglacial lakes, b) a belt of open spruce forest in newly deglaciated terrain beyond the ice margin, c) hummocky terrain with abundant kettles and melting ice,supporting perennial wetlands, surrounded by aspen, d) perennial wetlands probably surrounded by open grasslands, perhaps with some aspen in particularly sheltered or moist locations, e) grassland changing to open parkland terrain in the foothills. This transect roughly follows a trend of moisture-availability. Around 10,000-9,000 yr. BP, several records show a transition to clastic (windblown?) sediment that infilled wetland hollows. By this time, any residual buried ice and permafrost had melted. Further drying and sediment redistribution occurred during the Hypsithermal. Subsequent moisture increases, associated with cooler Late Holocene conditions were insufficient to produce permanent water bodies in these locales. This model suggests that there may have been more water sources on the Plains in the early Holocene than at any time since. Despite indications of climatic aridity, the Plains landscapes were probably well watered. Perennial water may have made these productive areas and attractive for human occupants, especially in summer. This model has implications for Paleoindian lifeways and occupation patterns in the Northern Plains.