Geology and quaternary environments of the first preglacial palaeolithic sites found in Alberta, Canada

Abstract

A pebble-tool industry, including two chronologically different stone artifact assemblages reminiscent of the Eurasian Palaeolithic, has been recorded in Late Pleistocene sections at two locations in the Bow River valley, southwestern Alberta. Authenticity and provenance of the deeply buried archaeological record is evidenced by culture-diagnostic percussion-flaked artifacts incorporated in preglacial fluvial gravels and overlying glacial diamictons and by identical textural patterns on stone tools found in and eroded from the exposures. Geological context suggests a fluctuating braided river setting during the earlier occupation. Discarded (lower series) quartzite and hard carbonate rock artifacts, subglacially entrained into the Cordilleran Bow Valley till, document distortion of the earlier site (Silver Springs) by a valley glacier emerging from the Rocky Mountain ice-lobe. Following the valley deglaciation, a later occupation episode is manifested by a formally analogous flaked lithic assemblage excavated in situ on top of the till at a nearby site (Varsity Estates). This more recent occupation surface was subsequently buried under 24 m of glaciolacustrine sediments after submergence of the river valley by a proglacial lake (Glacial Lake Calgary) dammed by the Laurentide ice advance into the eastern Calgary area, implying a minimum early Late Wisconsinan age (ca. >21,000 BP) for the lithic industry.The presence of the later (upper series) artifact assemblage and the associated palynological data do not support the view that envisages an extremely cold, inhospitable glacial environment on the eastern slopes of the Canadian Rocky Mountains throughout the Late Wisconsinan. Their stratigraphic position also indicates temporal asynchroneity between Cordilleran and Laurentide ice during the last glacial maximum in the Bow River valley, the area of presumed coalescence of the two ice-masses. Although a more rapid response of the western mountain glacier to climatic change is evident, the apparent absence of pedogenic alteration of the till surface and the fresh appearance of the excavated stone artifacts suggest that a short time span separated the two glacial events.The archaeological record provides evidence of an earlier Palaeo-American peopling of western interior Canada long before the emergence of the Final Pleistocene Palaeoindian cultures, characterized by elaborate bifacial stone projectile-point flaking technologies traditionally regarded as the earliest cultural manifestations in North America. Silver Springs is the first early site on the continent found below glacial deposits. Realization that other American Palaeolithic sites, potentially of considerable antiquity, should be recognized in similar geological settings, and introduction of adequate geoarchaeological site-survey techniques, have crucial relevance for elucidation of the earliest New World prehistory.