Article du Bulletin
Port Eliza Cave: raised sea cave stratigraphy and implications for the coastal migration route [Grotte de Port Eliza : stratigraphie d’une grotte marine soulevée et implications pour la route de migration côtière].
Ward B.C., Nagorsen D.W., Al-Suwaidi M., Wigen R.J. & Hebda R.J. · 2003 · Joint Annual Meeting of the Canadian Quaternary Association and the Canadian Geomorphology Research Group, Halifax, Nova Scotia, June 8-12, 2003.
Résumé
Timing of late Pleistocene glacial advance, retreat, relative sea level and environmental viability between 25 and 12.5 ka (14C yrs BP) remain key issues in the feasibility of a coastal migration route for the first North Americans. We present stratigraphic, radiometric and faunal data for Port Eliza cave, a raised sea cave on the west coast of Vancouver Island, BC. A 2.5 m deep excavation near the back of the cave revealed three units: (1) > 50 cm of relatively massive, silty-sandy diamicton containing bones, striated clasts and small dripstone fragments, (2) 2 m of laminated clay, and (3) 20 to 30 cm of oxidized silt and clay. Unit 1 represents the cave floor paleo-surface. Unit 2 represents deposition by suspension settling in a subglacial lake, indicating ice cover during the Late Wisconsinan. Unit 3 is interpreted as early postglacial and Holocene accumulation of resedimented fines. Unit 1 has yielded 4 radiocarbon dates from single bone fragments, of known species, ranging from 18.0-16.3 ka. These dates and others from the region show that ice cover on the outer coast was brief, ca., 15.5-14 ka. A diverse vertebrate fauna of marmot, vole, marten, cervid and various species of birds and fish indicates a partially treed landscape with the sea near its present level. The terrestrial vertebrates are consistent with a cool, open parkland environment with maximum summer temperatures cooler than present. However, pollen analysis indicates the landscape was covered in open herbaceous, and grassy cold dry steppe with a diversity of forb species with only minor scattered shrubby fir and pine. Although most fossils represent small mammals, presence of at least one cervid confirms viability for ungulates, a significant potential food source for humans. Marine fauna also indicates proximity to a rich marine environment. The existence of this diverse vertebrate fauna as late as 16 ka demonstrates both marine and terrestrial resources available to support humans, confirming feasibility of human coastal migration for this portion of the route.