STRATIGRAPHIC AND PALEOENVIRONMENTAL STUDIES IN RAISED SEA CAVES, BRITISH COLUMBIA: IMPLICATIONS FOR THE HUMAN COASTAL MIGRATION HYPOTHESIS

Raised sea caves form by wave action along exposed coastlines during periods of higher relative sea level. If the caves lie above the postglacial marine limit, they can preserve a distinctive stratigraphy that records glacial and nonglacial conditions. During glaciations, the cave entrance is blocked by ice and the cave fills with glacial meltwater, forming a subglacial lake, in which laminated fines are deposited. During nonglacial conditions roof-fall accumulates on the cave floor possibly accompanied by speleothem formation. Bone material is commonly found in association with these units, and coupled with the speleothem deposits, can provide both chronological control and paleoenvironmental data.

Port Eliza cave is a wave-cut cave 85m a.s.l. on the west coast of Vancouver Island, British Columbia. A multi-disciplinary study of sediments in this cave provide a record of the Last Glacial Maximum (LGM) on Vancouver Island that has important implications for human migration along the debated coastal migration route. Lithofacies changes from nonglacial diamict to glacial laminated silt and clay, then a return to nonglacial conditions with oxidized clay, colluvial block beds and speleothems, define glacial-nonglacial transitions. Preglacial faunal evidence shows a diverse range from small species, including birds, fish, vole, marten and marmot, to larger species, such as mountain goat. Marine fossils represent a rich, dominantly nearshore fauna and suggest the sea was close to the cave. Pollen data from the same unit show a cold, dry tundra environment with sparse trees. These data indicate that ice-free conditions lasted until at least 16 ka BP, and suggest that humans could have survived on a mixed marine-terrestrial diet in the Port Eliza area. Deglaciation occurred prior to an age of 12.3 ka BP on mountain goat. These data support the viability of the coastal migration route for humans prior to ~16 ka B.P. and then as early as ~13 ka B.P.