STRATIGRAPHIC AND PALEOENVIRONMENTAL STUDIES IN RAISED SEA CAVES, BRITISH COLUMBIA, CANADA: IMPLICATIONS FOR LATE PLEISTOCENE HUMAN COASTAL MIGRATION

Raised sea caves were initially evaluated for their stratigraphic and paleoenvironmental record in Norway, where a depositional model was developed. 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 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. Based on this model, a search for raised sea caves was carried out along the British Columbia coast.

A multi-disciplinary study of sediments of Port Eliza cave provides a record of the Last Glacial Maximum (LGM) on Vancouver Island that has important implications for human migration along the 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. Loss-on-ignition, paleomagnetic and sedimentological data show that there was continuous sedimentation through the LGM, implying a warm based Cordilleran Ice Sheet at this site. SEM and clay mineralogy confirm the laminated fines represent glaciation. Terrestrial floral and faunal data indicate a pre-LGM, cold, dry, steppe environment with rare trees. Marine fossils represent a rich, dominantly nearshore fauna and suggest the sea was close to the cave at a time when eustatic sea level would place the shoreline >15 km away. This implies significant isostatic depression from glaciers on Vancouver Island. These data indicate that ice-free conditions lasted until at least 16 ¹⁴C 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 ¹⁴C ka BP on mountain goat. Faulting in the laminated fines suggests postglacial reactivation of the cave fault.