Port Eliza Cave: example of the glacial stratigraphic potential of wave cut, marine caves.

Résumé

The Port Eliza cave is a wave cut, marine cave located on the west coast of Vancouver Island. It is approximately 60 m long and lies at 95 m asl, well above the Late Wisconsinan marine limit. A 2 m excavation near the back of the cave revealed a silty sand diamicton at the base that has the appearance of a till but contains abundant bones. This assemblage consists of well preserved specimens of amphibians, fish, birds and mammals. Mammals are represented mainly by the limb bones and teeth of voles, likely Microtus townsendii, Townsend's vole. Laminated clay makes up the rest of the sequence. A crust of speleothems with stalagmites up to 25 cm across covers portions of this sedimentary package. The lower diamicton is thought to represent debris flows from a glacier that incorporated bones on the floor of the cave. The laminated clays were deposited subglacially in standing water when a warm-based glacier covered the cave entrance. The speleothems were deposited after deglaciation. Nineteen oriented samples were taken for paleomagnetic study from the laminated clay. Fluctuations in declinations suggest secular variation spanning a few hundreds to a few thousands of years. Preliminary radiocarbon ages of two of the vole mandibles are 18,010±100 (41.1 mg, CAMS-74624) and 16,340±60 (43.3 mg, CAMS-74625) and a piece of charcoal from just below the stalagmite is 9,540±40 (4.0 mg, CAMS-74626). These results will be placed into a regional context and the utility of stratigraphic studies in marine caves will be discussed.