THE SISTERS-CREEK FORMATION - PLEISTOCENE SEDIMENTS REPRESENTING A NONGLACIAL INTERVAL IN SOUTHWESTERN BRITISH-COLUMBIA AT ABOUT 18 KA

Sisters Creek Formation is formally defined, stratotypes are establish ed for it, and the time-space chart is updated for the Fraser Lowland, southwestern British Columbia. The Sisters Creek is a Pleistocene for mation comprising in situ and reworked organic-rich sediments, and non organic silt, sand, and gravel. The formation was deposited during the Port Moody interstade (within the Late Wisconsinan Fraser Glaciation; delta(18)O stage 2) between the Coquitlam stade (early Fraser Glaciat ion) and the main Vashon stadial maximum that occurred about 14.5 ka. The Sisters Creek Formation represents a glacial recession in southwes tern British Columbia that generally coincided with the timing of the last global glacial maximum. The new time-space chart implies that, in Fraser Lowland, the Fraser Glaciation represents the rapid advances a nd retreats of glacial lobes issuing from surrounding mountains, which remained ice-covered during interstades.