Late Quaternary geology and geochronology of the central continental shelf of western Canada

Piston cores and high-resolution seismic profiles from Queen Charlotte Sound have yielded new information on the late Quaternary history of this part of the western Canada continental shelf. Cores in three major troughs (Goose Island, Mitchell's and Moresby), up to 130 km apart, sample a similar sedimentary sequence. This sequence comprises five units: The lowest unit (A), which is up to 40 m thick, is a laminated to massive mud containing coarse ice-rafted debris deposited between pre- 13.6 ka and 12.9 ka during deglaciation of Queen Charlotte Sound. This unit is overlain by a sequence of stratified sediments (units B1–B3) up to 20 m thick deposited during the transition from the Pleistocene to the Holocene. Unit B1 directly overlies, and is similar to, unit A but lacks ice-rafted detritus. Unit B2 is sandy mud (locally gravelly) deposited during a period of lagging and winnowing from about 12.9 to 10.2 ka when sea level in Queen Charlotte Sound was lower, relative to the land, than it is today. Unit B3 is a laminated to massive mud similar to Unit B1 deposited when water depths in Queen Charlotte Sound rapidly increased at the end of the Pleistocene due to the combined effect of eustatic sea-level rise and forebulge collapse. The sedimentary sequence is capped by up to 10 m of mud (unit C) which is more organic-rich and contains more clay than any of the other units. It was accumulating under present-day conditions as early as 9.7 k.y. ago.