A GLIMPSE AT HOWE SOUND SEDIMENTATION FROM THE LATE PLEISTOCENE TO LATE HOLOCENE, BRITISH COLUMBIA CANADA

Howe Sound (HS) lies is directly north of Vancouver. It is the southernmost fjord on the mainland coast of British Columbia. Five sediment cores were collected from three sedimentary settings in this previously uncored fjord. These contain a partial record of sedimentation over the last 13,000 years (regional marine reservoir correction of 801±23 yr on marine shell material). Sediment cores 42, 43, and 44 were collected from the eastern margin of Collingwood Channel (CC) (area of 49.380 N, 123.41 W) at the mouth of HS. Sediments intersected in cores record active ice marginal sedimentation of silty mud and dropstones from icebergs between about 12.7k and 12.0k yr BP. Dropstone sedimentation ceased with deglaciation of HS ca. 10.7k yr BP. The rate of sedimentation was drastically reduced in CC following deglaciation. This was largely a consequence of reduced delivery of sediment into HS from glacial sources. Radiocarbon ages previously determined on sea lion bone and marine bivalves on adjacent Bowen Island document relative sea level 80 m higher than contemporary sea level ca. 12-13k yr BP.

Sediment cores 40 and 41 were collected from the eastern side of HS (area of 49.450 N, 123.255 W). They span from early to late Holocene. Multibeam bathymetric imagery (MBI) indicates that these cores were collected from the submarine fan of Lone Tree Creek (41) and adjacent sedimentary apron deposits (40). MBI and sediment analysis show the submarine fan to have been sculpted and built by submarine sediment gravity flows: it contains intertidal fauna at more than 100 m depth and angular fragments of rock derived from uplands immediately to the east. Radiocarbon ages on shell material are repeated in the sediment core suggesting stacking of mass wasting deposits. Similarly, core 40, which intersected uniformly fine and stoneless sedimentary apron sediments, also contains repeated radiocarbon ages. The repetition may be an artefact of bioturbation or stacking from recurring submarine failures.

The repetition of radiocarbon ages in cores 40 and 41 and the lack or paucity of Holocene sediments in cores 42-44 preclude an accurate estimate of the rate of Holocene sedimentation from sediment suspended in the water column in lower Howe Sound during the Holocene. The sediment record from cores 42-44 suggests that it could be a fraction of a mm/yr in CC.