|Title||Preliminary notes on the marine geology off southwest Newfoundland, based on a merged multibeam/LIDAR data set|
|Licence||Please note the adoption of the Open Government Licence - Canada
supersedes any previous licences.|
|Source||Geological Survey of Canada, Open File 6977, 2012, 24 pages, https://doi.org/10.4095/290202 Open Access|
|Publisher||Natural Resources Canada|
|Related||This publication is related to Cruise Report 97060, CCGS
Matthew, Ground-truthing of multibeam bathymetry data in western Newfoundland: Bonne Bay, Bay of Islands, Port au Port region, and St. George's Bay |
|Province||Eastern offshore region|
|NTS||12B; 12G/01; 12G/02; 12G/08; 12G/09; 12H/12|
|Area||Cape Ray Submarine Canyon; Cape St. George; St. George's Bay; Bay of Islands; Bonne Bay|
|Lat/Long WENS||-59.5000 -57.5000 49.7500 48.2500|
|Subjects||surficial geology/geomorphology; geophysics; marine geology; continental shelf; geophysical surveys; geophysical interpretations; holocene; side-scan sonar; bathymetry; continental shelf; sedimentary
rocks; tills; sands; glacial history; glacial deposits; lithology; LIDAR; Cabot Fault; Paleozoic; Carboniferous|
|Illustrations||location maps; profiles; images|
|Released||2012 06 19|
1) For purposes of description the area is divided into three areas (1-3). In the absence of seismics, grab samples, and photographs, estimates of sediment type and thickness are
based on bathymetric cross-sections and backscatter. Backscatter data were extracted but there are levelling differences between backscatter collected by CCGS Matthew and that collected by launches.
2) The coastline consists of coastal bluffs
composed of glacial sediments, resting on bedrock that is generally exposed at or above sea level.
3) Generally speaking the inner shelf is wave-dominated area in which bedrock is exposed at the sea floor adjacent to the coast. Two main types of
bedrock occur: 1) Carboniferous sedimentary bedrock in the north, recognized by numerous parallel ridges 1-2 m high; and 2) older, more-resistant bedrock with complex patterns of joints in the south. These two types are separated by the offshore
extension of a major structural lineation, the Cabot Fault. This runs southwest from the vicinity of Little Codroy.
4) Several large sand sheets are present on the inner shelf, usually above a depth of 50 m. These sand bodies are mostly thin (2-3
m at most) and, with two exceptions, do not reach the modern coast, are not linked with modern sediment sources, and can be considered relict.
5) In the north of the mapped area, crescentic bars on the barrier beach at Little Codroy (vicinity of
site 7) connect with offshore sand bodies. The bars are mobile during storm conditions. In the extreme south (near site 1) the large nearshore bar immediately offshore from a large barrier beach connects with a sand sheet that runs many kilometres
offshore. This bar also is mobile in response to changing wave conditions.
6) Farther offshore from the sand/bedrock zone the topography is muted, and bedrock disappears below a cover of Quaternary sediment, probably till. This is characterised by
high backscatter. Till in the extreme northwest of Area 1 is marked by relict iceberg furrows.
7) Areas of low backscatter between the inner shelf bedrock/sand zone and the outer glacial sediment zone probably comprise postglacial sandy mud of
8) A dominant feature in the survey area is a previously unrecognized submarine canyon, hereby informally named the Cape Ray Submarine Canyon. It comprises a headwall area, and a series of shallow (~5 m) channels that continue
into deeper water. This feature adjoins one of the large sand sheets. The sand sheet shows signs of sediment starvation where it adjoins the canyon. Based on published information on canyons on the outer continental shelves, it is suspected that this
canyon was created by resuspension of sediment near the shelf edge by oceanographic processes. There is no information on modern activity in this canyon. The hazard potential of canyons on the outer continental shelves with respect to submarine
pipelines has been discussed by Campbell and MacDonald (2006).