SHALLOW SUB-TIDAL SURFICIAL GEOLOGY OF A HIGH-ENEGRY, GLACIATED COAST, SHAD BAY, NS, CANADA

The Atlantic Coast of Canada is one of the highest energy coastlines in the world. A combination of ancient bedrock geology and recent glacial processes provide unique bedforms and supplies of sediment.

Shad Bay is an elongated north-south trending embayment southwest of Halifax, NS. The bedrock geology consists primarily of intrusive granitic bodies that have been sculpted into rock drumlins and roche moutonnee. The sculpted bedrock surface is overlain by a drape of till of varying thickness, which can be readily observed at the shoreline in eroding bluffs.

A suite of geophysical instruments including high-resolution sidescan sonar and marine magnetometers were deployed from a small, coastal vessel. Our goal was to map the surficial geology of the shallow sub-tidal area and identify magnetic anomalies for future investigation. Approximately 150 line km of sidescan sonar and magnetometer data were collected during August 2006. This dataset revealed a predominantly coarse seafloor. Boulder gravel was the most often observed seafloor texture and covered 58% of the area. Muddy units were not observed at the map scale and sandy units were restricted to a small pocket beach in the northern section of the area and in deeper water west of the area. Exposed bedrock was the second most observed seafloor texture. Bedrock outcrops appeared smoothed on the north side and plucked on the south side, as would be expected based on the local glacial flow direction. Bedforms were present only in the sandy area.