Abstract

Tunnel valleys are an erosional channel characterized by anastomosing, steep-sided channel systems formed by subglacial, confined meltwater flow. Our study uses two-dimensional (2D) industry reflection seismic on the Scotian Shelf near Sable Island to better constrain the geometry of tunnel valleys in the area. Here, U- to V-shaped buried channels north and west of Sable Island extensively branch, reconnect, and meander. They average 2–5 km wide and 150–700 m deep (below sea level) and have a dominantly north–south orientation. Immediately to the south and southwest of Sable Island, the channels become narrower (1–1.5 km), shallower (300–400 m maximum) and more widely spaced. Multiple tunnel valley generations may be present, but could not be separately mapped. There is a notable gap of 20–30 km between the ends of the detectable tunnel valleys and the shelf edge south of Sable Island. An exception is erosive features at the shelf edge at the head of Logan Canyon, but these channels are disconnected from the tunnel valley network further north and may not be tunnel valleys. The reason for the gap south of Sable Island is not clear; however, we do not believe it is due to data coverage or resolution issues. If the tunnel valleys genuinely end south of Sable Island, then the gap between them and the shelf edge means that between The Gully and Logan Canyon these subglacial meltwater channels did not empty directly at the shelf edge. This implies direct meltwater and sediment delivery by tunnel valleys to the Scotian Slope during the Pleistocene may have been limited in this area.

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