Marine slopes are bona fide geological settings in themselves, but from a geotectonic perspective they are the region where continental crust is transitional to oceanic crust, and where sediment bypasses the shelf as it heads towards the deep ocean floor – typically as submarine fans. Slopes, as their name suggests, have significantly greater dip than an adjacent shelf; the break between the shelf and slope is defined by this break in sea floor gradient. Slopes frequently are cut by gullies and submarine canyons; the gullies tend to be localized across the shelf-slope break, whereas canyons extend across the shelf (sometimes coming within a few 100m of the shore), to the full depth of the slope. Gullies and canyons focus sediment transfer to the ocean deep. The Black’s Beach and Point Lobos canyons were visited on an AAPG trip with Tor Nilsen; the Bowser Basin examples I worked on in the late 1980s – early 90s.
Pt Lobos and Black’s Beach, California
Bowser Lake Group, Bowser Basin, northern British Columbia
