Model of the Atlantic Continental Shelf and Slope built during 1964 by a Woods Hole Oceanographic Institution - U.S. Geological Survey team. The model is patterned after a three-sheet map series of the shelf and slope at a scale of 1 inch = 16 miles. With vertical scale exaggerated, this view shows the ocean bottom contours around Florida. Credit: U.S. Geological Survey.
A continental shelf is the portion of a landmass that is submerged in the ocean to a depth of less than 200 meters (650 feet), resulting a rim of shallow water surrounding the landmass. The outer edge of the shelf slopes towards the ocean bottom (see abyssal zone), and is called the continental slope.
The continental margin is a region of the ocean floor that lies between the shoreline and the deep-ocean floor. It includes the continental shelf, the continental slope, and the continental rise – the gently sloping region of the continental margin at the foot of the continental slope (an area of thick deposits of sediments carried down by currents off the continental shelf.
A continental shelf can be quite narrow, as, for example of the west coast of South America, but in places can be more than 150 kilometers (90 miles) wide – for example, in the North Sea and around Britain. The shallows contain rich food for fish, and therefore some of the world's major fishing grounds are on continental shelves. Other areas of continental shelf, such as the North Sea and the Gulf of Mexico have been exploited for oil and natural gas.