Geology

Passive continental margins develop along coastlines that are not tectonically active, including much of the Atlantic Ocean coastline. Many passive continental margins have a continental rise, a very low‐angle ridge of sediment that forms between the continental slope and the abyssal plain (Figure ). The sediments that form the continental rise are deposited on oceanic crust by turbidity currents, contour currents, which flow parallel to the edge of the continental slope, and regular ocean currents.

Figure 1

A Passive Continental Margin

Abyssal plains are flat‐lying expanses of horizontally deposited sediment that accumulates on the ocean floor at the base of the continental rise. The abyssal plain can be very thick and completely bury large‐scale topographical features of the ocean floor. Some sections show graded bedding that indicates deposition from turbidity currents. Abyssal plains are some of the flattest features in the world.