CHAPTER IN PERSPECTIVE
Chapter 4: Ocean Basins
In this chapter you learned how difficult it has been to discover the shape of the seabed. Even
today, the surface contours of Mars are better known than those of our ocean floor.
We now know that seafloor features result from a combination of tectonic activity and the
processes of erosion and deposition. The ocean floor can be divided into two regions: continental
margins and deep ocean basins. The continental margin, the relatively shallow ocean floor
nearest the shore, consists of the continental shelf and the continental slope. The continental
margin shares the structure of the adjacent continents, but the deep-ocean floor away from land
has a much different origin and history. Prominent features of the deep-ocean basins include
rugged oceanic ridges, fl at abyssal plains, occasional deep trenches, and curving chains of
volcanic islands. The processes of plate tectonics, erosion, and sediment deposition have shaped
the continental margins and ocean basins.
In the next chapter you will learn that nearly all the ocean floor is blanketed with sediment.
Except for the spreading centers themselves, the broad shoulders of the oceanic ridge systems
are buried according to their age— the older the seabed, the greater the sediment burden. Some
oceanic crust near the trailing edges of plates may be overlain by sediments more than 1,500
meters (5,000 feet) thick. Sediments have been called the “memory of the ocean.” The memory,
however, is not a long one. Before continuing, can you imagine why that is so?