Oceanic basin
Hydrologically, an
oceanic basin may be anywhere on Earth that is covered by seawater, but geologically
ocean basins are large
geologic basins that are below sea level. Geologically, there are other undersea
geomorphological features such as the
continental shelves, the deep
ocean trenches, and the undersea mountain ranges (for example, the
mid-Atlantic ridge) which are not considered to be part of the ocean basins; while hydrologically, oceanic basins include the flanking continental shelves and shallow, epeiric seas.
Some consider the oceanic basins to be the complement to the continents, with erosion dominating the latter, and the sediments so derived ending up in the ocean basins. Others regard the ocean basins more as basaltic plains, than as sedimentary depositories, since most sedimentation occurs on the continental shelves and not in the geologically defined ocean basins.
Hydrologically some
geologic basins are both above and below sea level, such as the
Maracaibo Basin in
Venezuela, although geologically it is not considered an oceanic basin because it is on the continental shelf and underlain by continental crust.
Earth is the only planet with bimodal
hypsography, reflecting the different kinds of crust,
oceanic crust and
continental crust. Oceans cover 70% of the Earth's surface. Because oceans lie lower than continents, the former serve as
basins that collect sediment eroded from the continents, known as
clastic sediments, as well as precipitation sediments. Ocean basins also serve as repositories for the skeletons of carbonate- and silica-secreting organisms such as
coral reefs,
diatoms,
radiolarians, and
foraminifera.
Geologically, oceanic basins may be actively changing size or may be inactive, depending on whether there is a moving
plate tectonic boundary associated with it. The elements of an active - and growing - oceanic basin include an elevated
mid-ocean ridge, flanking
abyssal hills leading down to
abyssal plains. The elements of an active oceanic basin often include the
oceanic trench associated with a
subduction zone.
The
Atlantic ocean and the
Arctic ocean are a good examples of active, growing oceanic basins, whereas the
Mediterranean Sea is shrinking. The
Pacific Ocean is also an active, shrinking oceanic basin, even though it has both spreading ridge and oceanic trenches. Perhaps the best example of an inactive oceanic basin is the
Gulf of Mexico, which formed in
Jurassic times and has been doing nothing but collecting sediments since then. The
Sea of Japan and
Bering Sea are also good examples of inactive oceanic basins.
Major basins include:
*
Angola Basin*
Argentine Basin*
Brazil Basin*
North American Basin*
South East Pacific Basin*
South West Pacific Basin*
West Australian Basin*
Central Polar Basin*
North Polar Basin*
Norwegian Basin*
List of Oceanic basins
