How is the ocean basin defined?
An ocean basin is the land surface under an ocean that includes the various topography below the water.
Geologically, ocean basins are large geologic basins that are below sea level. It may be actively changing size or may be relatively tectonically inactive, depending upon whether there is a moving plate tectonic boundary associated with it.
The Atlantic Ocean and Arctic Ocean are good examples of active growing oceanic basins. About 70% of the planets surface is made up of ocean basins.
Modern sources regard the ocean basins more as basaltic plains than as sedimentary depostories, since most sedimentation occurs on the continental shelves and not in the geologically defined ocean basins.