List of submarine topographical features

Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains are among the flattest, smoothest and least explored regions on Earth.

Abyssal plains cover more than 33% of the ocean floor (about 23% of Earth's surface),[2] but they are poorly preserved in the sedimentary record because they tend to be consumed by the subduction process.

[1][3][4] The abyssal plain is formed when the lower oceanic crust is melted and forced upwards by the asthenosphere layer of the upper mantle.

Abyssal plains result from the blanketing of an originally uneven surface of oceanic crust by fine-grained sediments, mainly clay and silt.

They are the deepest parts of the ocean floor, and they define one of the most important natural boundaries on the Earth's solid surface: the one between two lithospheric plates.

The physical manifestations of this were elevated atmospheric and oceanic temperatures, a significant sea-level transgression, and a period of widespread anoxia, leading to the extinction of 26% of all genera.

[51] These eruptions would also have resulted in the emission of large quantities of carbon dioxide into the atmosphere, leading to global warming.

This runaway greenhouse effect was probably put into reverse by the decline of the anomalous volcanic activity and by increased CO2-driven productivity in oceanic surface waters, leading to increased organic carbon burial, black shale deposition, anoxia and mass extinction in the ocean basins.