The Aleutian Basin is an oceanic basin

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...

 under the southwestern Bering Sea

Bering Sea

The Bering Sea is a marginal sea of the Pacific Ocean. It comprises a deep water basin, which then rises through a narrow slope into the shallower water above the continental shelves....

. While the northeastern half of the Bering Sea overlies the North American Plate

North American Plate

The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

 in relatively shallow water, the Aleutian Basin consists of oceanic plate—the remnant of the Kula Plate

Kula Plate

The Kula Plate is an oceanic tectonic plate under the northern Pacific Ocean south of the Near Islands segment of the Aleutian Islands. It is subducting under the North American Plate at the Aleutian Trench and is surrounded by the Pacific Plate...

 that was mostly subducted

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

 under the North American Plate.

Subduction of the Kula Plate ceased after the creation of the Aleutian Trench

Aleutian Trench

The Aleutian Trench is a subduction zone and oceanic trench which runs along the southern coastline of Alaska and the adjacent waters of northeastern Siberia off the coast of Kamchatka Peninsula. It is classified as a "marginal trench" in the east as it runs along the margin of the continent, and...

 to its south. What remained of the Kula Plate attached to the North American Plate. This former subduction zone is now the Beringian Margin, which now hosts sixteen submarine canyons, including Zhemchug Canyon

Zhemchug Canyon

Zhemchug Canyon is a giant underwater canyon located in the middle of the Bering Sea. This submarine canyon is the largest canyon in the ocean. The canyon has a vertical relief of 2600 metres dropping from the shallow shelf the Bering Sea to the depths of the Aleutian Basin. Zhemchug Canyon is...

, the world's largest.

The deep-water part of the Bering Sea is separated into the Commander and Bowers basins by the submarine Shirshov Ridge

Shirshov Ridge

The Shirshov Ridge is located on the eastern border of the Commander Basin below the Kamchatka Peninsula. It extends directly southward for a distance of 750 km toward the Aleutian arc in the eastern part of the Bering Sea ....

  and Bowers Ridge

Bowers Ridge

The Bowers Ridge is located in the southern part of the Aleutian Basin. It extends over 900 km in an arc, starting in the southeast at the Aleutian Arc and terminating to the northwest at the Shirshov Ridge. The Bowers Ridge arc separates the Aleutian Basin from the Bowers Basin, which it...

. The Commander Basin

Commander Basin

The Commander Basin is located between the Shirshov Ridge and the Kamchatka Peninsula. Its southern boundary is the Aleutian arc and occupies the western part of the Bering Sea. The Kamchatka Strait provides a deep water access to the basin from the southwest.The basins sedimentary cover is less...

 occupies the western part of the Bering Sea, with the Shirshov Ridge on its eastern border. The Shirshov Ridge extends 750 km southward from the Russian Olyutorskii Peninsula to connect with Bowers Ridge. The Bowers Ridge extends in the form of an arc over approximately 900 km from the Aleutian Islands Arc to the northwestern termination, where it meets Shirshov Ridge. This former island arc

Island arc

An island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates....

, Bowers Ridge, is a prominent semi-circular-shaped geological that meets the Aleutian arc and, together with the Aleutians, bounds Bowers Basin.
The northern part of the Shirshov Ridge formed 95 My before the present. The ridge grows younger as it goes south, with the southern part of the Shirshov Ridge formed 33 My ago (Early Oligocene). Bowers Ridge was formed 30 My before the present (Late Oligocene).