How does sediment accumulate on oceanic crust after it forms?

After oceanic crust forms at mid-ocean ridges through extrusive igneous activity, it moves laterally away from the ridge crests as part of the seafloor spreading process. As the crust ages and travels further from the ridge, it accumulates an increasingly thick layer of marine sediment.12

Sediment accumulation occurs through several mechanisms:

• Biogenic Deposition: In the deep ocean, far from continents, sediments are primarily composed of the skeletal remains of marine organisms, such as diatoms, radiolarians, and foraminiferans. These accumulate slowly to form pelagic sediments or ooze.1
• Turbidity Currents: Near continental margins, dense, sediment-laden density currents triggered by underwater slumping transport large volumes of sand, silt, and gravel from continental shelves and slopes onto the deep seafloor, forming turbidites.1
• Other Sources: Sediment also accumulates from volcanic ash, chemical precipitates, and materials originating from the atmosphere or outer space.13

Because the seafloor is constantly moving, the sedimentary layer becomes progressively older and thicker with increasing distance from the ridge crests, until the crust is eventually destroyed at deep-sea trench systems.12