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Why is sediment usually thickest near continental margins?

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World map highlighting major features of the ocean basins, including trenches, ridges, basins, and plateaus labeled throughout the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. Continents are shown with shaded terrain, and prominent undersea features such as the Mid-Atlantic Ridge, Mariana Trench, and Kerguelen Plateau are marked across the map. — ocean basin Major features of the ocean basins.

Sediment is typically thickest near continental margins primarily because these areas serve as the initial, primary depositional sites for land-derived sediment transported from the continents by rivers, wind, and ice.123

The accumulation of these materials is driven by several key processes:

Proximity to Source: Continental margins are the shallowest parts of the ocean and are located closest to the source of terrigenous material, meaning much of the sediment load is deposited before it can reach the deep-ocean floor.13
Gravity and Transport: Sediments accumulate on the continental shelf and continental rise through various mechanisms. Submarine canyons act as major conduits, allowing turbidity currents—dense, sediment-laden flows—to transport massive volumes of material from the shelf down to the base of the continental slope.14
Rapid Deposition: Unlike the deep-sea abyssal plain, where pelagic sediments accumulate very slowly, sediments near margins often build up rapidly, creating thick sequences that can reach several kilometres in depth.15