Pelagic sediments are primarily found in the:
•• continental shelf ••
continental slope ••
continental rise ••
abyssal plain

Pelagic sediments are primarily found in the Abyssal Plain .

Explanation:

Abyssal Plain

The abyssal plain is an underwater plain on the deep floor of the ocean, At the depths of 3000 meters, this was found lying between the continental rise and mid ocean ridge these plains covers more than 50 percent of the earth's surface.They are flattest, smoothest and lease explored regions.They are key geologic elements of ocean basins .

And , hence , Pelagic sediments are primarily found in the Abyssal Plain .