The type of sediment made up mainly of the shells of diatoms and radiolarians is called biogenic silica.

Here's a breakdown:

* Diatoms and radiolarians are microscopic organisms that have hard shells made of silica (SiO2).

* When these organisms die, their shells sink to the ocean floor and accumulate over time, forming biogenic silica sediment.

* This type of sediment is often found in areas of high biological productivity, such as upwelling zones.

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