Final answer:
The silica-rich oozes of the Pacific Ocean are formed by the accumulation of siliceous skeletal remains from organisms such as diatoms and radiolarians, accumulating in areas with the right preservation conditions and low levels of terrigenous sediment.
Step-by-step explanation:
The silica-rich oozes of the Pacific Ocean are primarily due to the accumulation of skeletal remains from siliceous organisms such as diatoms and radiolarians. When these organisms die, their silica-based skeletons settle to the seabed, forming thick deposits of siliceous ooze over time.
The Pacific Ocean is conducive to this accumulation because it is distant from the sources of terrigenous sediment, like large river outputs that dilute the concentration of biogenic silica. The silica ooze accumulates mainly in regions where the rate of supply of skeletal remains is greater than the rate at which the silica can dissolve.
In areas where water is highly supersaturated with silica, and there are adequate conditions for the preservation of silica, these depositions can become quite thick. Notably, the right environment for the dissolving of silica skeletons is less common in deep ocean waters, allowing these oozes to persist and accumulate. Furthermore, oceanic crust, composed of mafic magma eruptions and deep marine sediments, typically has a layer on top in which such siliceous oozes can form.