Calcareous ooze is one of the several types of soil that can be found on the floors of deep oceans. Not surprisingly, such layers occasionally contain an aquifer.
Calcareous ooze is a type of pelagic sediment. It is formed by particles of calcium carbonate, as opposed to siliceous ooze, which is formed by the silica in diatoms and other microorganisms.
Undersea soil densities from "Geotechnical Properties of Deep Continental Margin Soils"
Undersea soils are fairly dense, being compacted.