Siliceous Ooze

Siliceous ooze is a pelagic sediment in which biogenic opaline silica, from diatom frustules and radiolarian skeletons, exceeds 30 percent of the deposit. It dominates two belts: the Southern Ocean opal belt and the equatorial Pacific upwelling zone, plus the North Pacific, where surface productivity is high. Because opal-A dissolves slowly and has no sharp compensation depth, siliceous ooze persists below the CCD where calcite is gone, so red clay and siliceous ooze cover most of the deepest abyssal sea floor. Diatomaceous ooze and radiolarian ooze are its two named varieties, split by the dominant microfossil.