Siliceous ooze is a soft siliceous pelagic sediment that covers large areas of the deep ocean floor. Siliceous oozes consist predominately of either diatoms or radiolarians. Sometimes, it contains lessor proportions of sponge spicules or silicoflagellates. Diatoms are golden-brown algae that construct an opaline silica microscopic shell that is known as a “frustule”. Silicoflagellates are a minor group of marine algae that construct microscopic shells composed of opaline silica. Radiolarians are marine protists that also construct microscopic shells composed of opaline silica and are distant relatives of the foraminifera.[1]
Siliceous ooze accumulates on the ocean floor where the bottom waters are close to saturation in respect to silica and the opaline remains of either diatoms, radiolarians, silicoflagellates, and sponge spicules, or combinations of these are rapidly buried. These conditions exist within areas of high biological productivity associated with volcanic islands and nutrient-rich upwelling zones. As the least common type of pelagic sediment, it covers only 15% of the ocean floor. It accumulates at a slower rate than calcareous ooze: 0.2-1 cm / 1000 yr. [1]
After burial, most siliceous oozes remain unconsolidated. However, a fraction siliceous oozes will dissolved and reprecipitate as a result of diagenesis to form chert beds or nodules. When siliceous oozes are incorporated into orogenic belts associated with subduction zones, they will also be altered by diagenesis and lithified to form chert, i.e. radiolarian chert. [1]