The remains of diatoms and other silica-utilizing organisms are found, as opal sediments within pelagic deep-sea deposits. Pelagic sediments, containing significant quantities of siliceous biogenic remains, are commonly referred to as siliceous ooze. Siliceous ooze are particularly abundant in the modern ocean at high latitudes in the northern and southern hemispheres. A striking feature of siliceous ooze distribution is a ca. 200 km wide belt stretching across the Southern Ocean. Some equatorial regions of upwelling, where nutrients are abundant and productivity is high, are also characterized by local siliceous ooze.
Siliceous oozes are composed primarily of the remains of diatoms and radiolarians, but may also include other siliceous organisms, such as silicoflagellates and sponge spicules. Diatom ooze occurs mainly in high-latitude areas and along some continental margins, whereas radiolarian ooze are more characteristic of equatorial areas. Siliceous ooze are modified and transformed during burial into bedded cherts.