Definition
Siliceous ooze is a type of pelagic marine sediment predominantly composed of microscopic silica-rich skeletal fragments, chiefly the remains of diatoms, radiolarians, and silicoflagellates. It accumulates on the deep ocean floor where the rate of biogenic silica production exceeds dissolution.
Overview
Siliceous ooze forms part of the broader category of pelagic oozes, distinguished from calcareous oozes that are based on calcium carbonate shells. These sediments are typically found in high-productivity regions of the world’s oceans, such as upwelling zones and areas with abundant siliceous plankton. Over geological time, siliceous ooze can lithify into chert or other siliceous rocks.
Etymology/Origin
The term combines “siliceous,” derived from Latin silex (flint) and meaning “containing silica,” with “ooze,” an English word historically used in geology to denote soft, unconsolidated marine sediments that settle out of the water column. The phrase “siliceous ooze” entered scientific literature in the mid‑20th century as oceanographic studies clarified the composition of deep‑sea deposits.
Characteristics
- Composition: Primarily biogenic silica (SiO₂·nH₂O) from the siliceous shells (frustules and skeletons) of diatoms, radiolarians, and silicoflagellates. Minor contributions may include volcanic ash, detrital quartz, and organic matter.
- Texture: Fine‑grained, generally less than 0.063 mm in particle size, with a loosely consolidated, mud‑like consistency when fresh.
- Distribution: Concentrated in oceanic regions with high siliceous plankton productivity, such as the Southern Ocean, the North Pacific, and parts of the equatorial Pacific.
- Formation process: After the death of siliceous plankton, their silica shells sink, partially dissolve in the water column, and eventually deposit on the seabed. The balance between production, dissolution, and removal determines the thickness of siliceous ooze layers.
- Geological significance: Serves as a recorder of past oceanic productivity and silica cycling. Its transformation into chert provides a fossil record for paleoclimatic and paleoceanographic reconstructions.
- Physical properties: Low bulk density (~1.2–1.4 g cm⁻³), high porosity, and relatively high silica content (often exceeding 70 % by weight in pure siliceous ooze).
Related Topics
- Calcareous ooze – pelagic sediment dominated by calcium carbonate shells (e.g., foraminifera, coccolithophores).
- Biogenic silica – the silica mineral form produced by marine organisms; central to the formation of siliceous ooze.
- Chert – lithified siliceous sedimentary rock derived from the diagenesis of siliceous ooze.
- Marine sedimentation – the broader processes governing the deposition of materials on the ocean floor.
- Silica cycle – the biogeochemical cycle of silicon in marine environments, encompassing dissolution, transport, and deposition of siliceous material.