Pelagic

Depth of water

Bathypelagic - Abyssopelagic (2,000 - 6,000 m)

Circumstances

Ocean floors a few hundreds km far from continents. Deposits are mainly composed of remains of calcareous or siliceous oceanic planktons together with fine terrestrial clastic particles. The deposition rate of calcareous sediments is 0.5 - 60 mm per 1,000 years, that of siliceous sediments is 1 - 10 mm per 1,000 years, and that of pelagic terrestrial sediments is 0.2 - 60 mm per 1,000 years. Calcareous sediments are originated from coccoliths or foraminifera having calcareous frames. Siliceous sedimentsa are originated from diatoms or radiolarians. Radiolarian-based siliceous sediments are dominant at epiplagic zones of upwelling area near the equator where surface productivity is high. Diatom-based siliceous sediments are dominant at high-latitude area. Calcareous sediments are on ocean floors shallower than 3,000 - 4,000 m as they are dissoved deeper than the Carbonate Compensation Depth (CCD) which is typically 4,500 m for calcite and 3,500 m for aragonite. Calcarious sediments are widely distributed on ocean floors but they do not preserved as they are dissolved at the deeper circumstances than CCD in the process of accretion to continents.

Sedimentary facies (Sediments)

Siliceous sediments such as chert.