9.3 Sea-Floor Sediments

GEOL1340

Terrigenous (Lithogenous) Sediment

Mineral grains and rock fragments weathered from continental landmasses and transported to the oceans by rivers, wind, waves, ice, or gravity.

Pelagic Carbonate Sediment

Biogenic sediment derived from marine organisms (like foraminifera and coccolithophores) that construct their shells out of calcium carbonate (calcite).

Pelagic Silica Sediment

Biogenic sediment derived from marine organisms (like diatoms and radiolaria) that construct their tests out of microcrystalline quartz (silica).

Hydrogenous Sediment

Minerals (such as iron and manganese nodules or evaporites) that precipitate directly out of seawater or hydrothermal solutions.

Cosmogenous Sediment

Extremely rare deposits of extraterrestrial dust and micrometeorites settling from outer space.

Pelagic Ooze

A deep-sea biogenous sediment containing more than 30% skeletal remains (tests) of microscopic marine plankton by volume.

Calcareous Ooze

A pelagic biogenous sediment composed primarily of calcium carbonate ($\text{CaCO}_3$) shells from planktonic foraminifera and coccolithophores.

Siliceous Ooze

A pelagic biogenous sediment composed primarily of microcrystalline silica ($\text{SiO}_2$) tests from single-celled diatoms and radiolarians.

Chalk

The soft, fine-grained, lithified sedimentary rock equivalent of accumulated calcareous ooze.

Diatomite or Chert

The hard, cryptocrystalline quartz sedimentary rock equivalents formed from lithified siliceous ooze.

Carbonate Compensation Depth (CCD)

The critical ocean depth (typically around 4,000 to 4,500 meters) below which cold, high-pressure seawater becomes acidic enough to dissolve calcium carbonate faster than it accumulates.

Neritic Sediments

Coarser terrigenous sediments (sand, silt, gravel) that accumulate rapidly in nearshore environments across continental margins.

Abyssal Clays (Red Clays)

Fine-grained terrigenous muds that settle very slowly in the deepest, most remote parts of the ocean basins.

Sediment Thickness Trends

Sediments are thickest along passive continental margins and major river deltas, and thinnest or absent near active mid-ocean spreading ridges.

Methane Hydrate

An ice-like crystalline solid composed of water and methane gas that forms under high pressure and low temperatures ($4^\circ\text{C}$) in deep-sea sediments (500 to 1,000 meters depth).