Hydrogenous

Hydrogenous refers to materials formed by precipitation of dissolved constituents from water, especially seawater, rather than by biological activity or terrestrial transport. In marine geology, hydrogenous sediments are chemical or authigenic deposits that precipitate directly from seawater as it becomes supersaturated with certain ions. They contrast with biogenous sediments, derived from the remains of organisms, and terrigenous sediments, derived from continental sources.

Formation and processes: Mineral precipitation occurs when dissolved ions in seawater exceed their solubility limits due to changes in concentration, pH, temperature, or oxidation state. On the deep ocean floor, this leads to the accumulation of minerals in nodules or crusts and can form certain carbonates, phosphates, sulfates, and oxides.

Common examples: Manganese nodules and ferromanganese crusts are the best-known hydrogenous deposits, consisting mainly of manganese and iron hydroxides with trace metals such as nickel, copper, and cobalt. Other hydrogenous deposits include various carbonate and phosphate minerals formed by direct precipitation, often at very slow rates, on the seafloor.

Distribution and significance: Hydrogenous sediments are more common in relatively quiet, deep-ocean settings away from strong riverine inputs. Growth rates are typically slow, making exploration and extraction challenging, but they are studied for both resource potential and paleoceanographic records.

See also: Ocean floor sediments, Ferromanganese nodules, Hydrothermal vent deposits, Biogenous sediment, Terrigenous sediment.