Overview
This lecture covers hydrogenous sediments formed from substances dissolved in seawater and cosmogenous sediments derived from extraterrestrial sources, highlighting their formation, types, and significance.
Hydrogenous Sediments
- Hydrogenous sediments are formed from dissolved substances that precipitate out of seawater.
- These sediments make up a small portion of total ocean sediments compared to lithogenous (land-derived) sediments.
- Common types include manganese nodules, phosphates, carbonates, and evaporites (e.g., salt).
- Manganese nodules are round lumps (5–20 cm) that grow extremely slowly—about 5 mm per million years.
- Manganese nodules mainly contain manganese oxide, cobalt, and copper, which are valuable for electronics.
- Mining of manganese nodules is under investigation but poses environmental concerns.
- Nodules have a ring-like growth pattern, possibly affected by environmental spurts or biological activity.
- Major nodule mining areas include the Clarion-Clipperton Zone in the North Pacific, but nodules are found worldwide.
- Phosphates are found in the ocean but are more commonly mined on land.
- Metal sulfides form near hydrothermal vents along mid-ocean ridges.
- Carbonates form in areas with high biological productivity.
- Evaporites, such as table salt (sodium chloride), form in coastal areas where seawater evaporates.
- Salt is harvested by allowing seawater to evaporate, then collecting the remaining minerals.
Cosmogenous Sediments
- Cosmogenous sediments originate from extraterrestrial sources, such as space dust or meteorites.
- Though their total volume is small, about 10 kg (over 40 pounds) of cosmogenous material falls to Earth every second.
- Cosmogenous particles include spherules, which are tiny, smooth, glassy balls formed by impacts or collisions in space.
- Tektites are glass-like globules produced from meteor impacts and settle first due to their density.
Key Terms & Definitions
- Hydrogenous sediment — sediment formed by precipitation of dissolved substances from seawater.
- Lithogenous sediment — sediment derived from land.
- Manganese nodule — a round hydrogenous deposit rich in metals like manganese, cobalt, and copper.
- Phosphate — a mineral often found as marine sediment or mined on land.
- Carbonate — sediment formed from calcium carbonate, often in biologically active areas.
- Evaporite — mineral deposit formed by evaporation of seawater (e.g., table salt).
- Cosmogenous sediment — sediment derived from extraterrestrial sources.
- Spherule — small, smooth, glassy cosmogenous particle formed by impacts.
- Tektite — glassy globule formed from meteorite impacts.
Action Items / Next Steps
- Review the types of hydrogenous and cosmogenous sediments and their formation processes.
- Prepare for questions on definitions and significance of each sediment type for upcoming assessments.