What are the different types of seafloor sediments and what are the factors that control the distribution of each major sediment type? Where does each major seafloor sediment type tend to accumulate in greatest quantity?
The different types of seafloor sediments can be broadly categorized into four major types: terrigenous, biogenous, hydrogenous, and cosmogenous sediments.
1. Terrigenous Sediments: These sediments originate from land and are primarily made up of weathered rocks, minerals, and organic matter carried by rivers, wind, and glaciers into the ocean. They are the most common type of seafloor sediments. The factors that control their distribution include:
- Proximity to sources: Areas close to large river systems, such as the mouths of major rivers, tend to have higher amounts of terrigenous sediments.
- Currents and wave action: Strong currents and wave action can transport terrigenous sediments over long distances and distribute them evenly across the seafloor.
- Topography: The shape and depth of the seafloor can influence the accumulation of terrigenous sediments. Depressions or basins may trap sediment, while steeper slopes may have less accumulation.
2. Biogenous Sediments: These sediments are composed of the remains of marine organisms such as shells, skeletons, and other organic materials. They can include the remains of plankton (planktonic), shells from bottom-dwelling organisms (benthic), and coral reefs. Factors controlling their distribution include:
- Biological productivity: Areas with high biological productivity, such as upwelling zones or nutrient-rich areas, tend to have more biogenous sediments.
- Depth and temperature: Biogenous sediments tend to accumulate in greater quantities in deeper, colder waters due to increased biological productivity.
- Dissolution rates: Some biogenous sediments dissolve more easily in certain water conditions. For example, calcium carbonate shells may dissolve in more acidic conditions, affecting the distribution of these sediments.
3. Hydrogenous Sediments: These sediments form directly from seawater through various chemical processes. They include minerals precipitated from seawater, such as manganese nodules, evaporites, and phosphates. Factors influencing their distribution include:
- Chemical composition of seawater: The concentration of specific elements in seawater influences the formation and distribution of hydrogenous sediments.
- Depth and temperature: Some hydrogenous sediments require specific temperature and depth conditions for their formation, leading to localized accumulations.
- Water chemistry: Variations in pH, salinity, oxygen levels, and other chemical parameters can influence the formation and distribution of hydrogenous sediments.
4. Cosmogenous Sediments: These sediments originate from extraterrestrial sources, such as meteorites and cosmic dust. They are less abundant compared to the other types. Factors controlling their distribution include:
- Proximity to impact sites: Areas closer to impact sites or regions with higher meteorite activity are more likely to have cosmogenous sediments.
- Atmospheric circulation: Wind currents can transport cosmic dust particles over long distances and deposit them on the seafloor.
- Sedimentation rates: Cosmogenous sediments tend to accumulate slowly and may be mixed with other sediment types, making their distribution more variable.
In terms of accumulation in greatest quantity, the specific locations can vary depending on the sediment type and local conditions. However, terrigenous sediments are generally found in greater quantities near river mouths or areas with high terrestrial inputs. Biogenous sediments tend to accumulate in regions with higher biological productivity, such as in upwelling zones or cold-water areas. Hydrogenous sediments can accumulate in specific depth and temperature conditions, while cosmogenous sediments can have more sporadic distributions. It's important to note that actual sediment distribution is influenced by complex interactions between multiple factors, and studying these sediments through sediment cores and geophysical methods can provide detailed information on their abundance and distribution.