Marine sediments form the basis of oceanic geological studies, providing essential clues about the Earth’s history. These sediments are categorized into four primary types: terrigenous, biogenous, hydrogenous, and cosmogenous. Each type has a unique origin and distribution, contributing differently to the marine ecosystem.
Terrigenous Sediments
Terrigenous sediments are the most abundant marine sediments, derived from land-based sources through erosion, volcanic activity, and dust carried by winds. The term “terrigenous” originates from the Latin words “terra” meaning Earth, and “generare” meaning to produce.
- Origin: Terrigenous sediments are transported to the oceans primarily through rivers, glaciers, and wind. The erosion of rocks on continents and volcanic eruptions are significant contributors. Wind-blown dust and debris can travel thousands of kilometers over land and sea before settling on the ocean floor.
- Composition: These sediments are rich in quartz, clays, and other silicate minerals. Quartz sand is common in coastal areas, while clays are predominant in deep ocean basins due to their ability to be suspended and transported over long distances.
- Distribution: Terrigenous sediments dominate the continental margins, abyssal plains, and polar ocean floors. They constitute about 45% of the ocean floor. Near coastlines, these sediments tend to be coarser, consisting of sands and gravels. As distance from the shore increases, finer particles like clays settle in deep-sea environments.
Biogenous Sediments
Biogenous sediments are derived from the remains of marine organisms, particularly those with calcium carbonate or silica skeletons. These sediments accumulate on the ocean floor after the death of these organisms.
- Origin: Biogenous sediments originate from the hard parts of marine plankton such as foraminifera, diatoms, and radiolarians. Calcareous ooze forms from organisms with calcium carbonate skeletons, while siliceous ooze forms from those with silica skeletons.
- Composition: Calcareous and siliceous materials dominate biogenous sediments. Calcareous sediments consist primarily of foraminifera and coccolithophores, while siliceous sediments are derived from diatoms and radiolarians. These sediments can also include organic-rich materials that can turn into fossil fuels like oil and gas over millions of years.
- Distribution: Biogenous sediments are more common in areas of high biological productivity, such as continental margins and regions of upwelling where nutrient-rich waters support vast amounts of plankton. Calcareous oozes cover a significant portion of the ocean floor in shallower depths, while siliceous oozes dominate deeper waters, particularly below 5,000 meters. These sediments cover about 55% of the ocean floor.
Hydrogenous Sediments
Hydrogenous sediments form directly from the chemical precipitation of minerals from seawater. This category of sediments, also known as “authigenic sediments,” is the result of chemical reactions occurring within the ocean.
- Origin: The formation of hydrogenous sediments occurs when dissolved minerals precipitate out of seawater. This process is often facilitated by the presence of bacteria or by interactions with existing particles on the seafloor. The minerals can also be precipitated around hydrothermal vents and along mid-ocean ridges where hot, mineral-rich waters rise from below the Earth’s crust.
- Composition: Common hydrogenous sediments include manganese nodules, phosphorite deposits, and metal sulfides. Manganese nodules are the most widely recognized form, consisting of concentric layers of iron and manganese hydroxides around a core. Phosphorites typically form in regions with high biological productivity and are associated with oceanic upwelling zones.
- Distribution: Hydrogenous sediments are less abundant compared to terrigenous and biogenous sediments, covering less than 1% of the ocean floor. Manganese nodules are found scattered across vast expanses of the abyssal plains. Phosphorite deposits, on the other hand, are more common along continental margins.
Cosmogenous Sediments
Cosmogenous sediments are the rarest type of marine sediments, originating from extraterrestrial sources such as meteorites and cosmic dust.
- Origin: These sediments are formed from interplanetary dust and debris from meteorites. Micro-meteoroids enter the Earth’s atmosphere and, upon contact with it, melt due to friction, forming tiny spherical particles known as microtektites. When larger asteroids strike the Earth, they can generate vast amounts of debris, some of which falls back to Earth as cosmogenous sediment.
- Composition: Cosmogenous sediments include iron-rich spherules, tektites, and microtektites. These particles are often glassy in appearance and are highly resistant to dissolution in seawater. The most common forms are silicate and iron-rich particles.
- Distribution: These sediments are scattered across the ocean floor in extremely low concentrations. Even though interplanetary dust constantly rains down on the Earth, it constitutes only a tiny fraction of the total marine sediment. In rare instances, cosmogenous sediments make up a larger portion of the sediment record when Earth experiences a significant impact event from a large asteroid.
The Importance of Marine Sediments
Marine sediments are not just geological curiosities; they hold significant value in understanding Earth’s history, climate change, oceanic processes, and even biological evolution. The distribution and thickness of these sediments can vary dramatically. For instance, sediments are thickest near continental slopes and thinnest along mid-ocean ridges, where new ocean crust is constantly being formed. By studying these sediments, scientists can trace historical shifts in ocean currents, sea level changes, and climate patterns.
Furthermore, marine sediments are rich sources of natural resources. Oil and gas deposits, often found within biogenous sediments, play a critical role in the global economy. Minerals like manganese, iron, and phosphorites extracted from hydrogenous sediments are also valuable.
Conclusion
The four types of marine sediments — terrigenous, biogenous, hydrogenous, and cosmogenous – provide a comprehensive record of both Earth’s internal and external processes. By studying these sediments, we can gain a better understanding of the dynamic processes shaping our oceans and our planet. Whether derived from land, biological activity, chemical precipitation, or space, these sediments hold essential clues to Earth’s past, present, and future.
Multiple Choice Questions
1. What are marine sediments primarily used to study?
A) Marine animals
B) Ocean currents
C) Earth’s history and climate
D) Tides and waves
2. Which type of marine sediment originates from land-based sources?
A) Biogenous
B) Terrigenous
C) Hydrogenous
D) Cosmogenous
3. Terrigenous sediments are primarily composed of which mineral?
A) Manganese
B) Silica
C) Quartz
D) Calcium carbonate
4. Biogenous sediments primarily consist of what?
A) Organic material
B) Mineral particles
C) Weathered rock fragments
D) Remains of marine organisms
5. Calcareous ooze is made up of the remains of which marine organisms?
A) Diatoms
B) Foraminifera and coccolithophores
C) Radiolarians
D) Sponges
6. What are hydrogenous sediments formed from?
A) Biological remains
B) Chemical precipitation from seawater
C) Dust from space
D) Eroded land materials
7. Which type of sediment is the least abundant in the ocean?
A) Terrigenous
B) Biogenous
C) Hydrogenous
D) Cosmogenous
8. Cosmogenous sediments come from what source?
A) Deep-sea hydrothermal vents
B) Land erosion
C) Extraterrestrial bodies like meteorites
D) Plankton remains
9. Manganese nodules are an example of which type of sediment?
A) Cosmogenous
B) Biogenous
C) Hydrogenous
D) Terrigenous
10. Which process is mainly responsible for transporting terrigenous sediments to the ocean?
A) Hydrothermal vents
B) Volcanic eruptions
C) Rivers, glaciers, and wind
D) Deep-sea currents
11. What percentage of the ocean floor is covered by biogenous sediments?
A) 20%
B) 45%
C) 55%
D) 75%
12. Which of the following is NOT a source of terrigenous sediments?
A) Rivers
B) Glaciers
C) Volcanic eruptions
D) Meteorite debris
13. Where are hydrogenous sediments most commonly found?
A) Mid-ocean ridges
B) Continental shelves
C) Abyssal plains
D) Coastal zones
14. Which marine sediment type provides clues about extraterrestrial impacts?
A) Biogenous
B) Terrigenous
C) Cosmogenous
D) Hydrogenous
15. Siliceous ooze is formed from the remains of which marine organisms?
A) Diatoms and radiolarians
B) Coccolithophores
C) Sponges
D) Corals
16. What is the primary mineral found in calcareous sediments?
A) Silica
B) Calcium carbonate
C) Iron
D) Manganese
17. Which of the following sediments is mostly found near hydrothermal vents?
A) Terrigenous
B) Hydrogenous
C) Cosmogenous
D) Biogenous
18. What is a key characteristic of cosmogenous sediments?
A) Derived from marine organisms
B) Found only in coastal regions
C) Created from space debris
D) Rich in calcium carbonate
19. Which type of sediment forms large deposits of oil and gas over millions of years?
A) Terrigenous
B) Cosmogenous
C) Biogenous
D) Hydrogenous
20. The term “terrigenous” refers to sediments that come from which source?
A) The ocean floor
B) Outer space
C) Marine organisms
D) Land
Answers:
- C
- B
- C
- D
- B
- B
- D
- C
- C
- C
- C
- D
- A
- C
- A
- B
- B
- C
- C
- D
