1. Marine Science - Sternschein
Chapter 5 Sediments
Marine Science - Sternschein

2. Sediments Vary In Appearance
Sediments – particles of organic or inorganic matter
Originate mainly from weathering and erosion of rocks and activity of living organisms
Ocean floor slowly dusted by continuous rain of sediments
Marine sediments have broad range of sizes/types
Colors vary from white/creams to red/browns
Very few areas of sea bed are free of overlying sediment

3. Sediments by Size

4. Sediments – by Particle Size
Particle size frequently used to classify sediments.
The smaller the particle, the more easily it can be transported (via streams/waves/currents)
Coarser grains tend not to travel as far as finer grains
Clays can remain suspended for long periods of time over great distances
Well-sorted sediments = particles of mostly one size, form in environment where energy fluctuates in narrow limits
Poorly-sorted sediments = mixture of sizes, form in environments where energy fluctuates over a wide spectrum

5. Sediments by Source

6. Classification by Source cont.
Can be classified by origin; 4 categories
Terrigenous sediments = most abundant, originate on continents/islands from erosion, volcanic eruptions, and blown dust
Rocks of Earth’s crust are made up of minerals, inorganic crystalline materials with specific chemical compositions

7. Classification by Source cont.
Biogenous sediments = next most abundant marine sediment, silicon-containing/calcium carbonate- containing compounds, making sediments of biological origin
Over millions of years can form fossil fuels
Hydrogenous sediments = minerals that precipitated directly from seawater
Cosmogenous sediments = extraterrestrial origin, least abundant
Two major sources: interplanetary dust and rare impacts by large asteroids/comets

8. Cycling of Sediments

9. Sediment by location
Sediments on ocean floor rarely come from a single source; most sediment deposits are mixtures
Neritic sediments (neritos, “of the coast”) consist primarily of terrigenous material
Greater proportion of deep-sea sediment is biogenous
Pelagic sediment = sediments of the slope/rise/deep-ocean floor, originate in the ocean

10. Location cont.
Currents distribute sand/larger particles along the coast, while wave action carries silts/clays to deeper water
Finest sediment may come to rest or continue to be transported by the turbulence of deep currents
Leads to sorting of particles: Large grains near the coast to relatively small grains near shelf break.
Lithification = conversion of sediments into sedimentary rock by pressure-induced compaction or by cementation

11. Different types of pelagic sediments
Thickness of pelagic sediments are highly variable
Atlantic Ocean bottom – covered by sediments to a thickness of about 1km (3,300ft), while Pacific floor has an average thickness of less than 0.5km (1,650ft)
Atlantic Ocean is fed by greater number of rivers, and is smaller in area, thus getting more sediment for its size
Dilute mixtures of sediment/water periodically rush down the continental slope in turbidity currents
Turbidity currents are thought to help cut submarine currents, moving onto adjacent abyssal plains before eventually coming to rest, making deposits called turbidites
Turbidites = graded layers of terrigenous sand imbedded with finer pelagic sediments typical of deep-sea floor

13. Oozes
Ooze = deep-ocean sediment containing at least 30% biogenous material
Named after dominant remnant organisms constituting them
When these organisms die, their shells settle slowly toward the bottom, mingle with fine-grained terrigenous silts and clays, and accumulate as ooze

14. Coccoliths (top right) contribute to calcareous ooze, such as that on Dover’s cliffs.
Figure 5.14 Dover’s famous white cliffs are uplifted masses of lithified coccolithophores. This chalk-like material was deposited on the sea-bed around 100 million years ago, overlain by other sediments, and transformed into soft limestone by heat and pressure.

15. Nodules Hydrogenous sediments also accumulate on deep- sea floors
Most famous hydrogenous sediments = manganese nodules, consist primarily of manganese and iron oxides

16. Oolites
Molecules of calcium carbonate may precipitate around shell fragments or other particles
Oolite sands = sands comprised of ooliths

17. Tools used to study sediments
Cameras – actual views but limited visibility
Clamshell sampler – collects & retrieves sediment (limited depth)
Piston corer – collects intact samples at greater depths
Seismic profiling – computer-aided images produce a more detailed image

18. Sampling tools

19. Importance of Sediments
Reveals clues to the past (paleontologist)
Substantiated theory of plate tectonics
Sediments are used in building materials
Petroleum is extracted from sediments
A source of manganese and iron