Download Key Concept Review (Answers to in-text “Concept Checks”) Chapter

Key Concept Review (Answers to in-text “Concept Checks”)
Chapter 5
1. Sediment is particles of organic or inorganic matter that accumulate in a loose,
unconsolidated form.
2. The marine processes that generate sediments are widespread. Sediment particles
may consist of the remains of once-living organisms, bits of windblown dust,
volcanic ash, etc., that pervade the marine environment.
3. As you learned in Chapter 3, tectonic processes form and destroy the seabed over
time. Because of subduction, seabed older than about 180 million years is rare.
4. Most marine sediments are made of finer particles: sand, silt, and clay.
5. The smaller the particle, the more easily it can be transported by streams, waves, and
currents.
6. Sediments composed of particles of mostly one size are said to be well-sorted
sediments. Sediments with a mixture of sizes are poorly sorted sediments. Sorting is a
function of the energy of the environment—the exposure of that area to the action of
waves, tides, and currents.
7. Marine sediments may be terrigenous (from the land), biogenous (of biological
origin), hydrogenous (formed in place), or cosmogenous (from space).
8. Terrigenous sediments are most abundant. The largest terrigenous deposits form near
continental margins.
9. Biogenous sediments cover the greatest area of seabed, but their total volume is less
than terrigenous sediments.
10. Cosmogenous sediments are very rare. They originate from interplanetary dust that
falls constantly into the top of the atmosphere and rare impacts by large asteroids and
comets.
11. Most sediment deposits are a mixture of biogenous and terrigenous particles, with an
occasional hydrogenous or cosmogenous supplement. The dominant type gives its
name to the mixture.
12. Neritic sediments consist primarily of terrigenous material. Deep-ocean floors are
covered by finer sediments than those of the continental margins, and a greater
proportion of deep-sea sediment is of biogenous origin. Sediments of the slope, rise,
and deep-ocean floor that originate in the ocean are called pelagic sediments.
13. The bulk of neritic sediments are terrigenous; they are eroded from the land and
carried to streams, where they are transported to the ocean.
14. Neritic sediments can undergo lithification: They are converted into sedimentary rock
by pressure-induced compaction or by cementation.
15. Much of the Colorado Plateau, with its many stacked layers easily visible in the
Grand Canyon, was formed by sedimentary deposition and lithification beneath a
shallow continental sea beginning about 570 million years ago.
16. When averaged, the Atlantic Ocean bottom is covered by sediments to a thickness of
about 1 kilometer, while the Pacific floor has an average sediment thickness of less
than 0.5 kilometer.
17. A turbidity current is a dilute mixtures of sediment and water that periodically rushes
down the continental slope. The resulting deposits (turbidites) are graded layers of
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terrigenous sand interbedded with the finer pelagic sediments typical of the deep-sea
floor.
18. The organisms that contribute their remains to deep-sea oozes are small, singlecelled, drifting, plantlike organisms and the single-celled animals that feed on them.
The silica-rich residues give rise to siliceous ooze, the calcium-containing material to
calcareous ooze.
19. At the calcium carbonate compensation depth (CCD), the rate at which calcareous
sediments are supplied to the seabed equals the rate at which those sediments
dissolve. Below this depth, the tiny skeletons of calcium carbonate dissolve on the
seafloor, so no calcareous oozes accumulate.
20. Most hydrogenous sediments originate from chemical reactions that occur on
particles of the dominant sediment. The most famous hydrogenous sediments are
manganese nodules.
21. Evaporites are hydrogenous deposits that include salts that salts precipitate as water
evaporates from isolated arms of the ocean or from landlocked seas or lakes.
22. Cameras are used to visualize the bottom, and direct samplers (clamshell, piston
corers) are used to obtain specimens. Reflected sound can image strata beneath the
surface covering.
23. The discovery that marine sediments are comparatively young (compared with
terrestrial sediments) is a prime proof of the tectonic theory. Remember what
happens at subduction zones!
24. Because the deep sea sediment record is ultimately destroyed in the subduction
process, the ocean's sedimentary "memory" does not start with the ocean’s formation
as originally reasoned by early marine scientists.
25. Scientists now have instruments capable of analyzing very small variations in the
relative abundances of the stable isotopes of oxygen preserved within the carbonate
shells of microfossils found in deep sea sediments. These instruments allow them to
interpret changes in the temperature of surface and deep water over time.
26. In 2008 an estimated 38% of the world’s crude oil and 33% of its natural gas will be
extracted from the sedimentary deposits of continental shelves and continental rises.
27. Toothpaste contains finely-ground diatomaceous residue, and gravel for concrete is
often of marine origin. And then there’s gasoline, heating oil, natural gas, and the
raw material of plastics. The list is long.
28. Sand and gravel are the second most valuable physical marine resource.
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