OCE1001 Ch 4 Marine Sediments

What is the approximate depth of the calcite compensation depth (CCD) in the ocean?

3 miles (4.5 kilometers)

In which of the following environments would you expect lithogenous sediment to be the dominant sediment type?

a sandy beach, at the base of the continental slope , the abyssal plains

Why does calcareous material dissolve below the CCD?

Below the CCD, weak acid is formed, which dissolves calcareous material.

Of the following, which energy resource(s) can be extracted from marine sediments?

Gas hydrates, Petroleum

What are the characteristics of hydrogenous sediment?

Hydrogenous sediment includes manganese nodules, phosphates, carbonates, metal sulfides, and evaporates that precipitate directly from water or are formed by the interaction of substances dissolved in water with materials on the ocean floor. Hydrogenous sediments represent a relatively small proportion of marine sediment and are distributed in many diverse environments.

The two major types of microscopic, planktonic organisms that produce siliceous oozes are __________ and __________.

diatoms; radiolarians, Diatoms, which are microscopic algae, and radiolarians, which are protozoans, build a protective covering made of silica around their cells.

Forams, which are composed of calcium carbonate, __________ above the CCD and __________ below the CCD.

do not dissolve; dissolve

Diatomaceous earth, which is composed of silica, __________ above the CCD and __________ below the CCD.

does not dissolve; does not dissolve

What are the characteristics of lithogenous sediment?

Lithogenous sediments reflect the composition of the rock from which they were derived. Sediment texture—determined in part by the size, sorting, and rounding of particles—is affected greatly by how the particles were transported (by water, wind, ice, or gravity) and the energy conditions under which they were deposited. Coarse lithogenous material dominates neritic deposits that accumulate rapidly along the margins of continents, while fine abyssal clays are found in pelagic deposits.

Of the following sediments, which one(s) is/are considered biogenous?

tests of foraminifers, radiolarian ooze

How are marine sediments collected, and what historical events do they reveal?

Sediments that accumulate on the ocean floor are classified by origin as lithogenous (derived from rock), biogenous (derived from organisms), hydrogenous (derived from water), or cosmogenous (derived from outer space). The existence of sea floor spreading was confirmed when the Glomar Challenger began the Deep Sea Drilling Project to sample ocean sediments and the underlying crust, which was continued by the Ocean Drilling Program's JOIDES Resolution. Today, the Integrated Ocean Drilling Program continues the important work of retrieving sediments from the deep-ocean floor. Analysis and interpretation of marine sediments reveal that Earth has had an interesting and complex history including mass extinctions, the drying of entire seas, global climate change, and the movement of tectonic plates.

Of the following types of lithogenous sediment, which one(s) would you expect to find very far from the location of origin?

Volcanic ash, Quartz silt

What is calcareous ooze?

a fine-grained, deep ocean sediment containing the skeletal remains of calcite-secreting microbes

Which of the following conditions allows for calcareous ooze to exist beneath the CCD?

A layer of clay buries the ooze before the sea floor subsides.

How are pelagic and neritic deposits distributed?

Although most ocean sediment is a mixture of various sediment types, it is usually dominated by lithogenous, biogenous, hydrogenous, or cosmogenous material. The distribution of neritic and pelagic sediment is influenced by many factors, including proximity to sources of lithogenous sediment, productivity of microscopic marine organisms, the depth of the ocean floor, and the distribution of various sea floor features. Fecal pellets rapidly transport biogenous particles to the deep-ocean floor and cause the composition of sea floor deposits to match the organisms living in surface waters immediately above them.

What are the characteristics of biogenous sediment?

Biogenous sediment consists of the hard remains (shells, bones, and teeth) of organisms. These are composed of either silica (SiO2) from diatoms and radiolarians or calcium carbonate (CaCO3) from foraminifers and coccolithophores. Accumulations of microscopic shells (tests) of organisms must comprise at least 30% of the deposit for it to be classified as biogenic ooze. Biogenous oozes are the most common type of pelagic deposits. The rate of biological productivity, relative to the rates of destruction and dilution of biogenous sediment, determines whether abyssal clay or oozes will form on the ocean floor. Siliceous ooze will form only below areas of high biologic productivity of silica-secreting organisms at the surface. Calcareous ooze will form only above the calcite compensation depth (CCD)—the depth where seawater dissolves calcium carbonate—although it can be covered and transported into deeper water through sea floor spreading.

What would happen if the depth of the CCD were above the top of the mid-ocean ridge?

Calcareous ooze would not be found below the CCD.

What are the characteristics of cosmogenous sediment?

Cosmogenous sediment is composed of either macroscopic meteor debris or microscopic iron-nickel and silicate spherules that result from asteroid collisions or extraterrestrial impacts. Minute amounts of cosmogenous sediment are mixed into most other types of ocean sediment.

Which of the following statements correctly interpret the environmental conditions associated with types of biogenous deposits?

Diatomaceous ooze on the sea floor indicates cool surface water above, Foraminifer ooze on the sea floor means warm surface water above, Coccolith ooze on the sea floor indicates the water is shallower than 4000 meters.

Which of the following are microscopic, single-celled floating algae that accumulate to form biogenous sediment?

Diatoms, Coccolithophores

Which of the following organisms are responsible for the creation of siliceous ooze?

Radiolarians, Diatoms

How does siliceous ooze accumulate on the seafloor if silica-based residues are dissolved slowly at all depths?

Silica tests accumulate faster than seawater can dissolve them, Areas with high primary productivity of diatoms, for example, can lead to the formation of thick deposits of diatomaceous ooze on the seafloor.

What resources do marine sediments provide?

The most valuable nonliving resource from the ocean today is petroleum, which is recovered from below the continental shelves and used as a source of energy. Gas hydrates include vast deposits of ice like material that may someday be used as a source of energy. Other important resources include sand and gravel (including deposits of valuable minerals), evaporative salts, phosphorite, manganese nodules and crusts, and rare-earth elements.

Sediments derived from the remains of the hard parts of once-living organisms are called __________ sediments.

biogenous, Biogenous sediments are derived from the remains of the hard parts of micro- and macroscopic organisms.

Two common types of chemical compounds found in biogenous sediments are __________ and __________.

calcium carbonate; silica, Biogenous sediment is composed of calcium carbonate (CaCO3) and silica (SiOH2).

You take a sediment sample from the ocean floor at a depth of 5500 m. The area has low biological productivity and the CCD is at 4500 m depth. Your sample will probably consist of __________.

clay, The "default" sediment in areas of very low sediment input is abyssal red clay.

From smallest to largest, which list of sediment particle sizes is in the correct order?

clay, silt, sand, pebbles

You add sand, silt, and clay to a jar of water, shake the jar vigorously, and allow the sediment to settle. The resulting sediment will most closely resemble that of a(n) __________.

continental rise, The continental rise is composed of turbidites and other lithogenous sediments. The largest grains settle fastest and the smaller grains form successive layers on top.

What three steps are required for calcareous ooze to exist below the CCD?

deposition of calcite shells above the CCD, cover of these shells by a non-calcareous material, and movement of the sea floor over millions of years

Siliceous ooze is particularly abundant on the seafloor at __________ and at __________.

high latitudes; equatorial upwelling zones, High-latitude environments and upwelling zones have cool and nutrient-rich waters at the surface to support silica-secreting organisms.

Salt beds of the U.S. Gulf Coast are __________.

hydrogenous sediments, Salt is halite, an evaporite mineral.

Of the following sediments, which one(s) is/are considered hydrogenous?

manganese nodules, coatings of metal sulfides near black smokers

Marine sediment with more than 30% biogenous material is called __________.

ooze, Ooze can be either siliceous or calcareous; the descriptive name usually includes the dominant component organism, e.g., foraminiferal ooze.

The most abundant mineral in lithogenous sediments is __________.

quartz, Quartz is silicon dioxide, a very hard and chemically stable mineral under conditions at the surface of Earth.

Sediment samples from deep beneath the ocean floor are recovered by __________.

rotary drilling, Rotary drilling recovers core samples that are too deep to reach by other means.

Neritic sediments are most likely to be composed of __________.

sand, silt, and gravel, Coarser lithogenous sediments tend to be deposited on the continental margins.

Oozes are uncommon on continental margins because __________.

the biogenous component tends to be overwhelmed by the amount of lithogenous material derived from the nearby continent, There is high biological productivity over most continental margins, but the influx of lithogenous material tends to keep the proportion of biogenous sediment below 30%.

Marine sediments provide valuable clues about which of the following Earth history events?

the climate on Earth millions of years ago, the ancient geographical locations of ocean basins, previous ocean circulation patterns, past catastrophes, such as major extinction events, movement of the ocean floor

What is the calcite compensation depth, or CCD?

the ocean depth below which calcite is unstable and will dissolve quickly

Sediments with all grains of about the same size are classified as __________.

well sorted, If waves, current, or wind of a constant energy level transport sediment for a long time, large particles are left behind and small particles are carried away, producing sediment with a uniform grain size.