OCN Chapter 11 Review

ooze

"Type of pelagic deposit on the deep-ocean floor that is more than 30% biogenous by weight."

siliceous ooze

"Type of pelagic deposit on the deep-ocean floor that is primarily the skeletal and shell material of diatoms and radiolarian."

What is the relationship between the degree of sorting of a sediment deposit and the range in particle size exhibited by the individual sediments? Are well-sorted sediments more likely to be found in continental margins or on the deep-ocean floor? Explain your answer.

A well-sorted sediment deposit exhibits a relatively narrow range of particle sizes and a poorly sorted deposit displays a relatively broad range of particle sizes. Because of the greater distance traveled, marine sediments tend to be better sorted on the deep-ocean floor than in the continental margins.

Carbonate Compensation Depth (CCD)

" Depth of the ocean below which calcium carbonate (CaCO3) skeletal and shell materials dissolve and do not accumulate."

cosmogenous sediment

" Grains consist of tiny particles that bombarded Earth from outer space."

calcareous ooze

" Type of pelagic deposit on the deep-ocean floor that is predominantly the hard parts of coccolithophores, pteropods, and foraminifera."

delta

"Built at the mouth of sediment-laden rivers by larger-grained sediment accumulating on the continental margin, with water flowing in a series of branches channels."

bioturbation

"Churning of sediments as bottom-dwelling organisms rework the upper few centimeters or tens of centimeters of sediment as they consume organic matter, feed on other sediment dwellers, and build burrows."

tektites

"Cosmogenous sediment formed from silicate rocks thought to have been blasted off other planets or moons by meteorite impacts, which then became molten and rapidly cooled and solidified upon entering Earth's atmosphere, and resemble lithogenous sediment."

manganese nodules

"Dark brown, rounded lumps of rock, many of which are bigger than a large potato, a type of hydrogenous sediment, usually consists of 30% manganese dioxide, 20% iron oxide and 1-2% copper, nickel and/or cobalt, and the sources it believed to be hydrothermal vents."

sorted

"Describing sediment by the range of grain sizes in a deposit, a well-sorted deposit has a narrow range of grain sizes whereas a poorly-sorted deposit has a broad range of grain sizes."

fecal pellets

"Excreted fecal material formed from undigested food particles packaged together in animal guts."

pelagic deposits

"Fine-grained sediments that gradually accumulate, particle-by-particle, on the deep-ocean floor."

turbidite layers

"Graded beds of sediment on the abyssal ocean floor within which the largest grains are at the bottom and grain size progressively decreases upward, created by turbidity currents."

turbidity currents

"Gravity-driven flow of sediment (silt, sand, and gravel) on a continental shelf edge and slope after is becomes unstable and breaks loose, similar to an avalanche."

hydrogenous sediments

"Mineral particles chemically precipitated, often coating other sediment particles, formed under conditions where the chemistry of ocean water is altered."

neritic deposits

"Mostly lithogenous sediments that dominate the shallow ocean along the continental margin, encompassing a wide range of sediment sizes."

lithogenous sediment

"Particles weathered and eroded from terrestrial rocks by water and wind."

biogenous sediment

"Particles with a high proportion of the grains composed of the skeletal or shell material of marine organisms, primarily plankton."

isotopes

"Same atoms with different atomic weights."

stratigraphy

"Study of Earth's history through investigation of the sediment layers beneath the ocean floor as well as on land where sediments have been compressed and converted into sedimentary rock."

eolian transport

"Transportation of sediment to the ocean by wind, often where there is a large supply of loose sediment and little vegetation to protect it, such as in deserts."

phosphorite nodules

"Type of hydrogenous sediment composed of up to 30% phosphorus formed in areas of low dissolved oxygen and abundant phosphorous in the bottom waters of continental shelves, continental slopes and on some seamounts."

Why may buried sediments at an ocean floor location differ from those currently accumulating?

Buried sediments can differ from those currently accumulating at the same location because ocean conditions at the time of deposition may have changed. The type of particles deposited at a specific location depends on factors that change over geological time, affected by plate tectonic movements, climate changes, and changes in volcanic activity.

What are the two most common types of biogenous sediment on the ocean floor?

Calcareous and siliceous sediments are the two most common types of biogenous sediment on the ocean floor. Calcareous sediments consist of calcium carbonate shells of foraminifera, pteropods, and coccoliths. Siliceous sediments consist of the skeletal and shell remains of diatoms and radiolaria.

A deep-ocean manganese nodule is an example of what type of ocean sediment? Describe the ocean environment in which the largest nodules are found.

Manganese nodules are hydrogenous sediments. Since the nodules grow extremely slowly, the largest nodules are found on the ocean floor far from shore where the input of lithogenous and biogenous sediments is minimal.

What prevents many rivers on the Atlantic coast of North America from transporting significant amounts of sediment to the ocean?

Many rivers on the Atlantic coast of North America do not transport significant amounts of sediment to the ocean because their discharges pass through estuaries, e.g., Chesapeake Bay. The river flow slows as it enters an estuary and much of its sediment is deposited.

What are the four major groups of ocean sediments? Briefly describe the source of each sediment type.

Marine sediments are classified as lithogenous, biogenous, hydrogenous, and cosmogenous. The origin of most lithogenous sediment is the weathering and erosion of pre-existing rock. Biogenous sediments are from the excretions, secretions, and remains of organisms, and hydrogenous sediments are precipitated from ocean water. Cosmogenous sediments come from outer space.

Compare the locations and accumulation rates of neritic and pelagic ocean sediment deposits.

Neritic deposits occur on the continental margin and pelagic deposits on the deep-ocean floor. In general, neritic marine sediment deposits accumulate on the ocean floor at a much faster rate than pelagic marine sediment deposits.

How are oxygen isotopes used to reconstruct past climates?

Past climate information can be obtained from measurements of the ratio of oxygen isotope concentration in calcareous sediments. The ratio can be determined because the evaporation rates of water molecules are different depending on what oxygen isotopes they contain. The ratio of isotopes oxygen-16 to oxygen-18 in the calcium carbonate skeletal remains can be used to deduce climate characteristics and sea level at the time of deposition.

Why might it be uncommon to find carbonate ooze in the north central Pacific basin?

The North Pacific Ocean is deep. Any calcareous shells that are produced in the surface ocean dissolve as they fall through the water column.

What are the two types of pelagic deposits that are more than 30% biogenous by weight? Which type is unlikely to occur on the ocean floor at depths greater than about 4500 m (14,800 ft.) below sea level?

The two types of pelagic deposits are calcareous oozes and siliceous oozes. Calcareous oozes are unlikely to occur below 4500 m (the carbonate compensation depth); they tend to dissolve in deeper water.