Ocean lesson 6

How have studies of marine sediments advanced our understanding of plate tectonics?

Analysis of sediments and fossils from Deep Sea Drilling Project helped verify the theory of plate tectonics.

piston corer

this is plunged into the sediment and capable of extracting cores up to 90 feet long

diatom

A type of microscopic plantlike protist with a hard outer wall, contains silica

Seabed sediments have given us records of the glacial-interglacial climatic cycles of the last _____ mya

2

foraminiferan

A protist that moves and feeds by means of threadlike pseudopodia and has porous shells composed of calcium carbonate.

radiolarian

A protist, usually marine, with a shell generally made of silica and pseudopodia that radiate from the central body.

clamshell sampler

A sampling device used to take shallow samples of the ocean bottom.

Hydrogenous

A sediment formed directly by precipitation from seawater (from rock and sediment, fresh crust leaching at oceanic ridges, material issuingfrom hydrothermal vents, and substances flowing to the ocean in river runoff etc.)

well sorted sediment

A sediment in which particles are of uniform size. (occur in an environment where energy fluctuates within narrow limits. ex:deep-ocean floor)

poorly sorted sediment

A sediment in which particles of many sizes are found.

How do turbidity currents distribute sediments? What do these sediments (turbidites) look like?

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 terrigenous sand interbedded with the finer pelagic sediments typical of the deep-sea floor.

Would you say the "memory" of the sediments is long or short (in geologic time)?

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.

Which type of sediment covers the greatest seabed area?

Biogenous sediments

how are sediments studied?

Cameras are used to visualize the bottom, and direct samplers (clamshell, piston corers, deep water cameras, seismic profilers.) are used to obtain specimens. Reflected sound can image strata beneath the surface covering.

turbidity current

a downslope movement of dense, sediment-laden water created when sand and mud on the continental shelf and slope are dislodged and thrown into suspension

neritic sediments

Continental shelf sediment consisting of mainly terrigenous material (course, found in shallow waters)

Which type of sediment is rarest?

Cosmogenous

Oolite sands

Hydrogenous sediment formed when calcium carbonate precipitates from warmed seawater as pH rises, forming rounded grains around a shell fragment or other particle.

How do hydrogenous materials form?

Most hydrogenous sediments originate from chemical reactions that occur on particles of the dominant sediment. (manganese nodules- have not yet been mined from the deep sea floor.)

Do most sediments consist of a single type?

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.

pelagic sediments

Sediments of the slope, rise, and deep-ocean floor that originate in the ocean, more of biogenous source. (find, found in deep waters)

How might past climate be inferred from studies of marine sediments?

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.

clay

Sediment particle smaller than 0.004 millimeter in diameter; the smallest sediment size category.

biogenous

Sediment that is made up of the skeletons and shells of marine organisms.

where are sediments thickest

Sediments are thickest close to eroding land and beneath bio- logically productive neritic waters and thinnest over the fast- spreading oceanic ridges of the eastern South Pacific.

stratigraphy

Tbe study and description of layered sedimentary deposits

Which type of sediment is most abundant?

Terragenous

What are the four main types of marine sediments?

Terragenous, Biogenous, Hydrogenous & Cosmogenous

Why are very few areas of the seabed completely free of sediments?

The marine processes that generate sediments are widespread.

turbidite

a graded bed of sediment built up at the base of a submarine slope and deposited by turbidity currents

siliceous ooze

biogenous sediment composed of the silica based shells of single-celled animals and algae

At great depths seawater tends to become slightly acidic, and ____________ oozes will

calcareous

ccd

calcium carbonate compensation

How is sedimentary rock formed?

compression by other overlying sediments, weathering and erosion

The ______ and _______ of marine sediments tell us of relatively recent events in the ocean basin above

depth and composition

silt

fine sand, clay, or other material carried by running water and deposited as a sediment, especially in a channel or harbor.

Microtektites

glass particles that form when a large meteorite impacts the Earth

turbidites

graded layers of terrigeneous sand interbedded with finer pelagic sediments of the deep sea floor

minerals

inorganic crystalline materials with specific chemical compositions.

Most marine sediments actually originate on _____

land (carried to the sea by streams, rivers, and winds.)

Sediments

loose accumulations of particulate material.

Coccolithophores

microscopic algae with calcium carbonate shells, form the base of many marine food webs (biogenous sediment)

Why are Atlantic sediments generally thicker than Pacific sediments?

most of the sediment deposited into the Pacific ocean cannot reach much further than its continental shelves. The sediment is trapped in the peripheral trenches and does not reach the deep ocean basin.

Other than petroleum and natural gas, what is the most valuable material taken from marine sediments?

sand and gravel

what types of particles compose most marine sediments?

sand, silt, and clay.

ooze

sediment containing at least 30% biogenous material

Cosmogenous

sediment derived from outer space (from interplanetary dust that falls constantly into the top of the atmosphere and rare impacts by large asteroids and comets.)

Evaporites

sedimentary rocks formed from minerals left after water evaporates (from isolated arms of the ocean or from landlocked seas or lakes)

terrigenous

sediments originating from land (erosion, volcanic eruptions, and blown dust.)

two types of ooze

siliceous and calcareous

what is the origin of ooze

single-celled, drifting, plantlike organisms and the single-celled animals that feed on them.

ooliths

small spherical grains of calcium carbonate that form a limestone

Which particles are most easily transported by water?

smaller particles

paleoceanography

study of how ocean, atmosphere, and land interactions have produced changes in ocean chemistry, circulation, biology, and climate

The ocean is more than 4 billion years old, yet marine sediments are rarely older than about 180 million years. Why?

tectonic processes form and destroy the seabed over time. Because of subduction, seabed older than about 180 million years is rare.

sand

the coarsest soil, with particles 0.05,2.0 mm in diameter.

Lithification

the physical and chemical processes that transform sediments into sedimentary rocks

calcium carbonate compensation

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.