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Flashcards in L5 Deck (81):

How is sediment produced?

By weathering of rocks or the build-up of shells of dead organisms.


Where does most deposition in the ocean come from?

Erosion on the land and then deposition in the ocean.


What would be the net effect of erosion and deposition if it wasn't for techtonic processes?

It would even out earth's surface, cutting away its high points and deepening its low points.


How can sediments be clasified?

grain size and origin


Name from the largest to smallest particles common in sediment.

gravel, sand, silt and clay (colloids)


What two particle sizes are mixed to form mud?

silt and clay


What is terrigeneous sediment?

Terrigenous sediment: fine and coarse grain produced by weathering and erosion of rocks on land; typically sand and mud


what is biogenous sediment

Biogeneous sediment: fine and coarse grains derived from hard parts of organisms such as shells and bones; typically lime and siliceous muds


what is hydrogenous sediment

Hydrogenous sediment: particles that are precipitated by chemical or biochemical reactions in seawater near the seafloor; manganese and phosphate nodules are examples


what is volcanogenous sediment

Volcanogenous sediment: particles ejected from a volcano; eg ash


what is cosmogenous sediment

Cosmosgenous sediment: very tiny grains that originate from outer space and tend to be mixed into terrigenous and biogenic sediment


what are two methods of probing (sampling sections) of the seafloor, when would each be used and why

dredging - disturbs the sample and often mud is lost, this is often only used for hard rock samples
Grab samplers - spring - loaded metal jaws that bite out the bottom and close around the sample - often used over dredging to preserve layers in the sample


What is a method of deep sampling of soft sediment called?

gravity corer


what is the hollow metal tube of a gravity corer called?

core barrel


Describe briefly the process of ocean coring?

a hollow metal tube is pushed into the sediment by the force of gravity, the corer is lowered to the bottom where a heavy weight at the top of the device drives the barrel into the sediment. A plastic liner allows the oceanographers to extract the sediment core intact from the sampler and serves as a temporary storage container.


How long can a core obtained by a gravity corer be?

1-2 m


How long can a sediment core from a piston corer be?

longer than 20m


Describe briefly the process of piston coring

a piston slide up the core barrel as it penetrates the bottom, this action extrudes water from the core barrel allowing the sediment core to enter the liner with minimal disturbance and compactation. once this core is on deck the sample is extrude from the barrel and taken to a laboratory and examined.


What is at present the best the best technique for sampling the ocean bottom?

platform drilling


What are the advantages and disadvantages of platform drilling?

it is very expensive, however the scientific results are priceless, the marine geologists can recover more than 1km in length but can also drill into the hard rock of the crust.


What are the two major areas of sedimentation?

-The continental shelf which is shallow and has sedimentation from the land
-The deep sea, which is far from river supplies of sedimentation


over continental shelfs what is the most dominant process effecting the ocean bottom?



drawing from swimming experience on the beach and our knowledge about waves and turbulence what can we deduce?

bottom energy induced by surface-water wave must diminish with distance off shore due to water depths increasing seaward


what kind of sediment is expected at each part of the beach and why

-coarse sand and gravel on the beach
- fine sands further offshore
into muddy san
sandy mud
this is due to a decrease in energy further seaward


What has caused sea level to rise and fall over previous years, also leading to a move in sediment

galciation and deglaciation


how do glaciation and deglaciation impact sedimentation

due to the changes in water depths because of glaciation and deglaciation the level of the beaches have changed. this leads to relic sediment being mixed in with newer sediment at points on the beach


What have surveys of distribution of sediment on the continental shelf shown worldwide

that sediment types vary with latitude and depend on climate


what sediment is found on continental shelf at the equato and subtropics

deposits include:
coral reefs and grain fragment composed of calcium carbonate(shells and bones) of animals


Where is the equator and subtropic band of sediment on continental shelfs broader and why

western edges due to warm westward flowing equatiorial currents diverging at the equator and moving polewards along the western side of all basinis


What sediment is found on the continental shelf of thee middle or temperate lattitudes

- river supplied terrigenous deposits
principally sand-sized grains of quartz and feldspar


what sediment is found on the continental shelf of the polar shelves

littered with poorly sorted glacial deposits (glacial till) dumped by glaciers ore ice-rafted debris dropped from melting ice bergs


why is relic material not currently in equilibrium with present-day water depths?

because it was deposited long ago when shore lines were displaced seaward due to the holocene sea level rise being so rapid, sediments have not had sufficient time to regain equilibrium


why are dust storms so important for rainforests

because they supply lots of the essential nutrients


what is a red tide in Florida

dust-plume event which increases iron concentration and raises nitrogen levels. this devastates local ecosystems and kills millions of fish and hundreds of manatees


what is microbe transport

microorganisms transported in dust plumes that may have infected and killed coral reefs and orange froves


what human heath impacts are there from dust plumes

pesticides and hurbicides and burning of rubbish in northern africa, release toxins into air - these are inked to increase in asthma attacks in barbados


What effects the shelf bottoms on a short time scale ( thousand years to present)

- wind
- tidal currents


How does wind effect the shelf bottoms on a short time scale ( thousand years to present)

small winds create waves and currents which grow in size
in storms a lot of sediment can be moved due to the high velocity of the water (hjulstorm curve)


How does tidal currents effect the shelf bottoms on a short time scale ( thousand years to present)

tidal currents by themselves are too weak to rework bottom sediment however if there is a large tidal range and a shallow bottom this creates an increase in the waves velocity ( prime example UK)


What effects the shelf bottoms on a medium time scale ( a million years to a thousand years)

glaciation and deglaciation meant the level of water was different and this could leave the continental shelves exposed


what were important modifications when the sea levels were low

- ice caps and glaciers extended on to the shelf proper ( particularly in high and mid lattitudes) and glaciers dumped debris on the shelf floor forming blankets, mounds and ridges of glacial till
- sea level dropped meaning rivers exteded their channels across continental shelves
- deposition and erosion rates in the deep sea increased
- coral reefs were killed


What effects the shelf bottoms on a long time scale ( 100 million years to a million years)

- passive atlantic-type margins
-pacific type margins


explain Atlantic type margins

1The seafloor at the edge of the continent sinks so that the build up of sediment is in line with the rate of subsidence
2Terrigenous sediment eroded from the continent accumulates on the shelf causing the continental margin to widen and deposits thicken.
3With continuing drifting the crust and underlying mantle at the passive edge of the continent cool, contract and are weighed down by sediment load. the edge of the continent continually providing room for incoming sediment
4 the sand fractions of the sediments are reworked by waves and currents and dispersed across the shelf but fine mud is kept in suspension and moved seaward where it will settle on the floor of the continental slope or reach the abyssal depths
5 this results in a long history of deposition and a broad smooth continental shelf.


explain pacific type margins

they receive sediment from the land but are also effected by subduction zones:
1 the strong techtonic forces squeeze beds of sediment between colliding plates, folding and faulting sedimentary layers
2 the sedimentary layers and basalt are being forced downward by the upper plate creating an accretionary prism
3 along with volcanic activity sedimentary debris is derived from the erosion of the volcanic flows and deposited mostly underwater
4 eventually these materials get crushed against and are added into the accretionary prism
5 this results in the continental shelf tends to be narrow and have an irregular surface


What conditions are needed for carbonate shelves or platforms to form?

low supply of river sediment
warm waters


What kind of water is needed for carbonate secreting organisms to survive?

clear, warm and shallow


why are carbonate shelves situated away from large river outputs

the terrigenous sand and mud make the water muddy and this interferes with the growth of reef organisms and dilutes carbonate contributions to the bottom sediments


what does carbonate rocks eg limestone in the rocky mountains, alps, Himalayas and andes show?

how changable environments are over long periods of times and the seas have repeatedly drowned the land and retreated


what are two sources of sediment to the deep ocean floor?

terrigenous mud and sand that have bypassed the continental shelf
the hard parts of surface-water microorganisms that settle to the deep-sea bottom


what are the three classifications of deep-sea deposits

bulk emplacement
pelagic sediment
hydrogenous sediment


What is bulk emplacement

when sea levels are low rivers deposit at the outer continental shelf and upper continental slople


what are slumps

slumps are sediment piles that slide downslope intact, there is little internal disturbance of the sedimentary package


what is a slurrie

a mud flow or debris flow, they destroy any previous bedding that has existed


what are turbidity currents

powerfull bottom currents that transport sediment to the deep sea (sediment laden slurries)


what happens to turbidity currents when the sea bottom flattens

the current slows and deposits sediment rapidly on the deep sea bottom


how are deep submarine canyons formed

for a long time it was not known
now - combination of sediment slumping and turbidity currents that have deepened a gully or depression in the sea bottom


how do deep submarine canyons affect how deposition is distributed

serves as a chute and channels large quantaties of mud and sand from the shelf and slope to the deep sea


what is graded bedding

as a current slows the suspension is dropped according to size with largest first and smallest last, leading to a sorted deposit


what are beds of sediment laid down by turbidity currents called



what is a turbidites

beds of sediment laid down by turbidity currents


what are deep sea fans

turbidities deposit at the mouth of a submarine canyon and form a thick sequence of cone-shaped deposits


what is ice rafting

ice bergs carry sediment, then melt further out at sea depositing the sediment


what is glacial marine sediment

produced by ice rafting, poor sorted and heterogenous composition of tock and mineral fragments


what is hemipelagic sediment

a type of marine sediment that consists of fine-grained biogenic and terrigenous material


what is the inorganic type of pelagic deposit

red clay - oceanographers call this brown clay or pelagic clay


where does pelagic clay originate from

derived from several sources weathering of granitic and volcanic rocks, dust plumes fallout from extraterrestrial space dust and precipitation from seawater


what is pelagic clay made from

kaolinite, chlorite, felspar and quarts


what is a biogenouse ooze

30% or more of skeletal debris of microscopic organisms
70% or less of inorganic mud particles


what are the two major types of biogenous deposits

calcareous ooze and siliceous ooze


what are calcareous oozes made of

mainly tiny shells of zooplankton such as formanifera, pteropods and phytoplankton such as coccolithophores


what is the carbonate compensation depth

the level below which the preservation of CACO3 shells in surface sediment in negligible


what does CCD stand for

carbonate compensation depth


what does the CCD depend on

acidity, temperature and pressure


what do siliceous oozes contain

remains of diatoms and radiolaria


what are authigenic deposits and and example

chemical precipitates that form in places witi an ocean basin - ferromanganese nodules


typically where do carbonate oozes form

the seafloor that is shallower than CCD


typically where do siliceous oozes accumulate

in the deep water below the CCD


what do ferromaganese consist of

concentric layers of various metal oxides - mainly oxides and iron


what is phosphorite

another mineral deposite


what normally happens when sediment is burried and compacted

slowly transformed into sedimentary rock


what two deposits were found in the Mediterranean that lead to the theory of it drying up

anhydrite - forms in hot arid desert conditions
stromatolites - also unrelated to sea environments