Oceanography Exam 2 Ch 4
Four main types of marine sediment exist:
(1) lithogenous = derived from rock, (2) biogenous = derived from organisms (3) hydrogenous = derived from water (4) cosmogenous = derived from outer space
The distribution of biogenous sediment depends on three fundamental processes:
1. productivity - number of organisms present in the surface water 2. destruction - when skeletal remains (tests) dissolve in seawater at depth 3. dilution - occurs when the deposition of other sediments decreases to the percentage of the biogenous sediment found in marine deposits
How far below sea level is the CCD on average?
4500 meters
Clay comprises up to this percentage by weight of deep-ocean sediments (even oozes).
70%
Where is abyssal clay located and how did it get there?
Abyssal clay is found in deep abyssal plains from being carried by winds or ocean currents. Abyssal clay gets deposited on the deep ocean and are commonly red or brown in color because of oxidized iron
Biogenous sediments are made up of what?
Biogenous sediments are made up of the hard remains of organisms (shells, bones, teeth). They are composed of either silica from diatoms and radiolarians or calcium carbonate from foraminifers and coccolithophores
How Calcareous ooze is created
Calcareous ooze is created by the accumulation of tests of organisms that prefer warm water conditions, such as coccolithophores and foraminifers
These are a type of microscopic, single-celled floating algae that make their tests out of calcite and accumulate to form biogenous sediment.
Coccolithophores Diatoms
What are coccolitohphores?
Coccolithophores are a single celled microscopic algae
What are cosmogenous sediments composed of?
Cosmogenous sediment is composed of either meteor debris or iron-nickel and silicate spherules that result from asteroid collisions
The formation of siliceous ooze:
Diatoms and radiolarians make their tests out of silica and accumulate to form siliceous ooze
What will substantially reduce the travel time of tests to the ocean floor?
Fecal pellets
Abyssal clay is composed of what?
Fine, clay sized particles from the continents
What are foraminifers?
Foraminigers are single celled protozoans, they do not photosynthesize. Foraminifers resemble the large shells that one might find at a beach
What are manganese nodules?
Manganese nodules are round hard lumps of manganese, iron, and other metals. -When cut in half they reveal a layered structured formed by precipitation -They are found on the deep ocean floor
How do Manganese nodules form?
Manganese nodules form in layers around a central nucleation object, such as a grain of sand or a shark's tooth
Marine sediments provide valuable clues about what Earth history events?
Marine sediments provide valuable clues about the ancient geographical locations of ocean basins past catastrophes, such as major extinction events previous ocean circulation patterns the climate on Earth millions of years ago movement of the ocean floor
Neritic deposits are found where?
Neritic deposits are generally found on continental shelves and in shallow water near islands they are generally coarse grained lithogenous sediment
Neritic deposits cover how much of the ocean floor and dominate what area?
One quarter Neritic deposits dominate continental margin areas
Pelagic deposits are found where?
Pelagic deposits are found in deep ocean basins and are made of fine grained lithogenous sediment
Siliceous ooze is formed by the accumulation of what?
Silica secreting organisms such as siliceous tests of diatoms and radiolarians
How Siliceous ooze is created
Siliceous ooze is created by the accumulation of tests of organisms that prefer cool water conditions, such as diatoms and radiolarians
Calcareous ooze is formed by the accumulation of what?
Tests of foraminifers and coccoliths and other calcareous secreting organisms
Pelagic deposits cover how much of the ocean floor and dominate what area?
Three fourths Pelagic deposits dominate deep ocean areas along the mid ocean ridge
The organisms that contribute to biogenous sediment are:
algae and protozoans
Where are most modern-day calcareous oozes found in the ocean?
along the mid-ocean ridge beneath warm surface waters
Accumulations of microscopic shells (tests) of organisms must comprise at least 30% of the deposit for it to be classified as what?
biogenic ooze
Both siliceous and calcareous oozes are ______ sediments found on the deep-sea floor in varying distributions depending on latitude and ocean depth.
biogenous
Radiolarian ooze and tests of foraminifers are considered what type of sediment?
biogenous
_____ oozes are composed of the hard remains of once-living organisms.
biogenous
The most common type of pelagic deposits are
biogenous oozes
How is most sediment transported from the continental shelf out to the continental rise?
by turbidity currents
Beneath the calcite compensation depth (CCD):
calcium carbonate dissolves in seawater
Neritic deposits are made up mostly of what and are found where?
coarse lithogenous sediments dominate neritic deposits and accumulate rapidly along the margins of the continents
Most chalk is made from ___________
coccoliths
Clues to a sediments origin are found in its
composition and texture
Populations of microscopic marine organisms in ocean surface waters closely match their abundance in sediments on the ocean floor, even though it takes 10 to 50 years for an individual particle to sink to deep-ocean depths. What accounts for this pattern?
concentration of the particles in fecal pellets
Siliceous ooze is associated with ________ surface water conditions
cool
Siliceous ooze on the sea floor indicates ___ surface water above
cool
What are important in transporting particles to the sea floor?
fecal pellets
Pelagic deposits are made mostly of what type of sediment?
fine abyssal clays
Two significant sources of calcium carbonate biogenous ooze are
foraminifers and coccolithophores
In sediments, what does the Wentworth scale describe?
grain size
Manganese nodules and coatings of metal sulfides near black smokers are considered what type of sediment?
hydrogenous
What type of sediment often have economic value?
hydrogenous
What do hydrogenous sediment include?
hydrogenous sediment includes: manganese nodules phosphates carbonates metal sulfides evaporites that precipitate directly from water or are formed by the interaction of substances dissolved in water with materials on the ocean floor.
Do manganese nodules speed up the sinking of particles?
manganese nodules do not speed up the sinking of particles
Most of the silica in biogenous ooze comes from
microscopic algae called diatoms and protozoans called radiolarians
Marine sedimentary deposits can be categorized as either
neritic or pelagic
Marine sediments provide a variety of important resources including:
petroleum, gas hydrates, sand and gravel, evaporite salts, phosphorite, and manganese nodules and crusts
Radiolarians are composed of _____
silica
This type of ooze can be found on the seafloor near the equator and at higher latitudes
siliceous
Examples of sediment-transporting media include:
streams, wind, glaciers, and gravity
Microscopic shells that create biogenous sediment on the sea floor are called:
tests
The only way for siliceous ooze to be preserved in the ocean is ___________
to have it accumulate faster than it dissolves
Hydrogenous sediments represent a relatively small proportion of marine sediment and are distributed in many diverse environments
true
Minute amounts of cosmogenous sediment are mixed into most other types of ocean sediment
true
The CCD is the depth, well beneath wave action, at which carbonates are dissolved as fast as they are deposited, thus preventing accumulation
true
Pelagic deposits accumulate slowly on the deep ocean floor and include particles from where
volcanic eruptions windblown dust
Calcareous ooze is associated with ________ surface water conditions
warm
Calcareous ooze on the sea floor indicates _____ surface water above
warm
Organisms that build their shells of calcium carbonate prefer what type of water?
warm
