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- Geological Oceanography
Geological Oceanography
Natural Science 1234 with Vetter at Hawaii Pacific University
About this deck
By: Rachel Knapstein
Created: 2010-12-10
Size: 128 flashcards
Views: 122
Created: 2010-12-10
Size: 128 flashcards
Views: 122
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Compaction
result of overburden pressure during sediment burial
decreasing volume
increasing density
expulsion of pore water
§ Cementation
· High pressure creates precips of new minerals in the pore space · Particles glued together · Reduces porosity and permeability
Diagenesis
· processes that cause disequilibrium on earth. Includes all chemical, physical and biological processes that take place in a sediment after it has been deposited at low temps
Lithification
destruction of pore space by compaction, cementation
Gibbs Free Energy
oxidants used in decreasing order of gibbs free energy yield of the redox reactions
order fror Gibbs free energy
§ Aerobic- Oxygen § Maganese reduction § Denitrification- nitrate reduction · Uses nitrate in place of oxygen, nitrate reduced to N2 gas § Iron Reduction § Sulfate reduction · Uses sulfate, produces hydrogen sulfide, produces bicarb, combines with Fe to produce FeS, burial of FeS= S removal · Absent in freshwater § Methanogenesis · Uses CO2 and H2 and organic matter to produce methane · Landfill/marsh gas
§ What determines the relative importance of the electron acceptor to overall benthic OM decomposition??
· Order of use- C LIMITED
· EA (electron acceptor) abundance – EA LIMITED
free energy
energy stored in the chemical bonds of an org
aerobic respiration
oxygen is the EA
two cases in ocean, carbon limited and oxygen limited
nitrate reduction
aka denitrification
· Uses nitrate in place of oxygen, nitrate reduced to N2 gas
manganese reduction / iron reduction
Solid phase (metal oxides) e-acceptor
• Mn4+ is reduced nearly simultaneously as NO3-
• Mn2+ is transported to overlying seawater and can
be reoxidized
• Sediment color changes, brown Fe(III) to green
Fe(II)
§ Sulfate reduction
· Uses sulfate, produces hydrogen sulfide, produces bicarb, combines with Fe to produce FeS, burial of FeS= S removal · Absent in freshwater
§ Methanogenesis
· Uses CO2 and H2 and organic matter to produce methane · Landfill/marsh gas
fermentation
use of organic matter to extract energy?
redox reaction
§ In areas where primary production is low (lots of oxygen because there are little orgs respiring/taking in O2) no anaerobic produx may occur § Where primary produx is high, or mixing of oxygen is low, all oxygen is consumed before all available org matter then aerobic respiration stops § Nitrate low, Fe and Sulfate in more important
alkalinity
neutralization capacity of water
=bicarb+2carbonate
Alk= [HCO3-] + 2 [CO3-2]
total carbonate
o Conc of carbonate = Alkalinity – total dissolved inorg carbon (CT or ΔΣCO2) o Alkalinity= neutralizing capacity of water o [CO3–2] ~ Alk – CT o CT ↑ , [CO3–2] ↓ o Alk ↑ , [CO3–2] ↑ o [CO3–2] ↑, Ω increases
1. What controls sequence of redox reactions
the electron acceptors as predicted by the free energy yield?
2. how does redox zonations occur in the deep sea sediments in the scenarios of high and low org matter supplies to the sea floor
high- carbon is abundance therefore reduction occurs. anaerobic respiration
low- lots of oxygen therefore aerobic respiration takes place
3.Thermodynamically, why does the deep sea favor CaCO3 dissolution
respiration lower pH. dissolution favored when pore water driven to undersaturation.
CaCO3 more soluble with increase pressure.
*4. how does the deep sea sed pore water del13Cdic profile show evidence of metabolic dissolution of CaCO3
Respiration of org carbon + dissolution of CaCO3 contribute to pore water DIC. 13C reflects the proportions of the two processes. (15.2-3)
-20 you know its from org mat, if 0-1 you know its from the dissolution
5. based on relationship between alkalinity and total carbonate, how do photosynthesis and aerobic respiration affect CaCO3 dissolution
[CO3-2]= alk-CT
ΔΣCO2 = -1, ΔAlk = 0, So Δ[CO3–2] = ΔAlk - ΔΣCO2 = 0 – (-1) = +1
facilitates precip of CaCO3 because ΔΣCO2 is positive?[CO3–2] increases, Ώ increases.
respiration-“CH2O” + O2 => CO2 + H2O
ΔΣCO2 = +1, ΔAlk = 0, So Δ[CO3–2] = ΔAlk - ΔΣCO2 = 0 – 1 = -1
causes dissolution of CaCO3 becuase it is neg. [CO3–2] decreases, Ώ decreases
Stratigraphy
places events in history and the preserved products in chronological order
Chronostratigraphy
each layer diff age
Biostratigraphy
each layer diff fossil assemblage
Principle of superposition
o Oldest at bottom, youngest at top
· Correlation
o Procedure for demonstrating correspondence between geographically separated parts of a geologic unit.
· Principle of Lateral Continuity
o Layer extends great distance, some may be eroded away, chunks can be correlated
· Principle of cross cutting relationships
o Fault before or after layers
o Conformable bed
§ Gradual vs sharp
unconformity
interruptions and breaks in deposition
§ 1- Non conformity § 2- Angular unconformity § 3- disconformity
§ 1- Non conformity
· Sedimentary rock above igneous or meta · Totally different appearance, obvious layers about areas of no layers · Inclusions- bits and pieces of one type in the other helps ID a nonconformity
§ 2- Angular unconformity
· Diagonal underneath, flat at top · Sedimentary on top of sedimentary
§ 3- disconformity
· squiggly” appearance of boundary layer indicating that weathering had occurred before new sed deposited
walthers law
facies that in conformable verticle succession of strata also occur in laterally adjacent enve
transgression/ retrogradation
rise in sea level (relative or
eustatic). As sea level rises, the coastline migrates
inland --> Marine facies overlie nonmarine facies
regression/ progradation
Lowering of sea level (relative or
eustatic). As sea level lowers, the coastline migrates
oceanward --> Nonmarine facies overlie marine
facies.
facies
rock expression of its env
the total textural, compositional and structural characteristics of a sedimentary deposit resulting from accumulation in a particular environment:
-Grain size, sorting, rounding
-Lithology
-Sedimentary structures
-Bedding type
depositional system
assemblage of multiple process-related sedimentary facies assemblages, commonly identified by the geography in which deposition occurs.
– Marine �� ocean, sea
– Transitional �� part land, part ocean
– Terrestrial �� land
sequence
stratigraphic unit bounded at its top and base by unconformities or their correlative conformities, and typically embodies a continuum of depositional environments, from updip (continental) to downdip (deep marine)
Subdivisions from biggest to smallest (Rock units)
(1) Group (comprised of several formations)
(2) Formation, the principal unit geologists start
with.
(3) Member (a distinctive subdivision of a
formation)
(4) Bed (thin unit, may not extend through whole
formation, but it is useful for subdividing part of the
formation)
Formation
the principal unit geologists start with.
bed
thin unit, may not extend through whole formation, but it is useful for subdividing part of the formation
group
(comprised of several formations)
Stratigraphic succession (time units)
(1) Era
(2) Period
(3) Epoch
(4) Age
(5) Chron
(6) an interruption in the time dimension is called a
hiatus, which is the time‐dimension equivalent of a
disconformity in the spatial dimension
stratigraphic succession (rock units with time significance)
(1) Erathem
(2) System
(3) Series
(4) Stage
(5) Chronozone (from magneto‐, bio‐, isotope
stratigraphy)
eustasy
Changes in sea level
• Sedimentation in the deep sea is commonly believed to be strongly controlled by eustasy:
• RSL fall and lowstand brings the shoreline close to, or below the shelf break, and provides a mechanism for rapid transfer of sediment to the deep-sea floor
sequence stratigraphy
a science used to subdivide the sedimentary section into chronostratigraphic packages.
A “sequence” is a relatively conformable succession of strata bounded by unconformities.
o Allogenic- external controls on patterns of deposition o Autogenic- controls that operate within depositional env o Eustasy o Subsidence o Sediment supply
sequence boundary -- What happens during SL rise or fall
surface caused by relative sea level fall due to the erosion of the exposed area?
A relative sea-level fall on the order of tens of meters or more will lead to a basinward shift of the shoreline and an associated basinward shift of depositional environments; commonly (but not always) this will be accompanied by subaerial exposure, erosion, and formation of a widespread unconformity known as a sequence boundary
radiometric dating
the source
of the dates on the
Geologic Time
Scale
radioactive decay
Some isotope atoms are not stable and will break up
spontaneously to turn into other more stable elements.
Energetic particles such as photons and protons are
emitted during the process. This is called radioactive
decay. It was discovered in 1896.
geochronology
Placing absolute dates on geological events
gechronometry equation
D* = N(eλt −1)
D = D0 + N (eλt − 1)
radioactive nucleotide(N) remaining at time t
D is the total number of radiogenic daughters,
D* is the number of radiogenic daughters present due to decay of parent
D0 is the number of radiogenic daughters in the rock at the time of its formation
To date a rock using radioactive decay, we must therefore know...
D, D0, N and λ.
D, N - measured by analysis using a mass spectrometer
λ - a constant, usually known
Carbon 14
o Half life =5,730 (5,730 only ½ is left) o 14N + neutron à 14C+1H o 14C produced in atm and incorporated into C02
14C in animals
§ CO2 is absorbed into plants during photosynthesis—they take on the 14C of atm · Animals take it up, so now they have 14C, exists in steady state. o Rate of production (cosmic)= rate of decay o As long as animal is alive it is equilibrium with atm · If something stops exchanging C, that 14C begins to decay
DeVries effect
Variations in 14C production rate
- fluctuations in cosmic-ray flux
- changes in magnetic field
Seuss Effect
Addition of fossil fuels adds dead carbon (12C) making ratio (14/12) smaller—so when we try to date it, things seem older
atomic bomb
o Atomic bomb added 14C making ratio larger— so animals appear younger
Ratio between stable 12C and unstable 14C allows us to date. how
o Animals dies, ratio is uneven—can look at whats left and the rate decay to see when it was last stable to tell age
8. Marine depositional system
§ Shallow/nearshore · Tide dominated · Wave dominated · Reef · AS during rise reduces sed supply to slope and deep sea § Shelf/platform · Carbonate · Clastic § Deep marine · Deep seafans · pelagic · RSL fall brings shoreline below shelf break and provides mechanism for sed to reach the deep sea. o RSL fall is associated with coarse grained sed flow, where turbidite flow follows out to sea
9. how do we use sequence stratigraphy to determine sealevel change
transgression, regression
sequence stratigraphy
facies migrate laterally with sea level change
10. how do we illustrate stratigraphy
stratigraphic columns
cross sections
geologic maps
11. primary objectives of stratigraphy
1- seds and sed rocks are the primary record of Es env
2- the goal is to place sequence of rock into time framework
how placed in time framework
establish which was deposited first
correlate one section to another
correlate age from type section (ex fossils from one type sec, fossils in another type sec would be from same time)
12. three types of stratigraphic units
?time units
rock-time units
lithostratigraphic units (formations members bed)
--or--
rock type, age, fossils?
*14. how is 14C produced into atm and what does it decay into
in upper atm, 14N gets an extra neutron yielding 14C +p
14N +n --> 14C + p
Decays into 14N as beta decay?
16. diff bet calendar and uncalibrated 14C year
<100 years in stagnant subtrop
>1000 years in mid depth pac
eustatic sea level change
vertical movement of ocean surface relative to center of earth
relative sea level change
vertical movement relattive to a moving datum
freeboard
long term mean height of land relative to sealevel
currently 800m
regional sea level change
aka tectonic
transgressions and regression are only on one shelf
produced by regional sinking or uplift (isostatic rebound- lithosphere rises to find equilibrium in absense of glacial load, drop in sealevel)
albedo
heat reflecting back to space
inc SL, inc water, inc sun is absorbed, so inc T of water, so inc SL
positive feedback
onlap
initially horizontal or inclined stratum terminates against a surface of greater inclination
dip of the underlying horizon is greater than that of the
terminating reflections – may be marine or non-marine
downlap
initially inclinded stratum terminates downdip against an initally horizontal or inclined surface
relatively steeply inclined strata terminate downdip
against an older surface, which may be horizontal or shallowly
inclined – almost always indicates a marine setting
toplap
termination of inclined stratum against an overlying,
lower angle surface. Sediments bypass the zone of toplap to be
deposited further basinward . Toplap is evidence of a
nondepositional hiatus.
rain out effect of oxygen isotopes
type of isotope fractionation
16O is lighter than 18O and 16H evaps easier than 18H
16H evaoporates from tropics, get transported to poles
18H more likely to get rained out
so the atm gets richer in the lighter 16O, and ocean gets richer in heavier 18O
as ocean T decreases, what happens to oxygen isotope
18O ratio increases (more 18 less 16) making the ratio more positive
*heavier isotopes concentrate where..
the bonds are strongest
ex: when mineral forms in water, heavier isotope will go the mineral
*vital isotope effects
calcareous orgs do not precip their shells in oxygen isotope equilibrium with seawater = disequilibrium precipitation
these orgs display vital effects-- ex: incorporating metabolically produced CO2 through respiration
isotope
element that has extra neutrons affecting the mass of the element
glacial scenario in 18O change
-low SL with lots of ice storing 16O, so seawater contains more 18O
-proortion in seawater is <16,>18
-this proportion is reflected in calcareous (forams) orgs, have more 18 in shells
interglacial scenario
-high SL, less ice, so less storage of 16O so 16O goes into water
-proportion in seawater is >16, <18
- orgs incorporate more 16 in shells
last glacial max
SL rises 120m , 21,000 ybp
if remaining glaciers melt
SL rise another 60m
18. four most important known mechanisms for changing global sealevel? How do these processes affect sea level
1. Tectonic- crust formation- spreading of/ creation of midocean ridge
2. Amount of cont margins- forming and breaking up of continents
3. changes in sea water temp- causes thermal expansion/ contraction
4. Climate- continental ice caps
updip
parallel to or in the direction of the dip up in bed near continent??
slow spreading ridge has inc/dec SL
dec
oceanic crusts cools and contracts, SL drops
fast spreading ridge has inc/dec SL
inc
more hot buoyant crust occupies more space, water is displaced, SL rises
more ice increases/ decrease SL . Rate?
decreases SL
water is taken from ocean and deposited into ice, so SL drops
100m SL change over 100Ka
breaking up of cont inc/dec SL
increases SL
more continents=more continental margins so SL rises bcz of displacement
pangea has inc/dec SL
dec SL
warming of ocean inc/dec SL
inc SL= thermal expansion
regionally, how does ice affect SL
ice pushes down lithosphere, so SL seems to rise
when the ice melts, lith comes back up and SL falls
Inc SL, (inc/dec) transfer of sed to deep ocean
dec bcz submerged shelves trap seds
22. How can the volume of ocean basin change?
- spreading rates
-fast- higher ridge, more volume, inc SL
-slow- lower ride, less vol, dec SL
-ice volume
25. how can we infer SL history based on 18O in forams
calcium carbonate contains 16O and 18O
changes in compostition results from ice volume changes (more ice, more 18 in ocean) and ocean Temp (warmer ocean, less 18, ratio smaller)
so 18O tells us about changes occuring at time (light isotope removed during ice age so 18O more positive and recorded in orgs developing during that time)
26. correct for ice vol effect when deciphering SL
10m change in SL produces 0.1 permil change in 18O of benthic forams
27.. how much temp change for 1 permil. sealevel?
-4-5 degrees C = 1permil
-10m SL= 0.1 permil (100m SL = 1permil)
28. SL stand at LGM? Salinity? 13O? Temp of tropics and poles
-SL +120m
- salinity= 1 in glaciers, 0.5 accounted for in rising temp-- 1
relationship between fractionation and temp
inverse relationship
as temp increases, fractionation decreases
29. how fast is SL rising now?
1degree C= 0.8m rise in SL
due to thermal expansion
6000 years, sealevel rising 2mm per year???
30. how do we measure SL
measured as relative changes to reference datum such as fixed (center of earth) or local (coastline.)
seismic stratigraphy
another branch of stratig to determine rock types/characteristics
chemo
chemical comp of rocks
downdip
pertaining to the positon parallel to or in teh direction of the dip of bed in deep ocean
14C age vs calendar age
calendar age is absoute age
14C is not always at equilirbium in atm, but not always exact bcz of stuff going on in atm
*marine resevoir effect
-less 14C in ocean than air.
- becuase there is less in ocean its going appear OLDER. (larger ratio 14/12 less decay has happened, so ocean is younger)
-the ocean and air are not at equlibrium!!!
chronostratigraphic chart
chart shows time and rock layers
how layers show time
biomarker
specific species with known chemical or physical growth requirments
can be organic molecules
Proxies in paleoceanography
Biomarkers
Radioactive decay dating techniques (ex: 14C ratio)
Stable isotopes (18O, 13C, 15N)
other chemical ratios indicators (Sr/Ca, Cd/Ca, Ba/Ca)
31. how can delC13DIC be used to trace carbon transfer between surface ocean and deep ocean
- photosynthetic rate- sets delC13 and nutrient level in the surface ocean. As water is downwelled, it carries the signals with it.
- These factors can produce regional differences inthe δ13CDIC. (-Deep waters in different ocean basins. – Monitors changes in deep water circulation with
time
31. cont. : Atlantic Deep water delC13
deep water formed in N. ATL have HIGH delC13 values, and LOW nutrient conc (bcz photosynthesis using up all nuts).
32. how del13Cdic changes along conveyor belt
- deep water formed in the n atl has high del13Cdic because there are limited nutrients
as it moves along the conveyor belt
intermediate waters formed in the S ocean have--
low del13C and high nutrients (high nuts=incomplete photosynthesis)
As organic carbon is used up (oxidized) what happens to delC13DIC
it is lowered bcz 12C rich CO2 is released which lowers del13Cdic (ages it)
- this is an example of what happens in the deep pacific
33.How do we use del13Cdic to illustrate past ocean circ
Strong evidence for anoxic warm deep sea during the cretaceous
• Deep ocean temperature ~15 degrees C (inc T, inc photosythesis, increases org mat, which makes less del13Cdic?)
– O2 less soluble
– Circulation much slower
– Warm earth and warm polar seas
oxidation makes del13Cdic (pos/neg)
neg
What does the Pac show in del13Cdic
more neg because it is older so it is accumulating CO2 (by traveling long distance) from the oxidation of org making it more neg.
oxidation of organic makes inc/dec del13Cdic
decreased
34. How does burial and weather affect del13Cdic. (on land)
- when the burial rate= weathering rate, the atm has stable isotope ratio.
- when burial rate > weathering rate, the heavier isotope is left in the atm
34. How does burial and weather affect del13Cdic. (in ocean)
- in oxygenated deep water, carbon isotopes are in balance. there is little burial, so decoposition--> isotopically light CO2--> phytoplankton-->isotopically light organic debris.
- in anoxic waters, burial of all the light carbon causes the heavy ones to accumulate in the water so the phytoplankton become rich in carbon 13.
34. continued
Burial of 13C depleted organic matter (anoxic?) leaves remaining DIC enriched in 13C
• Increases in δ13C of marine carbonates indicates an increase in the rate of burial of organic matter in ocean or on land
long story short, burial of ...
the light isotope makes more heavier isotopes (13C) in the surface water (or air)
35. possible causes for OAE in cretaceous
Increasing crust formation
Increasing SL
Increasing Temp
Increasing photosynthesis
Increasing org mat buried
Increasing black shale= ANOXIC so then decreasing del13Cdic?
BLAG hyp
(Berner, Lasaga, and Garrels)
- climate chages over millions of years are due to the rate changes of CO2 input driven by PLATE TECTONICS
- Changes in rates of spreading/subduction change the rate of input of CO2 to atm
slow SS
slow ss--> slow input or CO2--> colder climate--> dec weathering--> dec CO2 removal--> reduced cooling =NEGATIVE FEEDBACK
Fast SS
fast ss--> inc CO2 input--> warmer climate--> inc weathering--> inc CO2 removal--> reduced warming
About this deck
By: Rachel Knapstein
Created: 2010-12-10
Size: 128 flashcards
Views: 122
Created: 2010-12-10
Size: 128 flashcards
Views: 122
About StudyBlue
STUDYBLUE makes things that make you better at school.
Things like online flashcards with photos and audio.
Things like personalized quizzes and friendly reminders about when (and what) to study next.
Think of it as a digital backpack™: access to all of your study materials online and on your phone.
STUDYBLUE exists to make studying efficient and effective for every student, for free. Join us.
“Simply amazing. The flash cards are smooth, there are many different types of studying tools, and there is a great search engine. I praise you on the awesomeness.”
Dennis
Dennis