Final Exam Flashcards
Heinrich Events
Characterized by finding higher percentage of coarse grained material thought to have been transported by ice-rafted debris and deposited when the debris melts
What can Iceberg tracks or striations tell us
How far the ice-bergs got before they melted
What size is an iceberg
>5m across
Bergy bits
5-2m across
Growlers
<2m across
Red beds
hematite-stained grains
from heinrich events
Flux
the rate of flow of a property per unit area
[quantity]*[time]-1*[area]-1
Hardest part of flux is time
Ice-rafted debris in the North Atlantic
appears in marine sediments for several thousand years
events correlated with Greenland ice core
Where they show up is related to currents and rates of calving
Armadas of icebergs
foraminifera as a temperature indicator
left coiling (sinistral) = cold
right coiling (dextral) = warm
distribution also affected by temperature (latitude)
Mg/Ca
based on the idea that Mg is substituted for Ca in foraminifera lattice- reflects temperatures
Higher Mg/Ca ratios correlate with higher calcification temperatures
More Mg = higher temperatures
Oxygen isotopes at equilibrium
depend only on the temperature of precipitation and 18O/16O of the ambient water
Range of foram delta 18O values
0ºC = +4 per mil
20ºC = -2 per mil
colder temps means more positive
Paleo-temperature Equation
T°C = 16.9-4.2*(d18OCaCO3 - d18Owater )+0.1*(d18OCaCO3 - d18Owater )2
This is one of several equations available. Can change per species.
Vienna Standard Mean Ocean Water (VSMOW)
distilled ocean water collected from around the globe
Pee Dee Belemnite (PBD)
Carbonate from a fossil from the Pee Dee formation in South Carolina
CLIMAP
Climate: Long range Investigation Mapping, and Prediction
major project in 70s and 80s to produce map of climate conditions during the last glacial maximum
Most data from atlantic, lacking in Pacific. Not good for global representation.
Surface currents during LGM according to CLIMAP
surface currents were stronger
driven by winds which are dependent on horizontal temperature gradients
ice rim and polar front much closer to equator, temperature difference between ice and tropics was compressed into much shorter distance than present
Steeper temperature gradient = strong winds = stronger ocean currents
Currents during LGM according to CLIMAP
Coastal and equatorial upwelling was intensified
Productivity decreased at high latitudes because of ice cover
Productivity increased at mid latitudes because of intensified mixing
Productivity increased in the subtropics because of upwelling
Tertiary Oxygen Isotope Record
Overall cooling since the Cretaceous- from 18O benthic foram record
MM and EO on graph show what?
about where the cooling periods occurred involving high latitudes and deep ocean water masses
MM = midmiocene
EO = Eocene/oligocene
Cooling steps increase in frequency closer to present
Tertiary period
66Ma- 2.58Ma
Planktonic and Benthic foram records
planktonic is the top, benthic is the bottom
shows separate trends for low latitudes, but similar trends for high latitudes
So- cooling is high latitude and deep water phenomenon
Temperature gradients during Tertiary
increased since Oligocene (30-35mya)
caused stronger winds which increased coastal and equatorial upwelling
Evidence in increasing diatom supply in N Pacific and Antarctic
Ocean Hemisphere Partitioning
Plate tectonics affect configuration and circulation of the oceans
creation and destructions of gateways
Effects of ocean hemisphere partitioning during Tertiary
restriction of Southern Ocean- cold box
Average ocean has to be cold
Deep sea and cold-water fauna become global
Tropical and subtropical fauna become localized (closed off)
Antarctica glaciated
Albedo and ocean hemisphere partitioning
whitening of Antarctic continent
effect of pushing climatic zones northward
Northward movement of large continental masses during tertiary
set up monsoonal regimes favorable for northward heat transfer
himalayas intensified the monsoons
Uplift of Tibet and the Himalayas during the Tertiary
strengthened monsoons and increased weathering helping move heat north
Geographic configuration of Atlantic and Pacific during Tertiary
deflected westward-flowing equatorial currents sending them North strengthening/creating the Gulf Stream and Kuroshio currents
Effect of Panama straights closing during the Tertiary
Before- arid continent
After- warm air could move towards the poles, condense as snowfall feeding land glaciers
Big difference between Pleistoncene and Pliocene in amplitude of ocean temperature
Overall Results of Ocean Hemisphere Partitioning
Southern Hemisphere robbed of heat
Ice age preceeded in Antarctic, not in Northern latitudes
overall cooling
Overall cooling caused Earth to begin what cycles?
glacial/interglacial cycles
What was Earth like when it was warmer?
Stagnant ocean
Organic-rich sediments indicating either high supply or reduced losses b/c of low oxygen content in deep ocean (anoxia)–> Perhaps both
Black Sea and Baltic Sea- Modern Analogs for Tertiary warm period
restricted basins
little estuarine circulation
high supply of OM
How to get “black deposits”
increase productivity while keeping the oxygen supply constant, or decrease the oxygen supply, keeping productivity constant
During the Cretaceous, what was productivity and oxygen like?
No evidence for high productivity
low oxygen supply
Lots of OM deposited
distinct positive delta C-13 excursions
The continental shelf
Shallow, submerged extension of the continent
Extends from shoreface toe to shelf break
Sea level fluctations and the continental shelf
sometimes shelf is dry land
What dominates today doesn’t mean it dominated in the past
What processes impact the shelf during a sea-level cycle?
Erosion
Types of erosion on the continental shelf
Subaerial erosion (shelf exposed, rivers)
wave erosion- transgressive and regressive ravinements
Current erosions- deep sea currents, tides, storms
Two primary shelf classifications
Supply dominated
Accomodation dominated
(Interplay between water depth and sediments)
Progradational shelves
Sediment supply > rate of accomodation creation
Supply dominated shelf
Regressive sequence
Transgression
Sediment supply < Rate of accomodation creation
Accomodation dominated shelf
Little preservation of deposition
Subclassifications for shelves
Tide
Storm
Wave
Ocean-current
Classifying shelves based on hydraulic regime (qualitative)
Percentage of each subcategory of shelf dominated regimes
80% by storm waves
17% by tidal currents
3% by ocean currents
Examples of ocean current dominated shelves
Pennell coast- Antarctica
Campos margin- Brazil
South Africa margin (Agulhas Current)
Palimpsest shelf sediment
reworked older sediment, not new seds
align subparallel with tidal currents (example in North Sea)
Examples of Tide Dominated Shelves
North Sea, Celtic Sea, Georges Bank, East China Sea
What is a major feature on tide dominated shelves?
Tidal sand ridges
Dunes migrate
ridges on top of ridges
Wave and storm dominated shelves
longshore transport
Huthnance model for sand ridge formation
initial protruberance grows upwards then outwards
Then it migrates across the shelf
start with a bathymetric high, creates a pressure gradient and spurs deposition
Where did the term “delta” come from?
The Nile delta was triangular- looked like a delta
Types of Rivers
Meandering
Braided
Enastomosing
Straight
Anastamosing river
meandering on steriods
very sinuous
What does a dam do to a stream profile
causes a notch- upstream deposition, downstream erosion
What happens when you expose the continental shelf
rivers incise and deposit more to the deep sea
Braided Rivers
high gradient
large sediment load
small channel capacity
forms moving islands or bars
Meandering rivers
low gradient
humid areas
low sediment supply
large channel capacity
lots of vegetation in flood plain, stabilizes
Helicoidal flow
flow isn’t just straight downriver
think of Tony’s corkscrew dance
areas of maximum velocity shift from side to side
Homopycnal flow
river and basin water have same densities
rapid deposition of sediment load
forms a channel mouth bar
commonly found in rivers discharging into lakes
lobate and symetrical
Hypopycnal flow
River is less dense so it floats on top
can extend plume much farther offshore
delta is more spread out
river influence extends into deeper water
clays settle out futher into the bay (flocculation)
Hyperpycnal flow
Density of river water is greater than basin water
could be colder or heavy in sediments
plume hugs the bottom, carrys far, clear water on top
nepheloid layer (created at flood stage of a river, high seds)
Flocculation
clay-particle aggregation
physio-chemical processes: electrostatic force
clays are negatively charged, attracted to salts in seawater, flock together
Tides enhance process
wave dominated deltas
Ex: Nile
wings on either side of the delta
Waves breaking on muddy plume, not shallow topography
bar welds to shore creating beach ridges
In a wave dominated delta, what do beach ridges indicate?
Severe floods, not necessarily sea level fall
Tide-dominated deltas characterized by
tidal sand bodies along direction of tidal flow
shoreline has perpendicular sand bars and distributary channels that don’t link b/c they’re tidal channels- perpendicular channel mouth bars
These channels only carry water during flood stage
River dominated deltas
ex: Mississippi
long distributary channels extending seaward
large sediment supply
channels get choked on mouth bar and bifurcates
Lobes
delta lobe shifting
river shifts - avulsion - caused by flooding events and lack of accommodation space
waves rework front as the delta subsides
destructive process
- Reoccupation (form delta front)
- Abandonment (bay)
- Subsidence (lagoon to shallow marine)
how many orders of branching have been identified in the Mississippi River Delta?
at least 3
What percent of sediment discharge makes it to the Bengal Fan?
30%
How fast is the Ganges delta foreset advancing seaward?
50 meters/year
Dual clinoforms are present where?
large rivers discharge onto an energetic marine shelf
subaerial and subaqueous regions
Where are estuaries prevalent?
Along passive margins
What are 4 important considerations when talking about estuaries?
Sea level
coastal morphology
continental shelf morphology
tectonics
Definition of an estuary?
“a semi-enclosed coastal body of brackish water with one or more rivers or streams flowing into it and with a free connection to the open sea” (Pritchard, 1967)
What does the Pritchard 1967 definition of an estuary include (types of estuaries)?
drowned river mouth estuaries,
bar-built estuaries,
deltas,
tectonic estuaries,
fjords
definition and examples of drowned river mouth estuaries
It is what it is
galveston bay, north carolina
Bar-built estuary definition and examples
Bogue and Core sounds
oriented parallel to coast and have no major rivers discharging into them
estuarine component of Deltas
inter-distributary bay (like Barataria Bay, LA)
tectonic estuary
found along fault lines
Many of them are really drowned river mouth estuaries, but tectonics drives the drainage basin
Lots of mini basins, oddly shaped
Fjords
has brackish water
glacial feature
What is the Pritchard 1967 definition of an estuary based on?
Salinity
Very oceanographic
What is Dalrymple 2006 definition of an estuary?
“a transgressive coastal environment at the mouth of a river, that receives sediment from both fluvial and marine sources, and that contains facies influenced by tide, wave, and fluvial processes. The estuary is considered to extend from the landward limit of tidal facies at its head to the seaward limit of coastal facies at its mouth”
What is estuarine formation intimately tied to?
Sea level fluctuations
drives valley incisions
In estuarine formation, what does sea level fall, drainage basin, and maring morphology drive?
valley incision
That valley inundates during sea level rise to form estuaries
Stream power
increases across break in slope
Ω=ρgQS
Ω= Stream Power
ρ = density of water (1000 kg/m3)
g= acceleration due to gravity (9.8 m/s2)
Q= discharge (m3/s)
S= channel slope
Wave dominated estuaries
High energy at the mouth and head of the estuary
Width increases in middle bay
Barrier islands at mouth with inlet
Tide dominated estuaries
Missing middle bay and barrier island complex
Now you have sandbars perpendicular to shoreline
Generally have extensive salt marsh
Bayhead deltas
the landward side of estuaries
(Eg Roanoke)
Forcing mechanisms of change in estuarine evolution
Sediment accomodation
Sediment accumulation
Sediment accomodation
the space available for sediments to accumulate
aka base level
allogenic
external environment, global
ex: sea level rise, tectonics
autogenic
intrinsic, localized
ex: topography of land being inundatd, sediment compaction
Relationship between sea level rise and accomodation space
Can have steady sea level rise, but episodic changes in sea level because of accomodation space
Sediment accumulation
volume of sediment filling accomodation
What does sediment accumulation depend on?
sediment flux and sequestration
sediment flux
the amount of sediment delivered to the estuary over time
sources of sediment
fluvial
marine
bay-shore erosion
How do changes in climate and sea level impact sediment flux?
vegetation and discharge
storm frequency and magnitude
where sediments are deposited
Sediment sequestration
the ability of the estuary to trap sediments
How do climate and sea level affect sediment sequestration?
Storm frequency and magnitude
tidal inlet dynamics- number of inlets and tidal amplitude
barrier width
how does wave base modulate sedimentation rates in estuaries?
High tide, high wave base, large accomodation space
How does the shape of the estuary affect sedimentation rates
wider and deeper- more fetch, higher energy
Drainage basin characteristics
Interfluves
Drainage divide
Valley
Outflow has to do with precipitation, size of watershed, and climate
Deposition of sediments at river mouth
Larger settle out first
form a channel mouth bar, part of the delta front
friction dominated
Prodelta
composed mostly of silts and clays
below and basinward of delta front
Ages of Mississippi River lobes
Oldest lobe formed 7500 years ago
Newest is 1000 years old
Landscape topography and accommodation space
V-shaped - flat with steep sides; accommodation space creation almost linear with SLR
Flat - gets inundated quickly; creates accommodation space immediately
Terraced - slow beginning for accommodation space, floods one part then increases space quickly, then slows back down as upper part floods
Parts of a beach
Foreshore, backshore, dunes, berms, high intertidal, middle intertidal, low intertidal, and subtidal
Tributary Junctions
Width of tributaries equals the width of the secondary channel
Promote stabilization of estuaries because gradients increase in a non-linear way
What is a barrier island?
A narrow, elongate sand ridge rising slightly above the high-tide level and extending generally parallel with the shore, but separated from it by a lagoon, estuary, or marsh (Shepard, 1952)
theories of formation all include sea level rise
Strandplain Shoreline
Open ocean shoreline lacking a marsh or lagoon between it and the mainland. Commonly defined by beach ridges.
Chenier Plain
A strand plain with mudflats between the beach ridges. The ridges are trangressive, but the mudflats are regressive.
Shoreline processes
Tides
waves
currents
wind
Tides review
Response to gravitation of moon and sun
twice daily
Flood = rising
Ebb = falling
Dominated by moon
Affected by continents and shoreline configurations
Lunar tide
moon revolves around earth every 28 days
24:50 cycle
Spring tides
when sun and moon are aligned every two weeks
20% higher than average
Neap tides
when sun and moon are at right angle to each other
20% lower than average
Causes of wave generation
displacement by landslides, seafloor faulting, volcanoes
wind (velocity, fetch, duration)
Wave base
the depth the waves first are influenced by the bottom = L/2
Shoaling waves
wave height increases
wave length decreases
waves change direction due to refraction
Types of wave breaks
Surging
plunging
spilling
collapsing
Surging breakers
happen on steep slopes, wave doesn’t actually break, rolls onto steep beach, destructive
Plunging breakers
Happen on moderately steep beaches, normally curls over a tunnel until wave breaks, surfer waves.
Spilling breakers
occur on gentle slopes, break far from shore, surf gently rolls over the front of the wave
Beach morphology
not just a product of the waves interacting with the sand, underlying geology is important (outcrops, scarps)
Longshore currents
result from waves striking the shoreline at an angle
slow parallel to shoreline
transport and deposit large quantities of sand in the nearshore
Wave refraction
the bending of waves so that they more nearly parallel the shoreline
Longshore drift
the movement of sand along a shoreline by longshore currents
primary mechanism for distributing sand along a shoreline
Rip currents
narrow surface currents that flow out to sea through the breaker zone
mechanism for returning water that has built up in the breaker zone back out to sea.
waves approach parallel to shore
Types of barrier islands
attached
wave-dominated
mixed-energy
(no tide-dominated exist)
Wave-dominated barrier islands
long and narrow with few inlets
washover fans are common
inlets are unstable, have small or no ebb-delta, large flood deltas
Mixed-energy barrier islands
“drumstick barrier”
dominant longshore sediment transport
sediment transport reversal
Barrier classifications based on evolution
Transgressive
progradational (regressive)
aggradational
Delta morphologies
Theories on barrier island origin
buildup of an offshore bar
longshore transport, spit elongation, inlet breaching
drowning of coast-parallel antecedent topography
initiated on shelf, migrated landward, presently cut-off from origins
Attached barrier islands
Spit accretion
Barrier evolution
Sea-level rise and sediment supply are not the only forcing mechanisms
also storm climate, geologic framework, anthropogenic influence
stratigraphy of a beach ridge
Equilibrium Shoreface model
h = Ay2/3
h = water depth
A = scaling parameter based on sediment characteristics
y = distance offshore
Brunn Rule
Assumes that with a rise in sea level, the equilibrium profile of the beach and shallow offshore moves upward and landward.
R = S[L/(B+h)] = (S)1/tanØ
R = Recession
S = Sea level rise
B = berm height
Ø = active profile slope
h = depth of active profile base
L = width of active profile
Brunn Rule part 2
the upper beach is eroded due to landward translation of the profile
material eroded from the upper beach is transported immediately into the offshore and deposited (equal volumes, conservation of mass)
the rise in the nearshore bottom is equal to the rise in sea level, thus maintaining a constant water depth in the offshore
Response to sea level rise is instantaneous
Successive shoreface profiles
What is the preservation potential of shoreline deposits with sea level rise?
Movement of sediment from shoreline to inner shelf implies there is no preservation
may be preserved in deep facies, look at sediment type down core, indicates environment
CVI
Coastal Vulnerability Index
V Datum tool
Can look at maps and switch between MLLW and NAD83 elevation models
Rip-rap revetment
OGZ
Optimal growth zone
Oysters have to be in and our of tidal range
20-40% aerial exposure for a growing reef
Connection between wave climate and beach morphology
Ways to engineer the coast
Build hard structures (groins, jetties, seawalls)
beach nourishment
Groins
Groins are shorter and typically built in the middle of a beach
meant to be buried and bypassed by sand
Jetties
Built to protect waterways
Beach nourishment
important to consider compatible sand for wildlife and preservation of beach
Breakwaters
Tires make bad breakwaters
Geotubes
Large “soft” structures to protect against flooding and storm surges
filled with sand
Rate of sea-level rise and preservation potential
Depends on slope of beach
In figure, the lower photo has a higher rate of sea level rise, even though Za=Zb
Over time the upper figure will be impacted by storm waves because of longer exposure = lower preservation potential
THE HIGHER THE RATE OF SLR THE GREATER THE PRESERVATION POTENTIAL
Preservation can be enhanced by sediment lithification or diagenesis
How is preservation potential affected by gradient?
The lower the gradient, the higher the preservation potential
How is preservation potential affected by the rate of sea level rise?
Higher rate of sea level rise, the higher the preservation potential
Two ways to change the properties of sediment to make the shoreline more durable
lithification
digenesis
What does lithification do for the preservation of a shoreline?
Increases preservation
Impact of storms on barrier islands
Very important!! Will probably be on exam!
Waves and wave reworking needs to be factored in
You never return to inital state
Dynamic equilibrium
Overwash and shoreface fluxes sufficiently high and equivalent to maintain morphology of barrier during landward migration
SLR leads to increase in overwash flux
As barrier narrows, overwash flux increases
Height drowning
When overwash fluxes can’t maintain landward migration rate required to keep pace with SLR, barrier drowns, even though it maintains width
Width drowning
When onshore sediment transport is insufficient to maintain barrier geometry during landward migration
rate of shoreline migration exceeds dynamic equilibrium
Discontinuous retreat
Barrier undergoes rapid transgression and experiences large rates of overwash
Onshore fluxes from shoreface toe can’t compensate for overwash fluxes, barrier narrows as shoreface flattens
shoreface slope gets flat so barrier width increases
barrier widens to critical value and overwash flux to back-barrier shuts down
barrier stops landward migration - aggradational phase begins
Close to what’s happening in reality
Movement pauses, jumps landward, grows upward during pause, jumps again, etc. (has a recovery period)
What was the large-scale inlet activity during MWP and LIA due to?
increased hurricane activity and nor’easter’s
Washover fan stratigraphy
Fans continue to evolve long after storm subsides
When did most of the inlets of NC close?
over the last 300 years bceause of a more stable climate
Ripple scour depression
Sediment starved
Found along North Carolina coast
Gravel and Sand depressions
not good for beach nourishments
Common on storm dominated shelves
