Geology Exam 2
where are there high nutrients but low chlorophyll concentrations why would this happen
20 % of the world's ocean North Pacific Equatorial Pacific Southern Ocean too far from land
continental slope depth
200 to 3000 m water depth; gradient 4o (up to 90o
what are borings
Benthic organisms burrow downwards through rock. Organisms do not coincide with time of deposition.
describe turbidites
Fining-upwards succession ('Bouma Sequence'). Event deposits. - Originating from turbidity currents. Sharp lower boundary. Gradual return to 'normal'.
what are physical sedimentary structures
Formed by abiotic physical processes
what are biogenic sedimentary structures
Formed by physical/chemical activities of organisms
what are concretions
Hard features forming before lithification. Slow chemical changescementation. - Cement often calcite or siderite • Many form around a nucleus (particle in center). - can be a fossil • Consists of material delivered by the surrounding sediment!
why should we care about river deltas?
Human societies ecologic diversity carbon cycle
what are hydrogenous sediments
Hydrogenous authigenic, precipitated from seawater economically important
what is a turbidite current
a suspended layer needing a trigger to occur (storm or SL increase)
What is anastomosing
different patters forming from many rivers
where are the wave dominated shelves
southern ocean; wind is more common since there are no continents in the way
describe bedforms
Interface between fluid and moveable bed. Can infer flow depth, paleo-direction, and current strength. Can also be load structures.
Define stagnation
state of being inactive and not moving or changing
what causes a stronger contour current
steep slope
how do cuspate deltas form
strong wave influence
what is a popular example of cosmogenic sediments
KT boundary
what happens when continental shelves are widely exposed?
submarine canyons are cut and fluvial sediments more directly transported to deep ocean
what are turbidite beds
suspension clouds above sea bed
what determines the thickness of the cont self
tectonics dust deposits trade wind system
what is Estuarine Turbidity Maximum (ETM)?
Location of maximum suspended sediment concentration.
what is a primary sedimentary structure
Mechanical structures formed during the deposition of sediments (syn-depositional)
where are we trying crevasse splays approach?
Mississippi delta
what is the biggest delta
Mississippi i
what nutrients are important
N, P
4 types of sediment classes
terrigenous/Clastic Biogenic Hydrogenous Cosmogenic
describe water escape structure
Overburden weight lead to upward directed de-watering. Fluidization of either sand or mud beds. 'Chimneys' penetrating overlying beds.
what is the closest delta
Santee delta
what are cross beds
Sets of beds that are inclined relative to each other.
describe a bird foot delta
Widely spaced distributary lobes resulting in a claw like structure -RARE
what are turbidity currents
a rapid, downslope flows of water caused by high density due to a high suspension load.
what do carbonates tell us
a record of life and sea level, a record of ocean chemistry, insight into other planets, source of metals and hydrocarbons
describe cosmogenic sediments
• Permanent rain of cosmic dust. • Or... extra-terrestrial impact: rare, chemically unique stratigraphically important
what are terrigenous sediments made up of
• Siliciclastic grains + organic material + ferro-manganese crusts... • Detrital clay minerals, quartz, feldspars, ash...
how are burrows formed
•Benthic organisms burrow downwards through unconsolidated material.
describe bottom turbidity layer
➢Land-originating mud. ➢Suspended mud layer. ➢Suspension density controls where the layers will detach from the seabed.
accumulation rates calcareous ooze vs silicious ooze
calcareous is high accumulation in upwelling regoins
foraminifera
calcite tests, single celled ZOO PLANKTON
What forms lamination
- Pulse-like variations in sediment supply. • Tidal regime / Seasonal lake deposition / fluvial runoff changes. - Absence of bioturbation due to: • Either a very high sedimentation rate. • No oxygen available.
What does this mean for carbon sequestration?
-10 % of the marine carbon leaves the coastal ocean. -1 % of the marine carbon deposits permanently.
continental shelf depth
1 to ~140 m water depth; gradient <0.05o; average width ~78 km
threats to river deltas
1. Upstream river damming → Sediment retention 2. River embankment→ Reduction of flooding → Subsidence acceleration 3. Groundwater pumping 4. Land conversion 5. Sea level rise → Coastal erosion
downside of ocean iron fertilization
10 % of the emissions, 10 % of the ocean surface needed
Which of the following is not a problem associated with development in delta regions? 1) Flooding. 2) Nutrient-poor soils. 3) River channel avulsion. 4) Subsidence. 5) Salt intrusion. 6) Storm surges.
2) Nutrient-poor soils.
continental rise depth
3000 to 4000 m water depth; gradient: gentle and decreasing
What is lamination?
<1 cm beds of rich, organic material found in deep ocean
bottom boundary layer
= bottom nephdloid layer = bottom turbidity layer contains lots of suspended sediment
Describe graded bedding
As velocity decreases, large/dense particles settle first. Decrease in grain size from bottom of bed to top of bed.
why should we study the deep ocean
CO2 budget, Advancing energy extraction technology.
describe hydrogenous sediments
Clay minerals, cements - more volume; chemically important Often formed during diagenesis
where are we trying channelization?
Danube delta
how do contour drift deposits look?
Either as mounting elongated sandy deposits. Or as mud deposits covering very large area on the abyssal plain. (mountain or flat)
what causes the formation of turbidity currents
Pressure changes within the sediment (storms, sea level, earthquakes) Slope failures; fluidization of internal weak horizons
Types of sedimentary structures
Primary secondary physical biogenic
what are mud cracks
Reduction in water contentcontraction. Exposed/at surface shortly after deposition. Curl up = can indicate original orientation.
what are secondary structures
Structures formed after deposition (post-depositional)
why is the CCD higher in the pacific compared to Atlantic
The Pacific Ocean water is colder than the Atlantic Ocean water due to the global thermohaline circulation patterns
bounce marks
The tool approaches the sediment surface at a low angle and immediately bounces back into current
roll marks
The tool rolls over the sediment surface, producing a continuous roll mark
skip marks
The tool travels down current with a saltating movement, hitting the sediment surface at nearly regular intervals
What are turbidites and how do they form?
Turbidites are deep ocean sediments formed from the build up in the continental rise with mostly terrigenous sediments
what are flute casts
Turbulent currents scour the bottom and excavate tapered depressions = Erosion. • Typicallytear-dropshaped. • Tapered end points down stream. - Paleo-current indicators! circular shape
which of the following is not a major challenge faced by deltas in the next century a. increasing sediment supply b. rising SL c. development pressure d. river management
a. increasing sediment supply
why is our sediment distribution the way it is
above the lysocline Is carbonates so it is very productive
what does syndepositional mean
as it is depositing
beds become ____ towards lower boundaries
asymptotic
where are we trying the internal sub deltas approach?
atcbafalaya basin
what are the two carbon sources
atmospheric CO2 and biogeneous shells, test. limestone
where are cross beds common
beach deposits, sand dunes, river beds, tidal deltas
what results from wave dominated river deltas
beach ridges and spits
How are cross beds formed?
bedlam transport; sand moves along an eroded surface creating layers
example of carbonates
biogenous- cretaceous coccoliths
what shape of delta is the Mississippi delta
bird foot
3 shapes of river deltaa
bird foot arcuate cuspate
what happens below lysocline?
carbonate corrodes
how does turbidity maximum position change?
changes with tide cycle and water discharge
another name for turbidites
channel levee system
continental shelf sediment sources
clastic; Brought in, pre existing siliclastic vs carboclastic biogenous; produced in the ocean, silicious vs carbonaceous authigenic; formed post depositional (pyrite, phosphorite, evaporites)
are contourites fining or coarsening upwad
coarsening
what is reverse bedding
coarsening upward
what happens when we dam deltas?
conflict is created; interrupt sediment supply and they drown
where do continental rise sediments come from?
continental slope and submarine canyons
3 types of clastic deep sea deposits
contourites pelagite turbidite
what does the continental rise form?
create deep sea fans
what is herring bone cross bedding?
current changes direction through time
how do we fix delta flow?
cutting new channels, breaking banks to build crevasses, constructing small internal deltas in lakes and lagoons, or creating new larger lobes in areas protected from waves and tides
where are contourite drifts located
deep ocean; runs parallel to continental slope
describe turbidite systems
deep sea channel systems connected to continental slope canyons; leads into fine grained deep sea fans
difference between delta plane and mega delta plane
delta: 10 mi wide mega delta: 100-150 mi wide
what are turbidites
depositional beds resulting from turbidity currents
how is sediment supply transported
energy tidal forces (type of gradient; steep or shallow) sediment type size of deposit mouth
what might be an appropriate solution to prevent the agricultural land from flooding and address the same subsidence issue at the same time?
engineers cut into the embankment, and the river flows into a depression inside a polder called a beel. sediment is scoured from the river and deposited in the beel or washed downstream opening the river channel and raising the polders land
are boundaries erosional or depositional
erosional = time gap
how do you classify river deltas
estuarine coastline: low sediment supply deltaic coastlines: high sediment supply
What are cosmogenous sediments?
extraterrestrial origin stratigraphically important
true or false: the coastline supply to ocean is indirect
false; it is very direct
are turbidites fining or coursing upward
fining
are turbidites fining upward or coursing upward
fining upward
how do deltas keep up with rising SL
flooding; crevasse splays create layers on top of layers
where is flaser bedding common
floor/ebb currents
what current is associated with countourite current
geostrophic current
what are contourite drifts
geostrophic currents within water masses; long lasting
The Hjulstrom diagram shows the relationship between
grain size of transported sediment and water velocity
how does turbidity sediment move offshore
gravity with the gradient
what influences all types of sediments @ earth's surface?
gravity, life, climate
what results from tide dominated delta
great tidal range (200 m or so), reverse water flow, periods of stagnation, elongated bars
how has sediment supply increased
increased by 467% from anthropogenic soil erosion, construction activities, mineral mining
What is hummocky cross stratification?
indicator for storm deposits; goes up and down
difference between gradient size in delta front and pro delta
it is coursening upward; delta front is sandy, pro delta is silt and clay
what makes Mississippi delta fascinating
its a mega delta but has a small bottleneck
memorize CO2 buffer chart
kms
how do sandy bedforms with high sand supply look?
lots of sediment available, sand waves and sand banks
what are the units for river discharge
m^3/s
what occurs in the continental rise during SL low stand?
major sink of terrigenous sediment (receives more than it provides)
what are biogenic sediments
marine organism remains spatially important
how do we count phytoplankton cocentration
measuring chlorophyll concentration in the water column
how do river dominated deltas look
minor tidal influence with well defined levees and overbank areas - sediment building on levees create thin strips of land either side of the main channel
what is lenticular bedding
more mud present (calmer environment)
older water means what in terms of nutrients
more nutrients
What is flaser bedding?
more sand present; higher energy and more currents
what are depositional fans bordered with
natural levees
where are tide dominated continental shelves
near large ocean basins
what are bedforms
non depositional structures that preserve history
what causes a rise in the CCD/carbonate compensation depth?
ocean acidifies, carbonate levels drop
are we on a passive or active margin
passive
Coccolithophores
phytoplankton with calcareous plates SINGLE CELLED
what is primary productivity based of
phytoplanton
how do terrigenous sediments enter the ocean (2 main ways)
point source (rivers/fluvial input) dust input (africa)
describe a cuspate delta
pointy (tiber river delta in Italy)
are concretions post depositional or syndepositional
post depositional
what does coarsening upward mean
progradation or drop in SL
are bedforms progradational or retrogradational
progradational
most shelf sediments are..
relict deposits- older than holocene
what happens as global warming increases
river damming and riverbed mining decreases
what is sediment supply dependent on
river discharge
what is type of delta is the Mississippi River delta (___ dominated)
river dominated
what is dominant in a bird foot delta
river sediment supply
what is the nepheloid Layer
river sediment that goes into the ocean and can be surface, intermediate, or bottom depending on density. continuously occurs like a conveyor belt
How big are foraminiferans?
sand sized
what is dominant in an arcuate delta
sediment supply mixed with tides waves and ocean
what is bjerrum plot
shows buffering vs acidification
How big are coccolithophores?
silt size
memorize chart on sediment structures
slide right before fossil tracks
how does fine grain material transport
they cluster together (flocculation) which may eventually grow and break apart (occurs over and over)
where can we find carbonates
• Pelagic carbonates • Deep water mud-mounds • Cool-water carbonates • Terrestrial & Lacustrine • Soils • Travertine • Reefs
how do sediments lay on storm dominated clastic shelves
they fine offshore - Foreshore facies: sandy, shell fragments - Shore facies: sandy mud/muddy sand, bioturbated - Offshore facies: muddy deposits with well preserved organics
where do you find herring bone cross bedding?
tidal environment onlu
What is the dominant process controlling the shape of the Ganges River Delta coastline?
tides
brush marks
tool approaches sediment surface at very low angle
prod marks
tools reaching the sediment at a high angle
what does fining upward mean
transgression OR turbidite beds
what does detrital mean
transported by water
Describe an arcuate delta
triangular
what river basins make up the Mississippi River delta
upper Mississippi River basin, Ohio river basin, lower Mississippi River basin, red river basin, Arkansas river basin, Missouri River basin
where is the coarser material in a depositional fan
upper fan
describe the upper fan medial fan distal fan (draw them
upper fan: trunk channel medial fan: depositional lobes distal fan: pinching out
where do we see the highest chlorophyll contents
upwelling cells, wide continental shelves, arctic oceans
how does the trade wind system affect continental shelf
upwelling cycles blow water west towards Africa making it highly productive
what is a lamination called if they're deposited annually
varves
how do sandy bedforms with low sand supply look
very few sand ribbons, sand patches, and sand waves
How do sand particles look at tide dominated shelves
very sandy • Sand sheets with ripples: tidal currents <0.5 m/s • Sand waves (subaqueous dunes): tidal currents 0.5 to 1 m/s • Sand ribbons: tidal currents >1 m/s • Sand ridges: amalgamation of sand ribbons form sand ridges (tens of m high, many km across)
what type of climate do carbonates like
warm climate with lots of primary productivity
what do contourite drifts form from
water current + Coriolis force
what form oscillating ripples
wave motion back and forth
what are terrrigenous/clasic sediments
weathering & erosion of continents often brought in by rivers volumetrically important
study sediment distribution map
what card said
study pictures in notebook
what the term says
when do tide sheets form
when the tide is low
where do we use the lobe building approach
yellow river delta
describe siliceous ooze
• Biogenic silica• Mineral: opal• Diatoms, Radiolarians • Production Signal
Describe calcareous ooze
• Calcium carbonate Minerals: calcite, aragonite • Foraminifers, Coccolith - preservation signal
what controls the biogenic carbonate productivity
• Light • Nutrients • Turbidity/translucency • Water temperature - Salinity
what does carbonate solubility increase with
• Lower temperature.• Higher pressure.• Higher salinity.
