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Facies Models Final
river systems, glaciers, and general facies
74
Geology
Undergraduate 3
05/05/2012

Additional Geology Flashcards

 


 

Cards

Term
4 kinds of rivers
Definition
  1. straight
  2. meandering
  3. braided
  4. anastomosing
Term
3 ways to transport material in a river
Definition
  1. dissolved load
  2. suspended load
  3. bedload (saltate or roll/creep)
Term
3 river controls
Definition

1. gradient (vertical distance/horizontal distance)

2. bank stability (vegetation, sediments, etc.)

3. bedload (how much sediment you have within the flow)

Term
What affects the velocity of a river?
Definition

1. river gradient

2. friction (slows it down)

3. amount of water entering the system (# of tributaries)

4. discarge (amount of water passing over a specific point at a specific time (volume/time))

Term
Types of river flow
Definition

1. low flow: water is confined to channel and is well below the banks

2. high flow/bedload: water in channel but banks are full

3. overbank/flood: water escapes banks, spills onto the surrounding area (flood plain)

Term
What do younger rivers do?
Definition

1. downcut

2. headwater erosion

Term
What do mature/older rivers do?
Definition

1. move over landscape rather than through

2. have a graded profile (lateral)

Term
3 things to know aobut V-shaped rivers
Definition

1. really narrow

2. high velocity

3. found closer to mountains

Term
What is sinuosity?
Definition

the "curviness" of a river

actual path or channel length/ shortest path or down valley length

Term
What is fluvial capacity?
Definition
ability of channel flow to carry sediments aside from bedload
Term
What's the difference between braided and anastomosing rivers?
Definition

1. braided rivers have easily erodable banks while anastomosing rivers have cohesive banks that don't tend to move as much

2. the width to depth ration of anastomosing is less than braided 

3. anastomosing's main movement is veritcal while braided's main movement is lateral

Term
Where do you find braided rivers?
Definition
upper reaches of a system where there is intense erosion/ near source/ well above graded profile/ alluvial fans or glacial outwash
Term
What kind of sediments are found in braided rivers?
Definition
coarse to fine sands; trough x-beds, tabular x-beds, rippled sands; sand and silt overbank
Term
Describe the sinuosity of a braided river.
Definition
it has low sinuosity overall but individual channels can have high sinuosity
Term
Describe the discharge of a braided river.
Definition
discharge is low with high sediment load
Term
Describe the gradient of a braided river.
Definition
high gradient to low gradient transition (steep to less steep/level)
Term
Where are the coarser sdiemtns in a braided system found?
Definition
channel middle
Term
How are bars in a braided system formed?
Definition
by impediment to flow... a large object
Term
3 kinds of bars found in braided systems
Definition

1. longitudinal bars

2. traverse bars

3. cross channel bars

Term
Tell me about longitudinal bars.
Definition

1. They aggrade (the level rises by deposition) and migrate downstream.

2. they are found more often in upper reaches where there are coarse sediments and pebbles

3. strat: planar at the bottom, x-beds, finer sands in between from channel

 

Term
Tell me about Traverse bars.
Definition

1. they are broad and lobate

2. made up of finer sediments b/c they are found in the lower reaches 

3. during floods you get mega-ripples

4. structures: ripples, dunes, trough cross beds

 

Term
Tell me about Cross Channel bars.
Definition

1. are found where smaller channels enter larger channels

2. flow is more lateral or oblique

3. x-beds show flow perpendicular to main flow

4. strat: trough x-beds, scouring, coarse sed (channel base), fine sed (bar top), abrupt FU sequence, wide stacked lobes

Term
sinuosity of meandering river?
Definition
super sinuous (channel length high compared to distance)
Term
Gradient of meandering river?
Definition
low gradient (slower flow, caries suspended sed relative to bedload)
Term
velocity of meadering river?
Definition

velocity varies

1. high velocity = erosion = outer bend

2. low velocity = deposition = inner bend

Term
Tell me about the feautres of a meandering river.
Definition

1. point bar: where the velocity is low and sediment is deposited

2. cut bank: where the velocity is high and the land is eroded

3. oxbow lake: the really sinuous part of the river gets cut  off

4. meander scar: a dried up oxbow lake

5. neck: the part that cuts off the oxbow lake

6. crevasse splays: rising water causes levee to be breached and water spills out onto floodplain

7. avulsian: breached side of channel where new sinous course starts on flood plain

Term
sinuosity of straight rivers.
Definition

the name gives it away duhhh

it's straight and has LOW sinuosity

Term
gradient of a straight river?
Definition
HIGH gradient
Term
fWhere are straight rivers found?
Definition

at headwater where energy is very high

also found in areas where flow path may be controlled by underlying geology

Term
Are straight rivers popular?
Definition

NO. no ones likes them. 

jk. they're rare

Term
sinuosity of anastomosing rivers?
Definition
highly sinuous
Term
anastomosing systems are made up of.. 
Definition
a trunk (the main channel) and anabranches (smaller channels)
Term
What is a delta?
Definition
flowing water (high energy) meets standing water (low energy)
Term
How does the sed supply compare to erosion in a delta?
Definition
sed supply >> erosion
Term
What are the parts of a delta?
Definition

1. the upper and lower delta plain

2. the delta front/slope

3. the prodelta (submarine shelf)

Term
When does a delta have an elongated shape?
Definition
high supply and hyperpycnal (river water is more dense than receiving water body)
Term
When is the delta shape more like a lobe?
Definition
moderate supply + homopycnal (desnities are the same)
Term
Where are glaciers found?
Definition
at high latitudes and altitudes where it snows more than it melts
Term
How much of the earth do glaciers cover?
Definition
10% 
Term
Glaciers are good agents of...
Definition
transport and erosion (wind and water don't even compare!)
Term
What was a major time of glaciation?
Definition
carboniferous age and 7 million years ago during snowball earth
Term
Erosion from glaciers causes a lot of...
Definition
scouring which crates U-shaped valleys
Term
Cirque?
Definition
bowl shaped depression where erosion from glaciers start
Term
tarn?
Definition
cirque filled with water
Term
arete
Definition
a sharp ridge formation that is created when glaciers on both sdies of the mountain slide down. 
Term
horns?
Definition
a pointy mountain looking thing that is created from glaciers eroding
Term
deposits and sorting from glaciers?
Definition
all grain sizes from boulders to clay that are poorly sorted
Term
glacial four?
Definition
silt and clay
Term
Glacials are either advancing or retreating. What does this mean?
Definition
It's either boldozing forward or melting and ropping what its carrying
Term
moraine
Definition
ridges or mounds where it tells where snount is melting;
Term
recessional moraine
Definition
one ridge or mound behind the other as glacier retreats
Term
medial moraine
Definition
where two glaciers ran into each other
Term
lodgement tills
Definition
unsorted glacial sediment deposited at terminal moraine
Term
When do glacial lakes form?
Definition
When streams get blocked and a dam forms
Term
varves
Definition
the pattern of light dark sediments that get layered from glacial lakes that freeze and thaw ever winter and summer
Term
What happens when glacial lakes thaw?
Definition
lake becomes lighter because oxygen is introduced and the lake is oxidized
Term

What happens when glacial lakes freeze?

Definition
they become darker because reduction occurs from organics
Term
loess
Definition
wind blown glacial flour (silt and clay); the areas where the flour setlles become fertile farmland
Term
terminal moraines
Definition
furthest point that glacier got to
Term
4 parts to depositional history
Definition

1. sediment provenance/source

2. transport direction

3. geometry

4. chronology

Term
4 controls of facies
Definition

1. accomodation space

2. tectonics and sedimentation

3. climate

4. organics

Term
Tell me about sediment provenance/source
Definition

provides the weathered products/sediments

source tells you the mineral type

Term
Tell me about transport
Definition

1. size of the sediment is related to energy

2. roundness related to distance

3. imbricated to paleoflow direction

4. structures related to paleoflow direction and type

 

 

Term
Geometry- what kind of units and formations can we see in cross sections?
Definition
pinch out, thickness, facies, unconformity, biological changes
Term
What controls sediment preservation?
Definition
accomodation!
Term
In a one sided system...
Definition
flow is usually perpendicular to basin margin
Term
In a two sided system...
Definition
the trunk challen flows axial while the feeder system flows perpendicular
Term
Why do incisions occur?
Definition
because of drop in sea level
Term
Changes/succession in facies indicate..
Definition
changing conditions
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