ES1002 Flashcards
What sets the temperature of a habitable planet?
Sun is the energy source driving climate and (almost)
all life
How does the sun’s heat energy get to earth
through 150 million km of vacuum?
What is heat?
Heat is the bouncing around the energy of atoms. The faster the bouncing, the greater the heat energy, and the hotter a substance is.
What is light (physics definition)
Electromagnetic radiation (light) can be thought of as a stream of photons – tiny discrete packages of energy.
Photons move with different characteristic wavelengths
What is blackbody radiation?
A blackbody is a chunk of matter that can absorb and emit energy across all wavelengths.
The light given out by a blackbody is called blackbody radiation.
What is the greenhouse effect?
Not all energy emitted from Earth’s surface is lost directly to space: much of it is trapped by the atmosphere and re-emitted to Earth’s surface.
This is known as the greenhouse effect, and is analogous to the action of a blanket.
What is the solar constant?
Solar constant is the energy flux received from the sun
What is albedo?
Albedo is how much (%) solar energy reflected – high from snow/ice
- albedo from earth is 0.3 (30%)
Summerise the greenhouse effect
- The atmosphere makes it harder for photons to escape to space
- Some photons are re-emitted back to ground and are absorbed, causing warming.
- As ground warms the outgoing energy flux is increased (P/A = σ .T4)
- A new planetary energy balance is reached
where ground is warm enough that output
matches input
What is a key carbon-cycle reaction?
CO2 dissolves and reacts with water (hydrolysis)
These reactions happen inorganically (without biology) and are easily reversible
CO2 can also dissolve rocks!
Silicate weathering is the process by which silicate
minerals are broken down by reaction with CO2
What are the key climate change drivers?
Most (~2/3) warming due to CO2 – and CO2 will persist
Methane (CH4) next most important – from cows (~80%) & paddy fields (~20%). 5x lower concentration but 40x more powerful per molecule than CO2
Water (H2O) has strong greenhouse effect – but removes itself (rain!). So only acts as a feedback
What is structural geology?
The study of the structure (geometrical arrangement)
of rocks
“geometrical analysis”
What is deformation?
Deformation causes rocks to change shape,
size, location or orientation
What are the types of deformation?
– Change location
– Change orientation
* (tilt, rotate)
– Change shape
* Shortened
* Stretched
* Sheared
What kind of tests are for the structural analysis of rocks?
a) Descriptive analysis
Describe what you see!
b) Kinematic analysis
Changes in position or shape of the rock (easy if you know what it looked like before)
c) Dynamic analysis
Forces, or stress, acting on the rock. Rheology is important here
What are the ‘tectonics’ ?
A group of structures (local, if not regional scale) which
together reflect motion of the plates that make up
Earth’s crust
What is the Mohorovicic Discontinuity?
The Mohorovicic Discontinuity, or “Moho,” is the boundary between the crust and the mantle
Why is structural geology important?
Getting the structural geology correct is absolutely essential and errors have massive economic and more importantly environmental consequences
What is stress?
STRESS is the force applied to a given area and is defined per unit area by the formula:
Stress, σ = force / area
What are the hydrostatic vs differential stress differences?
Stress is rarely equal in all directions, but instead tends to be differential, i.e. concentrated in a particular direction
Hydrostatic or confining stress is equal in all directions
Differential or deviatoric stress is unequal
What is Brittle deformation?
The cracking and fracturing of a material, subject to stress
What is Ductile deformation?
The bending and flowing of a material, subject to stress
What types of stretching is co-axial? (stress)
Horizontal stretching
Horizontal shortening
What type of stretching is non co-axial? (stress)
Shear strain
RULE:
just flip n learn pls
the direction of the maximum principal stress bisects the acute angle acute angle between conjugate faults (Andersonian behaviour)
What is a Conjugate fault?
Faults in pairs dipping in opposite directions
What is strain
Strain is the resulting change in shape or position of the rock and can be described as pure (co-axial) or simple (non-co-axial)
Deformation can be:
- elastic (reversible, temporary strain)
- brittle or ductile (irreversible, permanent strain)
What does tthe deformation style depends on?
Temperature and depth (pressure);
mineralogy and grain size (lithology),
fabrics and fluids
and time (strain rate)
What is a fault?
- A structural break (fracture) in a rock across which there is notable displacement
- Important structures in the UPPER crust controlled by BRITTLE deformation
So what is a joint?
Fractures that have no appreciable displacement across them.
Recognising a fault; Fault Rocks
Faults are not discrete planes, they occur as “Fault Zones”
Fault zones containg many faults that grind up rocks in the fault zone
What is a reverse fault
Reverse dip-slip and thrust faults as a result of compression of the Earth’s crust = thickens the crust
Reverse faults (‘reversed’ normal faults) are steeper than Thrust faults
What is orogenesis
Making mountains!
What is a Sinistral sense of movement
Sinistral (left-lateral) – Strata on the opposite side of the fault plane is displaced to the left
What is a Dextral sense of movement
Dextral (right-lateral) – Strata on the opposite side of the fault plane is displaced to the right
What are Faults as conduits
Formation of hydrothermal ore deposits on the seafloor from fluid transport along faults
What are Faults as Mineralisation Zones?
Precipitation of ore minerals can occur within the fault and surrounding fractures
How do faults form?
Form either as a result of compression or extension of the Earth’s crust
What are the 3 categories of faults?
1) Dip-slip (normal and reverse/thrust)
2) Strike-slip (sinistral and dextral)
3) Oblique-slip faults
what are the faults associated with?
Faults are intimately associated with natural hazards:
Earthquakes, tsunamis, landslides
What is exposure
Any area of bare rock that is exposed at the surface of the Earth (geological structures are measured at exposures)
What is an outcrop?
The area occupied by a rock unit on the Earth’s surface or a geological map (note: it may not be exposed)
What is a subcrop?
The buried equivalent of the surface outcrop of a rock unit (interpreted from cross-sections)
What is a topographic map?
Topographic maps consist of lines
connecting points of equal elevation (height), “topographic contours”
What do topgraphic maps show?
Topo. maps show us how the topography (shape of the land) changes across an area. Each contour defines a height (in metres, or feet in older maps):
the closer together the contours are, the steeper the slope is; the further apart they are, the more gentle the slope.
What do cross sections do?
Cross-sections allow us to predict the geology underground and are most useful when constructed perpendicular to strike
How do folds form?
Folding is generally caused by compressive stress (i.e. shortening) acting parallel to the bedding planes in a body of rock
This is a DUCTILE deformation process
What is an antiform?
Fold closes upwards = Antiform
Angry Antiform
What is a synform?
Fold closes downwards = Synform
Smiley synform
What is an anticline?
Old rocks in the core of the fold = synformal anticline
What is a syncline?
Young rocks in the core of the fold = antiformal syncline
What is the facing direction?
The facing direction of a fold is defined as the younging direction measured along the axial surface.
Facing is simply stated as ‘up’ or ‘down’.
What is a symmetric fold?
limbs equal in length = symmetric folds
What is an asymmetric fold?
limbs NOT equal in length (no mirror plane of symmetry) = asymmetric folds
What is a fold system?
Folds are not just single, isolated antiforms or synforms but form a series of folds across an area
= fold system
What are the geometric features to describe folds by?
limbs
axial surface
hinge points
hinge line
plunge
symmetry
What do Siliciclastic rocks contain?
quartz
orthoclase (K) and plagioclase (Na) feldspar
lithics (pre-existing rock fragments)
Explain composition and sediment source briefly
Different sediment compositions result from the weathering and erosion of
different parent rocks created in different plate tectonic settings
Define sedimentary characteristics
Composition
mineralogical constituents
Define sedimentary characteristics
Texture
grain characteristics and relationships (size, shape, sorting)
Define sedimentary characteristics
sedimentary structures
types of bedforms and scale
Define sedimentary characteristics
bedding geometry, style and thickness
shape, orientation, lateral continuity
Define sedimentary characteristics
nature of bedding contacts
sharp, wavy or flat
Define sedimentary characteristics
fossils
species type and abundance, life position or disarticulated
Define sedimentary characteristics
colour
may be primary, but can be diagenetic reflecting chemistry of pore fluids
What are sedimentary facies?
A distinct set of lithological and fossil characteristics of a given sedimentologic unit, typically defined at the bed scale
How does the life cycle of a sedimentary rock reflect
provenance?
the source area where rock undergoes weathering and
erosion
How does the life cycle of a sedimentary rock reflect
Transport & deposition?
– Sediment transported by water and wind and is
deposited in a marine or non-marine environment
– Sediments change their composition, size and shape as they are transported
– Sediments become sorted during transport because of size, shape and density
What is a sedimentary basin?
A sedimentary basin is a low area in the Earth’s crust, of tectonic origin, in which sediments accumulate
What is accommodation space
Accommodation space is the space that is made available within a basin for either marine or non-marine sediment to be deposited.
What is subsidence
Subsidence is the gradual downward sinking of the land surface during sedimentation
Why is subsidence important?
. It is required for long-term accumulation and preservation of sediments. Compounded by weight of overlying sediments.
What are the causes of subsidence
the thinning of underlying crust,
tectonic loading,
changes in the thickness
density of adjacent lithosphere…
Why are sedimentary basins important?
Carbon sequestration
Water resources
Ore and mineral resources
‘Archive of Earth history’
^ That hurt me to type, ur welcome guys.
What is the formation of sedimentary basins
Weight of the mountain belt pushes down on the crusts surface
Downward slip on faults produces narrow troughs
The basin forms in the interior of a continent, perhaps over an old rift
Subsidence occurs over thinned crust at the edge of an ocean basin
Explain the termal processes of sedimentary basins when HEATED FROM BELOW
If lithosphere heated from below —> expands slightly and thus becomes less dense.
This less dense lithosphere adjusts isostatically to float higher in the asthenosphere
This produces crustal uplift. If the lithosphere cools back to its original temperature, there’s isostatic subsidence back to the original level.
Flip it a tad for ABOVE but I cba doing that :)
What is extensional thinning? (Sedimentary basin)
Upon recooling, the elevation of the top of the lithosphere is less than before the heating and extension
What is a rift basin?
Rift basins - Divergent (pull-apart) plate boundaries.
- Crust thins by stretching and rotational normal faulting.
- Thinned crust subsides.
- Sediment fills the down-dropped basin.
What is a passive margin basin?
Passive margin basins - Non-plate-boundary continental edge.
- Underlain by crust thinned by previous rifting.
- Thinned crust subsides as it cools.
What is a intracontinental basin?
Intracontinental basins - Interiors far from margins.
- Result from differential thermal subsidence.
- May be linked to failed crustal rifts.
What is a foreland basin?
Foreland basins - Craton side of collisional mountain belt.
- Flexure of the crust from loading creates a downwarp.
- Fills with debris eroded off the mountains.
What controls accommodation space?
- the global sea level change
- the sea floor (tectonic uplift / subsidence)
- changes in rates of sediment accumulation
How is sedimentary deposition in basins is strongly linked to sea level?
*Changes in sea level are commonplace geologically.
* Depositional belts shift landward or seaward in response.
* Layers of strata record deepening or shallowing upward.
What is transgression
Transgression - flooding due to sea-level rise.
Sediment belts shift landward; strata ‘deepen’ upward.
What is regression
Regression - exposure due to sea level fall.
Depositional belts shift seaward; strata ‘shallow’ upward.
Regression tied to erosion; less likely to be preserved.
What is al alluvial fan?
An alluvial fan is a fan- or cone-shaped deposit of sediment built up a river as it decreases in velocity (often associated with change in slope).
Explain an alluvial fan
accumulations of sediment formed by deposition as trunk streams emerge from upland drainage basins into some sort of lowland basin
fan shaped, steep slopes, +/- network of branching distributary channels
long profile: concave upward;
cross profile: convex upward
Where do alluvial fans occur?
particularly common in high relief areas, e.g., base of mountain range or below fault scarps
* semiarid/sparsely vegetated with infrequent but violent floods
* humid areas with intense rainfall
What is a dry alluvial fan?
Dry fans are those in semi-arid climates where flow over fan surface may be regarded as ephemeral.
What is a wet alluvial fan?
Dry fans those in semi-arid climates where flow over fan surface may be regarded as ephemeral.
What is a Debris flow-dominated alluvial fan?
characterized by lobes – poorly sorted, coarse sediments, muddy matrix
What is a debris flow? (sediments)
Where there is a dense mixture of water and sediment, transport and deposition are by debris flow, a viscous slurry of material that spreads out on the fan surface as a lobe.
Debris flows do not travel far and a small, relatively steep alluvial cone is built if this is the dominant process.
What are Stream flow-dominated alluvial fans
characterized by more sheet-like deposits of gravel,
sand, silt:
– moderately well sorted, cross-bedded, laminated or structureless
Dilute, water-lain fan deposits form fans with shallower slopes and greater radial extent
Sheet-flood deposits on an alluvial fan showing well developed stratification.
What are the processes of deposition determined by?
- availability of water
- amount and type of sediment being carried from the feeder canyon
- gradient of the fan surface
What is the significance of alluvial fans?
Provide insight into source rocks - eroded mountain chain.
Fans thought to be more common prior to the rise of land plants in the Devonian
What are the 2 main categories of fluvial systems?
- Meandering: sinuous, single channel
- Braided: multiple channels
What is sinuousity?
The length of stream channel to the length of the valley containing the river
What is a helical flow? (fluvial fan systems)
When the flow flows around the bend
- out towards the surface, in towards the bend
- erosion on the outside
- deposition on the inside (point bars, attached to the bank)
the material eroded from the channel
- lateral accretion
- characterized by cross-bedding and general fining upwards
How do oxbow lakes develop?
Continued meander migration leads to channel cut off or river avulsion
Slit and clay now deposit in the former channel conections
How are levees formed?
A cute wee flood occurs
During the flood:
Thick and course sediments are deposited at channel edges
Thin and fine sediments are deposited over outer parts of a floodplain
After the flood:
The deposits are left behind
Natural levees are built up by many floods depositing sediments there
What are the main morphological features of a meandering river?
fllodplain
cutbank
levee
point bar
crevasse splay
lateral accretion
overbank deposits
channel deposits
What are the main depositional architectural features of a meandering river?
active channels
point of avulsion
the abandoned channel :(
oxbow lakes
floodplains
overbank deposits
channel fill sands
What is avulsion?
The rapid abandonment of a river channel and the formation of the new channel
What are the controlling factors of fluvial channel morphologies
grain size
type of sediment load
fluid discharge
discharge regularity
size of drainage area
bank stability (lithology, vegetation)
What does the architecture of fluvial deposits depend on?
What does the architecture of fluvial deposits are determined by the rates of subsidence and frequency of avulsion
What is a delta?
Shoreline protuberances formed where rivers enter water (oceans, lakes, lagoons etc)
Deltas supply sediment more rapidly than it can be redistributed by basinal processes
What are the delta sub environments?
Delta plains
Delta front
Pro delta
What is a delta plain?
-subariel, flat, swampy plain
- fluvial processes generally predominate
- incised by fluvial distributor channels
What is a delta front?
- shallow submarine platform
- most sand accumulates (mouth bars)
What is a pro delta
- most distal
- bulk suspension settles out
What is the upper delta plain
Its above the tidal influence
Sedimentation occurs on distrututary channels and or the floodplain
What is the deltaic plain?
Lies between the low tide mark and the upper limit of tidal influence.
Sedimentation is mostly associated with tidal channels, levees, embayments, marshes and swamps
What is a subaqueous delta plain?
It is seaward of the low tide level
Seaward fining notable on the delta front through to the pro delta
What kinds of delta types are there?
River dominated
Small tidal range, weak storms and large sediment flux build delta out into the basin
Tide dominated
Large tidal ranges dominates transport, deposition and morphology
Wave dominated
Strong and repeated storms re-work delta sediment
What controls delta morphology
Its controlled by processes redistributing sediment within the basin
What is the bottomset beds? (sedimets)
- Lightest suspended particles settle farthest away from the active delta front, as the river flow diminishes into the standing body of water and loses energy.
- This suspended load is deposited by sediment gravity flow, creating a turbidite.
- These beds are laid down in horizontal layers and consist of the finest grain sizes.
What is the foreset beds? (sediments)
- Deposited in inclined layers over the bottomset beds as the active lobe advances.
- The sediment particles within forest beds consist of larger/more variable sizes, the river moves downstream by rolling and bouncing along the channel bottom. It rolls over the edge, and is deposited in steeply dipping layers over the top of the existing bottomset beds.
- As the foresets accumulate and advance, subaqueous landslides occur and re-adjust overall slope stability. The foreset slope, thus created and maintained, extends the delta lobe outward.
What is a topset bed
- Deposited in turn over the previously laid foresets, truncating or covering them.
- Topsets are nearly horizontal layers of smaller-sized sediment deposited on the top of the delta and form an extension of the landward alluvial plain.
- As the river channels meander laterally across the top of the delta, the river is lengthened and its gradient is reduced, causing the suspended load to settle out in nearly horizontal beds over the delta’s top.
What is adiabatic melting
(aka decompression melting)
Geologically sudden decrease in P
Suddenly, molecules in the rock have a lot more room to move about
They have a relatively high T for that amount of room
So melting occurs
What are the products of volcanic
eruptions come in three forms
- Lava flows—molten rock that moves over the ground
- Pyroclastic debris— fragments blown out of a volcano
- Volcanic gases—expelled
vapor and aerosols
How do we melt the mantle
(Yes, “we” melt it,just god fr)
To melt the mantle, you need to “disturb the geotherm”
- Add heat
- Reduce pressure
- Change the composition
What is the geotherm
Geotherm: Geothermal gradient is the rate of increasing temperature
with respect to increasing depth in the Earth’s interior
How do we form mid-ocean ridges
Decompression melting forms midocean ridge basalt
(MORB)
An example of a continental rift?
e.g. East Africa
Over time, will become an ocean
What is volitile assisted melting?
Changing the environment to melt in.
Adding ions to reduce energy needed to break bonds
Types of volcanism?
- Subaerial volcanism
- Submarine volcanism
- Volcanism on other planets, e.g.,
cryovolcanism (melts of ice or
clathrates)
Explosive volcanism is ….
Explosive
If u got that wrong, dropout.
What is viscosity
A measure of a fluid’s resistance to flow
What is magma rhelogy?
Ps this one is a chunky one.
Silica polymerisation
high concentration of
network formers means more
bonds between oxygens
=> a big energy to
deform the network
=> high viscosity magma
(rhyolite)
- a high concentration of network modifiers means a small amount of bonds between oxygen
=> smaller energy to deform the network
=>
magma less viscous (basalt)
