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Geodynamics
The study of the large scale evolution of the solid earth
Plate Tectonics
Broad area of study of how planets behave
Geoid
A reference surface representing the elevations. Worldwide, at which gravitational potential energy is the same
Plate
One of about 20 distinct pieces of the relatively rigid lithosphere
Divergent
Plates move apart Oceans form if process continues
Transform
Plates slide laterally; May involve a component of extension
Convergent
Plates collide If one or both plates are oceanic then subduction occur If both are continental then continental collision occur
Isostatic Equilibrium
The condition that exists when the buoyancy force pushing lithosphere up equals the gravitational force pulling lithosphere down
Pratt theory
Blocks of some mass are different densities Ocean vs continental crust explanation
Airy theory
Blocks of same density different masses Himalayas are high and Aus is close to sea level
Mid-Ocean Ridge
A k-km-high submarine mountain belt that forms along a divergent oceanic plate boundary
Rift
The process by which continental lithosphere stretches horizontally and thins vertically
Transform Boundaries
A boundary at which one lithosphere plate slops laterally past one another
Transform Fault
A fault marking a transform plate boundary; along mid-ocean ridges, transform faults are the actively slipping segment of a fracture zone between two ridge systems
Transpression
Makes narrow linear mountain belts
Transtension
Makes narrow linear basins
Subduction
The process by which one oceanic plate bends and sinks down into the asthenosphere beneath another plate
Subduction Zone
The region along a convergent boundary where one plate sinks beneath another
The Wilson Cycle
The balance of creation and destruction of tectonic plates
Metasomatism
The process by which a rock’s overall chemical composition changes during metamorphism because of reactions with hot water that bring in or remove elements
Subduction metamorphism
Metamorphism occurs both in the subduction zone and in the arc and back arc environment The P and T conditions are very different in each part
Obduction
The sideways and upwards movement of the edge of a crustal plate over the margin of an adjacent plate. Tectonic failure
Ophiolite
A slice of oceanic crust that has been thrust onto continental crust
Orogen(esis)
Mountain building process. Mountain belts
Shield
An older, interior region of a continent. North America has the Canadian
Supercontinent
A very large continent formed by the suturing together of smaller continents
Facies
A group of rocks and primary structures indicative of a given depositional environment Texture, Structures, Bedding Geometry, Bedding Contacts, Fossils, Colour
Cross bed
Internal laminations in a bed, inclined at an angle to the main bedding; cross beds are a relict of the slip face of dunes or ripples
Planar
Occurs when crest of the dune or ripple is a straight line which are called 2D Ripples
Trough
Occurs when cross beds have a curvy or non parallel forest leads to little scoops in the rock. The crest of the dune is not a straight line
Newtons 1st law
Inertia (object will remain at rest or in uniform motion unless acted on by an external force)
Newtons 2nd law
Force = mass x acceleration
Newton’s 3rd Law – equal and opposite reactions
When a grain reaches a constant settling velocity, only drag on the grain balances the net force between gravity and buoyancy
Archimedes’ principle of levers and torque
Work = force x length of lever (moment) arm = FL
Sediment Entertainment
When grains start to move
Suspended load
Grains remain in water column until conditions change
Bed load
Large particles such as sand, pebbles, or cobbles, that bounce or along a stream bed
Traction transport
The geologic process whereby a current transports larger, heavier rocks by rolling or sliding them along the bottom
Saltation
The movement of a sediment in which grains bounce along their substrate, knocking other grains to the water column (or air) in the process
Benoulli’s Principle
Within a horizontal flow of fluid, points of higher fluid speed will have less pressure than points of slower fluid speed, i.e. within a horizontal water pipe that changes diameter, regions where the water is moving fast will be under less pressure than regions where the water is moving slow. Just another way of saying that water will speed up if there;s more pressure behind it than in front of it.
Buoyant force
Buoyancy is an opposite and equal force to gravity if a grain is not in motion (but driven by the fluid density, not grain density)
Stokes Law
An expression describing the resis5ng force on a par^cle moving through a viscous fluid and showing that a maximum velocity is reached in such cases, e.g. for an object falling under gravity through a fluid.
Terminal velocity
The highest velocity attainable by an object as it falls through a fluid (air is the most common example). It occurs when the sum of the drag force (Fd) and the buoyancy is equal to the downward force of gravity (FG) acting on the object.
Tides
Motion of water around the Earth due to gravitational forces set up by the alignment of the sun, Earth and moon Highest high and lowest low water – spring tides (max. range) Lowest high and highest low water – neap tides (min. range)
Transitional waves
Transgression
flooding due to sea-level rise. Sediment belts shift landward; strata ‘deepen’ upward.
Retrogradation
is the landward change in position of the front of a river delta with time.
Regression
exposure due to sea level fall. Depositional belts shift seaward; strata ‘shallow’ upward. tied to erosion; less likely to be preserved.
Progradation
the growth of a river delta farther out into the sea over time.
Walther’s Law
Any vertical progression of facies is the result of a succession of depositional environments that are laterally juxtaposed to each other.
Hadean
4.5 Ga (formation of the earth) to 3.8 Ga (sometimes 4.0 Ga; the oldest preserved rock)
Late heavy bombardment (LHB)
~3.8-3.9 Ga? Created the majority of the moon’s craters
Zircon (ZrSiO4)
the oldest remaining mineral on Earth. Grains over 4 billion years old can reveal information about Hadean surface conditions Rocks can’t be used to determine if habitable conditions existed. Zircon is very resistant to melting and withstand many impaces
System component
reservoir of matter or energy, system attribute, or as subsystem
Positive coupling
a change in one component produces a change in the same direction in the linked component
Negative coupling
a change in one component produces a change in the opposite direction in the linked component
Archean-Proterozoic Boundary
2.5Ga Appearance of modern-style cover sequences (unconformity-bound sedimentary packages on continental crust) Sediments are being deposited over the cover sequence
Shaw Granitoid
(~3Ga) In AUS Weathered old rock that has been metamorphosed
Stolzenberg Pluton
(3.4-3.2 Ga) Multiple generations of magmatism
Greenstone belts
pillow upon pillow basalt…
Greenstone
mostly stones that are greenish and form belt shapes During low grade metamorphism basalt turns into a green colour Basalts are really abundant during the Archean
Komatiite
An Archean oddity Ultramafic extrusive rock. Commonly displays spinifex texture of large acicular olivine and pyroxene crystals Likely indicates very hot mantle melting conditions Its rare because it comes out to the surface and solidifies It was only abundant in the Archean Theory is that the mantle was much hotter in the ArcheanThe elements didn’t separate which created cement basically
Hydrothermal Barite (BaSO4)
Dark colour of otherwise white barite crystals reflects inclusions of fluids, minor organic matter, and pyrite Contains sulphur gas which makes it dark
Cross bedding in sandstone between pillow basalts
(3.4 Ga) Evidence of erosion and sediment transport Less quartz rich and less mature sediment Sedimentary process occurred similar to today
Stromatolites
microbial structures, orientated towards the Sun Microbial mats create a sticky organic film Photosynthesis locally removes CO2 and increases the pH
Strelley Pool formation
Stromatolite reef at 3.4 Ga Steep angle cones interpreted as evidence of sticky microbial mats that trapped sediment grains
The faint young sun paradox
The sun was dimmer in the Archean and has become hotter over timeThe modern greenhouse effect would not have been strong enough to keep the Earth above the freezing point of liquid water until about 2 Ga More greenhouse gases were needed to explain evidence of liquid water
Macropalaeontology
Invertebrate & Vertebrate
Micropalaeontology
e.g. forams, diatoms
Palynology
pollen, spores
Palaeobotany
fossil plants
Ichnology
trace fossils, e.g. burrows, tracks
Palaeoecolgy
interactions between fossil organisms and their environments
Phylogeny
Evolutionary relationships between biological taxa
Phylogenetic Trees
Phylogenetic trees may be used to investigate the sequence & timing of origination of particular features of organisms
Crown group
defined by a shared common ancestor of a clade, as well as all the descendents of the common ancestor
Stem group
a grouping of extinct species related to, but basal to (on the stem), the crown group
Clade
a group that includes an ancestor (node) and all of its descendants (all shallower nodes and terminal taxa that descend from that node) on a phylogenetic tree
Sister taxa/sister groups
Parts of terminal taxa/clades that branch from a common node
Morphology
The study of animal from. In palaeontology it refers to the study of bone anatomy and function, and the muscle reconstruction from evidence of muscle attachments on bone. May also be used to infer behaviour which is usually bases on anatomy and behavioural biology of modern day animals
Tomography
Most widely-used method to visualise fossils in 3D is X-Ray computed tomography. This allows non destructive, high resolution reconstruction of the whole fossil
Taphonomy
The process from death to fossilisation
Decay experiments
does decay introduce bias into the fossil record? Soft vs. hard tissue
Melanosomes
Contain melanin, the most common light-absorbing pigment found in the animal kingdom. Melanosomes are responsible for colour and photoprotection in animal cells and tissues
The Cambrian
541-485Ma
Cambrian ~515 Ma
Big diversification in animal taxa Swimming Predation Increased body size Defence Massive radiation in Phyla with bilateral symmetry
Burrowing Biomineralization
The Cambrian Explosion
Huge diversification of animal life Appearance of all major animal body plans Big changes in mode of life (burrowing) Marked predator/prey relationships
Burgess Shale
~508 Ma Discovered by Charles Walcott in 1909, in British Columbia, Canada soft - tissue preserved as carbonaceous remains
What caused the Cambrian Explosion?
Red Queen Hypothesis
Diversification driven by biological predator-prey relationships (biotic)
What caused the Cambrian Explosion?
The Court Jester Hypothesis Diversification drive by the physical environment (abiotic)
Trilobites (arthropoda; Trilobita)
First appearance 521 Ma, lasted until ~252 Ma (lasted ~270 Myr)
Bryozoa
Filter feeding zoids that form sessile colonies with a shared exoskeleton
GOBE
Great Ordovician Biodiversification Event
Planktonic Revolution
Late Cambrian-Early Ordovician Marks the arrival of fossil planktonic organisms into the fossil record Explosion in diversity of phytoplankton→basis of marine food chain Followed by various zooplankton
Graptolites
Colonial animals that lived in an interconnected system of tubes; skeleton made of collagen. Incredibly useful for relative dating and biostratigraphy throughout the Ordovician to the mid Devonian. Morphological Change Sessile to planktonic mode of life Single type thecae (Graptoloidea) Biserial stipes
What caused the GOBE?
Ordovician marked by a warm global climate → subsequent high sea levels result in flooding of continents and expanded shelf habitats Biotic factors → primary significance at the local, community level scale Abiotic factors → likely to have been of importance at the larger palaeocontinental scale orogenesis; tectonics; volcanic activity Palaeogeography increased tectonic activity resulted in numerous and widely separated continental platforms
Requirements for modern reefs
dominated by aragonite Scleractinian corals → corals can be fussy! Dominantly tropical waters Well-lit within the photic zone
Clear water symbiont photosynthesis; suspended sediments clog corallites
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