Lent Flashcards
What causes the mantle to melt?
When it moves past the solidus
What are 3 ways in which the mantle can melt?
Stretching - adiabatic cooling
Hotspots- adiabatic cooling
Subduction zones- flux melting
What are the first 3 crystal to crystallise?
Olivine
Pyroxene
Plagioclase
What do volcanic and plutonic mean?
Volanic- fine grained
Plutonic- coarse grained
What is a sill?
When the intrusion is concordant with the surrounding layers
What is a dyke?
When the intrusion is discordant with the surrounding layers
What are 4 factors effecting explosivity?
Volatiles
Environment
Viscosity (Si content)
Rate of lava emission
What are the features of intraplate mechanism and an example?
Hotspot
Basaltic
Low viscosity
Lava flow
Pahoehoe- wrinkled tops, fast moving
aa- crinkle, slower moving
Hawaii, USA & Yellowstone
What are the features of underwater volcanoes?
Pillow basalts
Phreatic/ Surtseyan- evaporates water into steam
What are the features of volcanoes on destructive plate margins and an example?
Rhyolitic/ Andesitic lava
Higher amount of volatiles, from flux melting of subduction plate
Philippines, Andes
What are released by volcanoes on destructive plates?
Pyroclastic flow (Mt St Helens)
Volcanic bombs
Lahars
How old is the oldest oceanic crust?
280Ma
What are passive margins?
Where continental meets oceanic, but there is no subduction
Form in pairs
E.g. at the edge of Atlantic
What type of melting at mid-ocean ridges?
Active Upwelling- movement of mantle due density
Passive Upwelling- movement of mantle due to space, pressure gradient
What is Iherzolite?
Fertile mantle, that hasn’t been melted
What is Harzbugite?
Mantle that has been melted, only contain olivine and pyroxene
What is the avg thickness of the oceanic crust?
6.5km-8km
What are the 5 pieces of evidence for the composition and structure of the oceanic crust?
1) Magnetic stripes
2) Topographic sequences
3) Seismic profiling (P-wave)
4) Submersibles
5) Deep sea drilling
What are ophiolites?
Parts of the oceanic crust that have been thrusted onto continental crust
What are the 5 layer sequences in the ophiolites?
Sediments
Pillow lavas
Dyke complex
Intrusive rocks (gabbro)
Mantle (Ultramafic)
How much more melting does hotspot cause?
15% from 25% to 40%
What does an eclogite contain? Describe it
Garnet pink
Pyroxene green
Same composition as basalt
How does slab pull occur and what are the mineral changes?
Minerals become more dense
Olivine to ringwoodite then perovskite
Why is magma from subduction zones richer in silica?
Magma conc is higher because it includes silica from plate as well as the mantle
Where are granite batholiths found?
Found at subduction zones because melt has to be from oceanic crust and not just the mantle
What is diapirism?
Rock buoyancy
Felsic(rhyolitic) less dense so move up
Form plume-like structure
What are the features of Rhyolitic lava and where can it be found?
High silica content
Like pure glass
Found at Yellowstone
What is metamorphism?
Formation of new minerals from pre-existing rocks
Solid state change occurs, which doesn’t involve melting
Why are metamorphic rocks preserved?
Preserved in metastable rocks
Where at current conditions wouldn’t be stable, however due to a lack of water, they are unable to reverse and become fully stable
What is a protolith?
An unmetamorphosed rock
What do basalts become after metamorphism?
Metabasites (greenshist, blueschist, eclogite)
What is the sequence for metabasites starting from low T and low P?
Greenschist (LP/LT)
Amphibolite (MP/MT)
Blueschist
Eclogite (HT/HP)
What minerals can be present in greenschist?
Chlorite (green shiny)
Epidote (pistachio green)
Green amphibole (dark green)
What process is necessary for metamorphism?
Plate tectonics
Normal burial will follow geotherm, however metamorphism requries movement in PT space around the geotherm
What are 3 ways the temp can be higher than the geotherm?
Heated from surrounding hotter basalt
Rapid erosion, bring hotter rocks to surface faster
Breakdown of radioactive isotopes
What process is present for metamorphism at High T and Low P?
Contact metamorphism
Igneous intrusion causing metamorphism
What process is present for metamorphism at High T and High P?
Regional Metamorphism
Occurs at collision plate boundaries
e.g. Himalayas
What process is present for metamorphism at Low T and High P?
Subduction of plate
Pushed down rapidly before equilibrium can be reached
What is diagenesis in rocks?
Chemical and physical processes that occur to sediments after deposition and before metamorphism
What kind of Temp/Depth profile does regional metamorphism at collision boundaries cause?
Saw-tooth profle
Because collision causes doubling of crust thickness
What is prograde metamorphism?
Metamorphism due to increased pressure leading to more shear stress
What is lineation and foliation?
Lineation- alignment of minerals
Foliation- formation of planes in rocks
How can relative time of mineral growth be seen?
Pre- fabric wraps around mineral
Syn- some incorporation, but also some wrapping
Post- Complete continuity of fabric
What are porphyroblasts?
Large crystal in metamorphic rocks, like phenocrysts in igneous rocks
How is granite formed?
Made at subducted plates
Si rich
Formed during mountain building
What is the contact Aureole?
Zone where contact metamorphism occurs
What are the 6 steps of the Wilson Cycle and what does it show?
Show formation of ocean, then closure, overall plate tectonics
1) Embryonic -separation of continental= rift valley
2) Young - formation of sea basin = red sea
3) Mature - formation of ocean = atlantic ocean
4) Subduction - Oceanic plates old, subduct= pacific ocean
5) Terminal - ocean contracts = Mediterranean
6) End - collision boundary = Himalayas
What is evidence for the Wilson Cycle?
Ophiolites
Magnetic stripes
Flood basalts
Fossils
Paired metamorphic belts
Granite plutons
What are fossils used for?
Biostratigraphy
Palaeoclimate
Palaeoenvironment
What are 3 types of fossils?
Trace fossils
Body fossils
Chemical fossils
What 4 minerals can organisms biomineralize into?
Calcium phosphate- bones, teeth
Calcium carbonate- (aragonite, calcite)
Silica
Magnetite
What are the 5 ways skeletons can form?
Accretion- addition of new materials
Agglutination- glue together
Addition- adding bits
Moulting- dispose of old skeleton
Remodelling- remodelling mineralized components
When do large multicellular eukaryotes begin to appear?
570Ma
What is the crown group?
Smallest group to contain all living members and their LCA
What is the stem group?
Group of organisms that are extinct and most closely related to a crown group than any other crown group
What is the molecular clock?
Idea that mutations occur at a certain rate
This is then used to estimate and reconstruct ancestor-descendant relationships
What is taphonomy?
Study of processes that happen from death to fossilization
What are ways in which biological information can be lost?
Weathering
Erosion
Disarticulation
Predation
Recrystallisation
Decay
Plate tectonics
What are the 2 steps in the taphonomic sequence?
Biostratinomy- death to burial
Diagenesis- after burial, alteration, fossilization
Why are marine organisms more likely to be preserved?
Less erosion in marine environments, compared to land environments
Commonly more deposition so faster burial
What are environments in which extraordinary fossils can be preserved?
Env where quickly removed from TAZ
Peat bog
Ice
Anoxic conditions
Rapid sedimentation (burial)
Burgess Shale, Canada
What are 3 processes that can occur during diagenesis organisms?
Recrystallisation- no longer stable
Dissolution- organism forms mould but no longer present
Perminerilization- infill of secondary minerals, eg petrified wood
How can rocks suggest the environment?
Silica permineralization- hot springs, acid volcanism
Cabonate permineralization- seawater
Pyrite- anaerobic degradation by bacteria
What is special about the Burgess Shale, Canada?
Excellent biostratinomy
Minimal bioturbation
Low O2 conc
Rapid burial
What is an intrusive igneous rock?
Lava that forms a feature which doesn’t erupt at the surface, e.g. dyke and sill formatin
What is an extrusive rock?
Lava that is erupted at surface forms extrusive features e.g. volcano
When did the Iapetus ocean close?
Began around Silurian times (400Ma)
What evidence is there for the presence of the Iapetus ocean?
1) Geological mapping (geology)
2) Paleontology (fossil change)
3) Geophysical data (magnetic stripes)
4) Collision & Mountain building
What 5 processes can regulate the amount of CO2 in the atmosphere at long geological timescales?
Biological processes
Glaciation- store of C
Plate tectonics
Solar Output- rates of weathering
Deep Ocean circulation- store of C
What factors may make the ocean and biosphere less effective at absorbing CO2 in the future?
Increasing temp- warmer water less CO2 uptake
Deforestation- less trees to take up CO2
Soil degradation- flooding from climate change, less env for trees
Overfishing- disrupts carbon cycle in the oceans
What do sulphide oxidising bacteria (SOB) do?
Fix carbon dioxide, without using much O2, instead use sulphide
What do sulphate reducing bacteria (SRB) do?
Breakdown sugar by using phosphate instead of O2
To produce energy (not as much as aerobic respiration however)
What does epifauna and infauna mean for benthic organisms?
Epi- live on surface
In- live in surface (burrows)
What are zooplanktons and phytoplanktons?
Phyto- photosynthesise
Zoo- heterootrophic, eat organisms and swim a little (jellyfish, krill)
What is the biological pump?
Incorporation of CO2 from the atmosphere into marine organisms
What are the 5 steps in reconstructing paleo ecology?
1) Trace fossils
2) Chemical fossils
3) Functional morphology
4) Phylogenetic inference
5) Fossil associations (gut contents etc.)
What are ecosystem engineers?
Organisms that contribute significantly to their environments
Humans would class
What is bioturbation?
Disruption of sediment layering and taphonomy due to biological processes such as burrowing or bioerosion
What 4 main organisms take up CO2 from the ocean?
Coral
Coccoliths
Forams
Plants
What does the presence of corals suggest?
The marine environment was shallow
In photic zone 50-100m
Warm seas
What is the calcite compensation depth?
Lies between 4-6km depth
Where rate of calcite formation is equal to rate of dissolution, begins to dissolve at low T and high P
Below CCD calcium carbonate is not present
What 6 features in index fossils are important for biostratigraphy?
Morphological distinction- show evolution
Facies independent- same in different env
Easily preserved- commonly fossilized
Abundant- can be found
Geographically widespread- tell time all over the world
Short stratigraphic ranges- create distinct boundaries between time periods (ammonites, brachipods have long ranges)
What is the Great American Interchange and when did it occur?
2.7Ma
Joining of S and N America
N.American organisms killed many S.American endemic species
What is analogy and homology in relation to heritage?
Analogy- similar functions, different evolutionary origin
Homology- similarity due to shared ancestry
What is convergent and divergent evolution?
Convergent- Independent evolution, to have common features
Divergent- Shared ancestry evolve differently
What are 4 requirements for Darwininan evolution?
1) Superfecundity- many offspring
2) Time
3) Variation/ Mutation
4) Heritability- pass on genes
What are 3 types of selection and their effect on evolution?
1) Stabilizing- offspring reach reproductive age, no change in beneficial trait (STASIS)
2) Directional- selection causes further development of trait (ANAGENESIS)
3) Disruptive- selection causes divergent evolution (CLADOGENESIS)
What are the big 5 extinction events and the main effects?
1) end Ordovician 443Ma
Glaciation, 86% species lost, second worst
2) late Devonian 360Ma
marine effected
3) end Permian 251.9Ma
Greatest, 90% of marine lost, due to Large igneous province, released lots of CO2 became toxic
4) end Triassic 201 Ma
LIP not as large
5) end Cretaceous 65.7Ma
Dinosaurs, asteroid
What does the term mass extinction mean?
When over 75% of biodiversity is loss
In a short period of time (few M years)
Caused by catastrophic event, climate, environment related usually
How can the analysis of isotope ratio help suggest the origin of sedimentation?
Biological organisms prefer to use light isotopes, C12 and S32
When was the Great Oxidation event and what is the evidence for it?
2.4 Ga
Rise of O2 in atmosphere caused oxidation of Fe, forming red beds
What is the difference between clastic and non-clastic sediments?
Clastic- made up of fragments of pre-existing rocks (sandstone, conglomerate, shale)
Non-clastic- formed in situ from evaporation or precipitation (limestones, dolomite, evaporites)
What is the difference between limestone and sandstone?
Limestone- CaCO3, low energy, from shells of shallow marine dwelling organisms
Sandstone- quartz, feldspar, high energy, aeolian, river deposit
What is lithification?
Process which turns sediment into rock
What is the theory of uniformitarianism?
Theory that processes have not changed, so the present is the key to the past
Same sedimentary environments existed back then and left similar sedimentary structures behind, e.g. dune cross-bedding
What are the two principles of biostratigraphy?
Superposition- sediments are laid down in layers one on top of the other
Walther’s Law- sedimentary environments that form adjacent components are likely to have formed around the same time, if there’s no unconformity, so vertical transition show lateral movement of environment. e.g. river bed changing shape
What is the purpose of understanding the sedimentary record?
Understand history
Engineering e.g. dam building
Urbanisation, construction on floodplains
Exploiting deposits coal, oil
CO2 sequestration
What are the 5 types of erosion?
Plucking
Abrasion
Incision
Rock fall
Slumping
What are the 2 components in ‘fluid properties’?
Viscosity
Density
What are the boundaries for Re number showing laminar or turbulent flow?
Laminar <500 (glaciers, debris flow)
Turbulent >2000 (air, water)
What is the Bernoulli effect?
Causes lift in an object
Fluid is constricted over the object
Vel increases, pressure decreases
Causing less static force, and the object can begin to lift off
What is the critical flow velocity?
Minimum velocity required for entrainment to occur
What is the Hjulstrom diagram and what does it show?
flow velocity against grain size/ sediment
2 lines= erosion & deposition
High vel required for erosion of very fine silt/mud due to its cohesive propoerties
What is Stokes’s Law? What are the requirements and what does it show?
Stoke’s law of settling
Explains sorting of grains from a fluid with a low Reynolds number
Settling depends on diameter of grain, larger dropped first
What is sorting and grading?
Sorting is by grain size, aeolian env well sorted, glacial env not well sorted
Normal grading is fining upwards
Reverse grading is coarsening upwards
What does the maturity of rocks mean?
Mature means
- well sorted
- commonly only containing quartz (most resistant)
- deposited in aeolian env
Immature would be a glacial deposit
What are the 3 layers in a water stream, distinguished by type of fluid flow?
Free stream- at the top, no frictional effect from the bed
Boundary layer- excludes the free stream, is effected/slowed down by bed
Viscous layer- lower most layer in contact with bed
What are the 2 sides of a ripple?
Stross, eroded side
Lee side, deposited side
What is the difference between dunes and ripples?
Dunes are larger (metres in length), ripples are smaller
So dunes are cross bedded instead of cross laminar
What features are present on the upper and lower PLANE bed?
No feature, continually eroded away
Lower- grain size greater than 0.7mm so doesn’t form
Upper- washed away dunes
How do antidunes form?
In upper flow regimes where water flows faster than the waves on the surface, develops supercritical flow (Froude number exceeds 1)
What is accommodation space?
Space for sediment to accumulate, required for sedimentary environments
What are sedimentary basins, rift basins and extensional basins?
Sedimentary- topography lows due to subsidence and plate tectonics
Rift basins- from faults grabens (down fault), horsts (up fault)
Extensional- thinning of lithosphere
What are flexural basins?
Formed due to elastic properties of the plate
How does glacial growth occur?
Accumulate > ablation in summer months
What are the fluid properties of ice?
Low density
High viscosity
What are the fluid properties of air?
Low density, low viscosity, picks up grains <0.5mm, usually quartz
What are the 5 types of dunes?
Transverse- lots of sediment
Barchan- less sediment
Linear- bi directional
Star- multi directional
Interdunes- gap between
What is the thermocline?
Boundary between the lower cold, and the upper warm layer in a lake
What is the epilimnion?
Upper warm layer that is heated by the sun, oxygenic as it’s near the surfac
What is the hypolimnion?
Lower cold layer, that can become anoxic. Area for good preservation fast biostratinomy
What types of sediments are found in saline/ ephemeral lakes?
Evaporites- gypsum- halite
mudstone
What is the difference between alluvial and fluvial?
Alluvial- deposition due to water
Fluvial- deposition due to rivers
What are alluvial fans and some examples
Debris flow like fan, usually in a mountainous area
Leads to reverse sorting
e.g. Death valley, USA
What is imbrication?
How conglomerates line up in a stone
Can suggest the paleoflow direction
What is Avulsion?
Movement in the location of a river channel
What 2 main features can a river have?
Braided channels
Meandering channels
Why aren’t the bars in a braided river well preserve in the sedimentology record?
Aren’t very stable bars
In floods are often moved and changed
So not well preserved, and not commonly colonised by plants
What feature forms in the inner bend of a river?
Point bars
What overbank deposits can a river leave?
Paleosols- fossilized soil
Calcretes- layers of CaCO3 formed due to early evaporation
What are the 4 parts of a delta?
Delta top- exposed
Front- shallow marine
Slope- shallow to deep marine
Prodelta- offshore, fine sediment
What are the features left behind from a delta?
Coarsening upwards
Avulsion of river channels
What are the 3 different types of dominated deltas and their features?
Wave- smooth coast
River- bird foot
Tide- elongate islands, out to sea
What are the processes and landforms found at coasts?
Longshore drift
Bars, lagoons, dunes, salt marshes, beaches
What are the 2 different environments for coasts and their landforms?
Warm- carbonate coast, biogenic material, ooids
Saline- evaporites, lagoons, sabkhas, gypsum (low hardness)
What are the requirements for carbonate production? (6)
1) Shallow marine environments
2) Temp 20-25
3) Salinity 30-40%
4) Oxygenic conditions
5) Photic (50-100m)
6) Has terrigenous sediment supply
Why are reefs so beneficial?
Corals provide shelter for organisms
Reefs cause wave breaking, so lower energy env behind the reef
Resistance to storms
What is the structure of shallow marine environments?
Continental shelf
Slope
Rise
What feature do tides cause in sedimentary rock?
Herringbone- cross stratification
looks like bi-directional cross stratification
How can the presence of stratification, hummocks and swales suggest water depth?
Only shallow beds would be effected significantly by wave action
So if features are present, it suggests that the area was quite shallow
What are turbidites and what feature do they leave behind?
Submarine debris flows,
Leaves reverse grading
Scour marks
And bouma sequence
What is the Bouma sequence?
Formed by turbidites
a= massive clasts, rapid deposition
b= parallel laminations
c= ripples, cross lamination
d= parallel laminations
e= mudstone
What are submarine fans and an example?
Formed by turbidites
Distal = far away, small sediment
Proximal= near source, larger sediment
e.g. Bengal fan, Indian Ocean
What is a clade?
Group of organisms including the extinct organisms linked to the last common ancestor
What is a stem group?
Group of extinct taxa which are most closely related to a crown group than any other. e.g. dinosaurs to birds and not reptiles
What is a crown group?
smallest group containing all living members and ancestors up to most recent common ancestor
What is the total group?
Crown group + stem group
What are synapomorphies?
Common shared features
Take time to develop
What group should be looked at to look for evolutionary origins?
Stem group not crown group
What are the 3 subclades in dinosauria?
Ornithischia, Sauropodomorpha, Therapoda
What is polytomy?
Where branch in phylogeny splits into more than 2 branches at one point
What are the causes of polytomy?
Hard polytomy- (real polytomy) Division of multiple descendants in short amount of time
Soft polytomy- Division due to lack of fossils and evidence of build up of synapomorphies
What are 3 dinosaur synapomorphies?
Perforate acetabulum (Cup shaped opening in pelvis)
Cervical epipophyses - bony projections from spine
Deltopectoral chest- (chest bone)
What are avian features (synapomorphies)
Pubic retroversion- convergent evolution with birds and ornithischian dinosaurs
Tooth loss
Skeletal Pneumaticity- air gaps in bones
What happens after a mass extinction allowing increased in biodiversity?
Niche filling
When there is less competition
What is evidence for the K-Pg mass extinction?
Cenotes- massive sinkhole in Yucatan region
Caused by meteor, diameter >10km
What are the 2 reasons for a specific niche of birds surviving?
1) Small - often reproduce faster, evolve faster, greater population numbers
2) Non-arboreal- trees were wiped out and so non tree dwelling birds are more likely to thrive
What is evidence for the ‘redevelopment’ of trees?
1) Pollen analysis, shows presence of angiosperms and ferns which thrived early on
2) Change in birds- from analysing bird feet can see evolution of arboreal birds
3) MRCA of all birds is non-arboreal, however arboreal birds exist now
What are the challenges with bird taphonomy?
Lack of teeth less fossilization
Bones less dense easier to move/ erode
What are ecological features of non-areboreal and arboreal birds?
Non-arboreal - long legs, above grass, larger feet
Arboreal- short legs, low centre of gravity, curved feet
What are examples of diagenetic processes in relation to sediments?
Soft sediment deformation
Compaction
Cementation
Dissolution/ Recrystallisation
Oxidation/ Reduction
State the minerals involved in the preservation of fossils
Calcium carbonate- commonly marine shells, as calcite or aragonite
Silica- replace material in plant tissue
Phosphate- apatite, preserve vertebrate teeth, bones
Iron minerals- hematite, as permineralization, replace organic material
Pyrite- formed in swamps, fool’s gold
What are the 5 mass extinction events and their causes?
1) worst= end Permian (90% marine lost), LIP in Siberia
2) second worst = end Ordovician (443Ma), glaciation of Gondwana
3) K-pg= 66Ma, loss of dinosaurs, meteorite in Yucatan region
4) End Triassic= LIP, not as large
5) Devonian (360Ma)= radiation
How are a variety of magma formed in a magma chamber?
Fractional crystallisation
Olivine and pyroxene crystallises out first (at higher temperatures)
So colder magma (800degrees) doesn’t have olivine and is more silica (quartz rich)
