Stratigraphy Yr 1 Flashcards
In 1729- 1797 James Hutton discovered what?
- Deep Time ~75000 yrs
- Using first principals saw breaks in rocks history (angular unconformity) - huttons unconformity
- After strata are deposited they are eroded, then deposition carries on atop the strata.
what did james hutton think of the idea of intrusions?
He knew you must melt rock to make large crystals (except salt which would dissolve in water)
Whats the first form of intrusions
Invented by james hutton, the idea magma rose to the surface pushing strata aside
When was the rock cycle invented
James Hutton 1729 - 1797
Who came up with the extinction theory and what date?
Baron Cuvier in 1769 - 1832
- using elephant jaws compared to mammoths anatomy
What date and who was the fossil collector in lyme regis of the first what?
Mary Anning 1799 - 1847
- Ichthyosaurs, pleiosaurs and pterosaurs
Who invented the gradualism theory?
Charles Lyell in 1797-1875
What did william ‘strata’ smith create?
Invented lithostratigraphy and biostratigraphy
Who went round mapping Britain’s geology on horse back?
William smith 1799-1815
- characteristic sediments with specific fossils
- first cross sections
Arthur holmes is famous for?
Attempting to date all of geological time with radioactive decay dating.
- roughly accurate
Who came up with the theory of continental drift and convection currents in the mantle?
Arthur Holmes
How old is the earth?
~4560Ma
How to date what is older or younger but no actual age (relative dating)?
- Fossils in each strata
- Cross cutting relationships
- magnetic data
- radiometric
Methods of absolute dating?
- Varves
- Glacial deposits (ice)
- Ice cores
- Radiometric (Zircons)
Where can zircons be found?
granite or volcanic ash layers and can form round each other or be much older than the rock surrounding it.
Name radioactive decay:
- Uranium to lead
- K to Pb
- Rb to Sr
- Carbon-14 on wood/bone/charcoal
The lithostratigraphic hierarchy:
- Supergroup
- Group
- Formation
- Member
- Bed
Boundary is defined at the BASE of the bed.
Whats the name given to beds of the same age across their full geographic extent?
Synchronous bed
What is the opposite to synchronus?
Diachronous
A good fossil is common and widespread name some other factors and give examples. (biomarker)
- small
- easily preserved
- rapidly evolving
- distinctive
- Forminifera (benthic and planktonic)
- Ostrocods (tiny arthropods)
- spores and pollen
- acritarchs
- conodonts
- coccoliths
- graptolite
- ammonites
What is a biozone?
A geological area named after a specific fossils key characteristics. Where they begin and end
Name the 5 sections of geochronology:
- Eon
- Era
- Period
- Epoch
- Age
Name the 5 sections of chronostratigraphy:
- Eonothem
- Erathem
- System
- Series
- Stage
Whats a golden spike?
The point in the worlds stratigraphy where the boundary between time periods is located.
How did the earth moon system form?
Telus (primal earth) impacted a planetoid the size of mars.
What occurred during the Hadean?
- Post impact solidifying of magma ocean a few km deep
- New moon
- the late heavy bombardment
- Steam condensed in atmosphere - oceans formed
what does the worlds oldest zircon suggest?
4.37Ga continent structures and oxygen in crystal suggests water.
The Archean saw the beginning of what?
- Rock formation (sedimentary in the oceans)
- The first single celled organisms - stromatolites
Describe the Archean.
Sun was 80% as hot, no oxygen so pyrite preserved at land surface and possible plate tectonics.
- Lewisian Gneiss formed 3Ga mountain belt 50km deep
What occurred in the Proterozoic?
- 5Ga - free oxygen from cyanobacteria
- took 0.1 Ga to create atmosphere
- Lewisian surfaced at 1 Ga followed by unconformity - torrodonian red sandstones (fluvial deposits)
- Dalradian drop stones (Namibia) - snowballearth
- Avalonia forming/ formed
What happened during the first snowball earth?
- world covered in ice
- drop stones in Namibia
- 800-700 Ma deglaciation was rapid (glacial till covered in cap carbonates)
- Avalonia forming/formed
Within 20Ma all metazoan groups appeared, name them:
Annelids, Arthropods, Mollusca, Brachiopods, Vertebrates
Why did the metazoan groups appear?
Oxygen levels, climate and biological grade
What is bioturbation?
When burrows and disturbed sediments are fossilised
- dont get them in anoxic condition
- fine lamination
The first skeletons were formed from?
CaCO3, phosphorous and silca
- Cloudina
In Cambrian the first what cleaned the sea water?
Filter feeders, possibly more oxygen.
During most of the palaeozoic the Iapetus ocean separated what? Closed?
North and south britain. It closed from the ordovician to the silurian (caladonian orogeny)
The southern uplands accreationary prism is evidence of what?
In early palaeozoic ocean closure 60km thick succession of near vertical rocks (grey wache + graptolite evidence)
In the southern uplands accreationary prism NW-SE mudstone - greywache transition becomes younger by:
1Ma with each thrust slice.
The southern uplands accreationary prism thust faults were overlain by what?
Sandstones from the laurentian mountains.
Southern uplands eventually destroyed due to thrust faults.
Climate change in the early palaeozoic led to:
Alternating beds of anoxic (warm) to oxic (cold).
- no bioturbation or benthic fauna in anoxic conditions
The Caladonian orogeny formed mounatins in:
North Wales, Lake Distict and across Scotland (Especially the highlands)
The Laurentian eroded mountains formed what continents?
~416Ma The ORS continent at the equator and Gondwana to the south separated by the Rheic ocean.
The rhynie chert occured when?
The devonian, a bog of the first plants (sporophyte and byrophytes) and insects that collonised land.
Devonian river deposits can include:
Burrows made by crustaceans and other organisms. Deposits are usually cross bedded and oxidised, overbanking muds and bogs etc.
where to find a good example of Devonian fish bones
Ludlow bone bed
Name iconic devonian fauna:
Euryptends (Sea Scorpions), Armoured fish, lung fish, tetrapod ancestors. Other fauna: - Jawless fish - Trilobites - brachiopods - Tabula/rugose corals -Crinoids
What occurred at the beginning of the Carboniferous
Marine transgression so most of UK = shallow subtropical sea.
Then major river delta came from north = millstone grit
Large tropical forests and peat bogs to create coal measures.
Where can u find evidence for carboniferous glaciation
Falkland isle -boulder clays and striations
~50Ma old. - this caused cyclothems
When did Pangaea form?
Permian as Gondwana moved north, closing the rheic ocean (Variscan orogeny)
What caused the Pennines and south Wales?
Hercynian/Variscan orogeny during the Permian
Due to the fact Britain was located in the center of Pangaea:
Very hot and arid, creation of the NRS, Salt deposits (zechstein sea) and dolomitic limestone.
What happened during the P/T extinction?
- Siberian trapps
- chemistry of oceans changed
- ocean anoxia
- global warming
- 95% species died out 50% of families
- Trees died out an ferns colonised land in their place
- Not alot of evidence in the UK as we are in the NRS
Where is the Permian - Triassic boundary?
Meishan china, Lots of fossils of both fauna and flora to mark evidently.
- such few fossils in the UK as its all wadi conglomerate and braided rivers (mudstone, sandstone, breccia etc)
End of Triassic there was what?
a marine transgression. global sea levels show it wasn’t an Isostatic change in the UK but eustatic, there was a change from NRS to shales.
why are there varying types of ammonites found in the uk
in the Jurassic the UK had warm and cold water therefore we can use ammonites to bring down to 0.1Ma
Why is there a high resolution of biostratigraphy in the jurassic
The ammonites evolved rapidly so speciation is very easy
What can you find east of leicester?
Jurassic Oolitic limestone
The Yorkshire coast is home to what?
Lias - many Jurassic fossils. Jet Rock is very carbon rich, more C-13/C-12 so indicates ocean anoxia.
What is the name of the jurassic global ocean anoxia event that can be seen on the yorkshire coast?
Toarcian hyperthermal
- very finely laminated
- no bioturbation
- plenty of fossils preserved
- due to release of methane into atmosphere increasing weathering on world wide scale.
What was in the south east (UK) in the cretaceous
large delta top and alluvial fan from mountains
- open antiforms and synforms
What occurred toward the end of the cretaceous?
- Sea level rose gradually, until the land was flooded - no sediment washing into the sea - chalk deposits form as deep sea ooze of coccoliths = biogenic.
- CO2 increase poles melted
- Chalk is white as no sediment, all CaCO3
- flint bands of pure silica
Give evidence for the K/T extinction
- Iridium layer
- glass spherules as rock vapourized on impact and condensed in atmosphere
- shocked quartz - laminae in quartz (Australia)
- Gravity anomaly
- impact melts and huge glass layer
- Deccan Trapps, India.
Name and date the 3 epochs in the Palaeogene
- Palaeocene 65Ma
- Eocene 55Ma
- Oligocene 35Ma
Name and date the 2 epochs in the Neogene
- Milocene 25Ma
- Pliocene 5Ma
Describe the tertiary ecosystem?
The land is covered in mammals from all sizes and angiosperms, the sea is full of bivalves and gastropods. Giant formanifera and more of a modern ocean floor.
What name and size are the giant tertiary formanifera?
Nummulites and size of 1p
What occurred around 34Ma
A huge climate change as antartica changed from climate like New Zealand to what it is today over ~200000yrs.
What happened geographically in the early Cenozoic?
Antartica broke away from australia and south america.
- resulting in circular cold polar current.
Closure of the tethys ocean and later the panama isthmus.
- stopping warm current at equatorial latitude.
- overall sea level drop of 300m
What was the magnitude of the drop in CO2 levels during the Palaeogene and when did it occur?
Eocene and Oligocene boundary there was a drop from 800 ppm to 400 ppm
At 55Ma what happened in the north sea?
The North Sea triple point formed leading to the north west Scotland Tertiary igneous province.
- flood basalts
- Gabbroic intrusions
- Granite intrusions
- Dyke swarms
Erosion in the Northern mountains meant:
As the UK tilted to the SE deposition occurred in the North Sea basin.
Where is there strong evidence for the Alpine orogeny?
Isle of wight, Near vertical folded succession.
What evidence is there of the late Neogene 3Ma environment?
- London clay indicates subtropical climate.
- Crag deposits 1/2km thick in east anglia indicative of a shallow sea. (rich in bryozoan fossils, shells indicate similar temp to today.
- Cross bedded sediments, like tidal dunes. suggests N.Sea a few km inland from today.
How long is the Quaternary?
2.6Ma
What was the initial idea for the quaternary geology formation and when did it change?
- Idea of a deluge ~200yrs ago.
- Ice theory in 1820-1830 but controversial
- Evidence like striations and u-shaped valley after studying the Alps.
- Accepted by end of 1800’s.
What was suggested in the 1950’s?
4 glaciations separated by warm interglacials, it was clear from till differences.
- Land deposits were patchy and incomplete so drilled into ocean floor for O2 isotope data.
- This gave evidence for temperature and global ice volume
- 50 major glaciations in quaternary
What are the three processes of the Milankovitch cycles? Describe them.
Eccentricity - change from near circular orbit to elliptical , 100000yrs
Obliquity - variation of the tilt of the earths axiz through the planet, 40000yrs
Precession - movement of the axis in a circular motion (like a wobbling spinning top), 20000yr cycle.
What are some problematic factors for the Milankovitch cycle?
- Changes in the amount of sunlight are very small, not enough to cause such big changes
- An Amplifying factor - represented by greenhouse gases
- Ice core record indicates amplification of milankovitch signal via G.gases
Describe the Pleistocene epoch.
Almost all of Quaternary made up of this,
- Bipolar ice ages across north and south hemisphere
- Deposits like till + outwash gravel/sand show two different advances of the ice
(straightline S.UK 400ka) and (humpback further north 20ka)
Describe the Holocene epoch.
The last 11.6ka
- time of stability (allowing us to develop)
- Transitions
- sudden warming for 2000yrs
- abrupt cooling 1000yrs
- Abrupt warming
- sea level rise by 130m
- deposits from present day (soils flood deposits, deltas)
What factors do we consider when contemplating the Anthropocene?
Chemistry change in oceans and atmosphere, concrete levels, temperature, sea ice, Extinctions.
