Lecture 2: The Great Detective Science Flashcards
Describe Sandstone
- grains mostly quartz (SiO2)
- metamorphoses to quartzite if pure
- usually few fossils (moderate to high energy)
- few chemical forensic clues
Where is sandstone found?
- deserts
- coastal dunes
- growing deltas
- river channels
What is metamorphism?
mineralogical and structural adjustments of solid rocks in response to physical and chemical conditions differing from those under which the rocks originally formed
Describe Limestone
- grains and cement mostly calcite (CaCO3 + Mg-)
- metamorphoses to marble if pure
- usually many fossils
- some chemical forensic clues
Where is limestone found?
- nearshore, lagoons, reefs
- deep sea (like calcareous oozes)
Describe siltstone, mudstone and shale
- grains mostly quartz, clay minerals and cements
- metamorphoses to slate then schist then gneiss
- few to many fossils
- many chemical forensic clues (chemically diverse)
Where are siltstone, mudstone and shale found?
- quiet. gentle environments
- lakes
- lagoons
- far continental shelf, slope, deep margin
- deep sea
What is an outcrop?
a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth
Describe Ooze (and red clay)
- grains mostly microfossils (calcite or silica)
- rarely metamorphosed (subducted)
- mostly microfossils (huge numbers)
- many chemical forensic clues
Where is Ooze found?
- deep sea
- red clay; mostly windblown dust where fossils rare
What is subduction?
destruction of ocean crust
Is low/marine ground good for geological evidence?
Yes, good deposition
Is high ground good for geological evidence?
No, too much erosion and weathering
Are subsiding/low basins and continental margins (far shelf, slope, rise) good for geological evidence?
Yes, good chances of deposition and long-term survival with physical and chemical integrity
Is oceanic crust good for geological evidence?
Yes, good chance of deposition
No, poor long-term survival
What is the survivorship of:
1) high ground
2) glaciated regions
3) palaeosol (fossil soil)
4) lake, swamp, channel
5) delta
6) desert
7) subsiding basin
8) continental margin
9) deep sea
1) very poor
2) very poor
3) moderate to locally good
4) moderate to locally good
5) moderate to good
6) moderate to good
7) good
8) moderate to good
9) >200 mya very poor
<175 mya moderate to good
1) What is lateral linking?
2) Why is it effective?
3) How are gaps inferred
1) rocks are sometimes linked by dead animal and plant fossils
2) evolution does not repeat itself
3) evidence of erosion, implausible environmental successions and fossil gaps
How are rocks aged:
a) relatively
b) absolutely
a) fossils, palaeomagnetism (oceanic crust)
b) parent-daughter radioactive decay sequences, chemicals, isotopes and biomarkers
How does Potassium help age rocks and what makes this method effective?
- Ratio between K and Ar
- new volcanic rock contains K and relatively no Ar
- K decays to Ar at a known rate
- unaffected by heat or pressure
- ratio determines age
What limits the K:Ar ration method and how can this be overcome?
- Ar can escape
- contamination can occur
- good sample collection required
What makes a good marker fossil?
- abundant species
- short duration
- good preservation potential (ie. no organisms lacking hard parts or birds)
- widespread habitat- preferrable globally
- lives/becomes deposited in different environments (planktonic graptolites are ideal)
- appears and becomes abundant/widespread quickly
- extinct everywhere at once quickly (not at a mass extinction boundary)
Give an example of a marker fossil?
- didymograptus leintwardinesis
- once existed abundantly in the sea surface, but died out at the same relative time
- rocks above Dl are younger, rocks below are older
What is a common biomarker used for aging rocks?
RUBISCO (most abundant enzyme on Earth)
1) What does RUBISCO do?
2) What does it stand for?
1) involved in the first step of carbon fixation during photosynthesis
2) Ribulose-1,5-bisphosphate carboxylase/oxygenase
