Interpreting past environments Flashcards
What is temporal framework?
- A geologic time scale
- The statisfatic timescale
- Date ash beds with radiometric dating
Spatial framework using remnant magnetism
- Rocks are deposited
- Metals within align to the poles
- Can plot where continents were located etc
- Plot out palaeogeography
How has sea level and continental configuration changed over time?
- Both changed in the short and long term
- The extent of the shelf seas and epicontinental seas (shallow seas on the continents) has varied considerably
- Higher sea levels and more continenta shelf with higher biodiversity = more fossil preservation
1/ The nature of sediments (relate to present day distribution).
Reconstructing past environments
- Sedimentologists can read rocks
- Know how rocks were deposited etc
2/ The nature of fossil content (relate to present day distribution).
Reconstructing past environments
- Look at fossils and work out clues as to what the environment was.
- E.g. If echinoderms are present this is an indication of a marine environment.
3/ The distribution of climatically sensitive sediments and fossils.
Reconstructing past environments
- By looking at the fossil and sediments in an area you can work out what the climate was like
- E.g. Palms and mangroves are only found in warm temperate regions
4/ Environmentally discriminating isotopes.
Reconstructing past environments
- Carbon types etc.
- Look at isotopic values within fossil
- Discriminate between light and heavy boron depending on how acidic the environment was.
- Can work out how much CO2 was in the environment
- Therefore content within the atmosphere
5/ Environmentally influenced characteristics of organisms.
Reconstructing past environments
- Tree growth rings
- No growth rings = tropical not seasonal
- Higher CO2 level the few stomata plants have
- Many examples of this.
What was the configuration of the world like during the triassic when the dinosaurs evolved?
- Huge land mass: Pangea
- Small tethys ocean
- Huge Panthalassic ocan that covered most of the earth
What was the configuration of the world like during the Jurassic?
- Early jurassic - minimal splitting
- Late jurassic - Many parts of the land splitting apart: North america split from gondwana
- Late cretaceous - Everything has split apart
What was the configuration of the earth during the late cretaceous?
- Africa and south america split
- Shallow warm seas that had high diversity
How did CO2 levels change over time?
Higher in triassic and gradually fall (still much higher than today’s levels)
How have O2 levels changed?
- Less O2 than today
- Less forest fires
- Carboniferous - high O2 lots of forest fires
When was the greenhouse world?
- Triassic, jurassic and cretaceous
- High CO2 levels
What is a polar forest?
Case study: Polar dinosaurs
- Polar regions had no ice (greenhouse world)
- Warmer climates in the past had forests
- Forests at the poles
- Cool / temperate forests
- Forests thrived in summers (sun didn’t set)
- 6 months darkness (shed leaves)
- No such thing as a polar forest today
- High CO2 regimes of weird sunlight
