1.5 Gelogical Structures Flashcards
What is the strike?
The orientation of the bed and has 2 directional components eg compass, clinometer
Explain how sedimentary beds are laid?
They are all horizontal
Principle of original horizontality (POOH)
They have dip angles measured from horizontal to top of bedding plane
What are unconformities and what do they represent?
A period of erosion that leaves a gap in the geology record
On a map unconformities are lines that cut across the beds
There are 4 stages:
1. Rocks deposited horizontally
2. Rocks deformed by tectonic forces and are dipping into the ground
3. Rocks uplifted and eroded at surface
4. New beds deposited above unconformity
Why are dipping rocks older than horizontal rocks?
The principle of original horizontality
All beds are originally horizontal and later deformed to have a dip
What are folds?
Folds occur when rocks deep in earth, where rocks are hotter and ductile, are subjected to compressional forces
There are anticline and syncline folds
On maps we identify folds by looking for symmetrical rock patterns
What are anticline folds?
The oldest rocks are found in the middle (core)
What are syncline folds?
Youngest rocks are found in the middle (core)
When do faults occur?
When rocks are brittle at lower temperature close to surface due to compressional or extensional forces
1. Normal upthrown fault FUN fault has a upthrown footwall and a downthrown hanging wall
Normal faults form due to extensional forces within the crust
2. Footwall downthrown reverse fault FDR fault caused by compressional forces within the crust - known as a thrust fault
3. Strike slip fault - only horizontal displacement and no vertical movement
What is displacement?
The amount on a fault - usually vertical or horizontal displacement
What is strike slip fault?
They show only horizontal displacement - no vertical movement
1. Left handed (sinistral)
2. Right handed (dextral)
Look across the fault plane to see which direction the marker bed has moved
