1. Supplemental Review and Exercises
Folds and Faults
This is a plunging anticline
Supplemental Review and Exercises

2. Deformation of Rocks
When rocks have been deformed, folding or faulting may result
How the deformation manifests its self is dependent on:
Temperature
Pressure
Rock type
Rocks under high pressure, warm, and flexible are more likely to fold
Rocks under low pressure, cold, and brittle are more likely to break or fault

3. Driving force of deformation……
Plate Tectonics:
The lithosphere is broken into “plates” free to move around on the Earth’s asthenosphere
These plates are free to move with respect to each other, either slipping along one another, colliding, or pulling apart
Forming three different plate boundaries which can result in various types of faulting and or folding.

4. The Plates

5. The Plate Boundary Types
Divergent Plate Boundary: plates move away from each other resulting in extension (tensional forces)
Convergent Plate Boundary: plates move toward each other resulting in shortening (compress ional forces)
Transform Plate Boundary: plates slide past each other results in lateral movement (shear forces)

6. Convergent Boundaries
Folding
Anticlines: Arch shaped structure
Synclines: Basin like structure
Faulting
Reverse Faults (shortening)
Vertical movements

7. Divergent Boundaries Normal Faults (Extension) – vertical movements

8. Transform Boundaries
Strike Slip Faults – lateral movement and shear forces
Shear

9. More on folds and inclined beds….
The axis of the fold divides it in half, separating the fold into two limbs the limbs of the fold have the same strike for a non-plunging fold but opposite dips
Describe orientation of the beds of rocks using strike and dip
Strike: the trend of a rock with respect to north, typically parallel to bed contacts and axis of fold
Dip: the inclination of the rock away from the horizontal down slope in a direction perpendicular to strike.

10. Strike and Dip Symbol
The strike and dip symbol resembles a “T”. However the strike line is longer than the dip line.
Click to insert strike and dip symbols on the below images.
You may want to think of the dip symbol as having an arrow on the end pointing in the direction the rocks are dipping downward

11. Rules for Strike and Dip
Older rocks dip in the direction of younger rocks
For an anticline, dips point away from each other on opposite sides of the axis of the fold
For a syncline, dips point toward each other on opposite sides of the axis of the fold

12. Age of the rock units play a role in interpretation….
Age is important for determining dip, and fold type.
Use the geologic time scale as follows:
Q – Quaternary (youngest)
T – Tertiary
K - Cretaceous
J - Jurassic
TR - Triassic
P - Permian
lP - Pennsylvanian
M - Mississippian
D - Devonian
S - Silurian
O - Ordovician
Є - Cambrian
PЄ – Pre Cambrian
NOTE: the law of superposition indicates that in undeformed rocks, younger rocks are on top of older rocks at a single point in a vertical succession

13. Looking at the Structures
Geologic Maps
Cross-Sections
Block Diagrams

14. Geologic Maps .
Geologic maps of course provide geologic information as related to rock type, age, and structure
Rock ages are described on the maps using the symbols previously discussed
Different rock types and ages are depicted as different colors on the map with the contacts between the units represented by a line.
The map symbols and configuration of the units provide structural information such as fold or fault type.
Geologic maps show the features as seen in “map view” what things look like on the surface as if you were flying or walking over an area

15. Geologic Cross-Sections
Provide information regarding the vertical configuration of the units
Similar to a topographic profile, but providing subsurface information.
A slice of the earth/feature to provide a side view, so what you would see if “cut” a vertical slice, like cutting a cake in half and seeing the layers inside

16. Block Diagrams
Incorporate the information from the map view and the cross-sectional view to show both the surface and subsurface
Seeing a block of the earth illustrated how it would look if you could cut a piece out like using a cookie cutter and see the top and the sides – allow you to get an idea of the feature in a three dimensional aspect

17. Map View and Cross Sectional View to a Block Diagram
The diagrams above are all illustrating the same features
just from in different views and or dimensions

18. The Anticline…
Anticline: an arch like structure with older beds near its center that are flanked by younger rock
Erosion
Cross-sectional View
Map View
Click to add Strike
And dip

19. The Syncline
Syncline: a basin like structure with younger beds near its center that are flanked by older beds
Erosion
Cross-sectional View
Map View
Click to add Strike
And dip

20. Plunging Folds (Map View)
In map view, non plunging folds have straight contact lines while plunging folds contact lines curve around axial trace.
For a plunging anticline the bed contacts converge around the fold axis in the direction the fold plunges and for a syncline the bed contacts diverge in the direction of dip around the fold axis

21. Three Types of Faults
Normal Fault: any fault where the hanging wall has moved down with respect to its footwall. Results in elongation of rocks on the surface due to tensional forces such as along a divergent plate boundary.
Reverse Fault: any fault where the hanging wall moves up with respect to its footwall. Results in shortening due to compressional forces such as along a convergent plate boundary
Strike Slip Fault: any fault where adjacent fault blocks move parallel to the strike or trend of the fault surface. Results in lateral movement due to shear forces such as along transform boundaries.

22. Hanging VS Foot Wall
If a tunnel was placed along the fault plane, a persons feet would be on the foot wall and their head by the hanging wall for a normal or reverse fault

23. Fault Rules
1.) The up thrown side of a normal or reverse fault will be eroded to the level of the down thrown side of the fault in time.
2.)Contact lines and associated rock formations (KEY BED) always shift in the direction of dip as the land surface is lowered by erosion.
The Key Bed is any layer of rock that may be traced along the fault even though the faulting may have displaced the bed tens to hundreds of feet, pick a bed to be the key bed to determine which fault is the up thrown block

24. Illustrating Rules 1 and 2
For a fault cutting inclined beds:
Erosion
Cross-sectional View of Fault
Erosion o S D
Map View of Fault

25. Additional Fault Exercises:
1.) Place appropriate strike and dip symbols on the diagram
2.) What is the up thrown side?
3.) What type of fault is illustrated?
Normal
4.) What is the dip of the fault plane?
East N
Up thrown
Side (West)

26. Answer the following for the diagram below:
1.) Place appropriate strike and dip symbols.
2.) Draw in the fold axis.
3.) What type of fold is shown?
Anticline
4.) What type fault is cutting the fold?
Normal
5.) What is the up thrown side?
Southwest is up Thrown

27. Answer the following for the diagram below:
1.) Place appropriate strike and dip symbols on the diagram
2.) What is the up thrown side?
3.) What type of fault is illustrated?
Reverse
4.) What is the dip of the fault plane?
North
North Side Up Thrown N