Earth and Life Science Week 5

Folding and Faults, Stratified Rocks, and Relative and Absolute Dating
Definition of Terms:
Faults – A breakage or fracture to the layer of rocks

Folds – results from bending or folding on layers of rocks
Lithification – the process of transforming sediments into sedimentary rocks
Strata – layers of lithified sedimentary rocks

Tectonic forces – driving forces that leads to formation of folds and faults
Types of Tectonic Forces:

1. Compressional Tectonic Forces
a. Direction of force is towards one another on opposite sides of a
plane
b. Plane is considered ductile (bendable); deformation is possible
without breaking
c. Results in convergent plate boundaries
d. Compressional forces result into folding
e. Folds – wavelike deformation in layered rock or sediment
f. When plane can no longer hold compression, it breaks and becomes fault
2. Tensional Tectonic Forces
a. Also known as tensile force
b. Direction of force is away from one another on opposite sides of a
plane
c. Results in divergent plate boundaries
d. Usually results in formation of faults
3. Shearing Tectonic Forces
a. Force that acts parallel to a plane
b. Causes rocks on either side of the plane to slide or to be smeared
from one another
c. Results in transform plate boundaries
d. Common whenever there is a shearing force
Types of Folds
1. Anticline
a. Also called “upfolds”
b. Upward arches in the layers of rocks
c. Highest point is called “anticlinal crest”
2. Syncline
a. Also called “downfolds”
b. Downward arches in the layers of rocks
c. Lowest point is called “synclinal trough”
*Fold limbs – layers between the anticlinal crest and synclinal trough
Classification of Folds
1. Symmetrical (simple)
▪ Simple fold with the same angle of fold limbs; vertical axial plate
2. Asymmetrical
▪ Compressional forces are not the same with steeper angle; one which axial plane is inclined
3. Overturn
▪ Fold limbs are tilted beyond vertical dip; axial plane inclined that strata on one limb are overturned
4. Recumbent
▪ Fold limbs lie horizontally due to over compression; axial plane is essentially horizontal
Faults
- Fold receives too much pressure that it can no longer hold, it will break and the breakage is known as fault
Types of Faults
1. Dip-slip faults – inclined fractures where the blocks have mostly shifted vertically
a. Normal fault – caused by tensional forces; block above the fault has moved downward relative to
the block below
b. Reverse fault - caused by compressional forces; upper block, above the fault plane. moves up and
over the lower block
2. Thrust faults – one section of land slips over another at a low angle when land is compressed
a. Caused by compressional forces

3. Strike-slip fault – blocks move mostly horizontally
a. Also known as “transform” or “lateral” faults

b. Caused by shearing forces
Stratified rocks
- Layered rocks
- Commonly contains fossils
- Fossils – valuable in the research and investigation of Earth’s history
Formation of Stratified rocks
- Lithification – process of transforming sediments into solid sedimentary rocks; involves processes like
accumulation, compaction, and cementation
- Compaction – sediments are accumulated and covered by another layer, pressing the grains and
making pores minimized, thus, some of it is contained water is released. The presence of mineral
components in the pores may contain solution that binds particles together resulting to cementation
Definition of Terms:
- Strata – layers of lithified sedimentary rock
- Stratigraphy – study of understanding strata
Relative and Absolute Dating

Relative Dating
- Determines the order or arrangement of rocks form youngest to oldest
- Follows the Law of Superposition
- Law of Superposition – new layer is formed on top of a previous layer
- Without using the actual ages or dates of rocks
Absolute Dating
- Identifies numeric age of rocks
- Uses the ratio of isotopes through radioactive dating
Examples:
- Tree rings
▪ Refer to age of a tree by counting the total number of rings
- Radiometric dating
▪ Calculates absolute ages of rocks and minerals that contain radioactive isotopes
- Varves
▪ Any sediment layer that shows a yearly cycle and are often seen in glacial lakes back to the ice age

Earth and Life Science Week 5

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Folding and Faults, Stratified Rocks, and Relative and Absolute Dating

Faults – A breakage or fracture to the layer of rocks

Strata – layers of lithified sedimentary rocks

Types of Tectonic Forces:

a. Caused by compressional forces

a. Also known as “transform” or “lateral” faults

Relative and Absolute Dating

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