Principals of Stratigraphy, Facies, & Stratigraphy

Question 1

What is Stratigraphy?

Answer 1

Stratigraphy is the observation, description, and interpretation of succession, age relations, geographic distribution, and temporal correlation of stratified rocks. Unstratified rocks are also dealt with (lithodemic units)

Question 2

Stratigraphy deals with?

Answer 2

Sedimentary rock layers
Distribution of rock layers in space and time
Genetic interpretation of rocks
Correlation of rock units, especially time correlations

Question 3

What are the 6 Principals of Stratigraphy?

Answer 3

1. The principle of Superposition:
   - In an undisturbed succession of sedimentary rock layers, the oldest layer is at the bottom and the youngest layer is at the top
2. Principle of original horizontality
   - Sediments are depositied in essentilly horizontal layers. Therefore, inclined layers must have been tilted post deposition
3. Principal of lateral continuity
   - Sediments extend laterally until it thins and pinches out or terminates against the edges of the depositional basin
4. Principal of Cross-cutting relationship
   - An igneous intrusion or a fault must be younger than the rocks it intrudes or displaces
5. Principal of Inclusions
   - A layer containing clasts from a different rock must be younger than the rock from which the clasts originate. This also applies to xenolits
6. Principal of faunal succession
   - Fossils occur in strata in a regular, non-repeating and predictable succesion. Same fossils found in rocks and different locations can be correlated

Question 4

Walther’s Law

Answer 4

Deals with lateral and vertical relationships of facies
It states that when depositional environments migrate laterally, sediments of one environment come to lie on top of sediments of an adjacent environment

It states that when depositinal environments migrate laterally sediments of one environment come to lie on top of sediments of an adjacent environment

Question 5

Facies

Answer 5

Facies is a body of rock caracterizes by particular combination of lithology, physical, and biological structures that bestow an aspect different from the bodies of rock above, below, and laterally adjacent

It is implicit in the concept of facies that different facies represent different depositional conditions and environments

Question 6

What are the kinds of Unconformities?

Answer 6

Angular Unconformity
- The older strata were deformed and then cut off by erosion before deposition of younger layers

Disconformity
- An irregular erosional surface between parallel strata. A disconformity implies cessation of sedimentation and onset of erosion but not tilting

Nonconformity
- Occurs when two very different rocks are in contact with each other

Paraconformity
-Two parallel sequences of rock in contact with each other with no significant erosional feature along the contact. With a time gap inbetween

Question 7

What is the significance of unconformities?

Answer 7

They are evidence that former seafloors were uplifted by tectonic forces and exposed to erosion

Preservation of a surface of erosion