Stratigraphy is a branch of geology which deals with the strat of rocks. It has some laws which refer as the principles of Startigraphy.

1. Presentation on
Principles of Stratigraphy
Presented by
AYON SAHA
ID : 14GLM019
Dept. of Geology & Mining
University of Barisal

2. Stratigraphy
Stratigraphy is the study of rock layers
(strata) and their relationship with each
other.
Stratigraphy provides simple principles
used to interpret geologic events.

3. Law of Stratigraphy
1. Principle of Superposition
2. Principle of Original Horizontality
3. Principle of Original Lateral Continuity
4. Principle of Cross-Cutting
Relationships
5. Principle of Uniformitarianism
6. Principle of Biological Succession
7. Principle of Inclusions

4. Law of Stratigraphy cont.
1. Law of Superposition : When sedimentary rock layers are
deposited, younger layers are on top of older deposits.

5. Law of Stratigraphy cont.
2. Law of Original Horizontality : Sedimentary rock layers are
deposited horizontally. If they are tilted, folded, or broken, it
happened later.

6. Law of Stratigraphy cont.
3. Law of Lateral Continuity : Sedimentary rock layers extend
in all directions horizontally unless a river erodes them or an
earthquake moves them

7. Law of Stratigraphy cont.
4. Law of Cross-Cutting Relationships: If an igneous intrusion
or a fault cuts through existing rocks, the intrusion/fault is
Younger than the rock it cuts through.

8. Law of Stratigraphy cont.
5. Law of Uniformitarianism : Markers of missing time
 When layers of rock formed without interruption, we call them
conformable.
An unconformity represents a long period during which deposition
ceased and erosion removed previously formed rocks before deposition
resumed.
Angular unconformities
Disconformity
Nonconformity
Paraconformity

9. Angular Unconformity Disconformity
Law of Unconformities cont.
 An angular unconformity is
an unconformity where
horizontally parallel strata of
sedimentary rock are
deposited on tilted and
eroded layers, producing an
angular discordance with
the overlying horizontal
layers
 A disconformity is an
unconformity between
parallel layers of sedimentary
which represents a period of
erosion or non-deposition

10. Non-conformity Paraconformity
Law of Unconformities cont.
 A nonconformity exists
when the sedimentary rock
lies above and was
deposited on the pre-
existing and eroded
metamorphic or igneous
rock
 A paraconformity is in which
strata are parallel; there is
little apparent erosion and
the unconformity surface
resembles a simple
bedding plane

11. Law of Stratigraphy cont.
6. Principle of Biological Succession : Systematic sequence
of fossils with time. Extinct fossils do not reappear in younger
rocks.

12. Law of Stratigraphy cont.
7. Principle of Inclusions: Any rock that contains fragments
of an adjacent rock must be younger than the adjacent rock.