Principles of Stratigraphy

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 C ontinuity : 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.