About History of Geology - Laws of Stratigraphy

2.  Alay Desai (130420106060)
 Jeet Donga (130420106061)
 Sarvesh Khanna (130420106062)
 Aalekh Shah (130420106063)
 Kaushal Kathiriya
 Nirav Deshmukh (120420106055)
 Prof. Pratima Patel
 Prof. Khushboo Berawala

3. Stratigraphy
Stratigraphy is the branch of Geology which deals with the
history of the rocks of the Earth’s crust with special
emphasis on their approximate time of formation and the
changes they have undergone since their formation.
Photo by W. W. Little

4. Stratigraphy Records History
The stratigraphic record preserves details pertaining to major
geologic events, such as:
• Mountain-building (orogenies)
• Land-Sea Relation
• Climatic fluctuation
• Glaciation
• Epeirogeny
• Age of rocks
•Evolution and migration of plants
Photo by W. W. Little

5. Principles of Stratigraphy
• Superposition
• Original Horizontality
• Lateral Continuity
• Crosscutting Relationships
• Faunal (biological) Succession

6. Principle of Superposition
Sedimentary layers become progressively younger upward
through a stratigraphic sequence.

7. Principle of Original Horizontality
At the time of deposition, sedimentary layers are horizontal. If they
are no longer horizontal, they have undergone some type of
deformation. The two most common types of deformation are folding
and faulting.

8. Tilting of Beds by Folding

9. Tilting of Beds by Faulting

10. Principle of Lateral Continuity
At the time of deposition, sedimentary layers are continuous for long
distances. If they terminate abruptly, they have either undergone
deformation or they have been eroded. The two most common causes
of abrupt bed termination are faulting and unconformities.
Sedimentary layers can taper laterally into other sedimentary units.

11. Bed Termination by Faulting

12. Bed Termination by Unconformity
An unconformity is a surface that represents an episode of missing
geologic time. During the formation of an unconformity, sediment is
either not deposited or it is deposited and subsequently removed by
erosion.

13. Types of Unconformities
Disconformity (paraconformity) Nonconformity
Angular
Unconformity
There are three types of unconformities based on the types of rocks
involved and their attitude with respect to each other.

14. Principle of Cross-cutting
Relationships
A rock body that is cut (crossed) by another rock body, structure, or
unconformity is older than what is cutting it.

18. Principle of Fossils or Faunal
(biological) Succession
Fossils are found in a consistent and predictable succession
everywhere on earth.

19. Fossils may be defined as remains or impression of
ancient animals and plants which have been preserved
in sedimentary rocks by natural processes.
It is like the calendar of an year. As an year is divided
into different months, weeks, days , geological time
scale is also subdivided into smaller and smaller unit to
suit stratigraphical study and correlation. The
unconformities subdivide geological time scale into
smaller units.

20. Geologic Time Scale

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