laws of stratigraphy
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About History of Geology - Laws of StratigraphyTRANSCRIPT
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Alay Desai (130420106060)
Jeet Donga (130420106061)
Sarvesh Khanna (130420106062)
Aalekh Shah (130420106063)
Kaushal Kathiriya
Nirav Deshmukh (120420106055)
Prof. Pratima Patel
Prof. Khushboo Berawala
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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.
Stratigraphy
Photo by W. W. Little
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Photo by W. W. Little
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
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Principles of Stratigraphy
• Superposition
• Original Horizontality
• Lateral Continuity
• Crosscutting Relationships
• Faunal (biological) Succession
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Sedimentary layers become progressively younger upward
through a stratigraphic sequence.
Principle of Superposition
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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.
Principle of Original Horizontality
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Tilting of Beds by Folding
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Tilting of Beds by Faulting
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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.
Principle of Lateral Continuity
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Bed Termination by Faulting
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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.
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There are three types of unconformities based on the types of rocks
involved and their attitude with respect to each other.
Types of Unconformities
Disconformity (paraconformity) Nonconformity
Angular
Unconformity
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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.
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Fossils are found in a consistent and predictable succession
everywhere on earth.
Principle of Fossils or Faunal
(biological) Succession
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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.
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Geologic Time Scale
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Geotechnics and Applied Geology by Dr. R. P. Rethaliya
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