Relative dating

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Relative dating
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• Relative dating is the process of determining the
  order that things happened in geologic time.

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Principles of Relative Dating

• Stenos Laws
•  The Principle of Superposition
•  The Principle of Original Horizontality
•  The Principle of Original Lateral Continuity
• The Principle of Intrusive Relationships
• The Principle of Cross-Cutting Relationships

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Stenos laws

• Principle of superposition- in a sedimentary
  sequence, the older beds are on the bottom, and
  the younger beds are on the top.

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• The Principle of Original Horizontality
• states that sediments are deposited in flat,
  horizontal layers.

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• The Principle of Original Lateral Continuity
• When sediment is deposited on the seafloor, the
  sediment will not only be deposited in a flat
  layer, it will be a layer that extends for a
  considerable distance in all directions. In other
  words, the layer is laterally continuous.

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The Principle of Intrusive Relationships

• Where an igneous intrusion cuts across a sequence
  of sedimentary rock, the relative ages of these
  two units can be determined. The sedimentary
  rocks are older than the igneous rock which
  intrudes them. (In other words, the sedimentary
  rocks had to be there first, so that the igneous
  rocks would have something to intrude.) Or, you
  could say, the intrusion is younger than the
  rocks it cuts.

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The Principle of Intrusive Relationships continued

• Diagram (1) Dike B is younger than Sedimentary
  Rock A. Erosion surface C is younger than Dike B.
  Sedimentary Rock D is younger than Erosion
  Surface C.
• Diagram (2) Sill B is younger than Sedimentary
  Rock A. Dike C is younger than sill B.
• Diagram (3) Stock B is younger than Sedimentary
  Rock A. Dike C is the youngest.

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The Principle of Cross-Cutting Relationships

• Where a fault cuts across a sequence of
  sedimentary rock, the relative ages of the fault
  and the sedimentary sequence can be determined.
  The fault is younger than the rocks it cuts. The
  sedimentary rocks are older than the fault which
  cuts them, because they had to be there first,
  before they could be faulted.

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The Principle of Cross-Cutting Relationships
continued

• Normal fault Reverse fault Examples of faults to
  illustrate cross-cutting relationships. (1) Unit
  A is the oldest, followed by B and C. Fault D is
  the youngest.
• (2) Unit A is the oldest, followed by B and C.
  Fault D is younger than C, but older than unit E

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• Using these basic principles, you may determine
  the order in which different events happened
  during geologic time.