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Laws of Stratigraphy Relative Dating

Laws of Stratigraphy Relative Dating. M. d’Alessio, 2004. 1. Stratigraphy. is the study of the formation, sequence and composition of r ock layers. 2. Relative Age Dating. tells that one rock is older (or younger) than another, but does not tell the rock’s absolute age in years.

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Laws of Stratigraphy Relative Dating

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  1. Laws of StratigraphyRelative Dating

  2. M. d’Alessio, 2004

  3. 1. Stratigraphy is the study of the formation, sequence and composition of rock layers.

  4. 2. Relative Age Dating tells that one rock is older (or younger) than another, but does not tell the rock’s absolute age in years.

  5. 6 Laws of Stratigraphy a. Uniformitarianism (James Hutton) - “The presentis the Key to the Past.” (The way geologic forces work today is the way they have always worked.)

  6. How did this get here?

  7. 6 Laws of Stratigraphy b. Horizontality - all sedimentary rock layers form flat(horizontal)on the floor of the continental shelf. If a rock layer is tilted, it was tilted by faulting or folding afterit was deposited.

  8. What Happened Here?

  9. 6 Laws of Stratigraphy c. Superposition - the bottom layer is the oldestlayer in a sequence (if the sequence is undisturbed – not flipped over)

  10. Superposition Original Horizontality YOUNGER OLDER Grand Canyon, Arizona http://www.earthscienceworld.org/imagebank/search/results.html?Category=$Category&Continent=$Continent&ImageID=hmwnq6

  11. 6 Laws of Stratigraphy d. Cross-Cutting • Igneous intrusions are youngerthan the layers through which they intrude. • Lava flows are youngerthan the rocks below them. • Faults are youngerthan the layers which they offset or tilt.

  12. Cross Cutting Relations MOST RECENT Grand Canyon, Arizona http://activetectonics.la.asu.edu/ramon/Images/Grand_Canyon/36grandcanyon.tif.jpg

  13. Cross Cutting Relationships

  14. 6 Laws of Stratigraphy e. Inclusions – inclusions are pieces of one rock layer which have broken off and are now part of another, newer rock layer. The layer that contains the inclusions must be younger than the layer from which the inclusions originally came.

  15. 6 Laws of Stratigraphy f. Fossil Succession – Fossils appear in a definite, determinable order. Any geologic period can be recognized by the range of fossils present.

  16. 6 Laws of Stratigraphy Index Fossils – these fossils indicate that the rock layer they are found in are from a very specific time frame. A good index fossil is common, widespreadand only existed for a shortamount of time.

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