Stratigraphy

1. Stratigraphy • The study of strata (layers) of rocks with an eye toward interpreting the geologic history of the region • Closely tied to dating methods • Uses a variety of methods - fossils, stable isotopes, paleomagnetics, sedimentary cycles - to correlate and distinguish layers • Very important for oil exploration and mining

2. Stratigraphic Principles • Principle of original horizontality • Every sedimentary layer is deposited horizontally

3. Stratigraphic Principles • Principle of cross-cutting relationships • Any layer that is cut by something else has to be older than that something else • Applies to igneous intrusions, faults, veins, erosional surfaces, etc. Granitic intrusion From D. McConnell, Geologic Time, http://lists.uakron.edu/geology/natscigeo/Lectures/time/gtime1.htm

4. Stratigraphic Principles • Principle of stratigraphic superposition • Oldest rocks are on the bottom • Youngest rocks are on the top Dead Horse Point, UT From D. McConnell, Geologic Time, http://lists.uakron.edu/geology/natscigeo/Lectures/time/gtime1.htm

5. Stratigraphic Principles • Principle of original lateral continuity • Sedimentary layers don’t just stop suddenly • They extend horizontally until they taper out Millroy, PA Pictures from D. McConnell, Geologic Time, http://lists.uakron.edu/geology/natscigeo/Lectures/time/gtime1.htm Graybull, WY

6. Stratigraphic Principles • Principle of unconformities • Some stratigraphic sections are incomplete • Any place where there is missing time is called an unconformity • Unconformities normally happen either through erosion or non-deposition

7. The Great Unconformity Grand Canyon, AZ

8. Angular Unconformity

9. Disconformity

10. Nonconformity

11. Stratigraphic Thinking From D. McConnell, Geologic Time, http://lists.uakron.edu/geology/natscigeo/Lectures/time/gtime1.htm

12. One possible interpretation...