Making Sense of Geologic Record

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Making Sense of Geologic Record
2014-02-09 15:45:17
geology 1020
Geology Unit 2 Learning Goals
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  1. Describe the different ways that rocks can be split up into stratigraphic units
    • 1.) Lithostratigraphy
    • - by physical attributes of rocks (like grain size, color, sorting, type, fossils)

    • 2.) Biostratigraphy
    • - by index fossils (chunking time based on fossils)

    • 3.) Chronostratigraphy
    • - by time of deposition (layers, radioactive dating)
  2. What is a formation?
    A basic unit for lithostratigraphy.

    • It must have:
    • - distinct upper and lower boundary (drastically different lithology/rock characteristics)
    • - laterally continuous (large event that occurred over a long period of time)
    • - mappable on a standard scale (not tiny, not covering half of the US)
  3. Steno's Three Laws, and other laws for relative dating of rocks
    • 1.) Principle of Superposition
    • - oldest is on the bottom (especially true for sedimentary layers)

    • 2.) Principle of Original Horizontality
    • - layers form horizontally (originally deposited flat)
    • - applies to sedimentary rocks (because they can't form at angles)
    • - not flat = major tectonic activity

    • 3.) Principle of Lateral Continuity
    • - layers are deposited, and then something else disturbs it (river cuts through) and layers are no longer connected, but still formed at the same time

    • 4.) Principle of Cross-Cutting Relationships (the other law)
    • - younger features can cross-cut older features/rocks
    • - faults cut layers = younger
    • - igneous intrusions

    • 4.) Principle of Inclusion
    • - a younger unit can contain pieces (clasts) of an older rock unit