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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)
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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)
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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
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