09. geologic time_06

09. geologic time_06 - GEOLOGIC TIME OBJECTIVES 1) Be able...

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GEOLOGIC TIME OBJECTIVES 1) Be able to reconstruct the geologic history of an area from a cross-section (using the principles of relative dating). In other words, know how to use the rules for relative dating. 1. The law of original horizontality – Most rocks laid down flat, and tilted only later during geologic events. 2. Law of superposition – Oldest rocks are at the bottom. 3. Law of cross-cutting relationships – A rock being cut by another rock or feature that is older. 4. Law of Inclusion – If a rock includes a piece of another rock A, the rock is older. 5. Law of lateral continuity – Most rock beds don’t end suddenly when originally laid down. 6. Law of fossil succession – Fossil assemblages change in an ordered succession through time. 2) Know the various forms of “up indicators”. Graded Bedding: Fossils such as tree stumps, animal burrows, root traces. Stratigraphic Superposition: Cross-bedding, sediment deposited on a slight slope in water or air. Mudcracks, raindrop impressions, infilled voids ( crystals on top, mud on
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09. geologic time_06 - GEOLOGIC TIME OBJECTIVES 1) Be able...

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