Rock type copy names over depositional environment

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Rock Type (copy names over) Depositional Environment Energy Level (low, intermediate, high) 3 2 1 3. Think about the changes between Time I and Time II. What geologic events could have caused the change in environment, and therefore the changes in energy level? Refer to Geologic History section in your pre-lab reading. ___________________________________________________________________________________ __________________________________________________________________________________________ 4. Think about the changes between Time II and Time III. What geologic events could have caused the change in environment, and therefore the changes in energy level? Refer to Geologic History section in your pre-lab reading. ___________________________________________________________________________________ __________________________________________________________________________________________ Activity 3: Compaction of Sediments If the rocks in a sequence were uplifted above sea level, and a stream were to cut through the rocks, we would see a stack of rocks in the canyon walls that all formed in the same location but at different times and in different depositional environments. How long does this take? Let’s investigate. 1. Deposition : the principle of uniformitarianism says that the processes that are going on today are the same as those that have acted in the past (“The present is the key to the past”). Modern depositional rates of limestone in the Caribbean Sea are 0.5cm/1,000 years (kyr). Given that rate, how long would it take to deposit just one layer from this rock sequence? Assume each layer is 100 m thick. Show your work (no calculations, no credit). __________________ years 2. Compaction : sediment gets substantially compacted during lithification. For limestone, a typical amount of compaction is 20% that of deposition. Given this, and using your previous answer, how long did it really take to deposit one layer? Show your work (no calculations, no credit). __________________ years 3. Assuming this rock sequence has 4 limestone layers, as well as a constant* compaction rate during the deposition of all layers, how long did it take to deposit the whole stack of rocks? Use your previous calculation to answer this question. *in reality, these rates change over time depending on many factors; we’re assuming constant here just to make the calculations simpler. __________________ years
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Lab #3: Sedimentary Rocks and Depositional Environments 63 Activity 4: Constructing A Geologic History By now you should have a good idea of how a single location can have lots of different rocks forming, depending on the water level and the environment of deposition at the time. Let’s use the skills we’ve learned and interpret the history of a real rock sequence. The picture below is of a rock sequence exposed in a canyon wall. The dashed lines indicate the contacts between the different rock layers. These layers are sedimentary rock layers formed long ago in the same way rocks formed in the previous activities. These rocks have since been exposed by erosion. Specifically, the river that is currently running through the bottom of the canyon eroded these rocks, but it didn’t form them.
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