The diagram below is a cross section that depicts a variety of geol...

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The diagram below is a cross section that depicts a variety of geologic features. The goal is to sort out the relative order of those features and when they occurred. Layers 1-13 are sedimentary rock layers. Fossil assemblages have been identified in layers 5-10. 13 12 F modern land surface 11 Jurassic fossils 10 9 Permian fossils 4 fossils 8 3 fossils 7 2 6 1 5 Schist 12.5% X, 87.5% indicates contact metamorphism Start by figuring out numeric ages where you can. You will need to use the %parent remaining vs # of half lives plot in the lecture images. 1. There is schist that has12.5% of a parent isotope X remaining. How many half lives have occurred since the schist formed? 2. If the duration of a half life for the X-Y pair (Y being the daughter isotope) is 1 billion years, then how old is the schist? 3. There is a basalt intrusion that has 50% of a parent isotope C remaining. How many half lives have occurred since the basalt formed? 4. If the duration of a half life for the C-D pair (D being the daughter isotope) is 480 million years, then how old is the basalt? 5. There is a granite intrusion that has 25% of a parent isotope A remaining. How many half lives have occurred since the basalt formed? 6. If the duration of a half life for the A-B pair (B being the daughter isotope) is 125 million years, then how old is the granite? 7. Sedimentary layers 1-4 contain no fossil shells or bones what so ever. But layer 1 does contain pieces of the schist, they are cross cut by basal and granite, and underlie layer 5, which does contain fossils (age on the figure). Use the Geologic timescale on p. 252 of your text and assign a likely relative age to these rocks (era or period). 8. Next label every unconformity you can identify on the figure (Dr. Budd counts 5 different ones). The type of unconformity changes laterally on some of the unconformities, so different letters are needed where those changes occur. Use the following letters and put them on the surfaces between rock units that are unconformities: A for an angular unconformity N for a nonconformity D for a disconformity 9. What about that little bit of sedimentary rock labeled "F" in the upper left of the diagram. It is the same as what other layer? Layer 10. What principle of relative ordering guided your interpretation? Principle of 11. If layer 11 formed in a different geologic period than layer 10, and there is no unconformity between the two layers, then what is the relative age (time period) of layer 11? (again, p. 252 of text will be useful On the next page, order ALL geologic features and events (not all events produce a rock) on the diagram. Fill in the lines to the left with the feature or process (e.g., layer 1, layers d to V, granite, unconformity, erosion, whatever. In the lines to the right, list the principles (Horizontality, Continuity, Superposition, Baked Contacts, Inclusions, Cross-Cutting Relations) or reasoning used to determine the ordering of each feature with respect to those formed before and after it. Don't forget to include events like tilting & erosion even though they do not necessarily correspond to a numbered feature. Put the Oldest event/feature on line 1. The first two lines and the last are done for you as examples. Feature or Event Principle / Reasoning used 1. schist forms oldest thing on the figure; everything overlies it 2. layer 1 forms layer 1 has inclusions of schist in it, so principle of inclusions 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. erosion layers 12 and 13 are no longer laterally continuous

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