Transcript of The Rock Record: Determining Relative Age Chapter 8.
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- The Rock Record: Determining Relative Age Chapter 8
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- Rocks Tell a Story!!!
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- How do we know what happened? 1.Relative Dating tells which one
is older, not actual age 2.Absolute Dating actual age
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- Determining Relative Age James Hutton discovered that the
present is the key to the past. Principle of
Uniformitarianism:
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- Layers of rock called strata tell the story of what came first.
A relative age (older vs. younger) can be determined with a few
simple laws.
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- Law of Original Horizontality Sedimentary rocks left
undisturbed will remain in horizontal layers.
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- Law of Inclusions Rock fragments (in another rock) must be
older than the rock containing the fragments.
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- ...granite is older....sandstone is older.
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- Law of Crosscutting Relationships A fault or an intrusion is
always younger than the rock layers it cuts through.
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- UNCONFORMITIES Gaps in the geologic record when deposition
stopped, rock was eroded away, and then deposition restarted. There
are 3 types: 1. Angular Unconformity 2. Disconformity 3.
Nonconformity
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- Angular Unconformity Boundary between a tilted layer and a
horizontal layer
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- Disconformity Nearly horizontal Boundary between layers of rock
that have not been deposited continuously A large time gap
exists.
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- Nonconformity Boundary where stratified (layered) rock rests on
unstratified rock
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- Possible Solution 1. Deposition of shale 2. Deposition of
conglomerate 3. Deposition of sandstone 4. Deposition of lithic
sandstone 5. Deposition of limestone 6. Deposition of quartz
sandstone 7. Deposition of limey shale 8. Deposition of mudstone 9.
Intrusion of granite. This may have occurred earlier. However, as
granites are emplaced at depth, it is assumed all the sequence was
deposited and lithofied prior to emplacement. 10. Uplift and
erosion to form current land surface. 11. Deposition of
alluvium
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- Possible Solution 1. Deposition of conglomerate 2. Deposition
of sandstone 3. Deposition of limestone 4. Deposition of shale 5.
Deposition of mudstone 6. Faulting 7. Intrusion of gabbro
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- Possible Solution 1. Deposition of Quarry Shale 2. Deposition
of Cave Bluff Limestone 3. Deposition of Redin Sandstone 4.
Deposition of Tinely Ashstone 5. Deposition of Clipton Volcanics 6.
Folding 7. Intrusion of basalt dyke 8. Faulting
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- Possible Solution 1. Deposition of Davin Shale 2. Deposition of
Hutt Ashstone 3. Deposition of Cabin Limestone 4. Deposition of
Lower Coal Seam 5. Deposition of Ravin Sandstone 6. Deposition of
Blackman Shale 7. Deposition of Fossil Bed Limestone 8. Folding 9.
Uplift and erosion (forming unconformity surface) 10. Deposition of
Basin Conglomerate 11. Deposition of Log Creek Mudstone 12.
Deposition of Loren Shale 13. Deposition of Jackson Sandstone 14.
Intrusion of basalt dyke 15. Tilting 16. Erosion to form present
landscape.