sept 3 - 3 Thursday, September 03, 2009 9:30 AM What is the...

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Intrusions can be close in age, or hugely later o Eg. Pilot Knob, local volcano help with providing extra information for the particular locality Ash falls -> fall on surface, incorporated; good at dating that depositional surface; tend to be weathered at the surface, Zr work better: in ash bed they determine the age of bed, in sandstone they determine the age of the source rock; some things in ashfall are useful, while others are not o Radiometric age dates have + or accuracy o What is the significance of “time rocks”? Dating is good for the Phanerozoic; radiometric age dating is better for Precambrian v. any fossils (due to lack of evolution, and sample size) Migration (ecologic time) o Speciation (short geologic time) o Ecologic v. Geologic Time stromatolites, cherts -> long lived organisms o Date: ash beds, rare minerals (glauconite), detrital grains of minerals -> age of source area eg. Zircon, tells you the age of the source rock not the age of the bed o Key examples
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sept 3 - 3 Thursday, September 03, 2009 9:30 AM What is the...

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