112lect10 - GY 112 Lecture Notes D. Haywick (2006) 1 GY 112...

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GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Significance of Fossils: Time Lecture Goals : A) Chronostratigraphy versus Biostratigraphy B) Paleontological correlations (facies changes) C) Index fossils Textbook reference: Levin 7 th edition (2003), Chapters, 3 & 4; Levin 8 th edition (2006), Chapter 6) A) Chronostratigraphy vs. biostratigraphy Last time we talked about the history of geological thinking and how geological ideas evolved. You will be glad to know that we are just about done with historical figures (some of you have confessed that you are not all that interested in people and places. “Bring us the rocks!” you have cried. I will do my best to satisfy your every wish; however, I suspect that you will regret your words once we really get into the rocks and fossils. William (Fossil Bill) Smith was one of the first people to use fossils to age rocks (okay so I lied, we will still occasionally talk about dead people). He used them to correlate strata from one place to another over the English country side. Correlation of rock units is not always easy. Take the following situation: Being able to trace rocks units is vitally important both for geological mapping and for stratigraphic correlation, but geologists are often faced with situations like that depicted here. Which of the limestones exposed in Mountain 2 is equivalent to the limestone exposed in Mountain 1? There are several ways that you can correlate these rock units. The first is by using absolute dating techniques. If you were to radiometrically date the limestones at each mountain, you could then match them up. This form of correlation is called chronostratigraphy (chrono means time). Unfortunately, it is generally not possible to use radiometrically dating on limestones. They just do not have enough radioactive isotopes within them to conduct radiometric dating. Another way to correlate the limestones is to match up their respective lithologies. True,
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112lect10 - GY 112 Lecture Notes D. Haywick (2006) 1 GY 112...

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