Biostratigraphy.ONLINE.F22

1 Environmental Geology 105L Name: ___________________________ Biostratigraphy This week’s lab builds on Lab 4 Lithofacies and Correlation. Please refer to Lab 4 for information to help with this lab exercise. Refer to Chapter 6 Biostratigraphy in the online lab manual, Biostratigraphy Animation, and the PowerPoint presentation posted on OAKS to help you answer the following questions. Your Prelab will also be of help with the lab exercises. Biostratigraphy — Using fossils to date and correlate beds Background: These fossils have been found in the sediment beneath Folly Beach, and have either .... o A Radiometrically Dated Absolute Age ... o When a fossil is dated using radiometric dating techniques, there is an age range within which the fossil falls. We are assuming that our fossils have been radiometrically dated in a laboratory and these are the results. They will NOT represent the total range for the species - just an individual OR o A known geologic range ... o The span of time in which the species first evolved (First Appearance) to when it went extinct (Disappearance), obtained by a compilation of fossil record data. PART 1 – Introduction to Biostratigraphy Refer to Chapter 6 Biostratigraphy in the online lab manual, Biostratigraphy Animation, and the PowerPoint presentation posted on OAKS to help you answer the following questions. Your Prelab will also be of help with the lab exercises. 1. We know the relative ages of rocks within a core because of the Law of Superposition - deeper layers of rock within a core are older than shallower ones. However, we need additional information in order to determine the age of the layers. a. What are two ways we can date stratigraphic rock layers (refer to lab 3 on Geologic Time)? 2. Read slide 2 to learn more about biostratigraphy. • You will need: o Internet o “Chapter 5. Lithofacies and Sea level change” provided on OAKS o The Powerpoint provided on OAKS o Biostratigraphy Animation on OAKS

2 a. Is biostratigraphy an example of relative or absolute dating? 3. Slide 3 shows a sample of fossiliferous limestone containing several different types of fossils (crinoid stem, bryozoan, bivalve, and gastropod). Together these fossils make up a fossil assemblage. a. What type of environment did this rock most likely form in (think back to Lab 1!)? 4. Slide 4 shows the geologic range of the fossil assemblage shown on slide 3 . The geologic range of an organism is when it is first seen in the geologic record, to when it is last seen. a. Which of the following is the geologic range of the gastropod ( choose all that apply )? ORDOVICIAN SILURIAN DEVONIAN MISSISSIPPIAN b. An index fossil is one that is ubiquitous and has a short geologic range. Therefore, when seen in the fossil record, it helps pinpoint the age of that layer. Which of the following fossils on this slide would be the best index fossil? CRINOID STEM BRYOZOAN BIVALVE GASTROPOD c. The concurrent range is the time period during which a group of fossils all lived at the same time (or are all found together in the fossil record). When we see that fossil assemblage in the rock record, we can use its concurrent range to help determine the age of that rock layer. What is the concurrent range of this fossil assemblage on slide 13 ? ORDIVICIAN SILURIAN DEVONIAN MISSISSIPPIAN 5. On Slide 5 , cores 1,2, and 3 contain different fossil assemblages. a. Which fossil assemblage is the oldest: A, B, C, or D? b. Which TWO fossil assemblages occur in all three cores? c. Which assemblage only occurs in core 2? 6. On Slide 5 , locate the X on core 2 , and the Y on core 3 . These are both sandstone layers. a. Were they deposited at the same time? b. Why or why not (use the fossil assemblages to explain your answer!)? 7. You are expected to know the bolded terms from this lab! PART 2: Using the fossil record to relatively date the layers in your cores 1. The table on slide 6 shows fossil specimens that were found at different depths in each of your 5 cores. Fossils that are all found at the same depth were all deposited at the same time, and make up a fossil assemblage for rocks at this depth. a. What fossils make up the fossil assemblage found at -6.5m depth (Assemblage 5)? 2. The graph on slide 7 shows the geologic ranges of each specimen. What is the geologic range for each specimen that you listed in question #4, above?

4 3. What is happening to the sea level (and potentially also the climate) as humans are showing up in the for the first time in our Folly fossil record? 4. If Core A is to the west and Core E is to the east , describe what happens to the sandstone layer through time using these directions. 5. As you are exploring the old coast guard station out by the Lighthouse Inlet, you find some darkened, fossil oyster shells in what appears to be mud and leaves at the base of the modern day dunes. a. Oysters live in the marsh, not in the dunes - so what are they doing there? b. What was the sea level like when these oysters were alive, relative to today? HINT: these oysters were found at the base of the dunes in Core B. 6. Given the history of sea level change through time, would you want to invest in ocean front property on Folly Beach? a. Why or why not?