ImpactCraterLab

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Texas A&M University *

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207

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Geography

Date

Oct 30, 2023

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pdf

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Uploaded by MegaWombatMaster197

1 Records of Impact Events Part I: A history of impacts (10 pts) On Canvas, there is a list of impact events, the ages of those events and the diameter of the crater in a file called “ImpactCraters.xls.” These data are from http://www.passc.net/EarthImpactDatabase/ where you can also view maps of the locations of the impact craters. The mean impact crater diameter is 15.7 km (stdev = 24; median = 8 km). Only the largest impacts are likely to have global effects. The top 1% of impacts are 62 km in diameter or greater. A. Using the provided data, make scatter plot where age of the impact is the x-axis and diameter of the crater is the y-axis. Clearly label your axes and paste your plot here: B. During what time interval are there the most impact craters? Why do you think we have more craters of that age? C. List the ages of the craters that are greater than 62 km in diameter for the last 260 Myrs. Name of Crater Age

2 C. Do any of these large craters correspond to mass extinction events in marine genera (see table to the right)? If so, which craters match to which extinctions? (Note: many of these ages have uncertainties associated with them, so don’t expect an exact match.) C. Go to the Paleobiology Database ( https://paleobiodb.org/navigator/ ) and search for all Dinosauria. Examine the diversity curve of genera by clicking on the chart icon on the left side of the screen. List the ages of the four greatest diversity declines in Dinosauria in the table below in order from greatest to least. If there is an associated impact event, list the size of the crater. Rank of Extinction Event Age of event Crater? (y/n) Size of Crater 1 (most severe) 2 3 4 (least) D. Given your data, do you think the all the extinctions were related to impact events? Some of the events? Make a claim about which events are impact related, provide your evidence, and explain your reasoning. If not impact related, what other mechanism do you think could have caused the extinctions?

3 Part II: Drilling the K/Pg Boundary (10 pts) There are many stratigraphic sections around the world where the Cretaceous/Paleogene boundary is preserved including in marine sediment cores. Ocean Drilling Project (ODP) Leg 171 to Blake Nose drilled three cores that intersected the K/Pg boundary (Right). A. Examine the three photographs from cores containing the K/T boundary. Using the provided worksheet, create a composite core log describing the lithology that you observe. Sections are numbered 1- 7 in order from top to bottom and the scale bar on the left is in centimeters. The last column labeled “cc” is the core catcher – ignore that portion. B. At what depth(s) do you think the K/Pg event is in each core? Why do you think this is the boundary? Describe the observations you made to determine the boundary location. (See Canvas for a hint sheet.) Example: U1419AH: Section 2, 25-30 cm, abrupt change in sediment color from tan to reddish brown 1049A17X: 1049B8H: 1049C8X: C. If you had access to analyze these cores, what data would you collect to test your hypothesis that the extinction event occurred at the depth interval you gave in B?

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4 D. If you had access to analyze the cores, what data would you collect to test the hypothesis that an impact event occurred coincident with the depth interval you gave in B? E. In the space below, sketch hypothetical results for two types of data you would collect with core depth on the y-axis and your hypothetical data on the x-axis. Label your axes so it is clear what type of data you are plotting and which direction is an increase in the values. Clearly indicate the depth interval that represents the extinction interval. Don’ t worry about numerical values for your axes, relative positions are fine.

5 Part III: Drilling the Chicxulub Impact Crater (10 pts) IODP Expedition 364 used a mission specific platform to drill into the Chicxulub impact structure in April- May 2016. This was primarily a geophysical expedition to understand how rocks respond to large impacts. However, because sediments overlying the impact record were also retrieved, we can see how life recovered at the impact site after initial sterilization by the impact. A. Examine the core photo and lithostratigraphic description containing the K/Pg boundary (Canvas file: Exp364SiteM0077Core 40R). How is the lithology different from the one at Blake Ridge? Describe your observations in terms of sediment color and texture. B. Relative to other locations around the world, would you expect the extinction and recovery to be expressed differently at the impact site? If so, what differences do you expect and why would you expect these differences? C. Test your hypotheses. Review the paper on Canvas by Lowery et al. 2018. (Data associated with the paper can be found here: https://www.nature.com/articles/s41586-018-0163-6#Sec6 ) Does the paper support or refute your hypothesis in B? D. Give two examples of data (either from figures, from tables, or from the supplement) that clearly supports or refutes your hypotheses and explain your reasoning regarding how the data supports or refutes your hypothesis.