HONR219D Homework 1 Due 2/6/18

Part I: Principles of Stratigraphy 1.) The image at right shows three rock

units, the Kaibab limestone, the Toroweap shale, and the Coconino sandstone exposed in the side of Walnut Canyon, AZ. List them in order from oldest to youngest. Which principle of stratigraphy enabled you to decide?

2.) The image at right shows three sandstone beds of sediment exposed at Sideling Hill, MD. Note that Bed 2 contains pebbles made of a darker material. Which is older, Bed 2 or the material making up the pebbles?

Which principle of stratigraphy enabled you to decide?

3.) The image at right layers of volcanic ash and cinders in the flank of volcano Ecuador in the Galápagos Islands. Also present is a dike that formed from the solidification of a sheet of molten magma, Which is older, the layers or the dike? Which principle of stratigraphy enabled you to decide?

A geologist is exploring a road-cut in which are exposed in cross-section: sedimentary beds (including B, C, D, and G), pebble-sized inclusions (E), a dike made of solidified magma (A), and an ancient erosional surface (F). Answer the following questions based on the diagram above.

4.) List the sedimentary beds B, C, D, and G in order from oldest to youngest. For each pairwise comparison of units indicated in your answer above (B and C, etc.), indicate which principle of stratigraphy told you that it was younger than the next older one. List all that apply. 5.) Which is older, sedimentary bed D or the inclusions it contains (E)? which principle(s) of stratigraphy told you? 6.) List from oldest to youngest volcanic dike A, sedimentary bed B, and erosional surface F

For each of the younger two, indicate which principle of stratigraphy told you that it was younger than the next older one. List all that apply.

Biostratigraphy: Questions 1 through 8 refer to the four schematic hypothetical stratigraphic columns given below. In these, letters A, B, C, and D refer to road-cuts at separate localities, while the blocks labelled with Roman numerals represent distinct rock units (layers.) Fossil taxa are shown by arbitrary numbered symbols.

7. Which of the fossil organisms do not appear to be good index fossils and why? 8.) Correlate the different stratigraphic sections using the fossils located in each stratum.

That is, identify groups of rock units that seem to be roughly contemporaneous. (The presence of the same fossil species in strata from the different regions might indicate this. At the very least, they show that both were deposited sometime during the history of that species). (Use this format: AI = BI = CIII, etc.)

9.) Create a composite section for the strata available. Using the space below, construct an idealized stratigraphic column for the four sections. To do this,

• Determine how many different discrete time units are represented and display these in the composite column.

• For each time unit, indicate the rock units in the original columns to which it corresponds (E.g.: A-I, B-III, etc.)

• Draw the fossil(s) which characterize each horizon as well. For this exercise only, assume that the original columns reflect constant uninterrupted

sedimentation. 10.) How many discrete time units are there in the composite section? Obviously, no one column in the original data encompasses all of the time represented by

your composite section. How would you respond to the criticism that your composite section is fictional?