Lesson 16: North American Craton II: Deformed Craton
This week's lesson is a continuation of last week's except that instead of exploring park lands in the stable interior of the North American craton we'll be looking at the processes that have shaped its deformed western margin. We'll start on the Colorado Plateau with its long history of platform sedimentation and then move on to the foreland basin that captured sediments shed from the fold-and-thrust belts and basement uplifts that developed in response to Mesozoic subduction along the western edge of the continent. We'll also return to our second writing assignment this week and complete the abstracts for our articles on hotspots.
As you read through the second part of chapter 10 and the supporting websites please take careful notes so that you can keep track of major points and recall them more easily when we refer to them later in the semester. Be sure that you are prepared to meet the learning objectives outlined below before you move on to the quiz at the bottom of the page.
Weekly Learning Objectives
Upon successful completion of this week's lesson, a student is expected to be able to:
- Outline the history of the western North American craton as told in the stratigraphic relationships between major rock units (basement rocks, platform sediments, and forearc deposits) found on the Colorado Plateau.
- Recognize common features formed in the sedimentary rocks of the Colorado Plateau, including cross-beds, hoodoos, arches, and natural bridges, and briefly explain what they tell us about the geologic history of the area where they are found.
- Differentiate among landforms created by the two different styles of foreland deformation—fold-and-thrust belts and basement uplifts—and briefly contrast them in terms of where, when, and under what tectonic conditions each was formed.
Reading and Browsing Assignment
- Read the second part of Chapter 10 (pages 228-236) and focus on the topics outlined in the learning objectives above.
- To learn a little more about the geologic history of the Colorado Plateau and the Rocky Mountain regions check out the brief introductions to these geologic provinces given on the USGS-NPS Geology in the Parks website. (Note that the Rocky Mountain page appears to be only partially completed.)
- Cross-beds are a striking feature of several of the sandstone units that were deposited on the Colorado Plateau during Mesozoic time. The sorting and rounding of the sand, as well as the presence of land animal tracks, indicate these were built by dunes that once lay in desert or coastal settings. To learn more about how dunes produce cross-beds, check out sand dunes on the USGS-NPS Geology in the Parks site.
- To learn more about the geology of two of the Laramide basement uplifts preserved in national park lands check out these brief summaries of the geologic histories of Rocky Mountain National Park and Grand Teton National Park.
- Finally, because it can be tough to get a sense of what the landscape was really like in the past from written descriptions and photos of modern outcrops, check out the beautiful paleogeographic maps of the western United States drawn by Ron Blakey at Northern Arizona University. For example, comparing the location of Zion Park shown on Figure 10.20 (p. 229) with the Jurassic paleogeography of the western United States can you see when the dunes that comprise the Navajo Sandstone must have covered the park area?
Exercise 16 (Due by 9:00 AM on Monday, 10-May-2010)
Once you recieve your outline back it will be time to prepare your second abstract. In the left-hand column of this page click on "Documents" and then scroll down and click on "Writing Assignment".
This week we'll be completing step three of the assignment. Working from your outline, write an abstract of your article's major points following the format of the "sample abstract" linked to the writing page. For the purpose of this abstract, act as though you are the author of the article. In this assignment format is very important, and the easiest way to make sure your abstract is formatted correctly is to download the "abstract template" linked to the writing page. Print one copy for reference and then simply "type over" each part of the digital copy on your computer with the appropriate information relevant to your article (title, author information and citation, abstract body, etc.) That way each part of the abstract will be formatted correctly and positioned correctly on the page. (Note that this template is in Word format. If you are using another word processor check the link on the writing assignment page for abstract specifications such as column widths, margins, etc.) When you are done, save your abstract in a place (and with a name) that you'll remember. This is the file you'll send a copy of to me.
The abstract template is a two column document, so if your text in the left-hand column is too long it will "push" the text in the right-hand column down. If this happens, shorten your abstract and remove any blank lines at the top of the right-hand column so that the first line of of text is flush with the title at the top of the left-hand column. Be sure to include your PIN (last five digits of your Etudes user id) and the course name and date at the appropriate places in the right-hand column. Also, pick three keywords that someone searching for your abstract might be expected to use in a search engine. Proper names (e.g., Mount Shasta) and accepted phrases (e.g., global warming) are okay, but otherwise try to stick to single words. Be sure to only capitalize keywords that are proper names.
Write your abstract in complete sentences and be sure that it is well organized and coherent. It's a good idea to check out the abstract grading rubric that is also linked to the writing page so that you can see which criteria I will use for evaluation. Complete your abstract and send it to me as an attachment (preferably a Word document) to Exercise 16 in the Etudes "Assignments, Tasks, and Tests" tool by next Monday 10-May-2010. I will score your abstract and return it to you with a copy of the grading rubric in about one week. Your abstract is worth twice as many points (20) as a typical weekly exercise, so take your time and think carefully as you write it.
Quiz 16 (Due by 9:00 AM on Monday, 10-May-2010)
After you feel you have mastered the learning outcomes outlined above, please complete Quiz 16 in the Etudes "Assignments, Tasks and Tests" tool. There are ten questions, each worth one point. If you can answer all of them correctly it means that you know your way around the deformed western part of the North American craton and pretty well and are ready to move on to learn about parklands formed by terrane accretion next week.