Lesson 15: North American Craton I: Undeformed Regions and Groundwater
During our last three weeks we'll be exploring the geologic "architecture" of North America as preserved in our national park lands. This week we'll consider two fairly distinct topics. First, we'll look at North America's "basement", both the Archean and Proterozoic rocks that form the core of the continent and the continental glaciation that has exposed much of this landscape. Second, we'll look at the relatively thin blanket of younger sedimentary strata that mantle much of the craton and at the caverns that groundwater has hollowed out in these nearly flat-lying deposits. Finally, because groundwater is such an important resource, will work on an exercise that will help you discover how geologists model groundwater flow and track down contamination when it occurs.
As you read through the first 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:
- Describe how the two major parts of the North American craton–the shield and platform–differ, and indicate—in words or on a map—where they are located relative to one another and to younger orogenic belts.
- Predict how the deposition of marine sediments on a continental platform is likely to be affected by a global change in temperature (formation or melting of land ice) and by a worldwide change in the amount of mid-ocean ridge spreading.
- Recognize common features, such as terminal moraines, kettles, and erratics, in a landscape that has been modified by continental glaciation.
- Explain why large caverns–such as Mammoth Cave and Carlsbad Cavern–occur in platform sediments that were deposited when North America lay in or near the tropics.
- Distinguish between the "hollowing out" and "filling in" stages of a cavern's development, and explain how common cave features—such as stalagtites, stalagmites, and sinkholes—are formed.
- Differentiate between the phreatic and vadose zones of an aquifer, and predict the approximate direction of groundwater flow from a contour map showing the elevation of the water table.
- Outline two major factors necessary to develop badland topography, and predict whether or not such terrain is likely to develop anywhere in the Canadian shield.
Reading and Browsing Assignment
- Read Chapter 10, pages 209-228, and focus on the topics outlined in the learning objectives above.
- To learn a little more about the two of the major provinces of the North American craton that occur in the United States, check out the descriptions of the Laurentian Upland (shield) and the Interior Plains (platform) on the USGS-NPS Geology in the National Parks website.
- For a brief introduction to the formation of limestone caverns, browse through the Geology of Caves section of the USGS-NPS Geology in the National Parks website.
- For an overview of glaciation, including continental glaciation, check out this site on the Lanforms of Glaciation by Michael Pidwirny.
- Finally, check out the Badlands National Park website for brief introductions to the region's geology and paleontology.
Exercise 15 (Due by 9:00 AM on Monday, 3-May-2010)
To learn a little more about groundwater, please load up your Hazard City CD and work through version 3 of the Ground Water Contamination assignment. This is a fairly involved project, so allow a couple of hours to complete it. I found it helpful to print out the various reports before I started calculating my water table elevations. Also, be sure to jot down any useful notes on procedure and have your final map in hand before you go to fill out the report at the end of the assignment. (I suggest printing the form provided, filling it in, and then adding any annotations that might be helpful.) Finally, go to the ETUDES "Assignments, Tasks, and Tests" tool to complete Exercise 15. There are only five questions in this exercise, so each is worth two points.
Quiz 15 (Due by 9:00 AM on Monday, 3-May-2010)
After you feel you have mastered the learning outcomes outlined above, please complete Quiz 15 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 North America's craton and platform pretty well and are ready to move on to learn about parklands in the deformed part of the platform next week.