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Chapter 12: Deep Time: How Old Is Old?

Geotours

Download Geotours.

Getting Started :

If you haven’t done it already, download Google Earth™ and install it on your computer.
If you haven’t done it already, download the Geotours.kmz file and save a copy to your desktop. (The Geotours.kmz file contains the Geotours for all chapters, so you only need to download this once!)
By downloading Geotours.kmz you acknowledge that it was created solely to accompany Steve Marshak's Earth: Portrait of a Planet and Essentials of Geology and is limited to use with only Steve Marshak's Earth: Portrait of a Planet and Essentials of Geology and may not be reproduced, stored in a retrieval system, or transmitted in any form by any means for any other purpose without the written permission of the publisher.
Double-click the Geotours.kmz file and Google Earth™ will open automatically.
In the left-hand sidebar you will see a Places menu, and in the Temporary Places folder you will see an EARTH_3e.kmz file. Double-click the file and you will see a list of Geotours for each chapter.
Then open the Geotour folder you want to explore! If you’d like to read more about the features of Geotours see Using Geotours, or go to our Helpful Resources section.

STOPS ON GEOTOUR 12: The Strata of the Colorado Plateau

Grand Canyon National Park, Arizona

See also Worksheet Problems 1-2
"What a Geologist Sees" Geofeatures: North Rim, South Rim, Bright Angel Canyon, Kaibab Limestone, Toroweap Formation, Coconino Sandstone, Hermit Shale, Supai Group, Redwall Limestone, Muav Limestone, Bright Angel Shale, Tapeats Sandstone, Zoroaster Granite (dike), and Vishnu Schist; Trace: The Great Unconformity

Vermillion Cliffs, Arizona

See also Worksheet Problem 3

Monument Valley, Arizona
Painted Desert, Arizona

See also Worksheet Problem 4

Upper Zion Canyon Park, Utah

See also Worksheet Problem 5
"What a Geologist Sees" Geofeatures: Navajo Sandstone, Kayenta Formation; Regional Joint Sets: Joints; Checkboard Mesa: Joint and Cross-Bed

Cedar Breaks, Utah

GEOTOUR 12 WORKSHEET

The Colorado Plateau encompasses portions of Arizona, Utah, New Mexico, and Colorado. Uplift of the region during the past 20 million years raised the land surface to elevations of 2 to 3 km. Erosion then cut down into the plateau to reveal portions of a 2-km-thick sequence of strata. These rocks, which are well exposed because of the plateau's present dryness, tell a story of changing climates and changing sea levels over the past half billion years. Google Earth^TM allows you to fly through the canyons and along the cliffs of this magical landscape to see the record in the rocks for yourself.

Grand Canyon National Park, Arizona
1. Double-click and check the box next to all of the placemarks/paths in the WAGS folder for the Grand Canyon, and then double-click on the placemark labeled Problem 1. You should see several placemarks and a red line delineating part of the Great Unconformity at Plateau Point—the unconformity can be traced down both sides of the Inner Gorge.

(a) What units lie below the unconformity?

(b) What unit underlies the broad shelf just above the unconformity?

(d) Is the unconformity tilted or nearly horizontal? (Hint: Does it stay at relatively the same elevation within the region of view?)

(e) Double-click on the placemark labeled “Zoroaster Granite (dike)” in the WAGS folder. You can see a nearly vertical, light-colored pegmatite dike cutting the darker granite. Based on cross-cutting relations between the dike and the Great Unconformity, is the dike older or younger than the unconformity?

2. The placemark labeled Problem 2 points to another unconformity between the Early Missississippian Redwall Limestone (below) and the Early Pennsylvanian Supai Group (above). The unconformity represents a hiatus of about 25 million years. What type of unconformity is this? (Hint: You know that both units are sedimentary. From the view you have, determine if the layers above and below the unconformity are parallel.)

Vermillion Cliffs, Arizona
3. Double-click on one of the placemarks labeled Problem 3. The area to the NW of the Vermillion Cliffs in Arizona shows the classic stair-step erosional pattern of nearly horizontal layers of sedimentary rock (this pattern led to the naming of the Grand Staircase National Monument).

Match the Vermillion Cliffs (Moenkopi Formation), White Cliffs (Navajo Sandstone), and Pink Cliffs (Claron Formation) with the placemarks labeled Problem 3a, b, and c. Note that the same unit occurs at both of the places marked Problem 3c. (Hint: From your view, determine which layer is highest, which lies below that one, and which layer is lowest. You may also want to zoom into each individual placemark as well. Then, use the stratigraphic column in your book to determine the stratigraphic relationship.)
• Moenkopi Formation
• Navajo Sandstone
• Claron Formation

Painted Desert, Arizona
4. The Chinle Formation is an extensive fluvial deposit that originated from NW-flowing Triassic rivers that carried quantities of volcanic ash from volcanoes to the west. The Chinle Formation is renowned for the abundant petrified wood that it contains. In Petrified Forest National Park (just south of the Painted Desert), preserved logs still remain and can just barely be seen with Google Earth^TM. The placemark for Problem 4a highlights Agate Bridge (a log over a wash). The placemark for Problem 4b shows a site where numerous logs have weathered out. Given that the Chinle Formation is a fluvial deposit and that the logs are petrified by silica derived from the volcanic ash, explain why the logs stand out in relief as the Chinle Formation is weathered away.

Upper Zion Canyon Park, Utah
5. Double-click and check the folder Checkboard Mesa in the WAGS folder for Upper Zion Canyon Park, Utah.

(a) Explain the origin of the checkerboard pattern on this famous landmark in Zion National Park.

(b) Which feature is older, the joints or the cross beds?

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StudySpace: Chemistry 2e.