Using the power of Google Earth, GeoTours take you on flyovers of key locations discussed in the text.
StudySpace student website and ebook icons in each GeoTour connect your to the text and online review materials.
Dialogue boxes accompanying each site include text, figures, photos.
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Geotour 10: The Strata of the Colorado Plateau
Relative Age Dating & Unconformities
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| 1a. Check and double-click the placemarks for Problems 1a-i, -ii, -iii, and -iv to fly to the east end of the Grand Canyon.
According to the principle of original continuity, which layer corresponds to the layer indicated by placemark Problem 1a-i?
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| 1b. According to the principle of superposition, what is the order of age of layering for placemarks Problem 1b-i (pink), -ii (dark), and -iii (variegated) from oldest to youngest?
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| 1c. According to the principle of cross-cutting relationships, which layer is younger: placemark Problem 1c-i (pink) or 1c-ii (tan)? Hint: trace the pink layer to the left and see what happens to it.
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| 1d. The surface dividing the units in Problem 1c is called the “Great Unconformity” because it separates older Precambrian units from the younger Cambrian unit with up to a 1 billion year gap in the rock record due to erosion. What type of unconformity is it at this location?
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| 1e. Check and double-click placemark Problem 1e to fly west to another exposure of the Great Unconformity. Here metamorphic rock and an igneous dike are overlain by the same tan Cambrian unit. Which is older: the dike or the tan rock layer?
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| 1f. What type of unconformity is the Great Unconformity at this location?
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| 1g. According to the principle of inclusions, which rock unit should have inclusions of the other?
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| 1h. The placemark labeled Problem 1h points to another unconformity between the Early Mississippian 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.
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Stratigraphic Formations in the Grand Staircase, UT
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| 2a. The Grand Canyon provides spectacular exposures of Paleozoic and Precambrian rock layers. As you travel north from the Grand Canyon, you encounter laterally extensive younger Mesozoic rock layers that have eroded into a series of cliffs and benches. Because of this stair-like erosional profile based on lithology, the area is known as the “Grand Staircase”. The Moenave Formation forms most of the “Vermillion Cliffs”, the Navajo Sandstone forms the “White Cliffs”, and the Claron Formation forms the “Pink Cliffs”.
Turn on the “Geologic Map of Grand Staircase, UT” map overlay. Check and double-click the placemarks for Problems 2a-i, -ii, and -iii. Which placemark corresponds to the correct cliff-forming unit?
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| 2b. The steep cliffs of Zion Canyon at Zion NP in Utah comprise one of the “steps” in the Grand Staircase. Check and double-click placemark Problem 2b and turn on the “Geologic Map of Zion NP” to determine which cliff forms Zion Canyon.
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| 2c. Checkerboard Mesa, one of the most famous landmarks in Zion NP, is comprised of this same cliff-forming unit. Check and double-click the Checkerboard Mesa folder to fly there. The “checkerboard” pattern is due to the intersection of cross beds (yellow) with joints (green). Which of these formed first?
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Rock Layers and Monoclines, Circle Cliffs, UT
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| 3a. The Circle Cliffs area allows us to not only look at the ages of some of the different rock layers exposed in the Colorado Plateau, but to also explore a geologic structure that is commonly associated with the Colorado Plateau area: the monocline. The Circle Cliffs erode into the monocline that forms the Waterpocket Fold of Capitol Reef NP in Utah.
Turn on the “Geologic Map of Circle Cliffs, UT” map overlay and locate the flat irons of Jurassic Kayenta and Wingate on the east and west sides of the Circle Cliffs area (placemarks 3a-i and -ii are two representative flat irons on the different limbs of the fold). Monoclines typically have a steeply tilted fold limb (forelimb) and then a shallowly dipping (sometimes sub-horizontal) backlimb. Which placemark corresponds to the steep forelimb?
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| 3b. Both monoclines and anticlines uplift and deform rock layers such that when eroded, certain ages of rocks are exposed in the center of the structure relative to the flanking limbs. What is the relative ages of the rocks exposed in the Circle Cliffs area (placemark Problem 3b)?
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