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Paleozoic and Mesozoic Seas

During the Paleozoic and Mesozoic, six marine transgressions and regressions caused sea level to rise over the continents, leaving evidence in rocks in the Grand Canyon and elsewhere.

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The Seas Go In and Out

The Seas Go In and Out

Credit: Igor Klisov
Source: http://www.flickr.com/photos/38778174@N07/3566581561
License: CC BY-NC 3.0

The Paleozoic rocks of the Grand Canyon formed in environments that didn’t look anything like the Grand Canyon does now. Shallow seas, beaches and sand dunes led to those rock layers.

Amazing But True!

  • The acronym DUDE summarizes the geology of the Grand Canyon: deposition, uplift, downcutting and erosion.
  • The D in the acronym DUDE stands for deposition. Specifically, it is about the deposition of the Paleozoic sedimentary rocks.
  • During the Paleozoic Era, shallow seas covered this region four times.
  • Here are the rock types and the environment where they are deposited: Sandstone – beach or nearshore; shale – shallow, low energy offshore; limestone – shallow marine.
  • Credit: U.S. States Department of the Interior
    Source: http://en.wikipedia.org/wiki/File:Stratigraphy_of_the_Grand_Canyon.png
    License: CC BY-NC 3.0

    Stratigraphy showing age, placement, thickness of rocks in the Grand Canyon [Figure2]

  • In a marine transgression the sea moves inland to cover the land. In a marine regression, the sea moves out and the land again becomes exposed.

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With the links below, learn more about the rocks of the Grand Canyon. Then answer the following questions.

  1. Give the names of the rock layers deposited as a shallow sea moves over the land in the Grand Canyon region.
  2. Give the names of the rock layers deposited during a marine regression.
  3. What was different about the environment of deposition for the Tapeats Sandstone versus the Coconino Sandstone? How do you know?
  4. What explanation is there for this statement: the Muav Limestone is thicker in the western areas of the Canyon than in the east?

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Image Attributions

  1. [1]^ Credit: Igor Klisov; Source: http://www.flickr.com/photos/38778174@N07/3566581561; License: CC BY-NC 3.0
  2. [2]^ Credit: U.S. States Department of the Interior; Source: http://en.wikipedia.org/wiki/File:Stratigraphy_of_the_Grand_Canyon.png; License: CC BY-NC 3.0

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