Stratigraphy_Puzzles_PDF.pdf

Week 14: Stratigraphy Puzzles Stratigraphy is the study of how sedimentary rocks are layered. For instance, you might wonder if the many layers of the Grand Canyon have dinosaur fossils. By studying these layers, stratigraphers determined that the rocks were too old and that many of them formed in marine environments. So no dinosaurs in the Grand Canyon. Directions: While reading this PowerPoint, jot down the correct answers for questions 1-22 and then enter your answers into the Canvas quiz.

1- The Law of Superposition This law states that sedimentary rocks are laid down over time with the lowest layer being the oldest and the top layer being the youngest. This cliff is located in the Virgin River Valley near Zion National Park. The top layers are part of the Chinle Formation which is about 230 million years old and contain some of the oldest dinosaur fossils. The bottom layers form the Moenkopi Formation which is about 240m.y. old and pre- date dinosaurs so they only contain reptile and amphibian fossils. Question 1 – Which layer is youngest – the Chinle or the Moenkopi? youngest oldest

1- The Law of Superposition Physical anthropologists use the principles of stratigraphy (layering of sedimentary rocks) to understand the age of hominid fossils. The Olduvai Gorge is a famous location that the Leakey family discovered in Tanzania. Question 2: Which bed is the oldest? Bed I, II, III or IV Research Gate Dec. 2012

2- Law of Original Horizontality Most sedimentary rocks are laid down in horizontal layers by water in rivers, lakes and the oceans. Over time these originally flat layers may folded and eroded. With folding and erosion, older layers can be brought up to the surface. Question 3 - In the top diagram, which is the oldest layer? A, B, C, D, or E Question 4- In the bottom diagram, how did the older layer D get to the surface? a) Layer D was laid down last b) Layer D was folded up and then overlying layers were eroded down c) Layer D was folded down and then covered by other eroding layers d) Layer D was laid down first D E d e D E Diagram 1 Diagram 2 Diagram 3 D E

2- Law of Original Horizontality Because of regional compression, many sedimentary rocks are folded and no longer horizontal. The red sandstones in this picture are also from the Moenkopi Formation and this hillside is near Dinosaur National Monument. The red color is from the oxidation of the original iron minerals to hematite . Question 5 – Which layer is youngest A, B, C, D or E? Question 6 – What causes the bright red color of the Moenkopi sandstones? a) volcanic ash layers b) organic material c) oxidation of iron d) reduction of iron A B C D E

3- The Principle of Lateral Continuity – states that sedimentary rocks form in continuous lateral beds that often extend for miles. Anything that interrupts the horizontal beds like a river or a canyon happened after the beds formed. The meanders in the San Juan River shown below cut through the horizontal layers that are laterally continuous throughout this landscape. You can visit this overlook at Goosenecks State Park in southwestern Utah. Question 7 - What came first here? The river or the horizontal sedimentary beds.

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