This moves rocks from the middle of the crust closer

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the asthenosphere. This moves rocks from the middle of the crust closer to the surface where continued erosion will eventually expose them. When we see a stream-cut canyon with sedimentary layers exposed in the canyon walls, we can interpret: 1. the layers on either side of the canyon were probably connected at one point, representing a broad layer of sediment that was deposited and lithified, 2. the oldest material is on the bottom and the rocks get progressively younger toward the top, and 3. the youngest event to occur in this canyon is the one that is going on right now, the erosion of the stream through the sediments (even if some of the rocks exposed in the canyon walls were deposited by a stream, that happened millions of years ago in a totally different stream system). Describing the events that took place and formed a rock sequence is called a geologic history . You’ll be asked to do this in your homework, so if you have any questions about interpreting the geologic history of an area, ask your TA. Figure 11. Sedimentary layering in Zion National Park.
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Lab #3: Sedimentary Rocks and Depositional Environments 57 In-Class Activities Activity 1: Identifying Common Sedimentary Minerals The purpose of this activity is to become familiar with common or important sedimentary minerals 1. Divide into groups of 3 or 4. Every group will use one set of sedimentary minerals ( tray 1 ). 2. Use Fig. 4 as a guide to the diagnostic properties that will help you identify the mineral samples in the tray. Sample # Mineral Name Best Identifying Characteristic (shape, reactivity, cleavage, etc.) 1 2 3 4 Which of these minerals are also common igneous minerals? _______________________________________ Activity 2: Describing Sedimentary Textures Identifying specific minerals in sedimentary rocks is sometimes very difficult, so we rely much more heavily on the texture of the rocks. Because sedimentary rocks are formed differently than igneous or metamorphic rocks, we use different textural terms to describe sedimentary rocks. Look at the table below, and look at the jars of sediment in tray 2 . 1. For each of the primary sediment characteristics (sorting, grain size and rounding), determine which of the sediments best fits the textural term listed. Sorting Grain Size Rounding well sorted poorly sorted large grain size small grain size rounded angular Sample # 2. What do these differences between the sediments mean with respect to the transport history?______________ __________________________________________________________________________________________ 3. What do these differences between the sediments mean with respect to the energy level of the environment in which they formed?________________________________________________________________________ __________________________________________________________________________________________ TA CHECK__________
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Lab #3: Sedimentary Rocks and Depositional Environments 58 Activity 3: Identifying Common Sedimentary Rocks Investigate the samples in tray 3 . In your groups, follow the steps below: Step 1: Make observations and determine diagnostic features and characteristics.
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