Read the diagram. The layers are undeformed. Use superposition to identify the oldest and youngest...

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11. Read the diagram. The layers are undeformed. Use superposition to identify the oldest and youngest sedimentary layers. Then use the cross-cutting relationship to compare the igneous intrusion with the layers it cuts.
12. Field scenario: A geologist examines a roadcut with three horizontal sedimentary layers. Shale sits at the bottom, sandstone is in the middle, and limestone is at the top. A narrow igneous dike cuts through the shale and sandstone but stops at the boundary below the limestone. Put the four rock-forming events in order from oldest to youngest, and explain how superposition and cross-cutting relationships help you determine this order.

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Oldest Layer: Layer D is the oldest because, according to the principle of superposition, the bottom layer is the oldest in an undeformed sequence of sedimentary rocks. Youngest Layer: Layer A is the youngest because it is at the top. The igneous intrusion is younger than all the layers it cuts through, which are Layers B, C, and D, according to the principle of cross-cutting relationships. Order of Events: Deposition of Shale (oldest) Deposition of Sandstone Intrusion of Igneous Dike Deposition of Limestone (youngest) Explanation: The principle of superposition indicates that the shale is the oldest since it is at the bottom, and the limestone is the youngest as it is at the top. The principle of cross-cutting relationships shows that the igneous dike is younger than the shale and sandstone because it cuts through them but does not cut through the limestone.

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Read the diagram. The layers are undeformed. Use superposition to identify the oldest and youngest...

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