1. Order of layers from oldest to youngest:
A (granite) -> B (limestone) -> C (tilted and folded sedimentary rock) -> D (volcanic ash) -> E (horizontal sedimentary rock)
2. Explanation for layer positions:
A (granite): Granite is an igneous rock formed deep underground by the solidification of magma. It's the hardest rock in this sequence and therefore the oldest based on the Principle of Original Horizontality.
B (limestone): Limestone is a sedimentary rock formed from the accumulation of marine sediments. It lies above the granite and below the tilted layers, suggesting it formed after the granite but before the tectonic activity.
C (tilted and folded sedimentary rock): The tilting and folding indicate deformation caused by tectonic forces. Since it's above the undisturbed limestone, it must have formed after the limestone and the tectonic activity.
D (volcanic ash): Volcanic ash fills in existing valleys and covers underlying layers, indicating it formed after the tilting and erosion of Layer C.
E (horizontal sedimentary rock): This layer lies above the volcanic ash and is undisturbed, suggesting it formed after the volcanic activity and represents the most recent layer in the sequence.
3. Unconformities:
There are two unconformities in this cross-section:
Between Layers A and B: This unconformity represents a period in which the granite was exposed to erosion before the limestone was deposited.
Between Layers C and D: This unconformity indicates a period after the tilting and folding of Layer C and before the deposition of the volcanic ash.
4. Environment of layer formation:
A (granite): Formed deep underground in a magmatic environment.
B (limestone): Formed in a shallow marine environment based on the presence of marine fossils.
C (tilted and folded sedimentary rock): Likely formed in a terrestrial or shallow marine environment, followed by tectonic activity that caused the tilting and folding.
D (volcanic ash): Formed in a volcanic environment with explosive eruptions that spread the ash across the landscape.
E (horizontal sedimentary rock): Likely formed in a relatively calm and stable environment based on the undisturbed horizontal layers.
The Complete Question
Relative Dating Lab 3.13F: Rock Layers and Time
In your lab manual for Relative Dating Lab 3.13F, you're presented with a geological cross-section showcasing various rock layers. Your task is to analyze these layers and determine their relative age relationships.
Here's the scenario:
Imagine you're exploring a canyon wall, and you observe the following rock layers from top to bottom:
Layer E: A thick layer of undisturbed, horizontal sedimentary rock.
Layer D: A layer of volcanic ash that has filled in valleys and covered some of the underlying layers.
Layer C: A layer of tilted and folded sedimentary rock with visible cracks and faults.
Layer B: A layer of limestone containing marine fossils.
Layer A: A layer of granite exposed at the base of the canyon.
Task:
Based on the principles of relative dating, including the Law of Superposition, the Law of Cross-Cutting Relationships, and the Principle of Original Horizontality, answer the following questions:
Order the layers from oldest to youngest: List the layers in the order they were formed, starting with the oldest at the bottom and ending with the youngest at the top.
Explain your reasoning for each layer's position: Briefly explain why you placed each layer in your sequence based on the observed features and relative dating principles.
Identify any unconformities: Are there any unconformities present in the cross-section? If so, explain where they are and what they indicate about the geological history of the area.
Describe the environment in which each layer formed: Based on the characteristics of each layer, what can you infer about the environment in which it formed (e.g., marine, terrestrial, volcanic)?