Based on the analysis of the geological block diagram, we can determine the relative ages of the rock units by applying the fundamental principles of stratigraphy: Superposition, Cross-Cutting Relationships, and Unconformities.
Here is the step-by-step reasoning:
1.
Oldest Layer: The lowest layer in the sequence is
slate. According to the Principle of Superposition, this is the oldest rock unit shown.
2.
Intrusion into Slate: A body of
granite intrudes into the slate. By the Principle of Cross-Cutting Relationships, the granite must be younger than the slate it cuts through.
3.
Further Intrusion: A
pegmatite vein cuts through both the slate and the granite. This means the pegmatite is younger than both the slate and the granite.
4.
Erosion and Deposition: An erosion surface lies above the granite, indicating a period of erosion before new deposition began. Above this erosion surface is the
sandstone layer. Therefore, the sandstone is younger than the granite.
5.
Continued Deposition: Above the sandstone is the
limestone layer. Following the Principle of Superposition, the limestone is younger than the sandstone.
6.
Cross-Cutting Feature: A
basalt dike cuts through both the limestone and the sandstone. This means the basalt dike is younger than both of these sedimentary layers.
7.
Another Erosion Surface: Another erosion surface is present above the limestone, indicating another gap in the geologic record.
8.
Youngest Layers: Above this second erosion surface are two more layers:
volcanic ash and, at the very top,
shale and siltstone. By superposition, the volcanic ash is older than the shale and siltstone, but both are younger than everything below the erosion surface.
Final Answer:
The rock layers, listed from most recent (top) to oldest (bottom), are as follows:
1. Shale and Siltstone
2. Volcanic Ash
3. Basalt Dike
4. Limestone
5. Sandstone
6. Granite
7. Pegmatite
8. Slate
Parent Tip: Review the logic above to help your child master the concept of relative ages of rocks worksheet.
