Identifying Regression in Geological Times

Which of the following times indicates a regression?

6. Sandstone and siltstone with coal
5. Gray shale with marine fossils
4. Sandstone with plant fossils and beach deposits
3. Shale and sandstone with marine fossils

Final answer:

The times that indicate a regression are option 6 (sandstone and siltstone with coal) and option 4 (sandstone with plant fossils and beach deposits).

In geology, regression refers to a period when the sea level falls, causing the shoreline to move seaward. This can result in the deposition of sediments that indicate a regression. Different types of rocks and fossils can provide clues about the environmental conditions during that time.

Let's analyze the options:

• Sandstone and siltstone with coal: This combination suggests a terrestrial environment with plant life and coal formation, indicating a regression.
• Gray shale with marine fossils: This combination suggests a marine environment with marine fossils, indicating a transgression.
• Sandstone with plant fossils and beach deposits: This combination suggests a terrestrial environment with plant life and beach deposits, indicating a regression.
• Shale and sandstone with marine fossils: This combination suggests a marine environment with marine fossils, indicating a transgression.

Based on the analysis, options 6 and 4 indicate a regression, as they both involve sandstone and suggest a terrestrial environment with plant life and beach deposits.