Final answer:
The best explanation for the changes indicated by the arrow in the formation is a shift in the facies environment. This could be due to processes like erosion, deposition, or tectonic activity. The degree of sea-level change can be determined by analyzing the characteristics of the sedimentary rocks and their depositional features.
Step-by-step explanation:
The best explanation for the changes indicated by the arrow in the formation is that it represents a shift or movement in the environment, specifically in the facies environment. Facies environments refer to different sedimentary conditions or settings in which rocks are deposited. Changes in the facies environment can occur due to processes such as erosion, deposition, or tectonic activity.
For example, if the arrow points to a layer of sedimentary rock that has changed from a marine facies (indicating a previous oceanic environment) to a terrestrial facies (indicating a previous land environment), it could suggest a transgression has occurred, where sea levels have risen and covered previously exposed land areas.
Additionally, the degree of sea-level change can be inferred by analyzing the characteristics of the sedimentary rocks and their depositional features. For instance, the presence of marine fossils in a layer of rock indicates a higher sea level during that time, while terrestrial plant remains suggest a lower sea level.