Final answer:
The sea level dropped from the time the Hakatar Shale was deposited to the time the Shinumo Quartzite formed. The shale suggests a deeper water environment, and the overlying quartzite, originally sandstone, indicates a shallow water environment, signifying a regression in sea level.
Step-by-step explanation:
To understand the changes in sea level between the deposition of Hakatar Shale and the overlying Shinumo Quartzite, which is a type of sandstone, we must consider the sedimentary environment in which each type of rock forms. Shale typically forms in deeper water settings where fine particles settle out of calm water, while sandstone forms in areas with more water movement, such as beaches or shallow seas near the shore. Since quartzite is a metamorphic rock that originated as sandstone, we know that the original sandstone must have been buried and subjected to heat and pressure to transform into quartzite.
The presence of quartzite atop shale suggests that there was a change in the environment indicating a regression in sea level. This regression would have allowed sand to deposit on top of the shale and then eventually become metamorphosed to quartzite. This concept is in line with Walther's Law, which states that the vertical sequence of sedimentary rocks reflects the lateral changes in environment. If sea level dropped, or regressed, it would expose the earlier sediments to erosion and allow newer, shallower water deposits, like sandstone that would later become quartzite, to form on top.