When studying sedimentary rocks, it is important to understand ...

[corkyiscool3328]

When studying sedimentary rocks, it is important to understand their environment of deposition. What is the environment of deposition and how can it contribute information about the geologic history of the rock?
 
  What will be an ideal response?

Question 2

The River Loop Trail at Black Hawk State Historic Site in Rock Island, Illinois, has exposures revealing nearly 130 million years of geologic history.
 
  At the base of the hill is Devonian-aged limestone containing brachiopods and bryozoans. Above the limestone is Pennsylvanian-aged shale, with an unconformity between the two. The black shale is rich with fossils of ferns and marsh grasses. Directly on top of the shale is Pennsylvanian-aged sandstone. Using the geologic materials described, determine the environment of deposition for each unit. How has the overall environment changed from the Devonian to the end of the Pennsylvanian?
  What will be an ideal response?

[pallen55]

Answer to Question 1

Answer: The environment of deposition is the geographic setting where the sediment is accumulating. Each environment of deposition is characterized by a specific set of geologic processes and environmental conditions. An understanding of the environment of deposition provides information about the paleoenvironment.

Answer to Question 2

Answer: The limestone represents a shallow marine environment, most likely a reef. Sometime after the deposition of the limestone, erosion created an unconformity. The shale represents a coastal swamp, complete with swamp grass. The sandstone represents a beach. The overall environmental change is that sea level is lowering.