The River Loop Trail at Black Hawk State Historic Site in Rock Island, IL, has e

Question

The River Loop Trail at Black Hawk State Historic Site in Rock Island, IL, 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?

Explanation / Answer

deposition of the limestone is mostly because of the phenomenon that the sedimentary rocks might have traveled that place because of ocean waves and then because of volcanic lava or other oceanic currents

there was a massive expanse of the ocean and then warm and saline type of climate devlops in the ocean , moreover larhe fishes were extinct and current fish fauna was developed

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