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Home Q & A Board Science-Related Homework Help Forensic Science
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Riq556 Riq556
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6 years ago
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 Pennsylvanianaged 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?
 
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#1
Staff Member
6 years ago
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 develops in the ocean , moreover the fishes were extinct and current fish fauna was developed
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#2
6 years ago
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.
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