HWS Homework Questions 1) The River Loop Trail at Black Hawk State Historic Site
ID: 114183 • Letter: H
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HWS Homework Questions 1) 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? Chemical and Organic Sedimentary RocksExplanation / 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 develops in the ocean , moreover the fishes were extinct and current fish fauna was developed.
In geology, depositional environment or sedimentary environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock record.
In most cases the environments associated with particular rock types or associations of rock types can be matched to existing analogues. However, the further back in geological time sediments were deposited, the more likely that direct modern analogues are not available (e.g. banded iron formations).
Types of depositional environments
Continental depositional environments
Transitional depositional environments
Marine depositional environments
Other depositional environments
Recognition of depositional environments in ancient sediments
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