In southern missouri you come across shale with mudcracks and a fossil crayfish?

describe the enviroment of depostion of the shale

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  • 1 decade ago
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    This sounds like a homework question, and as such is not suggesting that one debate the type of fossil or the geology of southern Missouri, but instead this is meant to help you build your understanding and geologic interpretative ability.

    The mudcracks are an important clue for describing the depositional environment. Consider where you might find mudcracks today. It would have to be in an environment where a muddy deposit of sediment (and shale often describes carbonaceous or dolomitic mudstones as well as purely siliceous mudstones) has settled and where the water was intermittent. A modern crayfish lives in river banks, so the purposeful addition of a crayfish suggests this depositional environment could be an overbank or crevasse splay deposit across a natural levee along a river. A shallow, intermittent lake, a sabkha-like environment or a tidal mudflat are other possibilities. All of these environments could have mud (later shale), occasional drying events to produce mudflats, and be inhabited by crayfish or other shrimp-like creatures.

    Obviously the suggestion that shales are from deep ocean environments is exactly what this question is meant to make you think about, and to realize that that generalization is sometimes not true.

    Here's a great photo of a crevasse splay:

    http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Cl...

    Source(s): geologist
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  • 1 decade ago

    Are you sure they are crayfish? Could it be ammonoid fossils? Shale is most typically thought to be deep ocean, or at least a long way from a shoreline. The mudcracks might suggest a still, shallow water environment, or possibly playa lake deposits.

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