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Undergraduate student Olivia Buchan and graduate student Jim Cook observing Pennsylvanian delta deposits exposed along Pennyrile Parkway north of Hopkinsville, KY.
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Burrows of animals moving through the sediment prior to its lithification into rock are common at this outcrop.
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Ripple marks with steep left sides indicate that a current was moving over this pre-lithified sediment from right to left.
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Thin beds of fine-grained sandstone (light-colored layers) alternating with finer-grained shale (dark-colored layers) reflect variation in the velocity of water flow in this environment over time.
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A burrow, probably made by a different kind of animal than that which made the burrow shown above. Fossilized burrows, along with fossilized trails and tracks, comprise a group of fossils called "trace fossils."
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The knobs present on this trace fossil demonstrate that it was produced by an animal with stiff appendages, probably an arthropod.
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The combination of ripple marks (formed by moving water or air) and alternating sandstone and shale layers documents the deposition by a moving fluid (water or air) characterized by fluctuation in flow velocity.
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"Ball and pillow structure" produced by sand sinking into fluidized muddy sediment.
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Very few animals were burrowing in this sediment, as indicated by undisturbed preservation of very thin beds.
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Sandstone bed which is more resistant to erosion than the underlying shale and therefore sticks out above the shale.
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Although most of this is gray siltstone deposited in water that was very quiet, the thin, light-colored layers of sand reflect increased current capable of transporting larger grains.
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Irregular trace fossils made by animals moving up and down (as opposed to moving in a horizontal plane) through the sediment.
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A trace fossil called Olivellites comprised of two lobes of packed sediment. It was originally thought to have been made by a snail, but prrobably is the work of an arthropod. It is found in deltaic deposits of Pennsylvanian age worldwide.
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