ORVEC Fossil: They Call Me Petoskey EarthCache
Hidden : 10/13/2012
Difficulty:
2.5 out of 5
Terrain:
5 out of 5

Size: Size: other (other)

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Geocache Description:




Petoskey

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What is a fossil? A fossil is the prehistoric remains of a plant or animal. Fossils are typically preserved when they are buried under many layers of sand and mud. Under great pressure the sand and mud become sedimentary rock. Minerals seep into the fossil replacing the organic matter and creating a replica in stone.

When was the Devonian Period? Known as the "Age of Fishes" because almost all known groups of fish appear during the Devonian period. It was also the "age of ancient coral" because more types of coral (now extinct) appear in the Devonian than any other Paleozoic period. This period spanned approximately 408-350 million years ago. The Devonian name comes from a county in England called Devon(shire). In the Kentuckiana area, Middle Devonian fossils can be found in the Jeffersonville Limestone (about 390 million years old) here at the Falls of The Ohio (FoTO).


Prismatophyllum polished into a Petoskey Stone


They call them Petoskey Stones because they are famous as polished rocks along the shore of Lake Michigan near the town of Petoskey. Up there, Petoskey stones were given their cobble shape from the action of Pleistocene glaciers. Here at the FoTO, we call them Prismatophyllum. That's their scientific name.

Prismatophyllum

The Devonian Period occurred between 395 and 345 million years ago. During that time, Indiana and Kentucky languished beneath a warm, tropical sea, and were located about twenty degrees south of the equator. Tectonic shifting of the earth's continents eventually moved this part of the earth's surface to its current location. During the 45 million year span of the Devonian Period, the oceans deposited layer upon layer of lime silt, sediments, and plant and animal remains.

Of these deposits, five distinct fossil layers lie exposed at the Falls:
  • The uppermost layer - or the youngest rock - is the Paraspirifer Acuminatus Zone, which contains fossils of brachiopods (including paraspirifers, a two-shelled animal similar to a clam); bryozoans (commonly called lace coral); trilobites; and some solitary, branching, and colonial corals.
  • Second is the Fenestrate Bryozoan-Brachiopod Zone. Named for the predominant fossils found there, here one also can find crinoid stems in abundance.
  • A six-inch-thick layer called the Brevispirifer Gregarius Zone follows, and contains fossils of brachiopods and gastropods (sea snails), horn corals, or cup corals, and one of the Falls' most unusual corals, the astromatoporoid.
  • The Amphipora Ramosa Zone, commonly called the Cave Zone. Pocket caves have developed here due to the powerful erosive powers of the Ohio River rushing across the rock. This zone occurs along the vertical cliffs of the river channel, where the cutting force of the river reaches its peak.
  • The oldest and most remarkable layer is the largest to be exposed. It bears the name Coral Zone because of its abundance of fossil corals - so many, in fact, that visitors find it difficult to walk on this layer without stepping on fossils exposed in the bedrock.


  • What Was it Like at the Falls 387 Million Years Ago? The local Devonian geography and climate was much different than today. The abundance of corals and limestone rock indicates this area was a warm, tropical, shallow sea.

    We know it was an ocean and not freshwater because the fossils are similar to animals that live in the ocean today. We are certain it was warm and tropical because limestone only forms under those conditions. And we are sure it was shallow because many corals, including some over 40 inches in diameter can be found upside-down. This indicates that strong currents, like those from a hurricane, tossed heavy corals.


    Fossils at FoTO


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    Optional: To share your experience please take a photo of yourself, the geology or just your GPSr at the waypoint.

    And to demonstrate the educational value of this Earthcache, please send answers to the following four questions:

    1. What is the diameter of the Prismatophyllum deposit seen here?
    2. Which ZONE is this fossil commonly found in?
    3. How many other examples can be seen within 15 feet of the waypoint?
    4. Based on your observations with a keen eye, is this a rare or common sighting here?

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    Please Do not wait on a reply from me. FOUND IT logs which do not meet requirements will be quietly removed.

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