Carmel Church taphonomy problem

One of the intriguing things about the Carmel Church deposits is the presence of an unusually dense bonebed together with a conglomerate made up of cobbles up to a foot in diameter, both of which are unique in these deposits. These photos show how the context of a fossil can be just as important as the fossil itself.

The photo above shows the nearly complete left lower jaw of a red drumfish (Sciaenops ocellatus) (from top to bottom, dorsal, medial, and lateral views). Fish jaws are made up of multiple bones and are quite fragile; when you find a jaw this well preserved you can be pretty certain that it hasn’t been reworked from an older sedimentary unit.

This photo was taken the day the jaw was discovered:

The jaw is the dark patch running diagonally upward from the top of the screwdriver. The big white blob above it is a rock, part of the Carmel Church conglomerate. The gray patches below and to the right of the jaw are more rocks. In this picture only the back half of the jaw is visible, because it turned out that the jaw had snapped in the middle and been folded in half.

This gives us some important information. We originally believed that the conglomerate was older than the bonebed. However, the presence of the conglomerate rocks both above and below the jaw shows that in fact the conglomerate and the jaw were deposited at the same time. Usually fossil bones in a conglomerate are carried to their final location by the same currents that form the conglomerate. But in this case, because the jaw is so fragile, we know that it wasn’t transported in with the rocks from a different location.

So, from this specimen, we can establish that the bonebed and the conglomerate were  deposited at the same time, and that the bones were originally deposited at this site and not washed in from elsewhere with the rocks. We still don’t know how the deposit formed, but with this information we can rule out certain possibilities.

Incidentally, if you visit VMNH in Martinsville, this specimen is on exhibit in the “Uncovering Virginia” gallery.

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This entry was posted in Carmel Church Geology, Carmel Church Osteichthyans, Carmel Church Quarry, Chesapeake Group, General Geology. Bookmark the permalink.

3 Responses to Carmel Church taphonomy problem

  1. Alton Dooley says:

    Brett discovered this specimen during our July 2003 excavation.

  2. Grenda says:

    Very interesting Dr. Dooley. I liked the explanation. And thanks for the note about Brett findng the drumfish jaw. Is she the Maeve Leakey of the dynamic duo? Hmm…..

  3. Alton Dooley says:

    It’s a source of both pride and embarrassment to me that Brett has found the majority of the really interesting fossils on excavations I’ve led.

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