Dry Dredgers Field Trip
Saturday, October 27, 2018
An Ohio Creek Bed
Bellevue and Corryville Formations

Photos by Bill Heimbrock


Take a look at this happy family.
They came with minnow nets but found only fossils.
Check out the heavily ladened net!

This year, the October field trip was to a creek in Keener Park, Westchester, Ohio. Unlike many creeks, this creek yields Late Ordovician marine invertebrate fossils that are not worn down from heavy water currents. The fossils are almost as good as those found on road cuts. We have visited this creek many times in the past. Our last visit was in March 2013.

The forecast was for light rain, which is about what we had, but the trees kept us from feeling most of it. There was no threat of flash flooding. A flash flood warning would have stopped this field trip. This creek drains quickly and the morning we visited only showed pooling of water with no flow. Just the same, some of our favorite trilobite spots were under water.

We came prepared with boots for shallow wading.  

Fossils Found That Day

Nautiloid Cephalopods

This site is most well known for the straight-shelled nautiloid cephalopods. Some are worn by the waters of the creek, like the one in the next picture.

Some of the nautiloid fossils we found were preserved in calcite rather than as silt casts or internal molds. In this next specimen, the outside looks fairly indescript. But if you look at the end of the specimen, you see a nice brown calcite preserving the interior of a chamber along with a dot that was the siphuncle or tube that ran down the center of the nautiloid shell.

Here are a couple more specimens that show the siphuncle running down the center of the nautiloid shell.

Here are a few more photos of nautiloid cephalopods we found in various states of preservation.

Trilobites

Despite the reputation  of this creek as producing numerous whole trilobites, none were found that day. They are weathering out of the blue-gray shale layers in the walls of the creek. You can see the fragments of Isotelus trilobites in one specific layer in this next photo.

Pelecypods (clams)

Clam fossils of Late Ordovician age were abundant at this site, particularly on the surface of slabs of rock. This first one shows the distinct surface features of Ambonychia sp..

Long, skinny clams, which were probably Cymatonata sp. were the most common of the pelecypods on slabs. (next 3 pics)

Gastropods (snails)

We saw a few snail layers on rocks. The first photo is a Cyclonema internal mold on a slab. The second photo is "gutter cast" with snails resting in the gutter when it was filled with silt

Brachiopods

Pavements of Rafinesquina of various species were seen on rock surfaces. The one pictured below is distinct for its unique profile and is abundant in the Corryville Formation. It's Rafinesquina nasuta.

Here's another photo of a Rafinesquina pavement.

Another common brachiopod we found was Vinlandostriphia ponderosa.

Some of the fragments of Vinlandostriphia ponderosa we found with smooth external shell features that were not worn by the creek water but rather from 440 million years ago when they were in a shallow sea.
 

Other fragments of Vinlandostrophia ponderosa showed internal features such as a deep muscle scar.

This Vinlandostrophia ponderosa is broken to reveal the calcite crystals inside.

Bryozoans

Many of the larger slabs were covered with ramose (branching) bryozoans. (next 3 pics)

The site is also famous for larger colonies of bryozoans that formed mats and leafy structures on the Late Ordovician Sea floor. The examples below are called trepostomate bryozans.  (next 3 pics)

Crinoids

Quite frankly, we didn't find a lot of crinoids. Here's one articulated stem.

And here is a very nice and artistic collection of crinoid stems on a rock surface. They seem to have star patterns, which help identify them as Cincinnaticrinus varibrachialus.

Ichnofossils (trace fossils)

There was plenty of shale on this site and so there was also plenty of trace fossils. Here is an example of the branching trace fossil called Chrondrites sp.  You can see it in the bottom of this picture.

That's it. Hope you enjoyed it.

See photos of previous field trips to this creek.

March 2013
September 2010
July 2009

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