Dolostone Trilobites-Caught in the Storm EarthCache

This site is located near an off ramp of the Bluegrass Parkway in Bardstown, Ky. The terrain rating is a 1.5 but if you go to the top of the road cut it would be a 2. This is not necessary to log the EC. Please note 2 pictures are required.

Dolostone Trilobites-Caught in the Storm

At this location we see relatively thick layers of dolomitic limestone. This is limestone with the presence of dolomite, a white or sometimes colorless mineral. Located within the layers are scattered fossil remains of prehistoric animals. Some are familiar such as snails similar to modern day specimens, while others have been extinct for millions of years, such as the trilobites.

Fossils form as animals or plant material gets covered by sediments. As the sediments are hardening by compaction, the animal or plant will eventually decay, leaving a mold (a hole in the material shaped like the animal/plant). What most people are interested in is the cast of the fossil, that portion that looks most like the animal, however a fossil may be either the cast or the mold of the animal or plant. Over time the sediments may harden into rock and the cavity will fill with minerals or other sediments, leaving a fossil cast perhaps to be found millions of years later by some lucky individual.

The Trilobite above was found on March 28, 2009 at the above coordinates in the loose stones near the bottom of the road cut. Most of the fossil is still encased in the stone but careful work can expose the entire remains of the animal. It is of the same Genus as the one pictured below, Gravicalymene, which shows both cast and mold fossils.

Trilobites are a group of prehistoric animals that have become extremely popular among fossil collectors and enthusiasts for many years. The hard outer bodies of Trilobites preserve well as fossils because their bodies took longer to deteriorate, leaving more time for the sediments to form the necessary “cast”. There are many genera listed in fossil books, some of which were free swimming, near surface dwellers while others seem to have been bottom feeders. The overall body plan of each species can give clues as to its habitat. Some physical proof of these animals lifestyle has been found such as the tracks they have left in soft muddy bottoms that have become fossilized.

Calymene clavicula

The above picture is one of the bottom dwelling Trilobites, while the drawing below depicts one of the free-swimming specimens.

Sedimentary rock may be originally deposited as thin layers such as shale or thin layered limestone an inch or two thick. This may be the result of ancient seasonal rains washing materials into the water and forming the thin layers found in many places in the state.

At this location we see the relatively thick layers of sedimentary rock ten inches or more in thickness. These may represent a more catastrophic occurrence than the thin layers mentioned above. The thicker layers may have been deposited as violent storms with torrential rainfall washed great amounts of sediments into the water. This sudden onrush of sediments seems logical, because here the fossils do not seem to be in any particular arrangement. Meaning that the trilobites do not seem to be in any logical position, some are horizontal while others at this location are preserved vertically or nearly so.

In places such as the Burgess Shale deposits in British Columbia, Canada it is generally believed a large mudslide entombed thousands of animals, including trilobites. At the Burgess shale location there are many soft bodied specimens which were fossilized. This is rather uncommon because the soft bodies decayed at a faster rate than those with hard bodies or shells, leaving less time for the fossilization process to preserve these animals’ remains. Also the soft bodies were often crushed by the sediments making them unrecognizable.

The photo above is of what appears to be a prehistoric worm, one of three we found at this location. We have had the best luck looking through the loose stones between the rock face and the ditch-line. This would have been one of the soft-bodied animals that was preserved by chance.

Note: The top of this road cut also contains many fossils; there are crinoid stem pieces and horn corals to be found in abundance there. The “Law of Supposition” (the oldest layers of rock or fossils is found on the bottom and the newest ones are on top) of course applies at this location.

Qualifications for credit:

To get credit for this EarthCache, email the answers to the following questions and then post a picture of you with your GPSr when you log your find. We will not accept pictures of just hands and GSPr units, so don’t be shy. Please do not log this as a find until you have a picture ready. Posts with no pictures or without emailing the answers will be deleted.

Questions:

This EarthCache requires that you post two pictures.

1. Find and photograph a fossil at this location. Describe this fossil as best as you can, ie size, type (if known), and post this picture as well as the one of you and your GPSr.

2. Why do we not find fossils of soft-bodied animals as often as those of shelled or hard-bodied animals?

3. What is the general texture of the rock at this location, rough, smooth, glassy, etc.?

Please be careful with children and pets. Although this is a subject that interests a lot of children, it is near the off-ramp, so be on the constant guard for automobiles.

Credits and Ammosuperman EarthCaches:

This EarthCache was created by a team of two Platinum EarthCache Masters, Ammosuperman EarthCaches are a collaborative effort. We have used resources such as the Internet and magazine articles as well as personal experience in visiting the sites, as research tools in its construction. Our goal is to learn more about our planet and to pass along what we have learned to others having similar interests. We hope you enjoy the experience.