Rusophycus: Trilobites on top of the Clinch EarthCache

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Hidden : 2/1/2010
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:

Behind the Clinch Mountain Lookout Restaurant, large trilobite rusophycus trace fossils are noticeably seen in the Slurian Clinch Sandstone of the Appalchian Fold and Thrust Belt. The Thorn Hill Section of Clinch Mountain is part of the Valley and Ridge province. You will be on US Highway 25E.


The Rusophycus

Many thanks to Mrs Krystal Scott, owner, for her gracious permission to list this EarthCache. This formation has been a long popular stop for several Universities and Colleges during their geology class field trips. In order for you to follow your GPSr to the site, you must go through the Clinch Mountain Lookout Restaurant. Tell the folks what you are doing and be sure to thank them. The current hours of operation are: 8AM to 6PM, seven days a week. During the spring and summer, the hours are longer. Be sure to time your visit for a meal!

Like all structures in the Appalachian fold and thrust
belt, the Clinch Mountain resulted from the Alleghanian Orogeny. Just what was this Alleghanian Orogeny? The Alleghenian orogeny is one of the geological mountain-forming events (an orogeny) that formed the Appalachian Mountains. Approximately 350 million to 300 million years ago, in the Carboniferous period, when Gondwana (later to become Africa) and what became North America collided, forming the super continent, Pangaea. This collision exerted massive stress on what is today the Eastern Seaboard of North America, resulting in a large-scale uplift of the entire
region.

Prior to the Alleghanian Orogeny, the Clinch Mountain was flat and was part of a great sea or a large inland body of water.. This sea left deposits of sand. With pressure and a lot of time, the sandy sea deposits became the solid rock. This rock is what we now call the sedimentary sandstone rock.

Sandstone is composed mainly of sand-size mineral or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions. The local Clinch sandstone is generally tan to red in color.

The formation of the Clinch sandstone involved two principal stages. First, a layer or layers of sand accumulated as the result of sedimentation from the water. Typically, this kind of sedimentation occurs by the sand settling out from suspension, i.e., ceasing to be rolled or bounced along the bottom of a body of water (e.g., seas or rivers). Finally, once it has accumulated, the sand became sandstone when it is compacted by pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains.
Some time before the Clinch Sandstone became sandstone, all kinds of sea creatures found the sand as home. These creatures existed above as well as below the sand. When these animals died, with the right conditions, often their bodies and the tracks of their travels, became fossils.


A Trilobite Party!

Before we talk about our rusophycus fossils, let's briefly define just what are fossils. According to the Britannica Encyclopedia fossils are: "Remnant, impression, or trace of an animal or plant of a past geologic age that has been preserved in the Earth's crust. A shell or bone that is buried quickly after deposition may retain organic tissue, though it becomes petrified (converted to a stony substance) over time. Unaltered hard parts, such as the shells of clams, are relatively common in sedimentary rocks. The soft parts of animals or plants are rarely preserved. The embedding of insects in amber and the preservation of mammoths in ice are rare but striking examples of the fossil preservation of soft tissues. Traces of organisms may also occur as tracks, trails, or even borings."


See.....I can roll up like a "Rolly- Polly"!

Some animals with shells died and settled to the bottom of the sea and later, much later, became limestone. But, in our case, there were probably no mollusks here and there little limestone found within the Clinch Mountain. Remember, this formation is sandstone. What we did have is very common animal, which is the trilobite. A trilobite is an extinct invertebrate marine animal (arthropod) whose skeleton is divided into three parts. If you were alive back in Paleozoic times, you would have seen many of them! The trilobite came in many forms and sizes. They varied from being microscopic to a foot or more in length. Seemingly, the most common sizes were an inch to three or four inches. Unfortunately, though, the trilobite has been reduced to a popular fossil group from that era and inhabited this and other areas. It is thought that the most likely animal which descended from the trilobite is today's horseshoe crab.


A Horseshoe Crab

Now that we have established what kind of rock is here (sandstone) and what kind of sea creature inhabited the area (trilobite), let's look at the fossils found within the stone. As mentioned earlier, one type of fossil is a trace fossil. A type of trace fossil is a trilobite ichnofossil: rusophycus. When a trilobite is resting, partially buried in the mud/sand, it leaves a bi-lobed impression called a rusophycus (see below photo). Another trilobite trace fossil is the cruziana which are the tracks of a moving (under the mud/sand surface) trilobite as opposed to the resting rusophycus. The third and last trilobite trace fossil is when a trilobite is walking freely upon the surface, it leaves paired leg marks called diplichnites. Here you will see the resting places of trilobites within the sandstone. These are our trace fossils and are referred to as rusophycus! Even though there are many layers of sandstone within the Slurian Clinch, few base layers have separated to expose what was between these layers. You will be viewing a crack or separation of the sandstone layers which allow us to view the rusophycus.


The three trace fossils of the trilobite


Notice the bi-lobed structure - rusophycus.

Please Note. In order or you to claim a find of the trilobite rusophycus you must email us answers to the following: 1. What are the colors you observe in the sandstone base? 2. Estimate the width of the separation between the layers of sandstone. 3. Estimate the average length of the rusophycus. Also, please post a photo of part of the trilobite rusophycus. We would love to see you in the photo but that is part is opitional! Enjoy and have fun.


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