July 24, 1999 - Pennsylvanian Fossils - Walker Co, AL

Walker
Alabama
Calamites
Lepidodendron
lycopod

Department of Physics and Astronomy
University of Alabama
Tuscaloosa, Alabama

This field trip was a very special one for the BPS. We visited a surface coal mine in Walker County. About 20 BPS members and guests attended the trip, which occurred on one of the hottest and most humid days of the year thus far.

This is one of the largest surface coal mining operations in the state. The area is part of the major Pottsville Formation, and is also known as the Warrior Basin. The BPS was hosted by Mr. Hendon, a mine engineer, who also brought his son along. Mr. Hendon first gave us a basic description of the mine, its history, its extent, and the geology of the area. He then took us on a tour of the mine, allowing us to park near a monster machine known as a "dragline". To access the coal seams, overlying soil and hard rock has to be removed, which is the principal task of the dragline. Usually there are 100-200 feet of solid rock to be removed, but on Saturday the dragline was mostly removing topsoil.


--Edited by Vicki Lais

dragline
The dragline. The 180 ton bucket is hanging in the middle of the photo.
climbing into the dragline
Climbing into the dragline.

lot of people in the bucketThe machine uses a 180 ton metal bucket to drag soil and rock forward for lifting, and then rotates to dump the material on an area that has already been mined. The machine is so large and so specialized that, according to Mr. Hendon, it cost $36 million when it was brand new. Not only were we allowed to view the dragline from close up, but we were also able to go inside and see how it works. The movements of the bucket can be efficiently operated by one person, but three other workers are usually present to keep the machinery functioning and oiled. The complex manipulations of the dragline depend on 16 giant motors of over 100 horsepower each, one of which we saw winding and unwinding the huge cables connected to the bucket. Other motors rotate the whole assembly and move it. We all visited the operator control room, as well as a second empty control room. Inside the machine, the noise was loud enough to necessitate the use of earplugs. After visiting the dragline, Mr. Hendon took us all to a second bucket no longer in use, where I took the group photograph shown here.

 

After this part of the tour, Mr. Hendon then led us all to an area where we could search for plant fossils. Like many other sites in Walker and Jefferson Counties, plant fossils from the Carboniferous period are present in abundance at Cedrum. Mr. Hendon first pointed out to us a couple of fossil stumps of arborescent lycopods, one of which was partly removed by BPS members James Lowery and Danny Brooks. The piece Danny Brooks showed me weighed about 100 lbs and showed characteristic scars of a likely Lepidodendron. Interestingly, the cross section of the stump showed scars as well, but I am not sure exactly what these represent. Danny has very graciously donated the specimen to the Southern Environmental Center, who plan a special display.
 
Other items found at the site included numerous medullary casts of the familiar Calamites, a member of the horsetail phylum. The largest piece shown to me was about 8 inches long and about 4 inches in diameter. All of the pieces I saw, including a small one I found myself, showed well-defined linear furrows and ridges aligned parallel to the direction of the stem. The raised furrows represent vascular bundles of the plant, and are basically inverse impressions of the life features. The narrower ridges, also inverse, are known as medullary rays. The casts represent the inner pith cavities of the plant, which were either hollow or had only soft tissue that quickly decayed. When these cavities filled with mud, the mud solidified and preserved an impression of the
stump in rock wall
inside of the plant. Some specimens looked broken at a node, a place where leaves and branches could emanate from the plant. The node is a horizontal ridge, and the small specimen I show here has two nodes. Sometimes a node may be preserved in cross-section. On splitting one rock, I found a large node impression with thin radiating structures, probably leaves. However, none of the inner structure of the node was preserved in this piece.
 

 

LepidophloiosOne of the most interesting fossils I noticed at this site was a modest-sized bark impression of Lepidophloios, a subgenus of the Lepidodendra. The leaf scars of Lepidophloios are very much like those of a normal Lepidodendron stem, only the scars are elongated horizontally, rather than vertically. Although I have read that fossils of Lepidophloios are the most commonly found plant fossil in Alabama, it was the first time I had seen a definitive example. It was easily distinguished from the better known Lepidodendron.

Also found at the site were various seed fern impressions, the most familiar ones I noticed being Alethopteris and Neuropteris. The latter were often found as disconnected and relatively large pinnules. One BPS attendee showed me a nice slab of intact Alethopteris ferns. He was so happy to have the slab, and it was so fragile, that he said he was going to carry it home on his lap! Related to these ferns, I believe I found what appear to be two branches of a likely tree-sized seed fern plant. The branches have a brownish color with some carbonized plant material remaining, and bear no resemblance to the branches of Calamites or the arborescent lycopods. No fern impressions are attached to these branches, but I have seen other similar specimens having attached ferns.
 

 

lycopod stump
Easily the most spectacular find of this trip was a 300-400 pound arborescent lycopod stump found by James Foshee. The specimen is about 1 foot thick and tapers from a diameter of about 2 feet to 3 feet from top to bottom. All around the rim, the stump is covered with beautiful, well-defined leaf scars, the appearance of which suggests to me that the specimen is of the genus Lepidodendron. From its curved shape, it looks like a part of the lower base of a much larger trunk. The preservation is as good as any I have seen of these trunks in museums. A happy day for James!

In summary, this was a really great field trip for the BPS. If it had not been so hot, it might have been even better!