Geotimes - October 2003 - Mine reclamation threatens tracksite

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Paleontology
Mine reclamation threatens tracksite

In a small corner of northwest Alabama, the most diverse and prolific Carboniferous tracksite known on this planet is in danger of being reburied. The 310-million-year-old fossil trackways, found only three years ago, are located at a former open-face coal mine in Walker County. Paleontologists have been trying to preserve the vertebrate and invertebrate trackways from bulldozing and subsequent burial, but federal law requires land restoration after mining operations end. Although owners of the New Acton Coal Mining Company want to donate their mine to science, a local farmer who owns rights to the reclaimed land has the law on his side.

Vertebrate — amphibian or maybe early reptile — tracks from the Carboniferous period. Photograph by Andrew Rindsberg, Geological Survey of Alabama.

Since the fossils’ discovery at the Union Chapel Mine in late 1999 by a high school science teacher, amateur and professional paleontologists from around the world have collected, logged and photographed nearly 2,000 slabs of fossilized trackways and other trace fossils — including amphibians, millipedes, horseshoe crabs, fish, insect larvae and perhaps early reptiles, as well as compressions and casts of tree-sized “ferns,” lycopods and horsetails. “The fact that we have vertebrate traces, invertebrate traces and plants here, in some cases all on the same surface, is enough to reconstruct much of the ancient community, plus the behavior of some of its species,” says Andrew Rindsberg, an ichnologist (a scientist who studies trace fossils) with the Geological Survey of Alabama.

Although some fossils were found in parts of the mine already reclaimed, the majority of the collected trackways have been found in broken rocks scattered on one side of a 25-meter highwall of unstable rock, which mining exposed. “We want to preserve this highwall as the only place in Alabama where we know for sure that in situ trackways can be found,” says Ronald Buta, an astronomer with the University of Alabama and an amateur paleontologist who has been involved in the Alabama Paleontological Society’s (APS) efforts to preserve the site.

But the wall sits on land a local farmer, Joseph Pugh, has a contract to buy from the mining company if the land is reclaimed. He owns the already-reclaimed mine land and grazes livestock there. He wants the mining company to finish reclamation, as mandated by the Surface Mining Control and Reclamation Act of 1977, which would eliminate the hazard of the highwall to his animals. This means bulldozing and burying the site.

Many of the fossil tracks have been found in slabs of rock in the shadow of a 25-meter highwall. The gray shale and sandstone highwall is stained orange by clay washing down from above. Photograph by Andrew Rindsberg, Geological Survey of Alabama.

“We see the Union Chapel Mine as an Alabama treasure to be preserved for future generations, but the rancher sees it as an ordinary area where he could graze his cows,” Buta says. Amateur and professional paleontologists, including APS and the Geological Survey of Alabama, are doing their best to preserve the site, which continues to yield large amounts of well-preserved material on each visit. “They’re not just repeats of the material already found either,” Rindsberg adds.

While most of North America was covered with great tropical swamps 310 million years ago, this bit of northwestern Alabama was a tidal mud flat for an inland sea. The mud was just right — soft, yet firm enough — that even very small creatures left tracks. With mud accumulating up to 1 centimeter per day, tracks became buried before they had a chance to be altered, leaving on each fossilized slab a surface representing hours of activity, rather than days, months or years.

“I would say that the Union Chapel Mine site is a Rosetta Stone for those trying to understand the Carboniferous trace fossil record,” says Spencer Lucas, curator of paleontology and geology at the New Mexico Museum of Natural History.

The mining uncovered trackways from the time when reptiles first began appearing in the evolutionary record, Buta explains. While it is difficult to ascertain whether it is only amphibians or also early reptiles that left these footprints, scientists agree that this time period is a critical juncture in egg-laying vertebrate evolution. They hope this site will yield more information about the creatures that inhabited the region or at least that used the mudflat as a means of going somewhere.

Some of the vertebrate trackways show turning, obstacle avoidance, sideways movements and other behaviors not usually recorded in the fossil record, let alone from 310 million years ago. The trackways capture subtle and abrupt changes in behavior, which is quite unusual, says Nick Pyenson, a graduate student at the University of California, Berkeley.

Individual footprints range in size from less than a centimeter to tracks nearly twice the size of an adult human hand, those of “Frogzilla” — a tetrapod, probably the size of today’s alligator. The thousands of trackways range from a few centimeters to several meters long, and the tracks show excellent preservation, including exact counts of how many digits an animal had and even the number of bones in each finger.

In August, the battle over the trackway site came to a head, with the Alabama Surface Mining Commission granting a stay of reclamation just three days before reclamation was legally required to begin. This month, a more formal hearing will determine the outcome. All interested parties, including the Alabama Paleontological Society, the mining company and the local farmer, will be allowed to present their arguments. Joining in the preservation effort is Rep. Robert Aderholt (R-Ala.), who introduced a bill in the U.S. House of Representatives in June to allow the mining company to donate the land to the Department of the Interior. This would exempt the mine from reclamation and settle the matter once and for all. As of Sept. 1, the bill was pending.

“We’re not throwing in the towel quite yet,” Buta says. But, even if the reclamation of the mine were to occur, he says that the efforts amateur and professional paleontologists have invested in documenting the tracks will still be valuable for many years to come.

Megan Sever

Links:

Alabama Paleontological Society's Project Site
Geological Survey of Alabama

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