The Pennsylvanian Pottsville Formation is a mapped bedrock unit in Pennsylvania, western Maryland, West Virginia, and Ohio. The formation is also recognized in Alabama. It is a major ridge-former in the Ridge-and-Valley Appalachians of the eastern United States. The Pottsville Formation is conspicuous at many sites along the Allegheny Front, the eastern escarpment of the Allegheny or Appalachian Plateau.
The exposed rock formation at ground zero runs for about half a mile along Jack Warner Parkway on the northern edge of the campus of the University of Alabama. It is a visible example of the Pottsville Formation. Relative age dating of the Pottsville places it in the early to mid Pennsylvanian period, or roughly 300 million years ago. During this geological period, much of what is now the central United States was covered by a shallow sea, the Rocky Mountains did not yet exist, and the Appalachians were much higher than today.
The Pottsville Formation consists of a gray conglomerate, fine to coarse-grained sandstone, and is known to contain limestone, siltstone and shale, as well as anthracite and bituminous coal. It is considered a classic orogenic molasse. The formation was first described from a railroad cut south of Pottsville, Pennsylvania.
The term "molasse" refers to the sandstones, shales and conglomerates formed as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse is deposited in a foreland basin, especially on top of flysch, for example that left from the rising Alps, or erosion in the Himalaya. These deposits are typically the non-marine alluvial and fluvial sediments of lowlands, as compared to deep-water flysch sediments. Sedimentation stops once the orogeny stops, or once the mountains have eroded flat. The molasse can sometimes completely fill a foreland basin, creating a nearly flat depositional surface, that nonetheless remains a structural syncline. Molasse can be very thick near the mountain front, but usually thins out towards the interior of a craton; such massive, convex accumulations of sediment are known as clastic wedges.
During the late 19th and early 20th century, a series of 17 locks and dams were built along the Black Warrior River to allow transport of material from the rich iron and coal deposits located in and around Birmingham, Alabama. These original locks and dams, mostly covered over by the river today, are believed to have been at least partially constructed by rocks quarried from this site.
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1. During what geologic period was the Pottsville Formation created? How long ago did it occur?
2. What type(s) of rocks do you observe here?
3. There are several large boulders in the area of GZ. What is the diameter of the largest one?
4. What part did water play, if any, in the formation of these rocks? Is there any evidence that water is still at work in this formation?
5. (Optional) Take a photo of yourself (or your GPS) in front of the rock formation to verify that you visited this site.
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