Coal Mine Classic 2014: Climbing out of the Coastal Plain
Today I drove 450 miles and slowly climbed from the flat, pine-dominate, coastal plain province onto the gently rolling hills of central Mississippi and Alabama, which are a transition to the Appalachian Highlands, which are identified by the long hills coming into and immediately north of Birmingham, AL. This photo shows the features of this transition area.
These are the terrace and braided stream deposits we saw at Sicily Island, Louisiana previously. They look like stream gravel. This blog isn’t summarizing the geology of the areas as we drive through them, but the region around Birmingham is a Paleozoic basin with sandstone, limestone, and shales that has actually been a major source of iron ore (from the limestone.); this means, rocks. The next couple of images show how these limestones vary from thick bedded to very thin bedded (they even contain coal).
The causes of the variations in bedding are not exactly known buy thick beds are interpreted to be deeper water with no contamination by sand and/or shale. The following image shows where the road cut had to be sloped because the rock was not solid enough to form a cliff.
After I cross the state line into Georgia, however, these rocks become massive (i.e. little bedding visible) and form Table Mtn.
We are further from the coastline (in Paleozoic time) and the limestone is pure; dirt screws up the lithification process (rock forming). This traverse is seen in a geologic map of MS-AL. The overlapping terraces cover the underlying linear structure that was formed when these rocks were folded during the Appalachian Orogeny (~325-260 million years).
For reference, today I drove from the southwest (lower-left) to northeast (upper-right) of this map.