It has been a beautiful spring day here in Alabama Black Belt.
We’ve just returned from taking our son fishing at a nearby creek. I grew fishing up in the same spot and so did my father and my grandfather before him. It is something that I want to pass on to my son because those experiences in my youth aroused my curiosity and attachment to my environment were important in shaping my worldview. It is why I have chosen to identify with this place.
The Midway Group is a geological formation that stretches through the Alabama Black Belt and the strata is full of mosasaur bones and other aquatic fossils because this area used to be underneath the Gulf of Mexico. It is why we have our marl bottomed creeks south of about Montgomery:
The American South is dominated by the Gulf Coastal Plain and the Atlantic Coastal Plain which is why the North was more geologically suited to developing heavy industry in the 19th century:
South Alabama is completely dominated by the East Gulf Coastal Plain:
In Alabama, we have 5 of the 9 physiographic regions found in the South:
The Highland Rim is found in extreme Northwestern Alabama. It is a sliver of the Interior Low Plateau which dominates Middle Tennessee and most of Kentucky. This region of Alabama was part of the ancient geological core of North America – Laurentia – and became part of the supercontinent Laurasia – which combined Laurentia with Eurasia – around 500 million years ago.
The Alabama Valley and Ridge province is the southern end of the Appalachian Mountains that runs through Northeast Alabama. Around 300 million years ago, the supercontinent Laurasia collided with the supercontinent Gondwana (Africa, South America, Australia, Antarctica, India) which thrust up the Appalachian Mountains, which at one time was the size of the Alps in Europe. This created the supercontinent Pangaea which united all the major continents on earth into one megacontinent.
Like the Valley and Ridge, the Cumberland Plateau was uplifted by the collision of Laurasia and Gondwana hundreds of millions of years ago, although the deformation was not as severe. Over millions of years, the erosion of the Appalachian Mountains deposited vast amounts of sandstone, shale and silt in the region, which in turn was severely eroded so that now only small areas of level land remain.
The Piedmont Upland contains the most ancient rocks found anywhere in Alabama. Some are billions of years old. The Piedmont Upland is the remains of a micro-continent that was smashed in between Laurasia and Gondwana when Pangaea was created.
As you can see, the Gulf Coastal Plain contains all or part of 45 of the 67 counties in Alabama and dominates around 70 percent of our state. When Pangaea broke apart 175 million years ago, it ripped away part of Africa and South America which was fused to North America. The fall line that divides the Gulf Coastal Plain from the other physiographic regions of Alabama used to be the shoreline of the Gulf of Mexico. The beach used to be around Auburn and Wetumpka.
Over the course of millions of years, an unimaginable amount of silt and sediment was carried down from the highlands to the coast where it was deposited in a shallow sea. In a series of stages, the shore of the Gulf of Mexico retreated to its present location leaving behind bands of sediment. In fact, the shoreline has advanced into and out of the Gulf Coastal Plain at least 20 times. The delta of the Mobile River used to be beyond Dauphin Island (there is a submerged forest off the coast) and what is now Mobile Bay is a flooded river valley. The same is true of Chesapeake Bay in Virginia and Maryland.
There has always been “climate change.”
This map contains a useful breakdown of the Gulf Coastal Plain.
In Southeast Alabama, we have the Fall Line Hills, the Black Prairie, the Chunnenuggue Hills, the Southern Red Hills, and the Dougherty Plain. Apparently, the geology of this part of the state was more influenced by sedimentary deposits from rivers while Southwest Alabama was more influenced by the sea that covered the area. This family excursion this afternoon was in the Chunnenuggue Hills.
Although you can’t see it from the map, I recently learned that the course of major rivers in Alabama has changed across history. The Alabama River used to flow south of its present location. The area that is now the Tennessee River in North Alabama used to be the headwaters of the Black Warrior River and the Tallapoosa River used to connect to the Conecuh River in Bullock County.
Anyway, I am getting carried away with the history and geology lessons. I just wanted you to understand why our creeks and rivers look the way they do in the Gulf Coastal Plain.