The Geologic history of the Carolinas is very interesting. It can tell us a lot about the past and what happened before humans roamed the earth. Through the science of Geology we have been able to better understand why things are the way they are today.
In our march through time we will first begin in the period know as the Ordovician. During this period we had a major mountain building event called the Taconic Orogeny. This orogeny occurred when the landmass Laurentia collided with an island arc about four hundred fifty million years ago starting the formation of the Appalachian Mountains. There were two parts of the Taconic Orogeny. The early, or Bluntian phase, which added the Charlotte Belt to what was then Laurentia during the middle Ordovician. The next phase of the Taconic Orogeny added the Carolina Slate Belt to Laurentia, enlarging it even more. The Carolina Slate Belt contains highly metamorphosed volcanics and other metamorphosed sedimentary materials. The boundaries of these two belts are now located at major fault zones. The first fault zone is the Burnsville Fault zone located between the Blue Ridge and the western Piedmont. The second fault zone is the Gold Hill Fault zone and it is located between the Charlotte Belt and the Carolina Slate Belt.
As we continue our march through time we next hit the Silurian Period. During the Silurian in North Carolina we had a beach environment. The shore back then looked a lot like the shore today, but it has moved about 150 miles eastward. Toward the end of the Silurian the climate became more arid. For that reason we see a lot of layers of salts, clay rich sands, and dark limestone’s that illustrate this change in climate.
The next period is the Devonian, which began about 408 million years ago. During this time magma buried in the earths crust began to rise to the surface through dikes. Since the crust had been heated by the metamorphism that had taken place there, the magma rising from the earth cooled slowly causing there to be large crystal sizes in the dikes. W also see a lot of rhyolitic tuff from this period that tells is there had been much volcanic activity in that period.
After the Devonian period comes the Carboniferous which dates back to about 360 million years ago. During this time the Avalon plate collides with the North American landmass. This starts the second phase of the Appalachian Mountain process called the Acadian Orogeny. This collision caused metamorphism of the rocks in that area. Also during the carboniferous period we had the final mountain building event take place, the Alleghenian Orogeny. This event marks the collision of the North American and the Euro-African continents. This cause extreme uplift of the Appalachian Mountains and subduction in other areas like the Carolina Slate Belt where it started to melt. Today this granite from the slate belt has been eroded and can be seen at the soil free landscapes where only special organisms are able to live.
Ending the Paleozoic era we have the Permian time period. This period include the times from about 288 to about 245 million years ago. During the Permian we see the completion of the Appalachian Mountains. By this time the Appalachian Mountains are not going to get any taller. They begin to erode and the sediments start to fill up the basins. All of the metamorphosed and folded rock formations that we saw reflect the past events of the Appalachian Mountain building events.
As we continue our march through time and begin a new era, the Mesozoic. The first period in the Mesozoic is the Triassic, which began about 240 million years ago and lasted about 40 million years. During this time we begin to see erosion of the Appalachian Mountains in full effect helping to destroy the tall mountains. The destruction of these mountains leads to much sediment being carried by the rivers and streams in this region. A lot of these sediments can been seen deposited into basins in the area.
The next period in our travel through time is the Jurassic period, which began about 210 million years ago. During this time the force that cause fractures in the crust began to increase causing folding and metamorphism. Some evidence suggests that there may have even been hot spots under the Carolinas at this time. On the surface we see lots of dikes and cracks in the rocks that have been filled with basalt as magma came up from the earth.
Our last period on our march through time is the Cretaceous, which lasted about 75 million years. During the Cretaceous we still saw heavy erosion of the Appalachian Mountains into streams and rivers in the area. During this time we also begin to see a dropping of the land below sea level west of the Appalachian Mountains. Also during this time we begin to see the rifting of Pangea. This caused rift basins to open up and with this we begin to see the construction of the coastal plain.
As you can see there have been many events that have shaped the Geologic history of the Carolinas. Many old theories have been thrown out and many new ones have been developed, but now I believe that we have a better understanding of what went on in the past.
this was part of my paper on the goelogy of nc…. Stewart K.G., and M. Roberson. 2007. Exploring the Geology of the Carolinas. The University of North Carolina Press.