The Supercontinent Breaks Up
About 750 million years ago, the supercontinent began to thin and rocks at depth pulled apart like warm taffy because of expansion of the continental crust. Then, about 540 million years ago, the continental crust split into pieces that drifted away from each other. Seawater spread into low areas between crustal plates and, in time, formed new oceans.
During the early part of the expansion of the continental crust (about 750 million years ago), a deep basin, known as the Ocoee Basin, formed on the margin of the supercontinent in what is now the western Carolinas, eastern Tennnessee, and northern Georgia. Seawater filled the basin. rivers from the surrounding countryside carried clay, silt, sand, and gravel to the basin, much as rivers today carry sediment from the midcontinent to the Gulf of Mexico. The sediment spread out in layers on the basin floor. The basin continued to subside, and over a long period of years, a great thickness of sediment accumulated.
The sediments of the Ocoee Basin now form the bedrock of the Great Smoky, Unicoi, and Plott Balsam Mountains. The layers in which these sediments were deposited on the ancient sea floor can still be seen in outcrops of the bedrock. In some rocks, even the pebbles and grains of sand are preserved.
The rocks that formed from coarse sediments, such as pebbles and sand, are very hard and are resistant to weathering and erosion. They form the high peaks and ridges of today. Rocks composed of fine-grained sediments, such as clay and silt, are softer and break down more easily. These rocks can be found in the lower areas. Erosion of the alternating layers of hard and soft rocks makes many of the landforms that we see today. As rivers cut their way through the layers, hard rocks form ledges that make waterfalls, and alternating layers of hard and soft rock make the riverbeds that produce whitewater rapids.
In 1843, a prospector who was looking for gold near Ducktown, TN, found copper instead. Disappointed, he moved on. Within 7 years, mining of the rich copper deposits near Ducktown began, and in time, the Copper Basin became the largest metal mining district in the Southeastern United States.
At the same time thatsediments and minerals were being deposited to form the Ocoee Basin, other areas that are now Virginia, the Carolinas, and Georgia were being subjected to volcanic eruptions.Still other areas,that are now the Valley and Ridge Province, were covered by a shallow inland sea.
- Volcanoes : At the time that sediments were being deposited and mineral deposits were forming in the Ocoee basin, volcanoes were erupting in areas that are now Virginia, the Carolinas, and Georgia.
- An Inland Sea : The rocks of the Valley and Ridge province formed in a setting very different from that of the Ocoee basin. For millions of years, a vast, shallow, inland sea covered the area.
- The Copper Basin : The rocks of the Ocoee basin contained some of the most important deposits of copper, zinc, iron, and sulfur in the eastern United States.
Encyclopedia ID: p1548
