Most of the rocks in Great Smoky Mountains National Park are sedimentary and were formed by accumulations of clay, silt, sand, gravel, and minor amounts of calcium carbonate in flat-lying layers. The oldest sedimentary rocks were formed during the Proterozoic Era some 800-545 million years ago. Vast amounts of unconsolidated clay, silt, sand, and pebbles were washed down into lowland basins from adjacent highlands. Rocks of the old highlands were over one billion years old, and were similar to the ancient granite and gneiss found in the southeastern parts of the park. These early sites of ocean bottom deposition were formed along the ancient margin of the North American continent as an older and larger supercontinent broke apart.
As more and more of these sediments were deposited, they were eventually cemented together and changed into layers of rock over nine miles thick. Today these rocks are known as the Ocoee Supergroup and are subdivided into many smaller divisions of differing rock types. The different rock types reflect the range of climatic and topographic conditions that existed during their formation.
The earth's outer crust is composed of huge, continental-size plates, driven by heat from below, that continually shift position. These moving plates grind past one another, collide into one another, and sometimes override one another. Also, where plate margins are separating or spreading apart, molten rock forces its way to the surface, solidifies and forms new crust. Plate movement is just a few inches a year, but throughout geologic time, this movement and the resulting plate interactions have caused devastating earthquakes, spectacular volcanoes, and the uplift of high mountain chains. The great thickness, variety, and distribution of rocks in Great Smoky Mountains National Park tell a fascinating story of continental-size plate tectonics spanning more than a billion years of earth history.
Metamorphosed sedimentary rocks are the dominant rock types in the park, but some igneous rocks also occur. Sedimentary rocks form through a cycle of erosion and deposition mostly in water. The eroded materials include cobbles, pebbles, sand, silt, and clay, or the accumulations of shells from ancient sea animals. Igneous rocks solidify from melted rock or lava.
Rocks become metamorphosed when they are subjected to heat and pressure, usually related to mountain building. Metamorphosed sandstone, siltstone, and shale, are most common in the park. However, metamorphosed limestone and dolomite are found in the Anakeesta Formation and unmetamorphosed limestone and dolomite are found on the floor of Cades Cove, below the Great Smoky fault. Siltstone metamorphosed at high temperatures and pressures forms schist, that is found in the eastern part of the park. Metamorphosed granite and granitic gneiss are the oldest rocks in the park and they occur near Bryson City, Ela, and Cherokee, North Carolina. Small bodies of metamorphosed igneous rocks, called dikes, are found from near Fontana Dam to Clingmans Dome. Quartz veins and pegmatite are also present. Geologists have named about 20 different "formations" of rocks in the Great Smoky Mountains.
Did You Know?
Ninety seven historic structures, including grist mills, churches, schools, barns, and the homes of early settlers, preserve Southern Appalachian mountain heritage in the park. More...