Continental shelf
Today, South Carolina’s continental shelf is a passive margin, meaning that it is not colliding with any other land, as it once did millions of years ago. Instead, it is trailing along North America’s active western margin that is presently leading the continent toward Asia.
The continental shelf that lies off South Carolina’s coast is part of a larger continental shelf that runs from Canada to Mexico. It is formed, in part, by a continuation of the sediments of the coastal plain that are covered by seawater. The continental shelf has been exposed as much as one hundred miles off the present coastline at various times during the geologic history of the state. This was due to ancient sea levels rising and falling many times over millions of years. Today, South Carolina’s continental shelf is a passive margin, meaning that it is not colliding with any other land, as it once did millions of years ago. Instead, it is trailing along North America’s active western margin that is presently leading the continent toward Asia. Sediments, therefore, have accumulated on South Carolina’s continental shelf to a thickness of thousands of feet over the past 225 million years.
Continental shelf sediments include clays, sands, shales, and sandstones that eroded from mountains to the north and northwest. This thick wedge of sediments lies atop older metamorphic and igneous continental Piedmont rocks. The heavy weight of these rocks, as well as the cooling of the crust, bent the shelf, a process that continues as more sediment is added through erosion of the land and deposition. The continental shelf also contains lava sheets, diabase dikes, and other remnants of volcanoes active during the Jurassic period as North America and Africa rifted apart. Limestone banks several thousand feet thick are located farther seaward and have been explored by oil companies, which found natural gas and oil deposits that may be economically useful in the future.
King, Philip B. The Evolution of North America. Rev. ed. Princeton, N.J.: Princeton University Press, 1977.
Murphy, Carolyn H. Carolina Rocks! The Geology of South Carolina. Orangeburg, S.C.: Sandlapper, 1995.
