File:Coast watch (1979) (20632897406).jpg

Title: Coast watch
Identifier: coastwatch00uncs_2 (find matches)
Year: 1979 (1970s)
Authors: UNC Sea Grant College Program
Subjects: Marine resources; Oceanography; Coastal zone management; Coastal ecology
Publisher: (Raleigh, N. C. : UNC Sea Grant College Program)
Contributing Library: State Library of North Carolina
Digitizing Sponsor: North Carolina Digital Heritage Center

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clJcAPE FEAR Approximate shoreline position during Castle Hayne formation A lot of geologic history has occurred since then—history that left North Carolina with rounded mountain tops, an ocean to its east, a gentle sloping coastal plain and a string of sandy barrier islands. It's a history marked by major move- ments in the continents, the formation of an ocean, and large fluctuations in sea level. It's a history that began when Pangaea started to break up. The earth's crust is divided into sections, or plates, that float on top of the mantle. The mantle is made of pliable rock. Thermal forces within the Earth cause the mantle to move, which, in turn, causes the continental plates to shift. About 160 to 180 million years ago, these thermal forces caused Eurasia and Africa to pull away from North and South America. As the continents pulled apart, new material was gener- ated inside the Earth and pushed to the surface at the rift. This material was dragged along with the parting conti- nents, creating an ever widening basin that gradually began to fill with water. (This process continues today. The Atlan- tic Ocean grows at a rate of about one centimeter each year.) During the development of the Atlantic Ocean, North Carolina's coastal plain and continental shelf began its for- mation. Eroded sediment from the Appalachian Mountains washed downstream via creeks and rivers to be deposited in coastal areas. And periodic invasions from the Atlantic Ocean deposited a variety of marine sediments. Throughout the 160 million-year formation of our coastal plain, the Atlantic Ocean rose and fell many times. These sea level fluctuations were caused by changes in the size of the ocean basins due to plate movement and by changes in climatic conditions. During one ice age, global ice volume was so great that sea level dropped to expose all of what is now the continental shelf. In warmer periods, the polar ice caps melted and the oceans swelled. During one warm period 5 million years ago, the Atlantic Ocean reached shghtly west of Wilson. By digging into the sediments of our coastal plain, geolo- gists can tell when the oceans were rising and falling, what minerals were present and what the climate was like. "Sed- iments are a recorded message of what's happening geolog- ically," says Sea Grant researcher Stan Riggs, a geologist at East Carolina University. But occasionally that message was interrupted. During periods of low sea level, sediment was often eroded, and during high sea level, sometimes little sediment was added. Basically, North Carolina's coastal plain is divided into four major sediment formations. They are: the Castle Hayne formation, the Pungo River formation, the York- town formation and the Croatan formation. During the Castle Hayne formation, about 45 million years ago, the coastal plain was coated with layers of lime- stone. Sea level was high (the ocean reached almost to Greenville), and the waters were warm. This limestone, or calcium carbonate layer was made up of the skeletons of invertebrate living organisms. The best exposure of this layer that can be found today is near Wilmington at Castle Hayne. The Pungo River formation, the next major formation, occurred 13 to 19 million years ago. Sea level was generally high (the shoreline reached Washington) and fluctuated often. The ocean was colder, and large quantities of phos-

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