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- 



