Approximate shoreline 

 position during Yorktown 

 formation 



[CAPE FEAR 



phate were deposited across the continental shelf. 



Although some geologists debate the source of the phos- 

 phate, Riggs advocates a theory based on ocean upwellings. 

 A buildup of phosphorus had occurred in the depths of the 

 ocean. But during this formation, the phosphorus was 

 transported from the ocean floor to the continental shelf. 



Riggs says this transportation occurred because of the 

 location of the Gulf Stream. If sea level rises, the Gulf 

 Stream moves inland. During the phosphate formation, the 

 Gulf Stream was moving landward when it bumped into 

 protrusions of the continental shelf. This deflected the 

 warm surface current offshore and allowed the ocean 

 water beneath to rise and spread over the continental shelf, 

 according to Sea Grant oceanographer Len Pietrafesa. This 

 cold nutrient-rich ocean is associated with phosphate 

 formation. 



Riggs says eventually the Gulf Stream moved onto the 

 shelf, cutting off the phosphorus supply and creating condi- 

 tions that favored carbonate deposition. Because sea level 

 fluctuated during this period, geogolists find alternating 

 layers of phosphate and carbonate in this formation. 



The Pungo River formation is a valuable one for North 

 Carolina. Phosphate is mined by Texasgulf Chemicals Co. 

 near Aurora on the Pamlico River and processed into 

 fertilizer. 



Some phosphate and carbonate were deposited in the 

 lower layers of the Yorktown formation, which was formed 

 between 3 1/2 and 5 million years ago. But this formation is 

 made up largely of quartz. Continental margin tempera- 

 tures alternated between warm and cold, and the shoreline 

 stood west of present-day Wilson. 



The youngest geological formation, the Croatan, flooded 

 less of the coastal plain (shoreline in the vicinity of Aurora) . 

 Warm seas during this era left behind dense layers of car- 

 bonate shell hash. 



But sediment formation isn't the only North Carolina 

 geologic feature to interest scientists. The ever mobile bar- 

 rier islands are another feature of study. 



Riggs says the present barrier islands formed about 

 18,000 years ago after a glacial era. Global warming caused 

 sea level to rise. In North Carolina, the ocean flooded low- 

 lying areas, but left behind strips of high-standing beach 

 that had formed from ocean and river deposits. 



North Carolina may have seen many such sets of barrier 

 lands during its formation. Multiple barrier formations can 

 be traced across the coastal plain. Greenville hes on one 

 such ridge, Tarboro on another. 



Today's barrier islands are a geologic feature in motion. 

 They are a product of the wave energy that builds, molds 

 and maintains them, Riggs says. In response to the con- 

 tinued rise in sea level (the world is still recovering from its 

 last glacier period, and sea level rises in North Carolina at a 

 rate of about one-half foot per century), the barrier islands 

 are moving inland via washover and inlet migration. And as 

 the islands move, the estuaries behind them also push 

 westward. 



Barrier island movement, rising sea level, the ever- 

 widening Atlantic basin and the continued deposit of sedi- 

 ments add up to a coastal plain still in creation. As geologists 

 delve in its sediments to reveal its past, they also use their 

 findings to predict its future. 



— Kathy Hart 



