bottom slopes of specified values. Figure 66 compares data for segments with 

 nearshore slopes to the 1.8-m depth contour of 1 on 300 or steeper. This fig- 

 ure shows that even with comparable steepness values there is substantially 

 less shoreline movement in reaches 6 and 7 than in coastal segments farther 

 south. Figure 67 compares shoreline movement for segments having nearshore 

 slopes to 5.5- and 9.1-m depth contours of 1 on 900 or steeper. A consider- 

 able difference is evident in shoreline movement between the two areas compar- 

 able to data in Figure 66. 



184. Figures 68 and 69 demonstrate graphically the contrast between 

 reaches 6 and 7 and other reaches by means of scatter diagrams having a common 

 scale. These diagrams clearly show consistent grouping of data points in 

 reaches 6 and 7 contrasted to wide scatter of data points for reaches 1 

 through 5. Reasons for these differences are not apparent. Differences in 

 wave climate, geology, sediment supply, orientation, coastal morphology, and 

 the fewer number of inlets in reaches 6 and 7 may have a combined influence 

 with nearshore slopes on shoreline stability. 



Geology 



185. The study area is located along the seaward margin of the Atlantic 

 Coastal Plain Province. Both emerged and submerged portions of the coastal 

 plain are topographically subdued and have a gentle seaward slope. Surficial 

 lower coastal plain deposits consist of a fringe of Holocene beach and back- 

 barrier sediments backed by a broad zone of Pleistocene sediments. These give 

 way inland to outcrops of Cretaceous and Tertiary formations. A complete geo- 

 logic description of the area is presented in Part II. 



186. Core data from the inner continental shelf between Cape Fear and 

 Cape Romain show that in many places older deposits either outcrop or lie 

 close beneath the shelf surface (Meisburger 1979, Frankenburg 1987, unpub- 

 lished CERC data) . Figure 70 shows positions of cores containing ancient 

 deposits and downhole depth to pre-Holocene deposits. Except for Eocene age 

 biogenic carbonate sediments near Cape Fear, these deposits are of Cretaceous 

 and Paleocene age . 



187. Shallow depth of these formations on the shelf suggests they may 

 lie close beneath the shoreface and beach in some areas, particularly along 

 the predominantly mainland arcuate strand shoreline between New River Inlet 

 and Cape Fear. Shoreface cores from the immediate vicinity of Myrtle Beach, 

 South Carolina, encountered hard substrate at shallow depth (Frankenburg 



138 



