distribution o£ known occurrences indicates that these clay deposits are 

 discontinuous; however, their similar character and consistent relation- 

 ship to underlying and overlying units suggest that they are genetically 

 related. Where present, type F deposits occur either in outcrop on the 

 sea floor or under shelf facies sand. The surface of the deposit is 

 level and creates no topographic expression in the sea floor, whether 

 exposed or within a few feet of the bottom. Thickness varies from about 

 1 to 5 meters (2 to 15 feet) ; maximum thickness within the study limits 

 is unknown since many cores bottomed within the deposit. 



The chief characteristics of type F clay are the dark-gray color 

 (Munsell Color Code N3) , the typical yellow mottling, and the high plas- 

 ticity when wet. Residues from washing representative samples through a 

 fine mesh (0.105 millimeter) screen were volumetrically very small and 

 usually consisted of quartz grains and partly decomposed vegetation (Fig. 

 21). In some samples the residue contained abundant selenite crystals, 

 possibly precipitated by partial drying during storage. Similarly, the 

 yellow mottling which appears to be due to accumulations of microscopic 

 iron sulfide particles could have formed during storage; if so, the 

 mottling may not characterize fresh samples. 



d. Carbonate Sediments and Rocks . A diverse group of carbonate 

 sediments and rocks occurs in the study area. They range in lithology 

 from calcareous silt to calcareous sandstone but the majority are bio- 

 genic calcarenite and calcirudite in various degrees of consolidation. 

 This material, which is classified as type G, appears to be part of a 

 single deposit. 



Other carbonate lithologies occur frequently, especially in eastern- 

 most Long Bay and off New River Inlet, but no single lithology of this 

 group is frequent enough to be treated as a specific type. These deposits 

 include calcareous sandstone, limestone, calcareous silt, and bryozoan 

 hash. Brief descriptions are given in the core logs (App. B) . 



Type G material consists of biogenic calcareous sand, gravel, and 

 rock and commonly occurs as fill in the large channels underlying parts 

 of Long Bay and southern Onslow Bay, south of Moore Inlet (Figs. 7 and 8). 

 However, there are a few occurrences that do not appear to lie in ancient 

 channels, suggesting that the deposit may once have been more widespread 

 but had subsequently eroded from the interfluve areas. If type G material 

 completely fills the channels, it probably exceeds the 45-meter thickness 

 in places, but core data are only available for the upper 6 meters. 

 Numerous and extensive outcrops of type G material occur on the inner 

 shelf floor and the large area of rock outcrops extending through the 

 mid-shelf region east of Cape Fear (Cleary, 1968) are likely exposures 

 of this material . 



Type G sediment and rock particles consist largely of barnacle plates, 

 bryozoa, and highly fragmented mollusk shells which range from silt to 

 small pebble size (Fig. 22). Calcium carbonate often comprises over 90 

 percent of type G material and detrital quartz particles are apparently 



47 



