Cretaceous strata of varied and possibly fine lithologies are close to 

 cropping out on the sea floor, the potential thickness is also 3 yards. 



m. Area M . Area M is unique because it contains the greatest number 

 of cores of any potential borrow area (Figs. 29 and 30). A total of 41 

 cores are located along three shore-normal transects which were estab- 

 lished to determine engineering conditions for two sewer outfall pipes, 

 one for Nassau County, which has since been constructed, and one planned 

 for Suffolk County. The 15 cores along the Nassau County line (Fig. 9) 

 are spaced about 300 yards (274 meters) apart and extend to a maximum of 

 -80 feet (-24.4 meters) MSL and provide excellent lithologic correlation. 

 All but one of the cores (core 250) show that the upper 12 to 30 feet 

 (3.6 to 9.2 meters) of shelf sediment in this region is composed of fine 

 to medium sand with lesser amounts of coarse detritus and minimal fine 

 silt and clay (Fig. 9; App. A). A continuous clay-silt surface (Gardiners 

 Clay) is present at -50 feet (-15.2 meters) MSL inshore in core 241 and 

 seems to slope offshore and then level off at about -66 feet (-20 meters) 

 MSL between cores 247 and 253. This surface provides the lower limits of 

 potential sand for this area and thus the minimum and potential thickness 

 (Table 5) is 6 yards (5.5 meters). 



The two core transects for the Suffolk County sewer outfall (Fig. 30) 

 are about 5 miles (8 kilometers) long, 1.25 miles (2 kilometers) apart, 

 and contain 26 cores, a maximum of 40 feet (12.2 meters) long. The 15 

 cores in the western transect (Fig. 30) are about one-third mile (0.5 

 kilometers) apart and extend down the shoreface slope and across a sub- 

 dued shoreface linear shoal. 



Most cores shoreward of the 50-foot (15.2 meters) bathymetric contour 

 contain a varied stratigraphic sequence of fine to medium to coarse sand 

 above and below silt-clay lenses, except cores V-13, V-7, and V-6 which 

 contain continuous sand sequences (Fig. 9; App. A). All of the eight cores 

 seaward of the 50-foot depth contour show 10 to 23 feet (3 to 7 meters) of 

 sand overlying a flat, featureless, silt-clay horizon (Gardiners Clay) at 

 about -73 feet (-22.3 meters) MSL (Fig. 9). This horizon is continuous 

 under the shoal which is analogous to data reported by Duane, et al., 

 (1972) for similar shoals studied along other parts of the Atlantic inner 

 shelf. Incomplete descriptive logs for some cores yield gaps in the strat- 

 graphic information; however, the information loss is generally minimal 

 except for core V-2. The shelf in this region is underlain at shallow 

 depths (relative to eastern and western Long Island) by Upper Cretaceous 

 strata (Monmouth Group) which show an anticlinal southeast dip on the 

 seismic records and are characterized by compact glauconitic, sandy, silty 

 gravels (Figs. 7 and 14). Based on the presence of glauconite (dark green- 

 ish grains) in the core descriptions from Appendix A, an assumed Coastal 

 Plain surface has been plotted in Figure 9. The silt-clay horizon which 

 underlies shelf sands seaward of the 50-foot-depth contour is apparently 

 the Gardiners Clay Formation (Sangamon age) which marks the lowermost 

 limit of sediment that may be considered suitable for borrow. 



The 11 cores along the eastern transect in Suffolk County (Fig. 30) 

 are approximately one-half mile apart and vary in length from 10 to 27 



75 



