maintenance and deepening of existing channels in surrounding kills and bays. Another 

 source was garbage, dumped in the ocean until 1897 when a reduction plant was put into 

 operation. The construction of Ambrose navigation channel (1900—07) is one example of a 

 major contribution of ocean-disposed dredge material. During those years about 50 million 

 cubic yards of assorted clean sand and gravel were removed from the sea floor and dumped 

 in the designated disposal area. (See Figure 10); (Wigmore, 1909.) 



ID. SURFACE AND SUBSURFACE SEDIMENT CHARACTERISTIC 

 AND DISTRIBUTION 



Most data on the character of the sea floor sediments in the study area were derived from 

 ICONS vibratory cores, which are fairly evenly spaced throughout the inner bight region and 

 provide a comprehensive overview of the total sediment distribution. (See Figures 2 and 14.) 

 The average length of recovered sediment in the cores is 10.7 feet. Other sediment data were 

 derived from grab samples and from reports submitted by dredge companies in the New 

 York vicinity. Based on examinations of the sediment data the region can be characterized 

 generally by five distinct sediment types. 



Sediment Type I (Figs. 14 and 15) occurs in the vicinity of Shrewsbury Rocks, New 

 Jersey where the seismic profiles (Fig. 5) show that Coastal Plain strata project toward the 

 sea floor and in places crop out as a cuesta. (Williams, 1973.) The sea floor consists of 

 reddish brown medium to coarse quartz sand with an abundance of quartzose pea gravel. 

 The coarse material appears to be a thin mantle of residual sediment resulting from erosion 

 of the underlying semiconsolidated Coastal Plain strata. This same sediment type possibly 

 extends along strike of the sea floor cuesta to the east of the Hudson Channel toward the 

 south shore of Long Island. 



Sediment Type II consists of coarse to very coarse sand (500 micrometers to 2 

 millimeters), and pea gravels (5 to 20 millimeters). (See Figure 16.) This material is found in 

 four discrete areas (Fig. 14) but, the cores indicate a much wider areal coverage beneath 

 finer-grained sea floor sediment. The mineralology of the patch of sediment Type II 

 northeast of Sandy Hook resembles glacially derived detritus, which apparently is exposed 

 as a result of removal of overlying recent sediment due to continuous channel dredging. 

 Competent tidal currents, often exceeding 0.5-knot (25.7 centimeters per second) velocities, 

 also effectively scour the sea floor between Sandy Hook and Rockaway Beach leaving a lag 

 of coarser sediment. (Cok, et al., 1973.) The large kidney -shaped area immediately off the 

 northern New Jersey mainland is characterized by Type II reddish brown sand which 

 apparently resulted from subaerial oxidation of iron-bearing minerals. The sedimentary 

 character and configuration of the material indicate that it may represent relict fluvial 

 deposits transported by the Navesink and Shrewsbury Rivers during the Pleistocene when 

 sea level was significantly lower than at present. Another hypothesis is that this sediment is 

 residual material from adjacent outcropping Coastal Plain strata which formed a headland 

 throughout the most recent marine transgression. This material may have since been 

 distributed over wider areas of the sea floor by wave action and longshore sediment 

 transport. 



41 



