region where sea floor sediment is constantly being agitated and winnowed 

 by wind and tide-induced bottom currents. Type IV sediment appears to 

 lack significance as a sea floor lithology in the Gardiners Bay-Block 

 Island Sound region of eastern Long Island. This omission can be 

 explained by the lack of adequate core spacing (only 12 cores available 

 for this area) needed to locate and define areas containing this sediment, 

 or alternately by the possibility that type IV sediment is indeed absent. 

 Omission may result because the sediment was not available in the source 

 material or the original environment of deposition was not conducive to 

 sedimentation of fine sand and silt. 



e. Type V Sediment . This last primary sediment class found in the 

 study area consists of fine-grained, uniformly textured mixtures of silt 

 and clay (<0.0625 millimeter; >4 phi) (Fig. 23). The sediment, generally 

 gray or brown in color (5Y 6/2) , is plastic and highly cohesive when 

 moist, and frequently exhibits an abundance of small mica plates. Type V 

 sediment is limited to two large areas in the Gardiners Bay and Block 

 Island Sound region where it was found at the top of cores 2, 4, 5, 8, 

 and 10. Presence of silt and clay west of Gardiners Island is supported 

 by cores 2, 4, 5, and 8 and by clear recognition of these sediment acous- 

 tic signatures on the seismic records. These fine-grained, flat- lying 

 sediments show no discernible internal structures or sedimentary features 

 on the seismic records and the sequence always overlies an erosional dis- 

 conformity interpreted to be a Pleistocene erosion surface. This rela- 

 tionship is evident in Figure 6 which allows extrapolation of the area of 

 type V sediments from western Gardiners Bay north to Plum Gut. The fine 

 sediments continue northeast of Plum Gut but as shown in core 1, they are 

 covered by an overburden of sand and gravel eroded from the Harbor Hill 

 Moraine crossing Pliim Island. Fine-grained, organic-rich sediments of a 

 similar nature have been reported by Frankel and Thomas (1966) south of 

 Fisliers Island, and by Antevs (1928) and Coch (1974) in Block Island Sound. 

 These sediments have been postulated as being remnants of extensive Pleis- 

 tocene freshwater lakes which occupied the region when sea level was sig- 

 nificantly lower than at present. Possibly the same origins also apply 

 to type V sediments in the Gardiners Bay area. 



2. Radiometric Dating and Land-Sea Relationships . 



Organic-rich layers (peat) closely associated with type V sediments 

 were encountered at varying depths in six cores (Fig. 24) and were radio- 

 metrically age-dated by laboratory C^'^ techniques (Table 4). Core 39 near 

 Moriches Inlet contains 2 feet of type III sediment overlying almost 3 

 feet of type V sediment. A peat layer 4 feet (1.2 meters) below the sea 

 floor was dated at 5,585 ±110 years B.P. Nearly 3 feet of pebbly type 111 

 sediment underlies the peat to the bottom of the core. Core 73 off Moriches 

 Inlet contains type V sediment for the top 12.5 feet (3.8 meters) with 

 1 foot of peat 5 feet (1.5 meters) below the sea floor which was dated at 

 7,585 ±125 years B.P. (Kumar, 1973; Sanders and Kumar, 1975). The bottom 



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