information contained in Grim, Drake, and Heirtzler (1970) concerning the 

 subbottom geologic character of the Sound, though use of the sparker profiles 

 in conjunction with the cores has provided more detail in many areas. 



a. Sea-Floor Reflector. The reflective character of the sea floor is 



dependent on the type of sediment comprising the upper parts of the sediment 

 column. The Sound is generally floored by sands and gravelly sand along 

 the north shore of the Long Island mainland and adjacent to many of the 

 islands, shoals, and reefs in the middle of the Sound, as well as toward the 

 Connecticut shore where glacial till and outwash detritus were deposited and 

 subsequently reworked by waves and currents. Modern muds composed of silt, 

 clay, and organic matter cover much of the central Sound and along the 

 Connecticut shore. The following three types of areas shown on the seismic 

 profiles are identified with the core information: 



(1) Type 1. The first type denotes a very soft bottom where the 

 upper several meters are composed of sandy silt or mud with high con- 

 tents of organic matter and gas. Records in these areas are almost 

 opaque with a marked absence of any subbottom reflectors. The soft 

 bottom acts as a sponge to the acoustic signal, absorbs the energy and 

 prevents any significant penetration to the deeper reflectors. 



(2) Type 2. The second type shows a high degree of stratification 

 starting at the surface and continuing with depth and allows the best 

 penetration to reveal the subbottom character. The cores show that 

 these areas are usually medium- and coarse-grained sands deposited as 

 deltas and outwash fans. Often the surface in these areas has sand 

 waves and megaripples as the result of the sediment being actively 

 transported primarily by tidal currents. 



(3) Type 3. The third reflector type is normally very dark or 

 strong on the seismic records and the region beneath is very light, 

 showing only faint subbottom reflectors. Because the bottom is so 

 hard there are normally three or more multiple reflectors on the 

 profiles. These areas are characteristic of regions where consoli- 

 dated bedrock is very close to the surface, where compacted glacial 

 till is present and there are parabolic reflectors in the water column 

 suggesting presence of boulders on the surface, and where very compact 

 and well-sorted fine sand makes up the sea floor. 



b. Pleistocene Sediments. The reflectors and sedimentary deposits 

 assigned to a Pleistocene age are by far the most abundant and the most 

 complex of any in the study area. Most of the information identifying the 

 various subreflectors is based on published geologic studies of the New York 

 and Connecticut mainland and of Long Island where only Pleistocene deposits 

 overlie the Paleozoic and Cretaceous bedrock. Although most of the Pleisto- 

 cene deposits are depositional, there is evidence of erosional episodes where 

 channels have been downcut or widened and deepened by glacial or fluvial 

 erosion and areas have been subjected to subaerial erosion. 



The thickest Pleistocene sediments occur in the bedrock valleys and chan- 

 nels where highly stratified and thinly bedded strata conform to the topog- 

 raphy of the underlying bedrock (Fig. 6). Where these sediments have been 

 penetrated by deep borings or exposed in surface excavations, they are thinly 



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