indicate that the transparent unit was once eroded and that the irregular 

 erosion surface carved into the unit was subsequently filled by stratified 

 deposits with locally complex bedding patterns. 



Both the lower transparent subunit with weak internal reflectors and 

 the upper transparent subunit with strong internal reflectors occur 

 together throughout most of the study area; where only one subunit is 

 present it is usually the lower. 



III. SEDIMENT CHARACTERISTICS AND DISTRIBUTION 



1. Sediment Characteristics . 



a. General . Data from 34 cores collected for this study and from i 

 26 cores collected for the MCMI (Willett, et al., 1972) provided most of 

 the information on surficial and shallow subbottom sediments within the 

 primary study area. In addition, 26 grab samples with most supplemented 

 by bottom photos, were collected within primary limits for the MCMI. 

 Eight ICONS cores from CERC, and 20 cores plus 37 grab samples from MCMI, 

 were in the north and south reconnaissance areas. The ICONS cores were 

 available for direct sampling and analysis. Data from MCMI were obtained 

 from logs, size analysis, and bottom photos contained in Willett, et al., 

 1972. 



Comparison of core top samples, grab samples, and bottom photos shows 

 that gravel occurs in grab samples more than twice as frequently as in 

 core tops. Some of the bottom photos also show cobbles and boulders where 

 grab samples, taken concurrently, do not reveal their presence (Willett, 

 et al., 1972). :;;^^This bias, previously noted by Schlee and Pratt (1970) 

 and Setlow (1973) from the same region, is a function of sampling tech- 

 niques. Core dimensions limit recovery to particles of less than 4 inches 

 in diameter and most grab samplers are not large enough to contain large 

 cobbles and boulders. The bottom photos which supplement the samples 

 provide an indication of the location, gross size, and variation of 

 gravelly sediment. Available bottom photos of the study area are limited; 

 since the photos are applicable only to surficial sediments and are 

 qualitative in nature, the sediment-size data should be treated with 

 caution. This is evident where recovered material is poorly sorted and 

 gravelly, indicating possible presence of cobbles and boulders. The 

 sampling problem on the glaciated northeast United States Continental 

 Shelf is discussed by Schlee and Pratt (1970). 



The Wentworth Scale for soil classification is used for describing 

 sediment texture in this report. This classification and the Unified 

 Soil Classification are compared in Table 2 (U.S. Army, Corps of Engineers, 

 Coastal Engineering Research Center, 1973) . 



b. Greenish- Gray Mud . The most common subsand-size sediment found in 

 both primary and secondary study areas is greenish-gray silty clay and 

 clayey silt, collectively identified as greenish-gray mud. This mud 

 occurs occasionally in outcrop, mostly under thin overburden. Typical 



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