interface, and subbottom interfaces between acoustically dissimilar mat- 

 erials. In general, the compositional and physical properties (e.g., 

 porosity, water content, relative density) which commonly differentiate 

 sediments and rocks also serve to produce acoustic contrasts which show 

 as dark lines on the geophysical paper records. Thus, an acoustic profile 

 is roughly comparable to a geologic cross section. 



Seismic reflection surveys of marine areas are made by towing variable 

 energy and frequency sound-generating sources and receiving instruments 

 behind a survey vessel which follows the predetermined survey tracklines. 

 The energy source used for this survey was a 50-to 200-joule sparker. For 

 continuous profiling, the sound source is fired at a rapid rate (usually 

 4 pulses per second) and returning echo signals from sea floor and sub- 

 bottom interfaces are received by an array of towed hydrophones . Return- 

 ing signals are amplified and fed to a recorder which graphically plots 

 the two-way signal travel time. Assuming a constant velocity for sound 

 in water at 4,800 feet per second and for typical shelf sediments of 

 5,440 feet per second, a vertical depth scale was constructed to fit the 

 geophysical record. Geographic position of the survey vessel is obtained 

 by frequent navigational fixes keyed to the record by an event marker. 



Detailed discussions of seismic profiling techniques can be found in 

 several technical publications (Ewing, 1963; Hersey, 1963; Miller, Tirey, 

 and Mecarini, 1967; Moore and Palmer, 1968; Barnes, et al . , 1972; Ling, 

 1972). 



c. Coring Techniques . The sea floor coring device used in this study 

 is a pneumatic, vibrating piston coring assembly designed to obtain core 

 samples (20-foot maximum length; 4-inch diameter) in Continental Shelf 

 granular- type sediments. The apparatus consists of a standard steel core 

 barrel, plastic inner liner, shoe and core catcher, with a pneumatic 

 driving head attached to the upper end of the barrel. These elements are 

 enclosed in a tripodlike frame with articulated legs, allowing the assembly 

 to rest on the sea floor during the coring operation. The detached state 

 of the core device from the surface vessel has the advantage of allowing 

 limited motion of the vessel during the actual coring process. Power is 

 supplied to the pneumatic vibrator head by a flexible hoseline connected 



to a large capacity, deck-mounted air compressor. After coring is complete, 

 the assembly is winched on board the vessel; the liner containing the core 

 is removed, capped at both ends, marked, and stored. A review of the 

 historical development of vibratory coring equipment is discussed by Tirey 

 (1972). 



d. Processing of Data. Seismic records are visually examined to 

 establish the principal bedding and geologic features in the subbottom 

 strata. After analyses are complete, record data are reduced to detailed 

 geologic cross-sectional profiles showing the primary reflective interfaces 

 within the subbottom. Selected acoustic reflectors are then mapped to pro- 

 vide areal continuity of reflective horizons considered significant because 

 of their extent and relationship to the general structure and geology of 

 the study area. Where possible, the uppermost reflectors are correlated 

 with core data to provide a measure of continuity between cores. 



