During the 1974 survey, a standard 7-kilohertz fathometer and a side- 

 scan sonar profiler were also used. The fathometer produced an accurate 

 profile of bottom topography at an expanded scale (vertical exaggeration 

 is approximately X 25, compared to about X 4 for the seismic reflection 

 equipment). The E.G.G. side-scan sonar consists of a towed "fish" that 

 emits a 100-kilohertz sonic beam only 1° wide in the horizontal plane 

 and 40° wide in the vertical plane. The sonic beam extends out across 

 the surface on either side of the fish and distinguishes by the character 

 of the reflected signal, change in surface lithology, bed forms, and man- 

 made structures (e.g., pipelines, wrecks). A variable-scale strip chart 

 allows examination of the sea floor up to 150 meters (500 feet) on either 

 side of the ship track. 



d. Collection of Offshore Cores and Onshore Borings . A hydraulic 

 vibrating hammer-driven coring assembly (OSE M30,000 corer) was used to 

 obtain cores from the survey area. The apparatus consisted of a standard 

 core barrel, liner, shoe, and core catcher with the driver element fas- 

 tened to the upper end of the barrel. These were enclosed in a self- 

 supporting frame which allowed the assembly to rest on the bottom during 

 coring, thus limiting the motion of the support vessel in response to 

 waves. Power was supplied to the vibrator by a flexible hose line from 

 a deck-mounted air compressor. After the core was driven and recovered, 

 the plastic liner holding the sample was removed, marked, and capped. 



Three onshore borings were collected from central Assateague by using 

 a truck -mounted power auger. The holes were cased with a slurry of drill- 

 er's mud, and individual samples were collected at 1.5-meter (5 feet) 

 increments by a split-spoon sampler. This technique yields reliable 

 samples from each horizon; if a given sample (average thickness of 21 

 centimeters or 0.7 foot) extends across a lithologic contact, it can be 

 readily determined and noted to avoid misinterpretation. 



4. Data Processing and Analysis . 



a. Acoustic Profiling . Seismic records were analyzed to establish 

 the principal bedding or structural features in the uppermost part of the 

 section. After preliminary analysis, profile data were reduced to de- 

 tailed cross-sectional profiles showing all reflective interfaces within 

 the subbottom. Selected acoustic reflectors were then mapped either to 

 provide a real continuity or because the horizons were considered signif- 

 icant due to their extent and relationship to the general structure and 

 geology of the study area. Where possible, the uppermost mapped reflector 

 was correlated with core data to provide a measure of continuity between 

 cores. Major emphasis was placed on the primary acoustic reflectors that 

 represented Quaternary sediment facies. Secondary or local reflectors 

 were analyzed for location, orientation, and depth of buried channels and 

 for presence and trend of internal stratification in the ridge topography. 



Fathometer profiles were studied to learn more about the shape (side 

 slopes, crest orientation and character) of major ridges on the Maryland 



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