MARINE GEOLOGY IN THE OFFICE OF OCEANOGRAPHY 



by 



Richard J. Malloy 



Office of Oceanography 



U. S. Coast and Geodetic Survey 



The Office of Oceanography pursues studies of marine geology through 

 the utilization of standard techniques and instruments, some of the methods 

 are: hydrography, continuous seismic profiling, gravimetric and magnetic 

 measurements, bottom photography, bottom sampling, heat probe, and tide 

 data. Two important omissions are seismic refraction and the lack of land 

 mapping to project the data to the marine environment. It is known now that 

 the Continental Shelf is similar in characteristics to the subaerial Coastal 

 Plain. 



The Office of Oceanography has three Sparker instruments with a power 

 range of 250 joules to 20,000 joules. A new sound source, the air gun, is 

 proving of major interest primarily because of its simplicity and effici- 

 ency. Another instrument, yet to be tested, is a signal correlating device 

 designed to analyze the air gun's outgoing signal and the returning signals, 

 rejecting mismatches, or random noise. If the test is successful (and it 

 is expected to be) , it will be possible to do more seismic profiling at 

 the same time hydrographic surveys are made. 



As an example, detailed seismic profiling and magnetic surveys were 

 completed along with hydrography in the Gulf of Maine in 1962. The map 

 shows strong northeast-southwest lineation which, according to very strong 

 evidence from our magnetic surveys is caused by regional structure. The 

 data illustrate a basin with Triassic sediments flanked by swarms of dikes, 

 including a large ring dike. Four maps have been prepared including bathym- 

 etry, total magnetic field, and bedrock morphology, and an isopachous map 

 , of the thickness of recent sediments overlying the polished basement floor. 

 From these data it is possible to classify the area as an extension of the 

 Appalachian physiographic province, strong ridge and trough topography. 



By virtue of the fact that the Coast Survey does detailed hydrographic 

 studies, it is in a unique position to do detailed seismic profiling. 

 Another instrument, the side-looking sonar, promises to be an aid in mapping 

 the sea floor in greater detail, possibly in three dimensions. Finally, we 

 are digitizing the magnetic and gravity data already collected in order 

 to make the data available in tabulated form, and in machine printed cross- 

 sections, as well as by contour maps. 



DISCUSSIO N 



Question: What resolution do you expect with the signal correlator? 



Answer: About a foot or two. 



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