where surficial layers of unsuitable fine-grained sediments are thick enough 

 to preclude economic access to underlying materials. Environmental factors 

 that may rule out the use of certain areas are usually related to the direct 

 mortality of desirable or rare organisms or alteration of the habitat to which 

 they are adapted. 



122. The main sources of information on these factors are the naviga- 

 tion charts and coastal pilots of the US coasts published by the National 

 Ocean Survey (NOS) . The charts provide a base for plotting the boundaries and 

 information on most of the factors noted above. The 1 : 80, 000 -scale coastal 

 charts published by NOS provide comprehensive coverage of the US coasts at a 

 common scale and are the most useful for boundary determination and plotting. 

 Larger scale charts of some areas are also available and should be on hand as 

 a supplement to the 1:80,000 series. Coastal pilots are useful for discus- 

 sions and explanations on navigation hazards and restrictions. 



Survey Layout 



123. Part of the planning process is to develop a plot of the explora- 

 tion area showing the position, alignment, and extent of tracklines to be run 

 by the geophysical survey boat, and sites where cores are to be taken. The 

 initial plots are based on such knowledge of the area which is available at 

 the time. Because of the usual dearth of information on most offshore areas, 

 the initial plots are tentative; advantageous alterations, additions, or dele- 

 tions to the trackline and core site coverage should be made in the field as 

 survey and coring operations develop a more reliable and comprehensive over- 

 view of the exploration area geology. 



124. Normally, the layouts of the tracklines and core sites are made on 

 the l:80,000-scale NOS charts, keeping the coverage within the boundaries pre- 

 viously established. Bathymetric charts are usually the chief, and often 

 only, source of information available for guidance in preparing trackline 

 plots and selecting core sites. The most important item of information that 

 can be gleaned from the charts is the sea or lake floor geomorphology . They 

 also contain surface sediment notations that are helpful in planning coverage. 

 While the published navigation charts reveal the major geomorphic features, a 

 much more detailed representation can be obtained from unpublished, larger 

 scale charts that were prepared as a step in compiling the published version 



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