prepared from nautical chart notations of bottom type. One 

 type shows bottom material classified descriptively as mud, sand, 

 gravel, rock, coral, shell, and various combinations of these. Another 

 can show the quality of the bottom in terms of hard, soft, sticky, rough, 

 etc. The third can show sedinnents classed according to origin and 

 composition, i.e., shell, coral, volcanic material, oozes (globigerina, 

 radiolarian, diatom, pteropod)^ blue mud, and red clay. The fourth 

 type of chart can show sediment color. 



Charts can be prepared for limited areas showing the surface 

 distribution of other properties of submarine sediments such as mineral 

 composition, chemical composition, statistical grain size parameters, 

 radioactivity, engineering properties, organic content, species of 

 planktonic foraminifera, paleomagnetism, and many others. Other 

 charts can show the vertical variations of these properties in the 

 bottom. However, such charts require information from cores and 

 carefully collected and analyzed sediment samples which are available 

 in sufficient quantities only for snnall areas. For most of the oceans 

 and seas such data can be presented only for widely scattered specific 

 locations, and no meaningful boundaries can be drawn showing the 

 extent of or change in any parameter except on very large scale charts 

 of small areas. 



IV. Relative Reliability of Data 



The value of bottom sediment data depends upon how reliably the 

 samples represent the population (sea floor) from which they are 

 drawn. Sediment data reliability varies according to sampling design, 

 type of sample, sampling instrument, accuracy of the ship's position, 

 handling, movement and storage of sample, type of analysis, and 

 initial purpose of collecting the sample. Rarely can the effect of all of 

 these be evaluated for a particular sample or suite of samples. Usually 

 only an estimate of how representative a sample is can be made. 



Sediment data can be divided into three major reliability groups, 

 which are relative and often overlap: 



A. The best data are those obtained from laboratory analysis of 

 core samples. These are usually less distorted in the sampling process 

 than other types of samples and therefore more representative of the 

 sediment as it exists on the sea floor. Core samples are usually more 

 carefully handled and analyzed than other types because of the longer 

 time requirements and greater expense of obtaining them. Considerable 

 differences in reliability exist between different types of coring devices 

 (gravity, piston, vibro-piston, hydrostatic) and the type of material 

 sampled. Coarse grained and hard sediments such as coarse sand. 



