Subsurface Laboratory Methods 



337 



lationship of shale density and shale porosity to depth of burial. ^^ D. C. 

 "Skeels, in a private report, has accumulated additional data, some of 

 which is shown on the accompanying figures. However, some geologists 

 believe that age of sediment as well as depth of burial may be a pertinent 

 factor. Therefore, arbitrary determinations of depth of burial from 



4000 

 DEPTH IN FEET 



Figure 141. Dry densities from well in Colombia. O = shale samples; X = sands and 

 sandy shales. (Measurements by W. G. Herlithy; reported by C. H. Acheson. 

 After Skeels.) 



straight density determinations should be used with care, particularly if 

 the inherent character of the sediment has been effected by secondary 

 mineralization. 



Major unconformities can sometimes be distinguished readily by 

 shale-density determination through breaks in density curves. Good ex- 

 amples have been observed in Western Venezuela (See figs. 138 and 139) 



" Hedberg, Hollis D., op. cit. 



