the scope of this book is somewhat restricted to the more practical aspects of 

 subsurface mapping, it is necessary to omit certain methods which occasionally 

 or locally do have practical applications but which are not generally useful in 

 lithologic mapping. The methods described below illustrate an approach to the 

 problems which may, in turn, stimulate further effort in evaluating complex 

 lithologic relationships. 



Lithofacies map is a comparatively new term in the geologist's vocabulary. 

 It denotes a map that shows by one means or another the changes in lithologic 

 facies of a formation, group, or system of rocks within a sedimentation basin. 

 A lithofacies map may show the different facies in either a qualitative or quanti- 

 tative way. Each is important in its own way. The definition of the term is 

 broad enough to include a rather wide variety of maps dealing with the litho- 

 logic aspects of a stratigraphic section. 



It is difficult, or impossible, to show by conventional maps what and where 

 facies changes take place in a highly diversified section, such as rapidly alternat- 

 ing beds of shale, sandstone, limestone, and anhydrite in lenses or discontinuous 

 beds. The relationships of each of these lithologic types to the others in the 

 section can be shown clearly on certain types of lithofacies maps. 



S 



^:: 



m 



m 



Total 

 Footage 



478 



H 



Lithologic Units 

 Re-combined 



Evaporites 



Limestones 



Shales 



Sandstones 



i 



160 



45 



Figure 24-25. Lithologic breakdown of a well log into four main rock types. 



483 



