CLASTICS 



PRECIPITATES 



EVAPORITES 



COARSE 



FINE 



CALCITIC 



DOLOMITIC 



SULPHATES CHLORIDES 



Browns 

 Yellows 



Grays 

 Greens 



Blues 



Purple: 



Black line patterns 

 Ruling Figures 



BtoiiJtu 



Gray 



Marine 



Darky 



Black- 



Dark, 



Doric 



^^ 



Med,. 



Darks 



Med.. 



Med,. 



-Light 



Med,. 



Light 



Light, 



I Stenruz, 



Light, 



Shy 



Magenta 



YeZZow 



Green, 



Prussian, 



Violet 



x x x x xx 

 x x x x x 

 x v x x x 



~v V V V 



V V V 

 V V V V 



J -I -I -1 -I 

 -1 -I -I J -I 



+ + + + 



Canary 



Light, 



Light, 



Tan, 



Darky 



Dark, 



Figure 24-34. Guide for coloring lithofacies maps. 



stratigraphic interval studied, the more precise the results will be. But the 

 different kinds of facies maps are also an excellent method for studying thick 

 series of strata which, because of monotonous repetition of similar units, cannot 

 be subdivided into thinner mappable units. 



An isolithic map, as explained earlier, shows the aggregate thicknesses of 

 beds in a specific lithologic class, but it does not necessarily differentiate the 

 rocks within this class on a mineralogic, chemical, or physical basis. There are 

 several ways in which this differentiation may be shown. One simple method is to 

 show such a breakdown by percentage contours superimposed on the contoured 

 isolithic map. Thus, on a sandstone isolith map the percentage of arkosic, silty, 

 or carbonaceous sands or maximum grain sizes may be shown by color bands 

 or a second set of contours. The thicknesses of rocks alone, sometimes fail to 

 reveal the sources of the sediments or the conditions under which they were 

 deposited ; but this information, together with that suggested above, often clarifies 

 an otherwise cloudy picture. 



A word of caution should be given in the interpretation of isolithic maps. 

 Apparent discrepancies in the locations of apparent highs and lows within large 

 basins are bound to occur if the predominance of one lithologic class in one lo- 

 cality is replaced by that of another class at other localities. For example, on a 

 coarse elastics isolithic map, the thickest deposits are likely to lie close to the 

 source materials near one edge of the basin and will thin out toward the central 

 part of the basin. Conversely, the limestones and evaporites may reach their 



492 



