956 



Subsurface Geologic Methods 



and thin trends of the selected reservoir sands will correspond in a general 

 way to the pattern of distribution of the entire sand content of the section. 

 In order to decipher the geologic history of a region in which major 

 uplifts and severe truncation have occurred, it is often necessary to re- 

 construct by isopach contours the original thicknesses of strata that have 



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\ \ 



V 



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Figure 518. Palinspastic map showing thicknesses restored by means of 

 lithofacies and isopach maps. 



been entirely eroded away. A map that shows the restored thicknesses of 

 rocks is called a palinspastic map. 



Figure 515 shows an isopach map of a series of limestones and dolo- 

 mites. Uplifts on which none of the sediments are present occur in the 

 northwest and northeast quadrants. From the constant rate of thickening 

 into the basinal regions, it can be inferred that the uplift in the northwest 

 predates the sediments represented by the isopach contours, or that erosion 

 has been uniform over the entire region. The axis of this uphft extends 

 far to the southeast from the granite area. 



