ISOPACH ANO LITHOFACIES MAP OF 



TOTAL "UPPER CRETACEOUS 

 ROCKS 



"Uppe r Cretaceous" r 

 | Thickness of "upper Cretaceous" stratc 

 (Dashed where inferred.) 



H^Sond- Shale Rotio- SLlConjIo, 

 r 1 Sh.tSilt. 



1 " " I H'flh volcanic content 



Figure 23-11. Isopach and sand-shale ratio of the total "Upper Cretacious" rocks. (Krumbein 

 and Nagel, courtesy American Association of Petroleum Geologists). 



STRATIGRAPHIC MAPS During the past 10 years, great advances have 



AND CORRELATION been made in presenting stratigraphic data in 



the form of contour maps. Among the many 

 leaders in this field of analysis are M. Kay of Columbia University, W. C. 

 Krumbein, L. L. Sloss and E. C. Dapples of Northwestern University, E. M. 

 Spieker of Ohio State University, E. D. McKee of the U. S. Geological Survey, 

 and J. W. Low of The California Company. 



The philosophy of preparing stratigraphic maps is based on the idea that 

 any stratigraphic variable (color, texture, composition, thickness, etc.) that 

 can be expressed numerically can be contoured. The more common lithofacies 

 maps include the isopach, clastic ratio, lithic percentage, and lithic ratio. 

 Convergence and paleogeologic maps have played a major role in regional and 

 local stratigraphic studies. Maps showing biologic aspects of stratigraphic units 

 are included, as well as those illustrating paleotectonic developments and trends. 

 These maps permit improved interpretation of structural changes, evaluation of 

 sedimentational history, and outlining paleogeographic patterns. 



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