CHAPTER 2 



STRATIGRAPHIC, STRUCTURAL, AND CORRELATION 

 CONSIDERATIONS 



L. W. LeROY 



Stratigraphy incorporates the study of the character, sequence, rela- 

 tionship, distribution, and origin of sedimentary rocks. As expressed by 

 Kay,^ "Stratigraphy is veritably the interpretation of the record of pro- 

 gressive movements (crustal) evidenced in sedimentation." Stratigraphy 

 constitutes the basis of correlation, and correlations are primary requisites 

 for surface and subsurface mapping and for the evaluation of structural 

 and sedimentational patterns. 



The basic principles of stratigraphic geology have remained more 

 or less unmodified, although methods and techniques applied in the solu- 

 tion and presentation of stratigraphic problems have greatly improved 

 during the last decade. In recent years emphasis has been placed on 

 graphic representation of stratigraphic data. The construction of litho- 

 facies, isopachous, log, paleogeographic, paleogeomorphic, paleoclimato- 

 logic, paleogeologic, and palinspastic maps has contributed enormously in 

 outlining stratigraphic trends and has introduced new avenues of strati- 

 graphic approach. The recent contributions by Krumbein,^ and Dapples, 

 Krumbein, and Sloss ^ ^ are examples of new lines of thought in strati- 

 graphic compilation. Block diagrams are being used frequently in order 

 to illustrate third-dimensional effects and to assist nongeologic personnel 

 better to understand stratigraphic concepts. Such diagrams are particularly 

 useful in preparing regional reconnaissance reports. 



Large sums of money are being spent annually by oil companies on 

 stratigraphic research and in the training of specialists in such fields as 

 micropaleontology, lithology, detrital mineralogy, insoluble residue, and 

 well logging. Some companies prefer training individuals who will sub- 

 sequently devote their major efforts to restricted phases of stratigraphic 

 geology; other companies favor personnel familiar with diversified strati- 

 graphic procedures. 



Many mineral concentrations occur in sedimentary rocks. They may 

 be of either primary or secondary origin. Silver chloride has been noted 

 in the cross-laminated Painted Desert sandstone in southwestern Utah. In 

 western Colorado and southeastern Utah uranium and vanadium minerals 



1 Kay, Marshall, Analysis of Stratigraphy: Am. Assoc. Petroleum Geologists Bull., vol. 31, no. 1, 

 pp. 161-181, Jan. 1947. 



^ Krumbein, W. C, Lithojacies Maps and Regional Sedimentary -Stratigraphic Analysis: Am. Assoc. 

 Petroleum Geologists Bull., vol. 32, pp. 1909-23, 1948. 



^Dapples, E. C, Krumbein, W. C, and Sloss, L. L., Tectonic Control of Lithologic Associations: 

 Am. Assoc. Petroleum Geologists Bull., vol 32, pp. 1924-47, 1948. 



* Sloss, L. L., Krumbein, W. C, and Dapples, E. C, Integrated Fades Analysis: Geo]. Soc. America 

 Mem. 39, pp. 91-123, 1949. 



