Stratigraphic, Structural, and Correlation Considerations 27 



In a classic paper on the sedimentary facies of the Gulf Coast, Low- 

 man "^^ says : 



As the search for oil turns more and more toward a search for new prov- 

 inces and new trends, we realize the inadequacy of present methods of eval- 

 uating the significance of sedimentary properties and their patterns of distri- 

 bution. . . . The problem of discovering sedimentary criteria for the recogni- 

 tion of petroleum provinces and trends surely involves the study of sedimenta- 

 tion, stratigraphy, and structural history. 



Lowman emphasizes that the logical place to begin a fundamental 

 investigation of facies would appear to be in the environments of deposi- 

 tion and states: 



In a search for sedimentary criteria by which we may identify environ- 

 ment of deposition of sedimentary rocks, it may be useful to classify the sedi- 

 mentary variables as "static" and "dynamic." Among the static variables may 

 be listed those properties which retain their original depositional characteristics 

 (although they may be somewhat modified by postdepositional processes) as 

 follows: (1) gross mineral composition of the solid rock, for example, lime- 

 stone, shale, or sandstone; (2) size, shape, and distribution of detrital grains; 

 (3) fossils; (4) sedimentary structures; and (5) possibly some mass effects 

 related to chemical composition, such as radioactivity and magnetic properties. 

 Among the dynamic variables might be included: (1) minor changes in gross 

 composition, for example, limestone to dolomite; (2) cement; (3) chemical 

 composition of rock fluid; (4) character of those parts of the mineral assem- 

 blage which are susceptible to postdepositional change through differential 

 loss of some minerals and authigenic gain of others; and (5) some physical 

 mass properties such as density and porosity. Stated in another way, the static 

 variables are those which should be useful in making interpretations of deposi- 

 tional environments. The dynamic class, on the other hand, should serve in 

 making interpretations of post-depositional change. 



Dapples et al -^ express a fundamental concept that cannot be min- 

 imized in facies interpretation. It is believed by these writers that: 



The tectonic behavior of the depositional area is the most important fac- 

 tor in the control of lithofacies, and the environment of deposition (littoral, 

 nertic, et cetera) plays a part which depends on the length of time environ- 

 mental conditions can affect the material before it is buried. The source 

 area, except in special instances, appears to be a less important factor. The 

 tectonic behavior of the depositional area itself includes several factors, among 

 which are the geographic distribution of tectonic elements, and the intensity 

 of the tectonism in each. 



Pettij ohn ^^ comments that : 



The fundamental cause of the observed differences in lithology and associ- 

 ated phenomena has been the rate of sedimentation which, in turn, is controlled 

 by the related rates of elevation and depression of the source area and the 



^Lowman, S. W., Sedimentary Facies in Gulf Coast: Am. Assoc. Petroleum Geologists Bull., vol. 33, 

 no. 12, pp. 1939-1997, Dec. 1949. 



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

 Am. Assoc. Petroleum Geologists Bull., vol. 32, no. 10, pp. 1924-47, 1948. 



^ Fettijohn, F. J., Sedimentary Rocks, p. 436, Harper's Geoscience Series, 1949. 



