24 Subsurface Geologic Methods 



and, as a result, considerable confusion prevails in its use. According to 

 Moore,^^ "sedimentary facies are areally segregated parts of differing 

 nature belonging to any genetically related body of sedimentary deposits." 

 He also states that the term "lithofacies" "denotes the collective characters 

 of any sedimentary rock which furnish record of its depositional environ- 

 ment." A sedimentary facies may involve a member or stratum, a forma- 

 tion or group, or a time-rock unit. 



The term "facies" has been used by some workers without reference 

 to stratigraphic units; for example, "red bed facies," "reef facies," "la- 

 goonal facies," "marine facies," and "evaporite facies." As regards this 

 usage, Moore comments, "There is value in this sort of classification of 

 sedimentary deposits and in comparing rocks presumed to have been formed 

 under like environments, without regard to age or local geologic settings." 



To prove the time equivalency of dissimilar facies is exceedingly 

 difl&cult, particularly when data are limited. The solution of this problem 

 lies in (1) establishing regional stratigraphic trends; (2) carefully plan- 

 ning areal mapping programs; and (3) detailing and correlating control 

 stratigraphic sections. 



Sloss ^^ et al in an excellent discussion on the facies problem have 

 suggested four methods of approach in analyzing sedimentary facies: (1) a 

 paleogeographic approach, wherein a study of facies and their distribution 

 patterns in time and space attempts a reconstruction of ancient source 

 areas and depositional environments and their distribution in past geo- 

 graphic patterns; (2) a biologic approach, which is based on the recon- 

 struction of paleoecology from the study of the biologic complex occurring 

 in fossiliferous strata; (3) an oceanographic approach, which involves the 

 collection and integration of environmental data governing recent sedi- 

 mentation, which in turn may be helpful in interpreting ancient deposits; 

 and (4) a tectonic approach, which is based on the study of the tectonic 

 behavior of any area and the facies response to such behavior. 



Facies changes vary in type and magnitude throughout the geologic 

 column. These changes may be pronounced in relatively short distances, 

 others may be gradual over extended distances. Several examples of facies 

 variations may be cited : the Middle Tertiary of central and south Sumatra, 

 the Upper Cretaceous of northern and central Egypt, the Upper Cretaceous 

 of the Rocky Mountain region, the Permian of Russia and of the Permian 

 Basin of Texas and New Mexico, the Tertiary of the Gulf Coast and 

 Pacific Coast of the United States, and the Tertiary of northern South 

 America. 



The Devonian of New York State presents an excellent example of shifting 

 facies, particularly in the post-Onondaga parts where the changes of sediments 

 have been traced from red beds in eastern New York to black shales and lime- 



" Moore, R. C, Meaning of Facies, Geol. Soc. America Mem. 39, pp. 1-34, 1949. 



^^ Sloss, L. L., Krumbein, W. C, and Dapples, E. C, Integrated Facies Analysis, Geol. Soc. America 

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



