Stratigraphic, Structural, and Correlation Considerations 21 



sidered: (1) the description of the type locality or area; (2) the detailed 

 and summary lithologic description; (3) a statement pertaining to thick- 

 ness variations; (4) a statement concerning the surface and subsurface 

 distribution of the unit; (5) a discussion of stratigraphic relationships; 

 (6) comments on detrital mineralogy and paleontology; (7) a statement 

 pertaining to physiographic expression; (8) a discussion of correlation; 

 (9) comments on environment of deposition; and (10) economic aspects. 

 Similar procedure should be followed in defining groups, members, lentils, 

 or other rock units. 



In naming subsurface rock units the American Commission on Strati- 

 graphic Nomenclature ^° recommends that : 



Subsurface units may be given formal names when such names are neces- 

 sary for adequate presentation of the geologic history of the region or when 

 the subsurface section is materially different from equivalent exposed beds. 



(a) Subsurface units, recognized and named from Avell logs, including 

 sample logs, core records, and electrical and other mechanically recorded logs, 

 with the assistance of paleontological determinations differ from surface units 

 in that the "type locality" cannot be visited and restudied from time to time 

 by subsequent workers. With the advent and wide dissemination of the elec- 

 trical log and the systematic saving of representative well cuttings, particularly 

 in areas of deep drilling, it frequently has become possible, in recent years, to 

 bring the "type locality" into the office or laboratory of any truly interested 

 worker. In fact, the log portion of the "type locality" can and should be pub- 

 lished. This condition lessens the need for restricting the number of names 

 of subsurface units to an irreducible minimum. If a subsurface type section is 

 definitely better and more typical than that available at any surface type local- 

 ity, the subsurface section may be designated as type. Otherwise, a surface 

 type locality shall be designated. 



(6) Names applied to subsurface units shall be governed by the same 

 restrictions and regulations as prevail for exposed units. [See Articles 7, 9, 10, 

 and 11 of the original paper.] 



(c) When it becomes possible to correlate a named subsurface unit with 

 a named surface unit, and when the surface and subsurface facies are suffi- 

 ciently similar that two names are unnecessary, the name of the surface unit 

 is to be applied, even though the subsurface name has priority, unless much 

 more extensive usage of the subsurface name renders its retention preferable or 

 necessary. 



(d) When beds are discovered which are equivalent and in similar facies 

 to a named subsurface unit, the name of the subsurface unit shall have priority. 



(e) When it is found that a subsurface unit has been named for but mis- 

 correlated with a named surface unit, a new name shall be given the subsurface 

 unit or it shall be renamed for its- true correlative on the surface. In rare 

 instances, exceptionally widespread use of the name by the subsurface unit 

 may make it advisable to permit the "pirating" of the name by that unit and 

 thus force the renaming of the surface unit from which it derived its name. 

 Such "pirating" should be held to a minimum and should be accepted for pub- 

 lication only after a favorable ruling by the American Commission on Strati- 

 graphic Nomenclature. 



^^ Naming of Subsurface Stratigraphic Units: Am. Assoc. Petroleum Geologists Bull., vol. 32, no. 3, 

 pp. 369-370, Mar. 1948. Prepared by W. V. Jones and R. C. Moore. 



