The definition of biostratigraphic units (biozones) is based on the paleont- 

 ological aspects of the section. Figure 23-3 demonstrates a common relationship 

 between boundaries of biozones and lithogenetic subdivisions. It is not uncom- 

 mon for the boundaries of these units to be nonconformant. Biozones are 

 recognized by a single species or genus, a simple or complex assemblage, or an 

 evolutionary development of paleontologic elements. Biozones play a major 

 role in establishing boundaries of time-stratigraphic units. 



A more detailed account relating to stratigraphic units is given by Ashley 

 and others (1932) and Moore (1947). 



SPACE-TIME CONCEPT The correlation of stratigraphic units requires 



IN CORRELATION an understanding and practice of the space- 



time concept, which involves three spatial 

 components and one time component. Such variables as composition, texture, 

 color, porosity, permeability, thickness, and paleontology must be evaluated 

 through time and along the space components in order to establish the con- 

 temporaniety or noncontemporaniety of deposits. The concept must be con- 

 sidered, also, during evaluation of tectonic problems. Figure 23-4 demonstrates 

 the lateral and vertical variations of three lithologies (facies) in space within a 

 time-stratigraphic unit. 



Shale.-Sandstone 

 7 



Carbona 

 Sandstone 



@ LIMESTONE 



@ SHALE 



H SANDSTONE 



Figure 23-4. Panel diagram showing space relationships of facies changes of a time- 

 stratigraphic unit. Dashed lines indicate the approximate lateral extent of the major 

 lithofacies. Data shown on this panel may be represented also by isopach and lithologic 

 percentage or ratio contours. Stratigraphic panels permit rapid space evaluation of 

 depositional relationships. 



442 



