Traditional methods of paleontologic correlation based on assemblage zones are not capable of establishing the fine, detailed subdivisions of the rock column which are needed to accomplish accurate time-stratigraphic geology. These methods are based on the local stratigraphic range of fossils and use of relative geochronologic time scale with unequal units such as geologic periods and epochs as subdivisions. At best, correlation zones established by the traditional methods are broad and not necessarily time equivalent.

The graphic correlation method proposed by Shaw (1964) is a new method of paleontologic correlation which is practical and capable of establishing fine time zones with definite boundaries which can be traced over wide geographic areas. The technique involves a graphic plot on a simple two-axis graph – a “standard reference section” always plotted on the horizontal axis, and another section plotted on the vertical axis. The graphic plot is based on the total stratigraphic range of the fossils contained in both sections, and visibly displays the best time correlation between the two sections.

The graphic method of correlation uses a workable chronologic scale which differs from both an absolute and relative geochronologic time scale. This new scale can be quantified and used as an accurate measure to subdivide the rock column into fine time stratigraphic zones (Composite Standard Units) with definite boundaries for local and regional correlations.

The method of determining the total stratigraphic range of fossils and of establishing the chronologic scale is explained and illustrated. Biostratigraphic correlations of Upper Cretaceous rocks of Colorado and Wyoming based on graphic correlations are used as illustrations. Applications of the method useful to petroleum exploration are discussed and illustrated.