Paleophysiography recorded by an unconformity is ordinarily delineated by either isopach-mapping the overlying rocks or by tracing the present-day configuration of the buried surface. A new approach to this problem has been developed through the plotting and contouring of biostratigraphic positions of scattered samples taken from the base of a transgressive unit. The resultant map shows the relative paleoelevations of the sample localities (the younger the sample, the higher its paleophysiographic position). In order to build this kind of map, the time of transgression must be biostratigraphically subdivisible; this requirement is met by the basal Sylamore Sandstone of Arkansas and Missouri (Polygnathus varcus through Siphonodella isosticha—S. cooperi conodont zones).

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