ON THE LABELING, LENGTH, AND OBJECTIVE BASIS OF FISCHER PLOTS

Fischer plots of the accumulation of shallow-marine carbonate cycles t rack the cumulative departure from mean cycle thickness through a vert ical sequence of contiguous upward-shallowing units. This is a simple, objective treatment of residuals in a time series, and is applicable to other stratigraphic phenomena. To reflect the noninterpretive const ruction of Fischer plots, the vertical axis should be labeled ''cumula tive departure from mean cycle thickness'' and the horizontal axis ''c ycle number''. The typical Fischer plot is an erratic bridge that begi ns and ends at the same elevation but has the form of an irregular tra in of asymmetric waves, which rise steeply and fall gradually. The asy mmetry of the individual waves arises because thinner-than-average cyc les typically outnumber thicker cycles two to one. The overall form of the wave train is sensitive to mean cycle thickness, but can guide co rrelation and may have considerable interpretive potential, provided t hat enough cycles are included to ensure a robust estimate of mean thi ckness. Runs tests demonstrate that Fischer bridges for peritidal carb onates are unlikely to be the result of random stacking processes. Sin ce this anticipated result does not emerge unequivocally for Fischer p lots of less than 50 cycles, however, we recommend against plotting su ch short sections.