Abstract

Fischer plots of the accumulation of shallow-marine carbonate cycles track the cumulative departure from mean cycle thickness through a vertical 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 construction of Fischer plots, the vertical axis should be labeled "cumulative departure from mean cycle thickness" and the horizontal axis "cycle number". The typical Fischer plot is an erratic bridge that begins and ends at the same elevation but has the form of an irregular train of asymmetric waves, which rise steeply and fall gradually. The asymmetry of the individual waves arises because thinner-than-average cycles typically outnumber thicker cycles two to one. The overall form of the wave train is sensitive to mean cycle thickness, but can guide correlation and may have considerable interpretive potential, provided that enough cycles are included to ensure a robust estimate of mean thickness. Runs tests demonstrate that Fischer bridges for peritidal carbonates are unlikely to be the result of random stacking processes. Since this anticipated result does not emerge unequivocally for Fischer plots of less than 50 cycles, however, we recommend against plotting such short sections.

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