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In 1964 A.B.Shaw presented a method of correlating fossilferous sedimentary rocks based on interpretation of graphic plots of first- and last-occurrences of taxa. Because there is no way to determine the true total ranges of fossil taxa, it is instructive to test the accuracy of the method using hypothetical datasets. The dataset used here consists of 16 taxa in six sections with differing known rates of rock accumulation. In all graphs, a single straight-line correlation was a reasonable interpretation. The resulting ranges after the first and third rounds of compositing reproduce the 'true' ranges but with small errors. Slight errors in the positioning of individual correlation lines are more likely to lengthen ranges artificially than to shorten them. Shaw's method works well because, whereas actually sampled ranges will be shorter than true ranges, errors in correlation will be likely to extend some ranges. This or any exercise using simulated data is useful only if the hypothetical situation resembles real geologic situations and if insights derived from the hypothetical dataset provide insights into real situations. The method is only as good as the available data. -Author
Additional Publication Details
Insights on why graphic correlation (Shaw's method) works.