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Textural differences between present-day sediments collected from fluviatile, beach and aeolian environments, can be demonstrated by plotting values of quartile deviation measures (QDa) against the medians (Md) on double-log paper for each environment. These plots can be delimited by trend envelopes whose bounding lines represent regressions one standard deviation either side of the average regression lines. Using these envelopes as a framework for comparison, several hundred QDa-Md plots calculated from the grain-size distributions of ancient sedimentary rocks have been examined. The majority of these plots fall well within their appropriate environmental envelope thereby demonstrating that the statistical technique is valid for the environmental discrimination of both modern and ancient deposits.
