Thursday, March 9, 2017

A Look Back: 60 Years—In Bars, Size Matters

Every student in undergraduate sedimentary geology class knows that fundamental descriptors of sediment include attributes of size and sorting. Examining a sand and gravel bar in the Brazos River near Hearne, Texas, this paper by Folk and Ward is the classic text for describing means to quantify these sedimentologic characteristics, and for showing the interpretive value of the data (as opposed to qualitative interpretation). The locals of Robertson County still enjoy their grains, as do geologists: “If one may be permitted to extrapolate from a small study such as this one and enter the seductive field of generalization,” the study ends one of the more penetrating conclusions in sedimentologic history: “Once a relationship is established in an ideal case, where the changes are laid out before the observer in their most perfect form, one soon learns to recognize the same relationships in less ideal examples, where the changes are obscure. The obscure examples, hitherto unfathomable, are explained in the light provided by the ideal examples. So it has been with the Brazos bar study.” The undergraduates memorizing Folk and Ward’s equations for skewness and kurtosis to impress at the party Friday night clearly are appreciative for the illumination, even if the utility of size is intuitively easier to grasp.

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