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.
Brazos River Bar: A Study in the Significance of Grain Size Parameters by Robert L. Folk and William C. Ward
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