Perhaps a review of the past may make us
better geologists in the future?
"Significant Features of Graded Bedding," by Ph. H.
Kuenen; AAPG BULLETIN, Vol. 37, #5, 1953.
"Graded bedding caused by volcanic eruptions should
be readily recognized by the nature of the materials. Deposits formed
by a river while its competency is changing should be graded . .
. The grading should ordinarily be from coarse at the bottom to
fine at the top.
"Graded marine graywackes are characterized by regularity
of bedding in thick and widespread series, absence of clear wash-out
channels or wind ripple marks, and by uniformity in direction of
Key arguments for attributing marine graded graywackes
to turbidity currents are:
- "Absence of tidal actions and symmetrical wave ripple marks."
- "Absence of autochthonous benthonic life in the graded beds."
- "Graded beds show a gradual and perfectly smooth decrease in
competency from a maximum at the start to a minimum at the close."
Those were glory years in sedimentology and the understanding
of sedimentary structures, and Kuenen developed many of the important
criteria for recognizing turbidites on which we still rely -- 50
I remember walking down an Arkansas road cut looking
at Lower Atoka sandstones in 1958. On the east side of the exposure,
"Boo" Bernard was detailing the reasons why the sandstones were
shallow water, low energy delta-front sandstones; on the west side
of the roadcut, Ken Hsu was describing Kuenen's work and identifying
the sandstones as deposited by turbidity currents in deep water.
Ken Hsu was right, of course -- but "Boo," a wonderful
Cajun contemporary of Rufus LeBlanc, easily won the story-telling