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Fig. 9.29 RASC distance-event level plot for Morgan Creek section. Spline-curve is for optimum
(cross-validation) smoothing factor SF
¼
0.382 (Source: Agterberg
1990
, Fig. 9.23)
study area. Nevertheless, final results in an application of both approaches to the
same dataset can be similar as illustrated in Fig.
9.31
for three of the seven sections
used for example in Shaw's (
1964
) topic. These results were obtained as follows.
First RASC distances estimated by scaling were plotted against event levels as
shown for the Morgan Creek section in Fig.
9.29
. Next the event level scales were
replaced by distance scales (Fig.
9.30
). The spline curves in these diagrams were
not only used for positioning the probable positions of cumulative RASC distances
in Fig.
9.31
but also to obtain modified error bars that are asymmetrical because of
curvatures of the spline curves.
Figure
9.31
shows three different types of correlation. Firstly, there are Palmer's
(1955) original zones obtained by conventional subjective paleontological reason-
ing. Secondly, there is Shaw's set of RTS value correlation lines based on his Riley
Composite Standard (RST). Finally, CASC correlation lines are shown for selected
values along the relative geologic time axis based on cumulative interevent dis-
tances as those previously shown for dataset (A) in Fig.
9.4
. Some of these values
are shown together with error bars (
one standard deviation transformed to depth
scale). The example shows either that sedimentation rate probably decreased from
high to low during deposition of the Riley Formation or, less likely, that there was a
change in rate of trilobite evolution. More details on this example based on 60 FOs
and LOs in at least MNS
5 of the seven sections can be found in Agterberg
(
1990
). Earlier applications of quantitative biostratigraphic techniques to Palmer's
(
1954
) Riley Formation trilobite data include Edwards and Beaver (
1978
), Hudson
and Agterberg (
1982
) and Guex (
1987
); for a more recent application of CONOP to
the same data set, see Kemple et al. (
1995
).
¼
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