tivity on the carmel faul

By using the isochron technique some seismite samples of high quality (e.g. DN-42e;
see Appendix I-II) did not plot along an isochron line and were therefore discarded. Yet
those samples have a very long depositional hiatus (Fig. 15) and wouldn’t have been
strong indicators of earthquakes by themselves. Therefore, the isochron method also
permits to sort data, using only statistically viable samples.
While the precise age of each isochron, or set of seismite samples, might be disputed,
it is clear that they do seem to plot and give a reasonable age, which is stratigraphicaly
plausible. Furthermore, no clear isochrons were obtained for non-seismite samples, and
when the DEM was factored in, the degree of isochron accuracy rose. The scattering of a
large number of the results could be explained by an inherent inaccuracy in the sampling
technique. It is therefore clear that the ages obtained are not random, and while they may
vary within their margin of error, they are considered to be indicators of strong
earthquakes that affected Denya Cave. This study suggests that three dimensional
isochron plots solved the problem of the single age correction value, or lack thereof, for
Denya Cave speleothems. Use of this method has also created a reasonable way to derive
sample age clusters, which might indicate seismic events.
4.2.3 Considerations concerning MSWD
MSWD (Mean Square of Weighted Deviates) is the degree to which the observed
amount of scatter of the U-series data points from the isochron lines (the best-fit line) can
be explained by assigned analytical errors (Ludwig and Titterington, 1994).
Consequently, a high MSWD either means underestimated analytical errors or the
presence of non-analytical scatter (Ludwig, 2003). Brooks et al. (1972) suggested that a
satisfactory isochron must have an MSWD value that is lower than 2.5. Yet Davidson et
al. (2005) noted that for a given data set the MSWD deteriorates as the errors on the data
point decrease (a correlation line is harder to pass within the error bars). Since assigned
errors are quite small when using the MC-ICP-MS, it is highly likely that the MSWD
value is magnified, which in turn translates into degradation in the precision of the
isochron.
In this study, results have shown that the MSWD has very little effect on the precision
of ages obtained through Isoplot. Indeed, there seems to be no correlation at all between
the amount of scatter of the data points and their MSWD values. Moreover, when
comparing the four point isochron of 147.6ka (MSWD = 5.4) to that of the eleven point
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