Quantitative Stratigraphy, Splining and Geologic Time Scales - Geomathematics: Theoretical Foundations, Applications and Future Developments - page 343

Fig. 9.27 Tracing of ten Foraminiferal events through six wells using the CASC method
to calculate the most likely depths. Black bars show deviations from the observed depths (Source:
Gradstein and Agterberg 1985 , Fig. 15)
considered were nearly coeval. Scaling can be modified by assigning different vari-
ances to different events. D'Iorio ( 1988 ) and D'Iorio and Agterberg ( 1989 ) conducted
the following study. An iterative procedure was developed in which the spline-based
correlation method of Fig. 9.25 was applied alternately with modified scaling with
different variances for different events. The procedure was continued until a stable set
of variances was reached upon convergence. Results of this modified RASCmethod as
applied to the Gradstein-Thomas database are shown in Fig. 9.28 . Mean deviation and
maximum observed deviation are plotted in addition to RASC position reached after
convergence. During the iterative process there was relatively little change in esti-
mates of the cumulative RASC distances. However, for some events such as highest
occurrence of taxon 50 ( Subbotina patagonica ) there was a significant decrease in