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Changes in the physical attributes of the rock are compared with differences in the relative abundance of certain fossil species within a vertical sequence of limestone and shale layers. Minor variations in the texture and composition of the rock reflect subtle changes in the depositional environment which had a direct influence on the organization of the faunal community. To plot these relationships, a continuous series of beds within the Richmond group (Upper Ordovician) were quantitatively studied in the field and in thin section.
The major sedimentation trends exhibited by the
field and laboratory data are separated from local fluctuations by using two smoothing formulas. A 21-term formula which loses ten observations at each end of the series is used to accentuate the long-period trends, and a 5-term formula losing only two observations at each end is used for the short-period changes. The IBM 7090 has been programmed to compute simultaneously both smoothed curves for 11 variables from a continuous series containing up to 500 units.
The smoothed curves for several lithologic characteristics including thickness, and percentages of calcite, dolomite, micrite, and sparite, are compared with curves based on the condition, size, orientation, and relative abundance of several fossil species. The influx of new species and the decline of others can be related to physical changes in the rock, which are the result of differences in the depositional environment.
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