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Ostracoda and Foraminifera have been used throughout the petroleum industry as paleoenvironmental indicators even when the reliability of the assemblages cannot be demonstrated. Such reliability can be evaluated only by knowing if the fossils have been subject to transport by water currents.
In this study, threshold velocities of shells were measured in a flume with a moveable sediment substrate. The velocities were different for the several genera and some species thereby providing a means of evaluating fossil assemblages. An assemblage composed of specimens with the same threshold velocities would have been transported (sorted) or represent the residual after other shells had been moved away. An assemblage with shells having different velocities would be undisturbed and would be reliable as an environmental indicator.
The best predictors of threshold velocity for the small calcareous shells are several measures of shape including the maximum projection sphericity and operational sphericity. They can be used to predict (.01 level) threshold velocities and provide a reliable objective means of testing the usefulness of fossil assemblages.
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