Smackover oncolites from the Chalybeat Springs field, Columbia County, Arkansas, exhibit evidence for penecontemporaneous cementation. "Flower spar" cement, previously reported only in caliche and vadose pisoliths, has been found as thin ribbons within the oncolites. Bivalve and polychaete borings penetrate both the concentric algal laminations and the bioclastic nuclei of the nodules. Boreholes are found around the entire periphery of the nodules indicating that the oncolites were mobile at the time boring occurred. Some borings have their openings capped by subsequent layers of algally bound material, implying that the oncolites were periodically lithifying while still accreting. Foraminifera, serpulids, and bryozoans are seen to encrust the oncolites suggesting that th nodules were indurated at the time of encrustation.

Smackover oncolites are characterized by micritic and pelletal laminations and contain blue-green algal filaments attributed to Girvanella. Thus, they closely resemble modern marine oncolites with the exception that modern forms are unlithified. Recent lithifying blue-green algae are known only from freshwater and hypersaline environments.

The density of these large (5 to 35 mm), hard, cemented grains would be considerably higher than that of modern marine oncolites. If the cemented oncolites are assumed to have the same specific gravity as recent freshwater oncolites, current velocities exceeding 100 cm/sec would be required to initiate movement.

A survey of ancient oncolites suggests that virtually all Mesozoic oncolites show evidence of penecontemporaneous cementation.

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