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The taphonomy of ancient microbial communities is understood via rare windows of microbes that are successfully entombed and preserved in the fossil record. Laboratory investigations using live bacterial cultures, combined with observations on microfossils preserved in ferriferous oolitic beds formed around 161 million years ago, were used to constrain conditions that are conducive to preservation by mineralization. Lab experiments confirmed redox conditions in conjunction with bacterial Fe metabolism as the critical parameter. When Fe was mobilized during the reductive dissolution of ferric hydroxide in laboratory studies, bacteria did not sorb sufficient amounts of ferriferous phases to result in casts. By contrast, iron-oxidizing bacteria sorbed sufficient ferric hydroxide to entomb the cells, although there was variation in Fe oxide sorption within a single culture. The comparison of information from lab and field investigations opens an avenue to infer processes of preservation by mineralization in a geological time frame.

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