Minerals, textures and shapes of sedimentary rocks may record metabolisms and environmental conditions that were present before the rise of atmospheric oxygen. For example, dolomite does not preserve fine microbial textures in modern seawater, but it commonly did so in the past. Furthermore, manganese oxides are only known to form in the presence of oxygen, so these minerals are used as proxies for the past presence of oxygen or oxygen-producing organisms. To better interpret the records of these minerals, we grew anoxygenic benthic photosynthetic microbial communities under chemical conditions that were likely present on the early Earth. We identify a range of conditions conducive to preservation of microbial textures by dolomitization in our cultures. We also demonstrate that some anoxygenic photosynthetic communities can oxidize Mn(II) in the absence of oxygen. Thus, manganese oxides are not robust proxies for the evolution of oxygenic photosynthesis and atmospheric oxygen.